How it Works
Datasheet
Loading...
LM12H458CIVF
Datasheet (NSC)
43 pgs1.06 Mb0

Datasheet LM12H458MWG-883, LM12H458MEL-883, LM12H458CIVF, LM12H458CIV Datasheet (NSC)

Download
Page 1
LM12454/LM12458/LM12H458 12-Bit + Sign Data Acquisition System with Self-Calibration
General Description
The LM12454, LM12458, and LM12H458 are highly inte­grated Data Acquisition Systems. Operating on just 5V, they combine a fully-differential self-calibrating (correcting linear­ity and zero errors) 13-bit (12-bit + sign) analog-to-digital converter (ADC) and sample-and-hold (S/H) with extensive analog functions and digital functionality. Up to 32 consecu­tive conversions, using two’s complement format, can be stored in an internal 32-word (16-bit wide) FIFO data buffer. An internal 8-word RAM can store the conversion sequence for up to eight acquisitions through the LM12(H)458’s eight-input multiplexer. The LM12454 has a four-channel multiplexer,a differential multiplexer output, and a differential S/H input. The LM12454 and LM12(H)458 can also operate with 8-bit + sign resolution and in a supervisory “watchdog” mode that compares an input signal against two program­mable limits.
Programmable acquisition times and conversion rates are possible through the use of internal clock-driven timers. The reference voltage input can be externally generated for ab­solute or ratiometric operation or can be derived using the in­ternal 2.5V bandgap reference.
All registers, RAM, and FIFO are directly addressable through the high speed microprocessor interface to either an 8-bit or 16-bit databus. The LM12454 and LM12(H)458 in­clude a direct memory access (DMA) interface for high-speed conversion data transfer.
An evaluation/interface board is available. Order num­ber LM12458EVAL.
Additional applications information can be found in applica­tions notes AN-906, AN-947 and AN-949.
Key Specifications
(f
CLK
=
5 MHz; 8 MHz, H)
j
Resolution 12-bit + sign or 8-bit + sign
j
13-bit conversion time 8.8 µs, 5.5 µs (H) (max)
j
9-bit conversion time 4.2 µs, 2.6 µs (H) (max)
j
13-bit Through-put rate 88k samples/s (min),
140k samples/s (H) (min)
j
Comparison time
(“watchdog” mode)
2.2 µs (max),
1.4 µs (H) (max)
j
ILE
±
1 LSB (max)
j
VINrange GND to V
A
+
j
Power dissipation 30 mW, 34 mW (H) (max)
j
Stand-by mode 50 µW (typ)
j
Single supply 3V to 5.5V
Features
n Three operating modes: 12-bit + sign, 8-bit + sign, and
“watchdog”
n Single-ended or differential inputs n Built-in Sample-and-Hold and 2.5V bandgap reference n Instruction RAM and event sequencer n 8-channel (LM12(H)458), 4-channel (LM12454)
multiplexer
n 32-word conversion FIFO n Programmable acquisition times and conversion rates n Self-calibration and diagnostic mode n 8- or 16-bit wide databus dmicroprocessor or DSP
interface
Applications
n Data Logging n Instrumentation n Process Control n Energy Management n Inertial Guidance
TRI-STATE®is a registered trademark of National Semiconductor Corporation. AT
®
is a registered trademark of International Business Machines Corporation.
July 1999
LM12454/LM12458/LM12H458
12-Bit + Sign Data Acquisition System with Self-Calibration
© 1999 National Semiconductor Corporation DS011264 www.national.com
Page 2
Ordering Information
Guaranteed Guaranteed Order See NS
Clock Freq (min) Linearity Error (max) Part Number Package Number
8 MHz
±
1.0 LSB LM12H458CIV V44A LM12H458CIVF VGZ44A
LM12H458MEL/883 EL44A
or 5962-9319502MYA
5 MHz
±
1.0 LSB LM12454CIV V44A
LM12458CIV V44A
LM12458CIVF VGZ44A
Connection Diagrams
DS011264-2
* Pin names in ( ) apply to the LM12454 and LM12H454.
Order Number LM12454CIV,
LM12458CIV or LM12H458CIV
See NS Package Number V44A
Order Number LM12H458MEL/883 or 5962-9319502MYA
See NS Package Number EL44A
DS011264-34
Order Number LM12458CIVF or LM12H458CIVF
See NS Package Number VGZ44A
www.national.com 2
Page 3
Functional Diagrams
LM12454
DS011264-1
LM12(H)458
DS011264-21
www.national.com3
Page 4
Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
Supply Voltage (V
A
+ and VD+) 6.0V
Voltage at Input and Output Pins
except IN0–IN3 (LM12454) −0.3V to V
+
+ 0.3V
and IN0–IN7 (LM12(H)458)
Voltage at Analog Inputs IN0–IN3 (LM12454)
and IN0–IN7 (LM12(H)458) GND − 5V to V
+
+5V
|V
A
+−VD+| 300 mV
Input Current at Any Pin (Note 3)
±
5mA
Package Input Current (Note 3)
±
20 mA
Power Dissipation (T
A
=
25˚C)
V Package (Note 4) 875 mW Storage Temperature −65˚C to +150˚C Lead Temperature
V Package, Infrared, 15 sec. +300˚C
EL and W Packages,
Solder, 10 sec. +250˚C ESD Susceptibility (Note 5) 1.5 kV
LM12458MEL/883 2.0 kV
See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” for other methods of soldering surface mount devices.
Operating Ratings (Notes 1, 2)
Temperature Range
(T
min
≤ TA≤ T
max
) LM12454CIV/ LM12(H)458CIV −40˚C ≤ T
A
≤ 85˚C
LM12458MEL/883 −55˚C ≤ T
A
≤ 125˚C Supply Voltage V
A
+, VD+ 3.0V to 5.5V
|V
A
+−VD+| ≤100 mV
V
IN+
Input Range GND ≤ V
IN+
≤ VA+
V
IN−
Input Range GND ≤ V
IN−
≤ VA+
V
REF+
Input Voltage 1V ≤ V
REF+
≤ VA+
V
REF−
Input Voltage 0V ≤ V
REF−
≤ V
REF+
−1V
V
REF+−VREF−
1V ≤ V
REF
≤ VA+
V
REF
Common Mode
Range (Note 16) 0.1 V
A
+
≤ V
REFCM
≤ 0.6 V
A
+
Converter Characteristics (Notes 6, 7, 8, 9, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, V
REF+
=
5V, V
REF−
=
0V,
12-bit + sign conversion mode, f
CLK
=
8.0 MHz (LM12H458) or f
CLK
=
5.0 MHz (LM12454/8), R
S
=
25Ω, source impedance for
V
REF+
and V
REF−
≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless
otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
ILE Positive and Negative Integral After Auto-Cal (Notes 12, 17)
±
1/2
±
1 LSB (max)
Linearity Error
TUE Total Unadjusted Error After Auto-Cal (Note 12)
±
1 LSB
Resolution with No Missing Codes After Auto-Cal (Note 12) 13 Bits (max)
DNL Differential Non-Linearity After Auto-Cal
±
3
⁄
4
LSB (max)
Zero Error After Auto-Cal (Notes 13, 17)
±
1
LM12H458
±
1/2
±
1.5 LSB (max)
Positive Full-Scale Error After Auto-Cal (Notes 12, 17)
±
1/2
±
2 LSB (max)
LM12(H)458MEL
±
2.5
Negative Full-Scale Error After Auto-Cal (Notes 12, 17)
±
1/2
±
2 LSB (max)
LM12(H)458MEL
±
2.5
DC Common Mode Error (Note 14)
±
2
±
3.5 LSB (max)
ILE 8-Bit + Sign and “Watchdog” (Note 12)
Mode Positive and Negative
±
1/2 LSB (max)
Integral Linearity Error
TUE 8-Bit + Sign and “Watchdog” Mode After Auto-Zero
±
1/2
±
3/4 LSB (max) Total Unadjusted Error 8-Bit + Sign and “Watchdog” Mode 9 Bits (max) Resolution with No Missing Codes
DNL 8-Bit + Sign and “Watchdog” Mode
±
3/4 LSB (max)
Differential Non-Linearity 8-Bit + Sign and “Watchdog” Mode After Auto-Zero
±
1/2 LSB (max)
Zero Error 8-Bit + Sign and “Watchdog” Positive
±
1/2 LSB (max)
and Negative Full-Scale Error
www.national.com 4
Page 5
Converter Characteristics (Notes 6, 7, 8, 9, 19) (Continued)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, V
REF+
=
5V, V
REF−
=
0V,
12-bit + sign conversion mode, f
CLK
=
8.0 MHz (LM12H458) or f
CLK
=
5.0 MHz (LM12454/8), R
S
=
25Ω, source impedance for
V
REF+
and V
REF−
≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless
otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
8-Bit + Sign and “Watchdog” Mode
±
1/8 LSB DC Common Mode Error Multiplexer Channel-to-Channel
±
0.05 LSB
Matching
V
IN+
Non-Inverting Input Range GND V (min)
V
A
+ V (max)
V
IN−
Inverting Input Range GND V (min)
V
A
+ V (max)
V
IN+−VIN−
Differential Input Voltage Range −V
A
+
V (min)
V
A
+ V (max)
Common Mode Input Voltage Range GND V (min)
V
A
+ V (max)
PSS Power Supply Zero Error V
A
+=VD+=5V±10
%
±
0.2
±
1.75 LSB (max)
Sensitivity Full-Scale Error V
REF+
=
4.5V, V
REF−
=
GND
±
0.4
±
2 LSB (max)
(Note 15) Linearity Error
±
0.2 LSB
C
REF
V
REF+/VREF−
Input Capacitance 85 pF
C
IN
Selected Multiplexer Channel Input 75 pF Capacitance
Converter AC Characteristics (Notes 6, 7, 8, 9, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, V
REF+
=
5V, V
REF−
=
0V,
12-bit + sign conversion mode, f
CLK
=
8.0 MHz (LM12H458) or f
CLK
=
5.0 MHz (LM12454/8), R
S
=
25Ω, source impedance for
V
REF+
and V
REF−
≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless
otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
Clock Duty Cycle 50
%
40
%
(min)
60
%
(max)
t
C
Conversion Time 13-Bit Resolution, 44 (t
CLK
) 44 (t
CLK
)+50ns (max)
Sequencer State S5 (
Figure 15
)
9-Bit Resolution, 21 (t
CLK
) 21 (t
CLK
)+50ns (max)
Sequencer State S5 (
Figure 15
)
t
A
Acquisition Time Sequencer State S7 (
Figure 15
)9(t
CLK
) 9(t
CLK
)+50ns (max)
Built-in minimum for 13-Bits Built-in minimum for 9-Bits and 2 (t
CLK
) 2(t
CLK
)+50ns (max)
“Watchdog” mode
t
Z
Auto-Zero Time Sequencer State S2 (
Figure 15
)76(t
CLK
) 76 (t
CLK
)+50ns (max)
t
CAL
Full Calibration Time Sequencer State S2 (
Figure 15
) 4944 (t
CLK
) 4944 (t
CLK
)+50ns (max)
Throughput Rate 89 88 kHz (Note 18) LM12H458 142 140 (min)
t
WD
“Watchdog” Mode Comparison Sequencer States S6, S4, 11 (t
CLK
) 11 (t
CLK
)+50ns (max)
Time and S5 (
Figure 15
)
www.national.com5
Page 6
Converter AC Characteristics (Notes 6, 7, 8, 9, 19) (Continued)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, V
REF+
=
5V, V
REF−
=
0V,
12-bit + sign conversion mode, f
CLK
=
8.0 MHz (LM12H458) or f
CLK
=
5.0 MHz (LM12454/8), R
S
=
25Ω, source impedance for
V
REF+
and V
REF−
≤ 25Ω, fully-differential input with fixed 2.5V common-mode voltage, and minimum acquisition time unless
otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
DSNR Differential Signal-to-Noise Ratio V
IN
=
±
5V
f
IN
=
1 kHz 77.5 dB
f
IN
=
20 kHz 75.2 dB
f
IN
=
40 kHz 74.7 dB
SESNR Single-Ended Signal-to-Noise V
IN
=
5V
p-p
Ratio f
IN
=
1 kHz 69.8 dB
f
IN
=
20 kHz 69.2 dB
f
IN
=
40 kHz 66.6 dB
DSINAD Differential Signal-to-Noise + V
IN
=
±
5V
Distortion Ratio f
IN
=
1 kHz 76.9 dB
f
IN
=
20 kHz 73.9 dB
f
IN
=
40 kHz 70.7 dB
SESINAD Single-Ended Signal-to-Noise + V
IN
=
5V
p-p
Distortion Ratio f
IN
=
1 kHz 69.4 dB
f
IN
=
20 kHz 68.3 dB
f
IN
=
40 kHz 65.7 dB
DTHD Differential Total Harmonic V
IN
=
±
5V
Distortion f
IN
=
1 kHz −85.8 dB
f
IN
=
20 kHz −79.9 dB
f
IN
=
40 kHz −72.9 dB
SETHD Single-Ended Total Harmonic V
IN
=
5V
p-p
Distortion f
IN
=
1 kHz −80.3 dB
f
IN
=
20 kHz −75.6 dB
f
IN
=
40 kHz −72.8 dB
DENOB Differential Effective Number V
IN
=
±
5V
of Bits f
IN
=
1 kHz 12.6 Bits
f
IN
=
20 kHz 12.2 Bits
f
IN
=
40 kHz 12.1 Bits
SEENOB Single-Ended Effective Number V
IN
=
5V
p-p
of Bits f
IN
=
1 kHz 11.3 Bits
f
IN
=
20 kHz 11.2 Bits
f
IN
=
40 kHz 10.8 Bits
DSFDR Differential Spurious Free V
IN
=
±
5V
Dynamic Range f
IN
=
1 kHz 87.2 dB
f
IN
=
20 kHz 78.9 dB
f
IN
=
40 kHz 72.8 dB
Multiplexer Channel-to-Channel V
IN
=
5V
PP
Crosstalk f
IN
=
40 kHz LM12454 MUXOUT Only −76 dB LM12(H)458 MUX −78 dB plus Converter
t
PU
Power-Up Time 10 ms
t
WU
Wake-Up Time 10 ms
www.national.com 6
Page 7
DC Characteristics (Notes 6, 7, 8, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, V
REF+
=
5V, V
REF−
=
0V,
f
CLK
=
8.0 MHz (LM12H454/8) or f
CLK
=
5.0 MHz (LM12458), and minimum acquisition time unless otherwise specified. Bold-
face limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
I
D
+VD+ Supply Current CS=“1”
LM12454/8 0.55 1.0 mA (max) LM12H458 0.55 1.2
I
A
+VA+ Supply Current CS=“1”
LM12454/8 3.1 5.0 mA (max) LM12H458 3.1 5.5
I
ST
Stand-By Supply Current (ID++IA+) Power-Down Mode Selected
Clock Stopped 10 µA (max)
8 MHz Clock 40 µA (max)
Multiplexer ON-Channel Leakage Current V
A
+=5.5V ON-Channel=5.5V 0.3 OFF-Channel=0V 0.1 µA (max) LM12(H)458MEL 0.5 ON-Channel=0V 0.3 OFF-Channel=5.5V 0.1 µA (max) LM12(H)458MEL 0.5
Multiplexer OFF-Channel Leakage Current V
A
+=5.5V ON-Channel=5.5V 0.3 OFF-Channel=0V 0.1 µA (max) LM12(H)458MEL 0.5 ON-Channel=0V 0.3 OFF-Channel=5.5V 0.1 µA (max) LM12(H)458MEL 0.5
R
ON
Multiplexer ON-Resistance LM12454
V
IN
=
5V 800 1500 Ω(max)
V
IN
=
2.5V 850 1500 Ω(max)
V
IN
=
0V 760 1500 Ω(max) Multiplexer Channel-to-Channel LM12454 R
ON
matching V
IN
=
5V
±
1.0
%
±
3.0
%
(max)
V
IN
=
2.5V
±
1.0
%
±
3.0
%
(max)
V
IN
=
0V
±
1.0
%
±
3.0
%
(max)
Internal Reference Characteristics (Notes 6, 7, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V unless otherwise specified.
Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
V
REFOUT
Internal Reference Output Voltage 2.5 2.5±4
%
V (max)
LM12(H)458MEL 2.5
±
6
%
∆V
REF
/∆T Internal Reference Temperature 40 ppm/˚C
Coefficient
∆
REF
/∆ILInternal Reference Load Regulation Sourcing (0<IL≤ +4 mA) 0.2
%
/mA (max)
Sinking (−1 ≤ I
IL
<
0 mA) 1.2
%
/mA (max)
∆V
REF
Line Regulation 4.5V ≤ VA+ ≤ 5.5V 3 20 mV (max)
I
SC
Internal Reference Short Circuit Current V
REFOUT
=
0V 13 25 mA (max)
∆V
REF
/∆t Long Term Stability 200 ppm/kHr
www.national.com7
Page 8
Internal Reference Characteristics (Notes 6, 7, 19) (Continued)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V unless otherwise specified.
Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
t
SU
Internal Reference Start-Up Time VA+=VD+=0V→5V 10 ms
C
L
=
100 µF
Digital Characteristics (Notes 6, 7, 8, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, unless otherwise speci­fied. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(Note 10) (Note 11) (Limit)
V
IN(1)
Logical “1” Input Voltage VA+=VD+=5.5V 2.0 V (min)
V
IN(0)
Logical “0” Input Voltage VA+=VD+=4.5V 0.8 V (max)
I
IN(1)
Logical “1” Input Current V
IN
=
5V 0.005 1.0 µA (max)
LM12(H)458MEL 2.0
I
IN(0)
Logical “0” Input Current V
IN
=
0V −0.005 −1.0 µA (max)
LM12(H)458MEL −2.0
C
IN
D0–D15 Input Capacitance 6 pF
V
OUT(1)
Logical “1” Output Voltage VA+=VD+=4.5V
I
OUT
=
−360 µA 2.4 V (min)
I
OUT
=
−10 µA 4.25 V (min)
V
OUT(0)
Logical “0” Output Voltage VA+=VD+=4.5V 0.4 V (max)
I
OUT
=
1.6 mA
I
OUT
TRI-STATE®Output Leakage Current V
OUT
=
0V −0.01 −3.0 µA (max)
V
OUT
=
5V 0.01 3.0 µA (max)
Digital Timing Characteristics (Notes 6, 7, 8, 19)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, t
r
=
t
f
=
3 ns, and C
L
=
100 pF on data I/O, INT and DMARQ lines unless otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all
other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(See
Figures 8, 9, 10
) (Note 10) (Note 11) (Limit)
1, 3 CS or Address Valid to ALE Low
40 ns (min)
Set-Up Time
2, 4 CS or Address Valid to ALE Low
20 ns (min)
Hold Time 5 ALE Pulse Width 45 ns (min) 6 RD High to Next ALE High
35 ns (min)
7 ALE Low to RD Low
20 ns (min)
8 RD Pulse Width
100 ns (min)
9 RD High to Next RD or WR Low
100 ns (min)
10 ALE Low to WR Low
20 ns (min)
11 WR Pulse Width
60 ns (min)
12 WR High to Next ALE High
75 ns (min)
13 WR High to Next RD or WR Low
140 ns (min)
14 Data Valid to WR High Set-Up Time
40 ns (min)
15 Data Valid to WR High Hold Time
30 ns (min)
16 RD Low to Data Bus Out of TRI-STATE
40 10 ns (min)
70 ns (max)
www.national.com 8
Page 9
Digital Timing Characteristics (Notes 6, 7, 8, 19) (Continued)
The following specifications apply to the LM12454, LM12458, and LM12H458 for VA+=VD+=5V, t
r
=
t
f
=
3 ns, and C
L
=
100 pF on data I/O, INT and DMARQ lines unless otherwise specified. Boldface limits apply for T
A
=
T
J
=
T
MIN
to T
MAX
; all
other limits T
A
=
T
J
=
25˚C.
Symbol Parameter Conditions Typical Limits Unit
(See
Figures 8, 9, 10
) (Note 10) (Note 11) (Limit)
17 RD High to TRI-STATE
R
L
=
1kΩ 30 10 ns (min)
110 ns (max)
18 RD Low to Data Valid (Access Time)
30 10 ns (min)
80 ns (max)
20 Address Valid or CS Low to RD Low
20 ns (min)
21 Address Valid or CS Low to WR Low
20 ns (min)
19 Address Invalid 10 ns (min)
from RD or WR High
22 INT High from RD Low 30 10 ns (min)
60 ns (max)
23 DMARQ Low from RD Low
30 10 ns (min)
60 ns (max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed speci­fications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: All voltages are measured with respect to GND, unless otherwise specified. Note 3: When the input voltage (V
IN
) at any pin exceeds the power supply rails (V
IN
<
GND or V
IN
>
(VA+orVD+)), the current at that pin should be limited to 5 mA. The 20 mA maximum package input current rating allows the voltage at any four pins, with an input current of 5 mA, to simultaneously exceed the power supply volt­ages.
Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
Jmax
(maximum junction temperature), θJA(package junction
to ambient thermal resistance), and T
A
(ambient temperature). The maximum allowable power dissipation at any temperature is PD
max
=
(T
Jmax−TA
)/θJAor the num-
ber given in the Absolute Maximum Ratings, whichever is lower. For this device, T
Jmax
=
150˚C, and the typical thermal resistance (θ
JA
) of the LM12454 and
LM12(H)458 in the V package, when board mounted, is 47˚C/W, in the W package, when board mounted, is 50˚C/W (θJ
C
=
5.8˚C/W), and in the EL package, when
board mounted, is 70˚C/W (θJ
C
=
3.5˚C/W).
Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 6: Two on-chip diodes are tied to each analog input through a series resistor, as shown below. Input voltage magnitude up to 5V above V
A
+ or 5V below GND will not damage the LM12454 or the LM12(H)458. However, errors in the A/D conversion can occur if these diodes are forward biased by more than 100 mV.As an example, if V
A
+ is 4.5 VDC, full-scale input voltage must be ≤4.6 VDCto ensure accurate conversions.
Note 7: V
A
+ and VD+ must be connected together to the same power supply voltage and bypassed with separate capacitors at each V+pin to assure conversion/
comparison accuracy. Note 8: Accuracy is guaranteed when operating at f
CLK
=
5 MHz for the LM12454/8 and f
CLK
=
8 MHz for the LM12H458.
Note 9: With the test condition for V
REF(VREF+−VREF−
) given as +5V, the 12-bit LSB is 1.22 mV and the 8-bit/“Watchdog” LSB is 19.53 mV.
Note 10: Typicals are at T
A
=
25˚C and represent most likely parametric norm.
Note 11: Limits are guaranteed to National’s AOQL (Average Output Quality Level). Note 12: Positive integral linearity error is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through positive
full-scale and zero. For negative integral linearity error the straight line passes through negative full-scale and zero. (See
Figure 6 Figure 7
).
Note 13: Zero error is a measure of the deviation from the mid-scale voltage (a code of zero), expressed in LSB. It is the worst-case value of the code transitions between −1 to 0 and 0 to +1 (see
Figure 8
).
Note 14: The DC common-mode error is measured with both inputs shorted together and driven from 0V to 5V.The measured value is referred to the resulting out­put value when the inputs are driven with a 2.5V signal.
Note 15: Power Supply Sensitivity is measured after Auto-Zero and/or Auto-Calibration cycle has been completed with V
A
+ and VD+ at the specified extremes.
Note 16: V
REFCM
(Reference Voltage Common Mode Range) is defined as (V
REF++VREF−
)/2.
DS011264-3
www.national.com9
Page 10
Digital Timing Characteristics (Notes 6, 7, 8, 19) (Continued)
Note 17: The LM12(H)454/8’s self-calibration technique ensures linearity and offset errors as specified, but noise inherent in the self-calibration process will result
in a repeatability uncertainty of
±
0.10 LSB.
Note 18: The Throughput Rate is for a single instruction repeated continuously. Sequencer states 0 (1 clock cycle), 1 (1 clock cycle), 7 (9 clock cycles) and 5 (44 clock cycles) are used (see
Figure 15
). One additional clock cycle is used to read the conversion result stored in the FIFO, for a total of 56 clock cycles per con-
version. The Throughput Rate is f
CLK
(MHz)/N, where N is the number of clock cycles/conversion.
Note 19: A military RETS specification is available upon request.
Electrical Characteristics
DS011264-22
V
REF
=
V
REF+−VREF−
V
IN
=
V
IN+−VIN−
GND ≤ V
IN+≤VA
+
GND ≤ V
IN−≤VA
+
FIGURE 1. The General Case of Output Digital Code vs the Operating Input Voltage Range
www.national.com 10
Page 11
Electrical Characteristics (Continued)
DS011264-23
V
REF+−VREF−
=
4.096V
V
IN
=
V
IN+−VIN−
GND ≤ V
IN+≤VA
+
GND ≤ V
IN−≤VA
+
FIGURE 2. Specific Case of Output Digital Code vs the Operating Input Voltage Range for V
REF
=
4.096V
www.national.com11
Page 12
Electrical Characteristics (Continued)
DS011264-24
V
REF
=
V
REF+−VREF−
FIGURE 3. The General Case of the V
REF
Operating Range
www.national.com 12
Page 13
Electrical Characteristics (Continued)
DS011264-25
V
REF
=
V
REF+−VREF−
VA+=5V
FIGURE 4. The Specific Case of the V
REF
Operating Range for VA+=5V
DS011264-4
FIGURE 5. Transfer Characteristic
www.national.com13
Page 14
Electrical Characteristics (Continued)
DS011264-5
FIGURE 6. Simplified Error Curve vs Output Code without Auto-Calibration or Auto-Zero Cycles
DS011264-6
FIGURE 7. Simplified Error Curve vs Output Code after Auto-Calibration Cycle
DS011264-7
FIGURE 8. Offset or Zero Error Voltage
www.national.com 14
Page 15
Typical Performance Characteristics (Note 9) The following curves apply for 12-bit + sign mode after
auto-calibration unless otherwise specified. The performance for 8-bit + sign and “watchdog” modes is equal to or better than shown.
Linearity Error Change vs Clock Frequency
DS011264-37
Linearity Error Change vs Temperature
DS011264-38
Linearity Error Change vs Reference Voltage
DS011264-39
Linearity Error Change vs Supply Voltage
DS011264-40
Full-Scale Error Change vs Clock Frequency
DS011264-41
Full-Scale Error Change vs Temperature
DS011264-42
Full-Scale Error Change vs Reference Voltage
DS011264-43
Full-Scale Error vs Supply Voltage
DS011264-44
Zero Error Change vs Clock Frequency
DS011264-45
www.national.com15
Page 16
Typical Performance Characteristics (Note 9) The following curves apply for 12-bit + sign mode after
auto-calibration unless otherwise specified. The performance for 8-bit + sign and “watchdog” modes is equal to or better than shown. (Continued)
Zero Error Change vs Temperature
DS011264-46
Zero Error Change vs Reference Voltage
DS011264-47
Zero Error Change vs Supply Voltage
DS011264-48
Analog Supply Current vs Temperature
DS011264-49
Digital Supply Current vs Clock Frequency
DS011264-50
Digital Supply Current vs Temperature
DS011264-51
V
REFOUT
Load Regulation
DS011264-52
V
REFOUT
Line Regulation
DS011264-53
www.national.com 16
Page 17
Typical Dynamic Performance Characteristics The following curves apply for 12-bit + sign
mode after auto-calibration unless otherwise specified.
Bipolar Signal-to-Noise Ratio vs Input Frequency
DS011264-54
Bipolar Signal-to-Noise + Distortion Ratio vs Input Frequency
DS011264-55
Bipolar Signal-to-Noise + Distortion Ratio vs Input Signal Level
DS011264-56
Bipolar Spectral Response with 1.028 kHz Sine Wave Input
DS011264-57
Bipolar Spectral Response with 10 kHz Sine Wave Input
DS011264-58
Bipolar Spectral Response with 20 kHz Sine Wave Input
DS011264-59
Bipolar Spectral Response with 40 kHz Sine Wave Input
DS011264-60
Bipolar Spurious Free Dynamic Range
DS011264-61
Unipolar Signal-to-Noise Ratio vs Input Frequency
DS011264-62
www.national.com17
Page 18
Typical Dynamic Performance Characteristics The following curves apply for 12-bit + sign
mode after auto-calibration unless otherwise specified. (Continued)
Test Circuits and Waveforms
Unipolar Signal-to-Noise + Distortion Ratio vs Input Frequency
DS011264-63
Unipolar Signal-to-Noise + Distortion Ratio vs Input Signal Level
DS011264-64
Unipolar Spectral Response with 1.028 kHz Sine Wave Input
DS011264-65
Unipolar Spectral Response with 10 kHz Sine Wave Input
DS011264-66
Unipolar Spectral Response with 20 kHz Sine Wave Input
DS011264-67
Unipolar Spectral Response with 40 kHz Sine Wave Input
DS011264-68
DS011264-12
DS011264-13
DS011264-14
DS011264-15
FIGURE 9. TRI-STATE Test Circuits and Waveforms
www.national.com 18
Page 19
Timing Diagrams V
A
+=VD+=+5V, t
R
=
t
F
=
3 ns, C
L
=
100 pF for the INT, DMARQ, D0–D15 outputs.
1, 3: CS or Address valid to ALE low set-up time. 2, 4: CS or Address valid to ALE low hold time. 5: ALE pulse width 6: RD high to next ALE high 7: ALE low to RD low 8: RD pulse width 9: RD high to next RD or WR low
10: ALE low to WR low
11: WR pulse width 12: WR high to next ALE high 13: WR high to next WR or RD low 14: Data valid to WR high set-up time 15: Data valid to WR high hold time 16: RD low to data bus out of TRI-STATE 17: RD high to TRI-STATE 18: RD low to data valid (access time)
DS011264-16
FIGURE 10. Multiplexed Data Bus
www.national.com19
Page 20
Timing Diagrams V
A
+=VD+=+5V, t
R
=
t
F
=
3 ns, C
L
=
100 pF for the INT, DMARQ, D0–D15
outputs. (Continued)
8: RD pulse width
9: RD high to next RD or WR low 11: WR pulse width 13: WR high to next WR or RD low 14: Data valid to WR high set-up time 15: Data valid to WR high hold time
16: RD low to data bus out of TRI-STATE 17: RD high to TRI-STATE 18: RD low to data valid (access time) 19: Address invalid from RD or WR high (hold time) 20: CS low or address valid to RD low 21: CS low or address valid to WR low
VA+=VD+=+5V, t
R
=
t
F
=
3 ns, C
L
=
100 pF for the INT, DMARQ, D0–D15 outputs.
22: INT high from RD low 23: DMARQ low from RD low
DS011264-17
FIGURE 11. Non-Multiplexed Data Bus (ALE=1)
DS011264-18
FIGURE 12. Interrupt and DMARQ
www.national.com 20
Page 21
Pin Description
VA+VD+ Analog and digital supply voltage pins. The
LM12(H)454/8’s supply voltage operating range is +3.0V to +5.5V.Accuracy is guaranteed only if V
A
+ and VD+ are connected to the same power supply.Each pin should have a parallel combina­tion of 10 µF (electrolytic or tantalum) and 0.1 µF (ceramic) bypass capacitors connected between it and ground.
D0–D15 The internal data input/output TRI-STATE buffers
are connected to these pins. These buffers are designed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. These pins allows the user a means of instruction input and data out­put. With a logic high applied to the BW pin, data lines D8–D15 are placed in a high impedance state and data lines D0–D7 are used for instruc­tion input and data output when the LM12(H)454/8 is connected to an 8-bit wide data bus. A logic low on the BW pin allows the LM12(H)454/8 to exchange information over a 16-bit wide data bus.
RD
Input for the active low READ bus control signal. The data input/output TRI-STATE buffers, as se­lected by the logic signal applied to the BW pin, are enabled when RD and CS are both low. This allows the LM12(H)454/8 to transmit information onto the databus.
WR
Input for the active low WRITE bus control signal. The data input/output TRI-STATE buffers, as se­lected by the logic signal applied to the BW pin, are enabled when WR and CS are both low. This allows the LM12(H)454/8 to receive information from the databus.
CS
Input for the active low Chip Select control signal. A logic low should be applied to this pin only dur­ing a READ or WRITE access to the LM12(H)454/8. The internal clocking is halted and conversion stops while Chip Select is low. Conversion resumes when the Chip Select input signal returns high.
ALE Address Latch Enable input. It is used in systems
containing a multiplexed databus. When ALE is asserted high, the LM12(H)454/8 accepts infor­mation on the databus as a valid address. A high-to-low transition will latch the address data on A0–A4 while the CS is low. Any changes on A0–A4 and CS while ALE is low will not affect the LM12(H)454/8. See
Figure 10
. When a non-multiplexed bus is used, ALE is continuously asserted high. See
Figure 11
.
CLK External clock input pin. The LM12(H)454/8 oper-
ates with an input clock frequency in the range of
0.05 MHz to 10.0 MHz.
A0–A4 The LM12(H)454/8’s address lines. They are
used to access all internal registers, Conversion FIFO, and Instruction RAM.
SYNC Synchronization input/output. When used as an
output, it is designed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. SYNC is an in- put if the Configuration register’s “I/O Select” bit is low. A rising edge on this pin causes the inter-
nal S/H to hold the input signal. The next rising clock edge either starts a conversion or makes a comparison to a programmable limit depending on which function is requested by a programming instruction. This pin will be an output if “I/O Se­lect” is set high. The SYNC output goes high when a conversion or a comparison is started and low when completed. (See Section 2.2). An internal reset after power is first applied to the LM12(H)454/8 automatically sets this pin as an input.
BW Bus Width input pin. This input allows the
LM12(H)454/8 to interface directly with either an 8- or 16-bit databus.A logic high sets the width to 8 bits and places D8–D15 in a high impedance state. A logic low sets the width to 16 bits.
INT
Active low interrupt output. This output is de­signed to drive capacitive loads of 100 pF or less. External buffers are necessary for driving higher load capacitances. An interrupt signal is gener­ated any time a non-masked interrupt condition takes place. There are eight different conditions that can cause an interrupt. Any interrupt is reset by reading the Interrupt Status register. (See Section 2.3.)
DMARQ Active high Direct Memory Access Request out-
put. This output is designed to drive capacitive loads of 100 pF or less. External buffers are nec­essary for driving higher load capacitances. It goes high whenever the number of conversion results in the conversion FIFO equals a program­mable value stored in the Interrupt Enable regis­ter. It returns to a logic low when the FIFO is empty.
GND LM12(H)454/8 ground connection. It should be
connected to a low resistance and inductance analog ground return that connects directly to the system power supply ground.
IN0–IN7 (IN0–IN3 LM12H454 LM12454)
The eight (LM12(H)458) or four (LM12454) analog inputs. A given channel is selected through the instruction RAM. Any of the chan­nels can be configured as an independent single-ended input. Any pair of channels, whether adjacent or non-adjacent, can operate as a fully differential pair.
S/H IN+ S/H IN−
The LM12454’s non-inverting and inverting in­puts to the internal S/H.
MUXOUT+ MUXOUT−
The LM12454’s non-inverting and inverting out­puts from the internal multiplexer.
V
REF−
The negative reference input. The LM12(H)454/8 operate with 0V ≤ V
REF−
≤
V
REF+
. This pin should be bypassed to ground with a parallel combination of 10 µF and 0.1 µF (ceramic) capacitors.
V
REF+
The positive reference input. The LM12(H)454/8 operate with 0V ≤ V
REF+
≤ VA+. This pin should be bypassed to ground with a parallel combination of 10 µF and 0.1 µF (ce­ramic) capacitors.
V
REFOUT
The internal 2.5V bandgap’s output pin. This pin should be bypassed to ground with a 100 µF capacitor.
www.national.com21
Page 22
Application Information
1.0 Functional Description
The LM12(H)454/8 have three modes of operation:
12-bit + sign with correction
8-bit + sign without correction 8-bit + sign comparison mode (“watchdog” mode)
The fully differential 12-bit-plus-sign ADC uses a charge re­distribution topology that includes calibration capabilities. Charge re-distribution ADCs use a capacitor ladder in place of a resistor ladder to form an internal DAC. The DAC is used by a successive approximation register to generate interme­diate voltages between the voltages applied to V
REF−
and
V
REF+
. These intermediate voltages are compared against the sampled analog input voltage as each bit is generated. The number of intermediate voltages and comparisons equals the ADC’s resolution. The correction of each bit’s ac­curacy is accomplished by calibrating the capacitor ladder used in the ADC.
Two different calibration modes are available; one compen­sates for offset voltage, or zero error,while the other corrects both offset error and the ADC’s linearity error.
When correcting offset only, the offset error is measured once and a correction coefficient is created. During the full calibration, the offset error is measured eight times, aver­aged, and a correction coefficient is created. After comple­tion of either calibration mode, the offset correction coeffi­cient is stored in an internal offset correction register.
The LM12(H)454/8’s overall linearity correction is achieved by correcting the internal DAC’s capacitor mismatch. Each capacitor is compared eight times against all remaining smaller value capacitors and any errors are averaged. Acor­rection coefficient is then created and stored in one of the thirteen internal linearity correction registers. An internal state machine, using patterns stored in an internal 16 x 8-bit ROM, executes each calibration algorithm.
Once calibrated, an internal arithmetic logic unit (ALU) uses the offset correction coefficient and the 13 linearity correction coefficients to reduce the conversion’s offset error and lin­earity error, in the background, during the 12-bit + sign con­version. The 8-bit + sign conversion and comparison modes use only the offset coefficient. The 8-bit + sign mode per­forms a conversion in less than half the time used by the 12-bit + sign conversion mode.
The analog input multiplexer can be configured for any com­bination of single-ended or fully differential operation. Each input is referenced to ground when a multiplexer channel op­erates in the single-ended mode. Fully differential analog in­put channels are formed by pairing any two channels to­gether.
The LM12454’s multiplexer outputs and S/H inputs (MUX­OUT+, MUXOUT− and S/H IN+, S/H IN−) provide the option for additional analog signal processing. Fixed-gain amplifi­ers, programmable-gain amplifiers, filters, and other pro­cessing circuits can operate on the signal applied to the se­lected multiplexer channel(s). If external processing is not used, connect MUXOUT+ to S/H IN+ and MUXOUT− to S/H IN−.
The LM12(H)454/8’s internal S/H is designed to operate at its minimum acquisition time (1.13 µs, 12 bits) when the source impedance, R
S
,is≤60Ω (f
CLK
≤ 8 MHz). When 60Ω
<
RS≤ 4.17 kΩ, the internal S/H’s acquisition time can be in-
creased to a maximum of 4.88 µs (12 bits, f
CLK
=
8 MHz). See Section 2.1 (Instruction RAM “00”) Bits 12–15 for more information.
An internal 2.5V bandgap reference output is available at pin
44. This voltage can be used as the ADC reference for ratio­metric conversion or as a virtual ground for front-end analog conditioning circuits. The V
REFOUT
pin should be bypassed
to ground with a 100 µF capacitor. Microprocessor overhead is reduced through the use of the
REFOUT,VREF+,VREF−
, and GND pins to the
internal V
IN+
and V
IN−
S/H inputs. This mode is activated by setting the Diagnostic bit (Bit 11) in the Configuration register to a “1”. More information concerning this mode of operation can be found in Section 2.2.
2.0 Internal User-Programmable Registers
INSTRUCTION RAM
The instruction RAM holds up to eight sequentially execut­able instructions. Each 48-bit long instruction is divided into three 16-bit sections. READ and WRITE operations can be issued to each 16-bit section using the instruction’s address and the 2-bit “RAM pointer” in the Configuration register. The eight instructions are located at addresses 0000 through 0111 (A4–A1, BW=0) when using a 16-bit wide data bus or at addresses 00000 through 01111 (A4– A0, BW=1) when using an 8-bit wide data bus. They can be accessed and pro­grammed in random order.
www.national.com 22
Page 23
2.0 Internal User-Programmable Registers
(Continued)
Any Instruction RAM READ or WRITE can affect the se­quencer’s operation:
The Sequencer should be stopped by setting the RESET bit to a “1” or by resetting the STARTbit in the Configura­tion Register and waiting for the current instruction to fin­ish execution before any Instruction RAM READ or WRITE is initiated.
A soft RESET should be issued by writing a “1” to the Configuration Register’s RESET bit after any READ or WRITE to the Instruction RAM.
The three sections in the Instruction RAM are selected by the Configuration Register’s 2-bit “RAM Pointer”, bits D8 and D9. The first 16-bit Instruction RAM section is selected with the RAM Pointer equal to “00”. This section provides multi­plexer channel selection, as well as resolution, acquisition time, etc. The second 16-bit section holds “watchdog” limit
#
1, its sign, and an indicator that shows that an interrupt can be generated if the input signal is greater or less than the programmed limit. The third 16-bit section holds “watchdog” limit
#
2, its sign, and an indicator that shows that an interrupt can be generated if the input signal is greater or less than the programmed limit.
Instruction RAM “00” Bit 0 is the LOOP bit. It indicates the last instruction to be ex-
Bit 1 is the PAUSEbit. This controls the Sequencer’s opera­tion. When the PAUSEbit is set (“1”), the Sequencer will stop after reading the current instruction and before executing it, and the start bit in the Configuration register is automatically reset to a “0”. Setting the PAUSE also causes an interrupt to be issued. The Sequencer is restarted by placing a “1” in the Configuration register’s Bit 0 (Start bit).
After the Instruction RAM has been programmed and the RESET bit is set to “1”, the Sequencer retrieves Instruction 000, decodes it, and waits for a “1” to be placed in the Con­figuration’s START bit. The START bit value of “0” “over­rides” the action of Instruction 000’s PAUSE bit when the Se­quencer is started. Once started, the Sequencer executes Instruction 000 and retrieves, decodes, and executes each of the remaining instructions. No PAUSE Interrupt (INT 5) is generated the first time the Sequencer executes Instruction 000 having a PAUSE bit set to “1”. When the Sequencer en­counters a LOOP bit or completes all eight instructions, In­struction 000 is retrieved and decoded. A set PAUSE bit in Instruction 000 now halts the Sequencer before the instruc­tion is executed.
Bits 2–4 select which of the eight input channels (“000” to “111” for IN0–IN7) will be configured as non-inverting inputs to the LM12(H)458’s ADC. (See Page 27,
Table1
.) They se­lect which of the four input channels (“000” to “011” for IN0–IN4) will be configured as non-inverting inputs to the LM12454’s ADC. (See Page 27,
Table 2
.)
Bits 5–7 select which of the seven input channels (“001” to “111” for IN1 to IN7) will be configured as inverting inputs to the LM12(H)458’s ADC. (See Page 27,
Table1
.) They select which of the three input channels (“001” to “011” for IN1–IN4) will be configured as inverting inputs to the LM12454’s ADC. (See Page 27,
Table2
.) Fully differential operation is created
by selecting two multiplexer channels, one operating in the
non-inverting mode and the other operating in the inverting mode. A code of “000” selects ground as the inverting input for single ended operation.
Bit 8 is the SYNC bit. Setting Bit 8 to “1” causes the Se­quencer to suspend operation at the end of the internal S/H’s acquisition cycle and to wait until a rising edge appears at the SYNC pin. When a rising edge appears, the S/H ac­quires the input signal magnitude and the ADC performs a conversion on the clock’s next rising edge. When the SYNC pin is used as an input, the Configuration register’s “I/O Se­lect” bit (Bit 7) must be set to a “0”. With SYNC configured as an input, it is possible to synchronize the start of a conver­sion to an external event. This is useful in applications such as digital signal processing (DSP) where the exact timing of conversions is important.
When the LM12(H)454/8 are used in the “watchdog” mode with external synchronization, two rising edges on the SYNC input are required to initiate two comparisons. The first rising edge initiates the comparison of the selected analog input signal with Limit
#
1 (found in Instruction RAM “01”) and the second rising edge initiates the comparison of the same ana­log input signal with Limit
#
2 (found in Instruction RAM “10”).
Bit 9 is the TIMER bit. When Bit 9 is set to “1”, the Se­quencer will halt until the internal 16-bit Timer counts down to zero. During this time interval, no “watchdog” comparisons or analog-to-digital conversions will be performed.
Bit 10 selects the ADC conversion resolution. Setting Bit 10 to “1” selects 8-bit + sign and when reset to “0” selects 12-bit + sign.
Bit 11 is the “watchdog” comparison mode enable bit. When operating in the “watchdog” comparison mode, the selected analog input signal is compared with the programmable val­ues stored in Limit
#
1 and Limit#2 (see Instruction RAM “01” and Instruction RAM “10”). Setting Bit 11 to “1” causes two comparisons of the selected analog input signal with the two stored limits. When Bit 11 is reset to “0”, an 8-bit + sign or 12-bit + sign (depending on the state of Bit 10 of Instruction RAM “00”) conversion of the input signal can take place.
www.national.com23
Page 24
2.0 Internal User-Programmable Registers (Continued)
A4 A3A2A1 Purpose Type D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 Instruction RAM R/W Acquisition Watch- V
IN−
V
IN+
0 to (RAM Pointer
=
00) Time dog 8/12 Timer Sync (MUXOUT−) (MUXOUT+) Pause Loop
111 (Note 20) (Note 20)
0 0 0 Instruction RAM R/W
0 to (RAM Pointer
=
01) Don’t Care
>
/
<
Sign Limit
#
1
111
0 0 0 Instruction RAM R/W
0 to (RAM Pointer
=
10) Don’t Care
>
/
<
Sign Limit
#
2
111
1 0 0 0 Configuration R/W Don’t Care DIAG Test RAM I/O Auto Chan Stand- Full Auto- Reset Start
Register (Note 21)
=
0 Pointer Sel Zero
ec
Mask by CAL Zero
Interrupt Enable R/W Number of Conversions Sequencer INT7 INT6 INT5 INT4 INT3 INT2 INT1 INT0
1 0 0 1 Register in Conversion FIFO Address to
to Generate INT2 Generate INT1
Address
R Actual Number of of INST7 INST6 INST5 INST4 INST3 INST2 INST1 INST0
1 0 1 0 Interrupt Status Conversion Results Sequencer
Register in Conversion FIFO Instruction
being
Executed
1 0 1 1 Timer R/W Timer Preset High Byte Timer Preset Low Byte
Register
1 1 0 0 Conversion R Address Sign Conversion Conversion Data: LSBs
FIFO or Sign Data: MSBs
1 1 0 1 Limit Status R Limit
#
2: Status Limit
#
1: Status
Register
Note 20: LM12454 (Refer to
Table 2
).
Note 21: LM12(H)458 only. Must be set to “0” for the LM12454.
FIGURE 13. LM12(H)454/8 Memory Map for 16-Bit Wide Databus (BW
=
“0”, Test Bit
=
“0” and A0
=
Don’t Care)
www.national.com 24
Page 25
2.0 Internal User-Programmable Registers (Continued)
Note 22: LM12454 (Refer to
Table 2
).
Note 23: LM12(H)458 only. Must be set to “0” for the LM12454.
A4 A3 A2 A1 A0 Purpose Type D7 D6 D5 D4 D3 D2 D1 D0
000
Instruction
RAM
(RAM
Pointer
=
00)
R/W V
IN−
(MUXOUT−) (Note 22)
V
IN+
(MUXOUT+) (Note 22)
0to0 Pause Loop
111 0 0 0 R/W Watch-
0 to 1 Acquisition Time dog 8/12 Timer Sync
111 000
Instruction
RAM
(RAM
Pointer
=
01)
R/W
0 to 0 Comparison Limit
#
1 111 000 R/W
0 to 1 Don’t Care
>/<
Sign 111 000
Instruction
RAM
(RAM
Pointer
=
10)
R/W
0 to 0 Comparison Limit
#
2 111 000 R/W
0 to 1 Don’t Care
>/<
Sign
111
10000
Configuration
Register
R/W I/O Auto Chan Stand- Full Auto- Reset Start
Sel Zero
ec
Mask by Cal Zero
10001 R/W
Don’t Care
DIAG (Note
23)
Test
=
0
RAM Pointer
10010
Interrupt
Enable
Register
R/W INT7 INT6 INT5 INT4 INT3 INT2 INT1 INT0
10011 R/W Number of Conversions in Conversion Sequencer Address to
FIFO to Generate INT2 Generate INT1
10100
Interrupt
Status
Register
R INST7 INST6 INST5 INST4 INST3 INST2 INST1 INST0
10101 R Actual Number of Conversions Results Address of Sequencer
in Conversion FIFO Instruction
being Executed
10110
Timer
Register
R/W Timer Preset: Low Byte 10111 R/W Timer Preset: High Byte 11000
Conversion
FIFO
R Conversion Data: LSBs 11001 R Address or Sign Sign Conversion Data: MSBs 11010
Limit Status
Register
R Limit
#
1 Status
11011 R Limit
#
2 Status
FIGURE 14. LM12(H)454/8 Memory Map for 8-Bit Wide Databus (BW=“1” and Test Bit=“0”)
www.national.com25
Page 26
2.0 Internal User-Programmable Registers
(Continued)
Bits 12–15 are used to store the user-programmable acqui­sition time. The Sequencer keeps the internal S/H in the ac­quisition mode for a fixed number of clock cycles (nine clock cycles, for 12-bit + sign conversions and two clock cycles for 8-bit + sign conversions or “watchdog” comparisons) plus a variable number of clock cycles equal to twice the value stored in Bits 12–15. Thus, the S/H’s acquisition time is (9 + 2D) clock cycles for 12-bit + sign conversions and (2 + 2D) clock cycles for 8-bit + sign conversions or “watchdog” com­parisons, where D is the value stored in Bits 12–15. The minimum acquisition time compensates for the typical inter­nal multiplexer series resistance of 2 kΩ, and any additional delay created by Bits 12–15 compensates for source resis­tances greater than 60Ω (100Ω). (For this acquisition time discussion, numbers in ( ) are shown for the LM12(H)454/8 operating at 5 MHz.) The necessary acquisition time is deter­mined by the source impedance at the multiplexer input. If the source resistance (R
S
)<60Ω (100Ω) and the clock fre-
quency is 8 MHz, the value stored in bits 12–15 (D) can be
0000. If R
S
>
60Ω (100Ω), the following equations determine
the value that should be stored in bits 12–15.
D=0.45 x R
SxfCLK
for 12-bits + sign
D=0.36 x R
SxfCLK
for 8-bits + sign and “watchdog” R
S
is in kΩ and f
CLK
is in MHz. Round the result to the next higher integer value. If D is greater than 15, it is advisable to lower the source impedance by using an analog buffer be­tween the signal source and the LM12(H)458’s multiplexer inputs. The value of D can also be used to compensate for the settling or response time of external processing circuits connected between the LM12454’s MUXOUT and S/H IN pins.
Instruction RAM “01”
The second Instruction RAM section is selected by placing a “01” in Bits 8 and 9 of the Configuration register.
Bits 0–7hold “watchdog” limit
#
1. When Bit 11of Instruction
RAM “00” is set to a “1”, the LM12(H)454/8 performs a “watchdog” comparison of the sampled analog input signal with the limit
#
1 value first, followed by a comparison of the same sampled analog input signal with the value found in limit
#
2 (Instruction RAM “10”).
Bit 8 holds limit
#
1’s sign.
Bit 9’s state determines the limit condition that generates a “watchdog” interrupt. A “1” causes a voltage greater than limit
#
1 to generate an interrupt, while a “0” causes a voltage
less than limit
#
1 to generate an interrupt.
Bits 10–15 are not used.
Instruction RAM “10”
The third Instruction RAM section is selected by placing a “10” in Bits 8 and 9 of the Configuration register.
Bits 0–7hold “watchdog” limit
#
2. When Bit 11of Instruction
RAM “00” is set to a “1”, the LM12(H)454/8 performs a “watchdog” comparison of the sampled analog input signal with the limit
#
1 value first (Instruction RAM “01”), followed by a comparison of the same sampled analog input signal with the value found in limit
#
2.
Bit 8 holds limit
#
2’s sign.
#
2 to generate an interrupt, while a “0” causes a voltage
less than limit
#
2 to generate an interrupt.
Bits 10–15 are not used.
2.2 CONFIGURATION REGISTER
The Configuration register, 1000 (A4–A1, BW=0) or 1000x (A4–A0, BW=1) is a 16-bit control register with read/write capability.It acts as the LM12454’s and LM12(H)458’s “con­trol panel” holding global information as well as start/stop, re­set, self-calibration, and stand-by commands.
Bit 0 is the START/STOP bit. Reading Bit 0 returns an indi­cation of the Sequencer’s status. A “0” indicates that the Se­quencer is stopped and waiting to execute the next instruc­tion. A “1” shows that the Sequencer is running. Writing a “0” halts the Sequencer when the current instruction has fin­ished execution. The next instruction to be executed is pointed to by the instruction pointer found in the status reg­ister. A “1” restarts the Sequencer with the instruction cur­rently pointed to by the instruction pointer. (See Bits 8–10 in the Interrupt Status register.)
Bit 1 is the LM12(H)454/8’s system RESET bit. Writing a “1” to Bit 1 stops the Sequencer (resetting the Configuration reg­ister’s START/STOP bit), resets the Instruction pointer to “000” (found in the Interrupt Status register), clears the Con­version FIFO, and resets all interrupt flags. The RESET bit will return to “0” after two clock cycles unless it is forced high by writing a “1” into the Configuration register’s Standby bit. A reset signal is internally generated when power is first ap­plied to the part. No operation should be started until the RE­SET bit is “0”.
Writing a “1” to Bit 3 initiates a complete calibration process that includes a “long” auto-zero offset voltage correction (this calibration averages eight samples of the comparator offset voltage when creating a correction coefficient) followed by an ADC linearity calibration. This complete calibration is started after the currently running instruction is completed if the Sequencer is running when Bit 3 is set to “1”. Bit 3 is re­set automatically to a “0” and an interrupt flag (Bit 4, in the In­terrupt Status register) will be generated at the end of the calibration procedure (4944 clock cycles). After completion of a full auto-zero and linearity calibration, the Sequencer fetches the next instruction as pointed to by the Instruction RAM’s pointer and resumes execution. If the Sequencer is stopped, a full calibration is performed immediately at the time requested.
Bit 4 is the Standby bit. Writing a “1” to Bit 4 immediately places the LM12(H)454/8 in Standby mode. Normal opera­tion returns when Bit 4 is reset to a “0”. The Standby com-
www.national.com 26
Page 27
2.0 Internal User-Programmable Registers
(Continued)
Bit 5 is the Channel Address Mask. If Bit 5 is set to a “1”, Bits 13–15 in the conversion FIFO will be equal to the sign bit (Bit
12) of the conversion data. Resetting Bit 5 to a “0” causes conversion data Bits 13 through 15 to hold the instruction pointer value of the instruction to which the conversion data belongs.
Bit 6 is used to select a “short” auto-zero correction for every conversion. The Sequencer automatically inserts an auto-zero before every conversion or “watchdog” compari­son if Bit 6 is set to “1”. No automatic correction will be per­formed if Bit 6 is reset to “0”.
The LM12(H)454/8’s offset voltage, after calibration, has a typical drift of 0.1 LSB over a temperature range of −40˚C to +85˚C. This small drift is less than the variability of the change in offset that can occur when using the auto-zero correction with each conversion. This variability is the result of using only one sample of the offset voltage to create a cor­rection value. This variability decreases when using the full calibration mode because eight samples of the offset voltage are taken, averaged, and used to create a correction value.
Bit 7 is used to program the SYNC pin (29) to operate as ei­ther an input or an output. The SYNC pin becomes an output when Bit 7 is a “1” and an input when Bit 7 is a “0”. With SYNC programmed as an input, the rising edge of any logic signal applied to pin 29 will start a conversion or “watchdog” comparison. Programmed as an output, the logic level at pin 29 will go high at the start of a conversion or “watchdog” comparison and remain high until either have finished. See Instruction RAM “00”, Bit 8.
Bits 8 and 9 form the RAM Pointer that is used to select each of a 48-bit instruction’s three 16-bit sections during read or write actions. A “00” selects Instruction RAM section one, “01” selects section two, and “10” selects section three.
Bit 10 activates the Test mode that is used only during pro­duction testing. Leave this bit reset to “0”.
Bit 11 is the Diagnostic bit and is available only in the LM12(H)458. It can be activated by setting it to a “1” (theTest bit must be reset to a “0”). The Diagnostic mode, along with a correctly chosen instruction, allows verification that the LM12(H)458’s ADC is performing correctly. When activated, the inverting and non-inverting inputs are connected as shown in Table I.As an example, an instruction with “001” for both V
IN+
and V
IN−
while using the Diagnostic mode typically
results in a full-scale output.
2.3 INTERRUPTS
The LM12454 and LM12(H)458 have eight possible inter­rupts, all with the same priority. Any of these interrupts will cause a hardware interrupt to appear on the INT pin (31) if
they are not masked (by the Interrupt Enable register). The Interrupt Status register is then read to determine which of the eight interrupts has been issued.
TABLE 1. LM12(H)458 Input Multiplexer
Channel Configuration Showing Normal
Mode and Diagnostic Mode
Channel
Selection
Data
Normal Diagnostic
Mode Mode
V
IN+
V
IN−
V
IN+
V
IN−
000 IN0 GND V
REFOUT
GND
001 IN1 IN1 V
REF+
V
REF−
010 IN2 IN2 IN2 IN2 011 IN3 IN3 IN3 IN3 100 IN4 IN4 IN4 IN4 101 IN5 IN5 IN5 IN5 110 IN6 IN6 IN6 IN6 111 IN7 IN7 IN7 IN7
TABLE 2. LM12454 Input Multiplexer
Channel Configuration
Channel
Selection MUX+ MUX−
Data
000 IN0 GND 001 IN1 IN1 010 IN2 IN2 011 IN3 IN3
1XX OPEN OPEN
The Interrupt Status register, 1010 (A4–A1, BW=0) or 1010x (A4–A0, BW=1) must be cleared by reading it after writing to the Interrupt Enable register. This removes any spurious interrupts on the INT pin generated during an Inter­rupt Enable register access.
Interrupt 0 is generated whenever the analog input voltage on a selected multiplexer channel crosses a limit while the LM12(H)454/8 are operating in the “watchdog” comparison mode. Two sequential comparisons are made when the LM12(H)454/8 are executing a “watchdog” instruction. De­pending on the logic state of Bit 9 in the Instruction RAM’s second and third sections, an interrupt will be generated ei­ther when the input signal’s magnitude is greater than or less than the programmable limits. (See the Instruction RAM, Bit 9 description.) The Limit Status register will indicate which preprogrammed limit,
#
1or#2 and which instruction was ex-
ecuting when the limit was crossed. Interrupt 1 is generated when the Sequencer reaches the
instruction counter value specified in the Interrupt Enable register’s bits 8–10. This flag appears before the instruc­tion’s execution.
Interrupt 2 is activated when the Conversion FIFO holds a number of conversions equal to the programmable value stored in the Interrupt Enable register’s Bits 11–15. This value ranges from 0001 to 1111, representing 1 to 31 conver­sions stored in the FIFO. A user-programmed value of 0000 has no meaning. See Section 3.0 for more FIFO information.
The completion of the short, single-sampled auto-zero cali­bration generates Interrupt 3.
www.national.com27
Page 28
2.0 Internal User-Programmable Registers
(Continued)
Interrupt 5 is generated when the Sequencer encounters an instruction that has its Pause bit (Bit 1 in Instruction RAM “00”) set to “1”.
The LM12(H)454/8 issues Interrupt 6 whenever it senses that its power supply voltage is dropping below 4V (typ). This interrupt indicates the potential corruption of data returned by the LM12(H)454/8.
Interrupt 7 is issued after a short delay (10 ms typ) while the LM12(H)454/8 returns from Standby mode to active opera­tion using the Configuration register’s Bit 4. This short delay allows the internal analog circuitry to settle sufficiently, en­suring accurate conversion results.
2.4 INTERRUPT ENABLE REGISTER
The Interrupt Enable register at address location 1001 (A4–A1, BW=0) or 1001x (A4–A0, BW=1) has READ/ WRITE capability. An individual interrupt’s ability to produce an external interrupt at pin 31 (INT) is accomplished by plac­ing a “1” in the appropriate bit location. Any of the internal interrupt-producing operations will set their corresponding bits to “1” in the Interrupt Status register regardless of the state of the associated bit in the Interrupt Enable register. See Section 2.3 for more information about each of the eight internal interrupts.
Bit 0 enables an external interrupt when an internal “watch­dog” comparison limit interrupt has taken place.
Bit 2 enables an external interrupt when the Conversion FIFO’s limit, stored in Bits 11–15 of the Interrupt Enable reg­ister, has been reached.
Bit 4 enables an external interrupt when a full auto-zero and linearity self-calibration has been completed.
Bit 5 enables an external interrupt when an internal Pause interrupt has been generated.
Bit 6 enables an external interrupt when a low power supply condition (V
A
+<4V) has generated an internal interrupt.
Bit 7 enables an external interrupt when the LM12(H)454/8 return from power-down to active mode.
Bits 8–10 form the storage location of the user-programmable value against which the Sequencer’s address is compared. When the Sequencer reaches an ad­dress that is equal to the value stored in Bits 8–10, an inter­nal interrupt is generated and appears in Bit 1 of the Interrupt Status register. If Bit 1 of the Interrupt Enable register is set to “1”, an external interrupt will appear at pin 31 (INT).
The value stored in bits 8–10 ranges from 000 to 111, repre­senting 0 to 7 instructions stored in the Instruction RAM. Af­ter the Instruction RAM has been programmed and the RE­SET bit is set to “1”, the Sequencer is started by placing a “1” in the Configuration register’s START bit. Setting the INT 1 trigger value to 000 does not generate an INT 1 the first time the Sequencer retrieves and decodes Instruction 000. The Sequencer generates INT 1 (by placing a “1” in the In­terrupt Status register’s Bit 1) the second time and after the Sequencer encounters Instruction 000. It is important to re-
member that the Sequencer continues to operate even if an Instruction interrupt (INT 1) is internally or externally gener­ated. The only mechanisms that stop the Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruc­tion execution), placing a “0” in the Configuration register’s STARTbit,or placing a “1” in the Configuration register’s RE­SET bit.
Bits 11–15 hold the number of conversions that must be stored in the Conversion FIFO in order to generate an inter­nal interrupt. This internal interrupt appears in Bit 2 of the In­terrupt Status register. If Bit 2 of the Interrupt Enable register is set to “1”, an external interrupt will appear at pin 31 (INT).
2.5 INTERRUPT STATUS REGISTER
This read-only register is located at address 1010 (A4–A1, BW=0) or 1010x (A4–A0,BW=1). The corresponding flag in the Interrupt Status register goes high (“1”) any time that an interrupt condition takes place, whether an interrupt is en­abled or disabled in the Interrupt Enable register. Any of the active (“1”) Interrupt Status register flags are reset to “0” whenever this register is read or a device reset is issued (see Bit 1 in the Configuration Register).
Bit 0 is set to “1” when a “watchdog” comparison limit inter­rupt has taken place.
Bit 1 is set to “1” when the Sequencer has reached the ad­dress stored in Bits 8–10 of the Interrupt Enable register.
Bit 2 is set to “1” when the Conversion FIFO’s limit, stored in Bits 11–15 of the Interrupt Enable register, has been reached.
Bit 3 is set to “1” when the single-sampled auto-zero has been completed.
Bit 4 is set to “1” when an auto-zero and full linearity self-calibration has been completed.
Bit 5 is set to “1” when a Pause interrupt has been gener­ated.
A
+<4V) has taken place.
Bit 7 is set to “1” when the LM12(H)454/8 return from power-down to active mode.
2.6 LIMIT STATUS REGISTER
The read-only register is located at address 1101 (A4–A1, BW=0) or 1101x (A4–A0, BW=1). This register is used in tandem with the Limit
#
1 and Limit#2 registers in the Instruc­tion RAM. Whenever a given instruction’s input voltage ex­ceeds the limit set in its corresponding Limit register (
#
1or
#
2), a bit, corresponding to the instruction number, is set in the Limit Status register. Any of the active (“1”) Limit Status flags are reset to “0” whenever this register is read or a de­vice reset is issued (see Bit 1 in the Configuration register). This register holds the status of limits
#
1 and#2 for each of
the eight instructions. Bits 0–7 show the Limit
#
1 status. Each bit will be set high (“1”) when the corresponding instruction’s input voltage ex­ceeds the threshold stored in the instruction’s Limit
#
1 regis­ter. When, for example, instruction 3 is a “watchdog” opera­tion (Bit 11 is set high) and the input for instruction 3 meets the magnitude and/or polarity data stored in instruction 3’s Limit
#
1 register, Bit 3 in the Limit Status register will be set
to a “1”.
www.national.com 28
Page 29
2.0 Internal User-Programmable Registers
(Continued)
Bits 8–15 show the Limit
#
2 status. Each bit will be set high (“1”) when the corresponding instruction’s input voltage ex­ceeds the threshold stored in the instruction’s Limit
#
2 regis­ter. When, for example, the input to instruction 6 meets the value stored in instruction 6’s Limit
#
2 register, Bit 14 in the
Limit Status register will be set to a “1”.
2.7 TIMER
The LM12(H)454/8 have an on-board 16-bit timer that in­cludes a 5-bit pre-scaler. It uses the clock signal applied to pin 23 as its input. It can generate time intervals of 0 through 2
21
clock cycles in steps of 25. This time interval can be used to delay the execution of instructions. It can also be used to slow the conversion rate when converting slowly changing signals. This can reduce the amount of redundant data stored in the FIFO and retrieved by the controller.
The user-defined timing value used by the Timer is stored in the 16-bit READ/WRITE Timer register at location 1011 (A4–A1, BW=0) or 1011x (A4–A0, BW=1) and is pre-loaded automatically. Bits 0–7 hold the preset value’s low byte and Bits 8–15 hold the high byte. The Timer is ac­tivated by the Sequencer only if the current instruction’s Bit 9 is set (“1”). If the equivalent decimal value “N” (0 ≤ N ≤ 2
16
−
1) is written inside the 16-bit Timer register and the Timer is enabled by setting an instruction’s bit 9 to a “1”, the Se­quencer will delay the same instruction’s execution by halt­ing at state 3 (S3), as shown in
Figure 15
, for 32 x N + 2
clock cycles.
2.8 DMA
The DMA works in tandem with Interrupt 2. An active DMA Request on pin 32 (DMARQ) requires that the FIFO interrupt be enabled. The voltage on the DMARQ pin goes high when the number of conversions in the FIFO equals the 5-bit value stored in the Interrupt Enable register (bits 11–15). The volt­age on the INT pin goes low at the same time as the voltage on the DMARQ pin goes high. The voltage on the DMARQ pin goes low when the FIFO is emptied. The Interrupt Status register must be read to clear the FIFO interrupt flag in order to enable the next DMA request.
DMA operation is optimized through the use of the 16-bit databus connection (a logic “0” applied to the BW pin). Using this bus width allows DMA controllers that have single ad­dress Read/Write capability to easily unload the FIFO. Using DMA on an 8-bit databus is more difficult. Two read opera­tions (low byte, high byte) are needed to retrieve each con­version result from the FIFO. Therefore, the DMA controller must be able to repeatedly access two constant addresses when transferring data from the LM12(H)454/8 to the host system.
3.0 FIFO
The result of each conversion stored in an internal read-only FIFO (First-In, First-Out) register. It is located at 1100 (A4–A1, BW=0) or 1100x (A4–A0, BW=1). This register has 32 16-bit wide locations. Each location holds 13-bit data. Bits 0–3 hold the four LSB’s in the 12 bits + sign mode or “1110” in the 8 bits + sign mode. Bits 4–11 hold the eight MSB’s and Bit 12 holds the sign bit. Bits 13–15 can hold ei­ther the sign bit, extending the register’s two’s complement data format to a full sixteen bits or the instruction address
that generated the conversion and the resulting data. These modes are selected according to the logic state of the Con­figuration register’s Bit 5.
The lower portion (A0=0) of the data word (Bits 0–7)should be read first followed by a read of the upper portion (A0=1) when using the 8-bit bus width (BW=1). Reading the upper portion first causes the data to shift down, which results in loss of the lower byte.
Bits 0–12 hold 12-bit + sign conversion data. Bits 0–3 will be 1110 (LSB) when using 8-bit plus sign resolution.
Using the FIFO’s full depth is achieved as follows. Set the value of the Interrupt Enable register’s Bits 11–15 to 11111 and the Interrupt Enable register’s Bit 2 to a “1”. This gener­ates an external interrupt when the 31st conversion is stored in the FIFO. This gives the host processor a chance to send a “0” to the LM12(H)454/8’s Start bit (Configuration register) and halt the ADC before it completes the 32nd conversion. The Sequencer halts after the current (32) conversion is completed. The conversion data is then transferred to the FIFO and occupies the 32nd location. FIFO overflow is avoided if the Sequencer is halted before the start of the 32nd conversion by placing a “0” in the Start bit (Configura­tion register). It is important to remember that the Sequencer
continues to operate even if a FIFO interrupt (INT 2) is in­ternally or externally generated. The only mechanisms
that stop the Sequencer are an instruction with the PAUSE bit set to “1” (halts before instruction execution), placing a “0” in the Configuration register’s START bit, or placing a “1” in the Configuration register’s RESET bit.
www.national.com29
Page 30
4.0 Sequencer
The Sequencer uses a 3-bit counter (Instruction Pointer, or IP, in
Figure 9
) to retrieve the programmable conversion in­structions stored in the Instruction RAM. The 3-bit counter is reset to 000 during chip reset or if the current executed in­struction has its Loop bit (Bit 1 in any Instruction RAM “00”) set high (“1”). It increments at the end of the currently ex­ecuted instruction and points to the next instruction. It will continue to increment up to 111 unless an instruction’s Loop bit is set. If this bit is set, the counter resets to “000” and ex­ecution begins again with the first instruction. If all instruc­tions have their Loop bit reset to “0”, the Sequencer will ex­ecute all eight instructions continuously. Therefore, it is important to realize that if less than eight instructions are programmed, the Loop bit on the last instruction must be set. Leaving this bit reset to “0” allows the Sequencer to execute “unprogrammed” instructions, the results of which may be unpredictable.
The Sequencer’s Instruction Pointer value is readable at any time and is found in the Status register at Bits 8–10. The Se­quencer can go through eight states during instruction ex­ecution:
State 0: The current instruction’s first 16 bits are read from
the Instruction RAM “00”. This state is one clock cycle long.
State 1: Checks the state of the Calibration and Start bits. This is the “rest” state whenever the Sequencer is stopped using the reset, a Pause command, or the Start bit is reset low (“0”). When the Start bit is set to a “1”, this state is one clock cycle long.
State 2: Perform calibration. If bit 2 or bit 6 of the Configu­ration register is set to a “1”, state 2 is 76 clock cycles long. If the Configuration register’s bit 3 is set to a “1”, state 2 is 4944 clock cycles long.
State 3: Run the internal 16-bit Timer. The number of clock cycles for this state varies according to the value stored in the Timer register. The number of clock cycles is found by using the expression below
32T + 2
where 0 ≤ T ≤ 2
16
−1.
State 7: Run the acquisition delay and read Limit
#
1’s value if needed. The number of clock cycles for 12-bit + sign mode varies according to
9+2D
where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D ≤ 15.
The number of clock cycles for 8-bit + sign or “watchdog” mode varies according to
2+2D
where D is the user-programmable 4-bit value stored in bits 12–15 of Instruction RAM “00” and is limited to 0 ≤ D ≤ 15.
State 6: Perform first comparison. This state is 5 clock
cycles long.
State 4: Read Limit
#
2. This state is 1 clock cycle long.
State 5: Perform a conversion or second comparison. This state takes 44 clock cycles when using the 12-bit + sign mode or 21 clock cycles when using the 8-bit + sign mode. The “watchdog” mode takes 5 clock cycles.
www.national.com 30
Page 31
4.0 Sequencer (Continued)
DS011264-19
FIGURE 15. Sequencer Logic Flow Chart (IP=Instruction Pointer)
www.national.com31
Page 32
5.0 Analog Considerations
5.1 REFERENCE VOLTAGE
The difference in the voltages applied to the V
REF+
and
V
REF−
defines the analog input voltage span (the difference between the voltages applied between two multiplexer inputs or the voltage applied to one of the multiplexer inputs and analog ground), over which 4095 positive and 4096 negative codes exist. The voltage sources driving V
REF+
or V
REF−
must have very low output impedance and noise. The ADC can be used in either ratiometric or absolute refer-
ence applications. In ratiometric systems, the analog input voltage is proportional to the voltage used for the ADC’s ref­erence voltage. When this voltage is the system power sup­ply, the V
REF+
pin is connected to VA+ and V
REF−
is con­nected to GND. This technique relaxes the system reference stability requirements because the analog input voltage and the ADC reference voltage move together. This maintains the same output code for given input conditions.
For absolute accuracy,where the analog input voltage varies between very specific voltage limits, a time and temperature stable voltage source can be connected to the reference in­puts. Typically,thereference voltage’s magnitude will require an initial adjustment to null reference voltage induced full-scale errors.
0.1 µF capacitor connected to the V
REFOUT
pin is recom­mended for low noise operation. When left unconnected, the reference remains stable without a bypass capacitor. How­ever, ensure that stray capacitance at the V
REFOUT
pin re-
mains below 50 pF.
5.2 INPUT RANGE
The LM12(H)454/8’s fully differential ADC and reference voltage inputs generate a two’s-complement output that is found by using the equation below.
REF+
=
2.5V,V
REF−
=
1V,V
IN+
=
1.5V
and V
IN−
=
GND. The 12-bit + sign output code is positive
full-scale, or 0,1111,1111,1111. If V
REF+
=
5V, V
REF−
=
1V,
V
IN+
=
3V,and V
IN−
=
GND, the 12-bit + sign output code is
0,1100,0000,0000.
5.3 INPUT CURRENT
A charging current flows into or out of (depending on the in­put voltage polarity) the analog input pins, IN0–IN7 at the start of the analog input acquisition time (t
ACQ
). This cur­rent’s peak value will depend on the actual input voltage ap­plied.
5.4 INPUT SOURCE RESISTANCE
For low impedance voltage sources (
<
100Ω for 5 MHz op-
eration and
<
60Ω for 8 MHz operation), the input charging current will decay, before the end of the S/H’s acquisition time, to a value that will not introduce any conversion errors. For higher source impedances, the S/H’s acquisition time
can be increased. As an example, operating witha5MHz clock frequency and maximum acquisition time, the LM12(H)454/8’s analog inputs can handle source imped­ance as high as 6.67 kΩ. When operating at 8 MHz and maximum acquisition time, the LM12H454/8’s analog inputs can handle source impedance as high as 4.17 kΩ. Refer to Section 2.1, Instruction RAM “00”, Bits 12–15 for further in­formation.
5.5 INPUT BYPASS CAPACITANCE
External capacitors (0.01 µF–0.1 µF) can be connected be­tween the analog input pins, IN0–IN7, and analog ground to filter any noise caused by inductive pickup associated with long input leads. It will not degrade the conversion accuracy.
5.6 NOISE
The leads to each of the analog multiplexer input pins should be kept as short as possible. This will minimize input noise and clock frequency coupling that can cause conversion er­rors. Input filtering can be used to reduce the effects of the noise sources.
5.7 POWER SUPPLIES
Noise spikes on the V
A
+ and VD+ supply lines can cause conversion errors; the comparator will respond to the noise. The ADC is especially sensitive to any power supply spikes that occur during the auto-zero or linearity correction. Low in­ductance tantalum capacitors of 10 µF or greater paralleled with 0.1 µF monolithic ceramic capacitors are recommended for supply bypassing. Separate bypass capacitors should be used for the V
A
+ and VD+ supplies and placed as close as
possible to these pins.
5.8 GROUNDING
It is recommended that stray capacitance between the ana­log inputs or outputs (LM12(H)454: IN0–IN3, MUXOUT+, MUXOUT−, S/H IN+, S/H IN−; LM12(H)458: IN0–IN7, V
REF+
, and V
REF−
) be reduced by increasing the clearance (+1/16th inch) between the analog signal and reference pins and the ground plane.
5.9 CLOCK SIGNAL LINE ISOLATION
The LM12(H)454/8’s performance is optimized by routing the analog input/output and reference signal conductors (pins 34–44) as far as possible from the conductor that carries the clock signal to pin 23. Ground traces parallel to the clock sig­nal trace can be used on printed circuit boards to reduce clock signal interference on the analog input/output pins.
6.0 Application Circuits
PC EVALUATION/INTERFACE BOARD
Figure 16
is the schematic of an evaluation/interface board designed to interface the LM12(H)454 or LM12(H)458 with an XT or AT
®
style computer. The board can be used to de-
www.national.com 32
Page 33
6.0 Application Circuits (Continued)
velop both software and hardware. The board hardwires the BW (Bus Width) pin to a logic high, selecting an 8-bit wide databus. Therefore, it is designed for an 8-bit expansion slot on the computer’s motherboard.
The circuit operates on a single +5V supply derived from the computer’s +12V supply using an LM340 regulator. This greatly attenuates noise that may be present on the comput­er’s power supply lines. However, your application may only need an LC filter.
Figure 16
also shows the recommended supply (VA+ and
V
D
+) and reference input (V
REF+
and V
REF−
) bypassing. The digital and analog supply pins can be connected together to the same supply voltage. However,they need separate, mul­tiple bypass capacitors. Multiple capacitors on the supply pins and the reference inputs ensures a low impedance by­pass path over a wide frequency range.
All digital interface control signals (IOR, IOW, and AEN), data lines (DB0–DB7), address lines (A0–A9), and IRQ (in­terrupt request) lines (IRQ2, IRQ3, and IRQ5) connections are made through the motherboard slot connector.All analog signals applied to, or received by, the input multiplexer (IN0–IN7 for the LM12(H)458 and IN0–IN3, MUXOUT+, MUXOUT−, S/H IN+ and S/H IN− for the LM12(H)454), V
REF+,VREF−,VREFOUT
, and the SYNC signal input/ output are applied through a DB-37 connector on the rear side of the board.
Figure 16
shows that there are numerous analog
ground connections available on the DB-37 connector. The voltage applied to V
REF−
and V
REF+
is selected using two jumpers, JP1 and JP2. JP1 selects between the voltage applied to the DB-37’s pin 24 or GND and applies it to the LM12(H)454/8’s V
REF−
input. JP2 selects between the
LM12(H)454/8’s internal reference output, V
REFOUT
, and the voltage applied to the DB-37’s pin 22 and applies it to the LM12(H)454/8’s V
REF+
input.
TABLE 3. LM12(H)454/8 Evaluation/Interface
Board SW DIP-8 Switch Settings
for Available I/O Memory Locations
Hexidecimal SW DIP-8
I/O Memory
Base Address SW1 SW2 SW3 SW4
(SEL0) (SEL1) (SEL2) (SEL3)
100 ON ON ON ON 120 OFF ON ON ON 140 ON OFF ON ON 160 OFF OFF ON ON 180 ON ON OFF ON 1A0 OFF ON OFF ON 1C0 ON OFF OFF ON 300 OFF OFF OFF ON 340 ON ON ON OFF 280 OFF ON ON OFF 2A0 ON OFF ON OFF
The board allows the use of one of three Interrupt Request (IRQ) lines IRQ2, IRQ3, and IRQ5. The individual IRQ line can be selected using switches 5, 6, and 7 of SW DIP-8. When using any of these three IRQs, the user needs to en­sure that there are no conflicts between the evaluation board and any other boards attached to the computer’s mother­board.
Switches 1–4, along with address lines A5–A9 are used as inputs to GAL16V8 Programmable GateArray (U2). This de­vice forms the interface between the computer’s control and address lines and generates the control signals used by the LM12(H)454/8 for CS, WR, and RD. It also generates the signal that controls the data buffers. Several address ranges within the computer’s I/O memory map are available. Refer to Table III for the switch settings that gives the desired I/O memory address range. Selection of an address range must be done so that there are no conflicts between the evaluation board and any other boards attached to the computer’s motherboard. The GAL equations are shown in
Figure 18
.
The GAL functional block diagram is shown in
Figure 19
.
Figures 20, 21, 22, 23
show the layout of each layer in the 3-layer evaluation/interface board plus the silk-screen layout showing parts placement.
Figure 21
is the top or component
side,
Figure 22
is the middle or ground plane layer,
Figure 23
is the circuit side, and
Figure 20
is the parts layout.
www.national.com33
Page 34
6.0 Application Circuits (Continued)
DS011264-26
Note: The layout utilizes a split ground plane. The analog ground plane is placed under all analog signals and U5 pins 1, 34–44. The remaining signals and pins are placed over the digital ground. The single point ground connection is at U6, pin 2, and this is connected to the motherboard pin B1.
FIGURE 16. Schematic for the LM12(H)454/8 Evaluation Interface
Board for XT and AT Style Computers, Order Number LM12458EVAL
www.national.com 34
Page 35
6.0 Application Circuits (Continued)
Parts List:
Y1 HC49U, 8 MHz crystal D1 1N4002 L1 33 µH P1 DB37F; parallel connector R1 10 MΩ,5%,
1
⁄4W
R2 2 kΩ,5%,
1
⁄4W
RN1 10 kΩ, 6 resistor SIP, 5%,
1
⁄8W JP1, JP2 HX3, 3-pin jumper S1 SW DIP-8; 8 SPST switches C1–3, C6, C9–11, C19, C22 0.1 µF, 50V, monolithic ceramic C4 68 pF, 50V, ceramic disk C5 15 pF, 50V, ceramic disk C7, C21 100 µF, 25V, electrolytic C8, C12, C20 10 µF, 35V, electrolytic C13, C16 0.01 µF, 50V, monolithic ceramic C14, C18 1 µF, 35V, tantalum C15, C17 100 µF, 50V, ceramic disk U1 MM74HCT244N U2 GAL16V8-20LNC U3 MM74HCT245N U4 MM74HCU04N U5 LM12(H)458CIV or LM12454CIV U6 LM340AT-5.0 SK1 44-pin PLCC socket A1 LM12(H)458/4 Rev. D PC Board
FIGURE 17. Parts List for the LM12(H)454/8 Evaluation Interface
Board for XT and AT Style Computers, Order Number LM12458EVAL
www.national.com35
Page 36
6.0 Application Circuits (Continued)
DS011264-32
FIGURE 18. Logic Equations Used to Program the GAL16V8
www.national.com 36
Page 37
6.0 Application Circuits (Continued)
DS011264-27
FIGURE 19. GAL Functional Block Diagram
DS011264-31
FIGURE 20. Silk-Screen Layout Showing Parts Placement on the LM12(H)454/8 Evaluation/Interface Board
www.national.com37
Page 38
6.0 Application Circuits (Continued)
DS011264-28
FIGURE 21. LM12(H)454/8 Evaluation/Interface Board Component-Side Layout Positive
www.national.com 38
Page 39
6.0 Application Circuits (Continued)
DS011264-29
FIGURE 22. LM12(H)454/8 Evaluation/Interface Board Ground-Plane Layout Negative
www.national.com39
Page 40
6.0 Application Circuits (Continued)
DS011264-30
FIGURE 23. LM12(H)454/8 Evaluation/Interface Circuit-Side Layout Positive
www.national.com 40
Page 41
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM12458MEL/883 or 5962-9319501MYA,
LM12H458MEL/883 or 5962-9319502MYA
NS Package Number EL44A
www.national.com41
Page 42
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Order Number LM12454CIV, LM12458CIV or LM12H458CIV
NS Package Number V44A
Order Number LM12H458CIVF or LM12458CIVF
NS Package Number VGZ44A
www.national.com 42
Page 43
Notes
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
National Semiconductor Corporation
Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com
National Semiconductor Europe
Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com Deutsch Tel: +49 (0) 1 80-530 85 85 English Tel: +49 (0) 1 80-532 78 32 Français Tel: +49 (0) 1 80-532 93 58 Italiano Tel: +49 (0) 1 80-534 16 80
National Semiconductor Asia Pacific Customer Response Group
Tel: 65-2544466 Fax: 65-2504466 Email: sea.support@nsc.com
National Semiconductor Japan Ltd.
Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
www.national.com
LM12454/LM12458/LM12H458
12-Bit + Sign Data Acquisition System with Self-Calibration
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
Loading...
Buy Points How it Works FAQ Contact Us Questions and Suggestions Privacy Policy Cookie Policy Terms of Use