Rainbow Electronics MAX1089 User Manual

General Description
The MAX1086–MAX1089 are low-cost, micropower, ser­ial output 10-bit analog-to-digital converters (ADCs) available in a tiny 8-pin SOT23. The MAX1086/MAX1088 operate with a single +5V supply. The MAX1087/MAX1089 operate with a single +3V supply. The devices feature a successive-approximation ADC, automatic shutdown, fast wake-up (1.4µs), and a high-speed 3-wire inter­face. Power consumption is only 0.5mW (VDD= +2.7V) at the maximum sampling rate of 150ksps. Autoshutdown™ (0.1µA) between conversions results in reduced power consumption at slower throughput rates.
The MAX1086/MAX1087 provide 2-channel, single­ended operation and accept input signals from 0 to V
REF
. The MAX1088/MAX1089 accept true-differential
inputs ranging from 0 to V
REF
. Data is accessed using an external clock through the 3-wire SPI™, QSPI™, and MICROWIRE™–compatible serial interface. Excellent dynamic performance, low-power, ease of use, and small package size, make these converters ideal for portable battery-powered data acquisition applications, and for other applications that demand low power con­sumption and minimal space.
Applications
Low Power Data Acquisition
Portable Temperature Monitors
Flowmeters
Touch Screens
Features
Single-Supply Operation
+3V(MAX1087/MAX1089) +5V(MAX1086/MAX1088)
AutoShutdown Between Conversions
Low Power
200µA at 150ksps 130µA at 100ksps 65µA at 50ksps 13µA at 10ksps
1.5µA at 1ksps
0.2µA in Shutdown
True-Differential Track/Hold, 150kHz Sampling Rate
Software-Configurable Unipolar/Bipolar
Conversion (MAX1088/MAX1089 only)
SPI, QSPI, MICROWIRE–Compatible Interface for
DSPs and Processors
Internal Conversion Clock
8-Pin SOT23 Package
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
19-2036; Rev 0; 5/01
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Ordering Information
AutoShutdown is a trademark of Maxim Integrated Products. SPI and QSPI are trademarks of Motorola Inc. MICROWIRE is a trademark of National Semiconductor Corp.
PART
MAX1086EKA-T -40°C to +85°C 8 SOT23 AAEZ
MAX1087EKA-T -40°C to +85°C 8 SOT23 AAEV
MAX1088EKA-T -40°C to +85°C 8 SOT23 AAFB
MAX1089EKA-T -40°C to +85°C 8 SOT23 AAEX
TEMP.
RANGE
PIN-
PACKAGE
TOP
MARK
TOP VIEW
1
V
DD
2
MAX1086 MAX1087
AIN2 (AIN-)
( ) ARE FOR THE MAX1088/MAX1089
3
4
MAX1088 MAX1089
SOT23-8
87SCLK
DOUTAIN1 (AIN+)
CNVST
6
REFGND
5
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= +2.7V to +3.6V, V
REF
= +2.5V for MAX1087/MAX1089, or VDD = +4.75V to +5.25V, V
REF
= +4.096V for MAX1086/MAX1088,
0.1µF capacitor at REF, f
SCLK
= 8MHz (50% duty cycle), AIN- = GND for MAX1088/MAX1089. TA= T
MIN
to T
MAX,
unless otherwise
noted. Typical values at T
A
= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
VDDto GND.............................................................-0.3V to +6V
CNVST, SCLK, DOUT to GND......................-0.3V to (V
DD
+0.3V)
REF, AIN1(AIN+), AIN2(AIN-) to GND..........-0.3V to (V
DD
+0.3V)
Maximum Current Into Any Pin ...........................................50mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SOT23(derate 9.70mW/°C above T
A
= +70°C) ....777mW
Operating Temperature Ranges.........................-40°C to +85°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
DC ACCURACY (Note 1)
Resolution 10 Bits Relative Accuracy (Note 2) INL ±1.0 LSB Differential Nonlinearity DNL No missing codes over temperature ±1.0 LSB Offset Error ±0.5 ±1.0 LSB Gain Error (Note 3) ±1.0 ±2.0 LSB Gain Temperature Coefficient ±0.8 ppm/°C
Channel-to-Channel Offset Channel-to-Channel Gain Matching ±0.1 LSB
Input Common-Mode Rejection CMR VCM = 0V to VDD; zero scale input ±0.1 mV
DYNAMIC SPECIFICATIONS: (f for MAX1087/MAX1089, 150ksps, f
Signal to Noise Plus Distortion SINAD 61 dB
Total Harmonic Distortion (up to the 5
Spurious-Free Dynamic Range SFDR 70 dB
Full-Power Bandwidth -3dB point 1 MHz
Full-Linear Bandwidth SINAD>56dB 100 kHz
CONVERSION RATE
Conversion Time t
T/H Acquisition Time t
Aperture Delay 30 ns
Aperture Jitter <50 ps
Maximum Serial Clock Frequency f
Duty Cycle 30 70 %
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
th
harmonic)
(sine-wave) = 10kHz, VIN = 4.096Vp-p for MAX1086/MAX1088 or VIN = 2.5V
IN
= 8MHZ, AIN- = GND for MAX1088/MAX1089)
SCLK
THD -70 dB
CONV
ACQ
SCLK
±0.1 LSB
8 MHz
PP
3.7 µs
1.4 µs
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= +2.7V to +3.6V, V
REF
= +2.5V for MAX1087/MAX1089, or VDD
= +4.75V to +5.25V, V
REF
= +4.096V for MAX1086/MAX1088,
0.1µF capacitor at REF, f
SCLK
= 8MHz (50% duty cycle), AIN- = GND for MAX1088/MAX1089. TA= T
MIN
to T
MAX,
unless otherwise
noted. Typical values at T
A
= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
ANALOG INPUT
Input Voltage Range (Note 4)
Unipolar 0 V
Bipolar -V
Input Leakage Current C hannel not sel ected or conver si on stop p ed ±0.01 ±1 µA
Input Capacitance 34 pF
EXTERNAL REFERENCE INPUT
Input Voltage Range V
Input Current I
REF
REF
V
= +2.5V at 150ksps 16 30
REF
V
= +4.096V at 150ksps 26 45
REF
Acquisition/Between conversions ±0.01 ±1
DIGITAL INPUTS/OUTPUT (SCLK, CNVST, DOUT)
Input Low Voltage V
Input High Voltage V
Input Leakage Current I
Input Capacitance C
Output Low Voltage V
Output High Voltage V
Three-State Leakage Current I
Three-State Output Capacitance C
IL
IH
L
IN
OL
OH
L
OUT
I
= 2mA 0.4 V
SINK
I
= 4mA 0.8 V
SINK
I
SOURCE
= 1.5mA
CNVST = GND ±10 µA
CNVST = GND 15 pF
POWER REQUIREMENTS
Positive Supply Voltage V
DD
MAX1086/MAX1088 4.75 5.0 5.25
MAX1087/MAX1089 2.7 3.0 3.6
VDD = +3V
Positive Supply Current I
DD
VDD = +5V
Shutdown 0.2 5
Positive Supply Rejection PSR
VDD = 5V ±5%; full-scale input ±0.1 1.0
= +2.7V to +3.6V; full-scale input ±0.1 ±1.2
V
DD
f
f
f
f
f
f
f
f
=150ksps 245 350
SAMPLE
=100ksps 150
SAMPLE
=10ksps 15
SAMPLE
=1ksps 2
SAMPLE
=150ksps 320 400
SAMPLE
=100ksps 215
SAMPLE
=10ksps 22
SAMPLE
=1ksps 2.5
SAMPLE
REF
1.0
/2 V
REF
/2
REF
V
DD
+50mV
0.8 V
V
-1 V
DD
±0.1 µA
15 pF
V
DD
-0.5
V
V
µA
V
V
µA
mV
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
4 _______________________________________________________________________________________
TIMING CHARACTERISTICS (Figures 1 and 2)
(VDD= +2.7V to +3.6V, V
REF
= +2.5V for MAX1087/MAX1089, or VDD= +4.75V to +5.25V, V
REF
= +4.096V for MAX1086/MAX1088,
0.1µF capacitor at REF, f
SCLK
= 8MHz (50% duty cycle); AIN- = GND for MAX1088/MAX1089. TA= T
MIN
to T
MAX,
unless otherwise
noted. Typical values at T
A
= +25°C.)
Note 1: Unipolar input. Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after offset and gain errors have
been removed.
Note 3: Offset nulled. Note 4: The absolute input range for the analog inputs is from GND to V
DD
.
Figure 1. Detailed Serial-Interface Timing Sequence
Figure 2. Load Circuits for Enable/Disable Times
PARAMETERS SYMBOL CONDITIONS MIN TYP MAX UNITS
SCLK Pulse Width High t
SCLK Pulse Width Low t
SCLK Fall to DOUT Transition t
SCLK Rise to DOUT Disable t
CNVST Rise to DOUT Enable t
CNVST Fall to MSB Valid t
CNVST Pulse Width t
CH
CL
C
DOT
DOD
DOE
DOV
CSW
= 30pF 60 ns
LOAD
C
= 30pF 100 500 ns
LOAD
C
= 30pF 80 ns
LOAD
C
= 30pF 3.7 µs
LOAD
38 ns
38 ns
30 ns
CNVST
SCLK
t
DOE
HIGH-Z
DOUT
DOUT
6k
GND
a) HIGH -Z TO VOH, VOL TO VOH, AND VOH TO HIGH -Z
• • •
t
V
t
DOT
DD
C
GND
CH
L
t
CL
• • •
• • •
6k
DOUT
C
L
a) HIGH -Z TO V
, VOH TO VOL, AND VOL TO HIGH -Z
OL
t
CSW
t
DOD
HIGH-Z
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(VDD= +3.0V, V
REF
= +2.5V for MAX1087/MAX1089 or VDD= +5.0V, V
REF
= +4.096V for MAX1086/MAX1088, 0.1µF capacitor at
REF, f
SCLK
= 8MHz, (50% Duty Cycle), AIN- = GND for MAX1088/1089, TA= +25°C, unless otherwise noted.)
INTEGRAL NONLINEARITY
vs. OUTPUT CODE
1.0
0.8
0.6
0.4
0.2
0
INL (LSB)
-0.2
-0.4
-0.6
-0.8
-1.0 0 400200 600 800 1000 1200
OUTPUT CODE
DIFFERENTIAL NONLINEARITY
vs. OUTPUT CODE
1.0
0.8
0.6
0.4
0.2
0
DNL (LSB)
-0.2
-0.4
-0.6
-0.8
-1.0 0 400 600200 800 1000 1200
OUTPUT CODE
380
330
280
SUPPLY CURRENT ( µA)
230
180
2.7 3.73.2 4.2 4.7 5.2
MAX1087/MAX1089
MAX1086-9 toc01
MAX1086/MAX1088
MAX1086-9 toc04
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
VDD (V)
INTEGRAL NONLINEARITY
vs. OUTPUT CODE
1.0
0.8
0.6
0.4
0.2
0
INL (LSB)
-0.2
-0.4
-0.6
-0.8
-1.0 0 400200 600 800 1000 1200
SUPPLY CURRENT
vs. SAMPLING RATE
1000
MAX1087/MAX1089
100
10
SUPPLY CURRENT (µA)
1
0.1
0.001 10 1000
MAX1086-9 toc07
1.0
SAMPLING RATE (ksps)
MAX1086/MAX1088
OUTPUT CODE
SHUTDOWN CURRENT (nA)
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
2.7 3.73.2 4.2 4.7 5.2
1.0
0.8
0.6
MAX1086-9 toc02
0.4
0.2
0
DNL (LSB)
-0.2
-0.4
-0.6
-0.8
-1.0 0 400 600200 800 1000 1200
1000
MAX1086/MAX1088
MAX1086-9 toc05
100
10
SUPPLY CURRENT (µA)
1
0.1
0.001 10 10001.0
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
VDD (V)
DIFFERENTIAL NONLINEARITY
vs. OUTPUT CODE
MAX1087/MAX1089
MAX1086-9 toc03
OUTPUT CODE
SUPPLY CURRENT
vs. SAMPLING RATE
MAX1086-9 toc06
SAMPLING RATE (ksps)
MAX1086-9 toc08
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= 3.0V, V
REF
= 2.5V for MAX1087/MAX1089 or VDD= 5.0V, V
REF
= +4.096V for MAX1086MAX1088, 0.1µF capacitor at REF,
f
SCLK
= 8MHz, (50% Duty Cycle), AIN- = GND for MAX1088/89, TA= +25°C, unless otherwise noted.)
0
100
50
250
200
150
300
-40 0 20-20 40 60 80
SHUTDOWN CURRENT
vs. TEMPERATURE
MAX1086-9 toc10
TEMPERATURE (°C)
SHUTDOWN CURRENT (nA)
-1.00
-0.40
0.60
-0.80
0.00
-0.20
0.80
0.60
0.40
0.20
1.00
-40 -20 0 20 40 60 80
OFFSET ERROR
vs. TEMPERATURE
MAX1086-9 toc11
TEMPERATURE (°C)
OFFSET ERROR (LSB)
-1.0
-0.6
-0.8
-0.2
-0.4
0.2
0.4
0.6
0.8
0
1.0
2.7 3.7 4.23.2 4.7 5.2
OFFSET ERROR
vs. SUPPLY VOLTAGE
MAX1086-9 toc12
VDD (V)
OFFSET ERROR (LSB)
-40 0 20-20 40 60 80
GAIN ERROR
vs. TEMPERATURE
MAX1086-9 toc13
TEMPERATURE (°C)
GAIN ERROR (LSB)
-1.0
-0.6
-0.8
-0.2
-0.4
0.2
0.4
0.6
0.8
0
1.0
2.7 3.73.2 4.2 4.7 5.2
GAIN ERROR
vs. SUPPLY VOLTAGE
MAX1086-9 toc14
VDD (V)
GAIN ERROR (LSB)
-1.0
-0.6
-0.8
-0.2
-0.4
0.2
0.4
0.6
0.8
0
1.0
-140.00
-120.00
-100.00
-80.00
-60.00
-40.00
-20.00
0.00
20.00
03015 45 60
FFT PLOT (SINAD)
MAX1086-9 toc15
FREQUENCY (kHz)
AMPLITUDE (dB)
180
280
230
330
380
-40 0-20 20 40 60 80
SUPPLY CURRENT
vs. TEMPERATURE
MAX1086-9 toc09
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
_______________________________________________________________________________________ 7
Detailed Description
The MAX1086–MAX1089 analog-to-digital converters (ADCs) use a successive-approximation conversion (SAR) technique and an on-chip track-and-hold (T/H) structure to convert an analog signal into a 10-bit digital result.
The serial interface provides easy interfacing to micro­processors (µPs). Figure 3 shows the simplified internal structure for the MAX1086/MAX1087 (2–channels, sin­gle-ended) and the MAX1088/MAX1089 (1–channel, true-differential).
True-Differential Analog Input Track/Hold
The equivalent circuit of Figure 4 shows the MAX1086–MAX1089s input architecture which is com­posed of a T/H, input multiplexer, comparator, and switched-capacitor DAC. The T/H enters its tracking mode on the rising edge of CNVST. The positive input capacitor is connected to AIN1 or AIN2 (MAX1086/ MAX1087) or AIN+ (MAX1088/MAX1089). The negative input capacitor is connected to GND (MAX1086/ MAX1087) or AIN- (MAX1088/MAX1089). The T/H enters its hold mode on the falling edge of CNVST and the difference between the sampled positive and nega­tive input voltages is converted. The time required for the T/H to acquire an input signal is determined by how quickly its input capacitance is charged. If the input signals source impedance is high, the acquisition time lengthens, and CNVST must be held high for a longer period of time. The acquisition time, t
ACQ
, is the maxi­mum time needed for the signal to be acquired, plus the power-up time. It is calculated by the following equation:
t
ACQ
= 7 x (RS+ RIN) x 24pF + t
PWR
Pin Description
Figure 3. Simplified Functional Diagram
NAME
PIN
MAX1086 MAX1087
1VDDV
2 AIN1 AIN+ Analog Input Channel 1 (MAX1086/MAX1087) or Positive Analog Input (MAX1088/MAX1089)
3 AIN2 AIN- Analog Input Channel 2 (MAX1086/MAX1087) or Negative Analog Input (MAX1088/MAX1089)
4 GND GND Ground
5 REF REF
6 CNVST CNVST
7 DOUT DOUT
8 SCLK SCLK Serial Clock Input. Clocks out data at DOUT MSB first.
MAX1088 MAX1089
DD
Positive Supply Voltage. +2.7V to +3.6V (MAX1087/MAX1089); +4.75V to +5.25V (MAX1086/MAX1088). Bypass with a 0.1µF capacitor to GND.
External Reference Voltage Input. Sets the analog voltage range. Bypass with a 0.1µF capacitor to GND.
Conversion Start. A rising edge powers-up the IC and places it in track mode. At the falling edge of CNVST, the device enters hold mode and begins conversion. CNVST also selects the input channel (MAX1086/MAX1087) or input polarity (MAX1088/MAX1089).
Serial Data Output. DOUT transitions the falling edge of SCLK. DOUT goes low at the start of a conversion and presents the MSB at the completion of a conversion. DOUT goes high­impedance once data has been fully clocked out.
FUNCTION
MAX1086–MAX1089
OSCILLATOR
CNVST
SCLK
INPUT SHIFT
REGISTER
CONTROL
AIN1
(AIN+)
AIN2
(AIN-)
REF
T/H
10-BIT
SAR ADC
DOUT
( ) ARE FOR MAX1088/MAX1089
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
8 _______________________________________________________________________________________
where RIN= 1.5k, RSis the source impedance of the input signal, and t
PWR
= 1µs is the power-up time of the
device.
Note: t
ACQ
is never less than 1.4µs and any source
impedance below 300does not significantly affect the ADCs AC performance. A high impedance source can be accommodated either by lengthening t
ACQ
or by placing a 1µF capacitor between the positive and neg­ative analog inputs.
Selecting AIN1 or AIN2
(MAX1086/MAX1087)
Select between the MAX1086/MAX1087s two positive input channels using the CNVST pin. If AIN1 is desired (Figure 5a), drive CNVST high to power-up the ADC and place the T/H in track mode with AIN1 connected to the positive input capacitor. Hold CNVST high for t
ACQ
to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. Be sure to clock out all 12 bits of data (the 10-bit result plus two sub-bits) before dri­ving CNVST high for the next conversion. If all 12 bits of data are not clocked out before CNVST is driven high, AIN2 will be selected for the next conversion.
If AIN2 is desired (Figure 5b), drive CNVST high for at least 30ns. Next, drive it low for at least 30ns, and then high again. This will power-up the ADC and place the T/H in track mode with AIN2 connected to the positive input capacitor. Now hold CNVST high for t
ACQ
to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at
DOUT after 3.7µs. Data can then be clocked out using SCLK. If all 12 bits of data are not clocked out before CNVST is driven high, AIN2 will be selected for the next conversion.
Selecting Unipolar or Bipolar Conversions
(MAX1088/MAX1089)
Initiate true-differential conversions with the MAX1088/MAX1089s unipolar and bipolar modes, using the CNVST pin. AIN+ and AIN- are sampled at the falling edge of CNVST. In unipolar mode, AIN+ can exceed AIN- by up to V
REF
. The output format is straight binary. In bipolar mode, either input can exceed the other by up to V
REF
/2. The output format is
twos complement.
Note: In both modes, AIN+ and AIN- must not exceed VDDby more than 50mV or be lower than GND by more than 50mV.
If unipolar mode is desired (Figure 5a), drive CNVST high to power-up the ADC and place the T/H in track mode with AIN+ and AIN- connected to the input capacitors. Hold CNVST high for t
ACQ
to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. Be sure to clock out all 12 bits (the 10-bit result plus two sub-bits) of data before driving CNVST high for the next conversion. If all 12 bits of data are not clocked out before CNVST is driven high, bipolar mode will be selected for the next conversion.
If bipolar mode is desired (Figure 5b), drive CNVST high for at least 30ns. Next, drive it low for at least 30ns and then high again. This will place the T/H in track mode with AIN+ and AIN- connected to the input capacitors. Now hold CNVST high for t
ACQ
to fully acquire the signal. Drive CNVST low to place the T/H in hold mode. The ADC will then perform a conversion and shutdown automatically. The MSB is available at DOUT after 3.7µs. Data can then be clocked out using SCLK. If all 12 bits of data are not clocked out before CNVST is driven high, bipolar mode will be selected for the next conversion.
Input Bandwidth
The ADCs input tracking circuitry has a 1MHz small­signal bandwidth, so it is possible to digitize high­speed transient events and measure periodic signals with bandwidths exceeding the ADCs sampling rate by using undersampling techniques. To avoid high fre­quency signals being aliased into the frequency band of interest, anti-alias filtering is recommended.
Figure 4. Equivalent Input Circuit
AIN2
AIN1(AIN+)
HOLD
GND(AIN-)
*( ) APPLIES TO MAX1088/1089
REF
GND
CIN+
CIN-
HOLD
V
DD
DAC
COMPARATOR
+
-
RIN-
/2
RIN+
HOLD
TRACK
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
_______________________________________________________________________________________ 9
Analog Input Protection
Internal protection diodes which clamp the analog input to VDDand GND allow the analog input pins to swing from GND - 0.3V to VDD+ 0.3V without damage. Both inputs must not exceed VDDby more than 50mV or be lower than GND by more than 50mV for accurate conver­sions. If an off-channel analog input voltage exceeds
the supplies, limit the input current to 2mA.
Internal Clock
The MAX1086–MAX1089 operate from an internal oscilla­tor, which is accurate within 10% of the 4MHz specified clock rate. This results in a worse case conversion time of 3.7µs. The internal clock releases the system micro­processor from running the SAR conversion clock and allows the conversion results to be read back at the processors convenience, at any clock rate from 0 to 8MHz.
Figure 5b. Single Conversion AIN2 vs. GND (MAX1086/MAX1087), bipolar mode AIN+ vs. AIN- (MAX1088/MAX1089)
Figure 5a. Single Conversion AIN1 vs. GND (MAX1086/MAX1087), unipolar mode AIN+ vs. AIN- (MAX1088/MAX1089)
t
CONV
CNVST
t
ACQ
SCLK
DOUT
HIGH-Z
t
t
ACQ
CNVST
SCLK
DOUT
HIGH-Z
B9
MSB
SAMPLING INSTANT
CONV
B9
MSB
B8 B7 B6 B5
B8 B7 B6 B5
41812
B4
B3 B2 B1
41812
B4
B3 B2 B1
B0
LSB
B0
LSB
S1 S0
S1 S0
HIGH-Z
HIGH-Z
SAMPLING INSTANT
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
10 ______________________________________________________________________________________
Output Data Format
Figures 5a and 5b illustrate the conversion timing for the MAX1086–MAX1089. The 10-bit conversion result is output in MSB first format, followed by two sub-bits (S1 and S0). Data on DOUT transitions on the falling edge of SCLK. All 12-bits must be clocked out before CNVST transitions again. For the MAX1088/MAX1089, data is straight binary for unipolar mode and twos comple­ment for bipolar mode. For the MAX1086/MAX1087, data is always straight binary.
Applications Information
Automatic Shutdown Mode
With CNVST low, the MAX1086–MAX1089 defaults to an AutoShutdown state (<0.2µA) after power-up and between conversions. After detecting a rising edge on CNVST, the part powers up, sets DOUT low and enters track mode. After detecting a falling-edge on CNVST, the device enters hold mode and begins the conversion. A maximum of 3.7µs later, the device completes conver­sion, enters shutdown and MSB is available at DOUT.
External Reference
An external reference is required for the MAX1086– MAX1089. Use a 0.1µF bypass capacitor for best per­formance. The reference input structure allows a volt­age range of +1V to VDD+ 50mV.
Transfer Function
Figure 6 shows the unipolar transfer function for the MAX1086–MAX1089. Figure 7 shows the bipolar transfer function for the MAX1088/MAX1089. Code transitions occur halfway between successive-integer LSB values.
Connection to Standard Interfaces
The MAX1086–MAX1089 feature a serial interface that is fully compatible with SPI, QSPI, and MICROWIRE. If a serial interface is available, establish the CPUs serial interface as a master, so that the CPU generates the seri­al clock for the ADCs. Select a clock frequency up to 8MHz.
How to Perform a Conversion
1) Use a general purpose I/O line on the CPU to hold
CNVST low between conversions.
2) Drive CNVST high to acquire AIN1(MAX1086/
MAX1087) or unipolar mode (MAX1088/MAX1089). To acquire AIN2(MAX1086/MAX1087) or bipolar mode (MAX1088/MAX1089), drive CNVST low and high again.
3) Hold CNVST high for 1.4µs.
4) Drive CNVST low and wait approximately 3.7µs for
conversion to complete. After 3.7µs, the MSB is available at DOUT.
5) Activate SCLK for a minimum of 12 rising clock
edges. DOUT transitions on SCLKs falling edge
Figure 6. Unipolar Transfer Function
Figure 7. Bipolar Transfer Function
OUTPUT CODE
11 . . . 111
11 . . . 110
11 . . . 101
00 . . . 011
00 . . . 010
00 . . . 001
00 . . . 000
0
123
FULL-SCALE TRANSITION
INPUT VOLTAGE (LSB)
MAX1086– MAX1089
FS = V
ZS = GND
1LSB =
FS
FS - 3/2LSB
REF
V
1024
REF
011 . . . 111
011 . . . 110
000 . . . 010
000 . . . 001
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
100 . . . 001
100 . . . 000
*V
COM
OUTPUT CODE
FS
ZS = 0
-FS =
1LSB =
- FS
V
/ 2 *VIN = (AIN+) - (AIN-)
REF
V
REF
=
2
-V
REF
2 V
REF
1024
INPUT VOLTAGE (LSB)
0
MAX1088/MAX1089
+FS - 1LSB
and is available in MSB-first format. Observe the SCLK to DOUT valid timing characteristic. Clock data into the µP on SCLKs rising-edge.
SPI and MICROWIRE Interface
When using SPI interface (Figure 8a) or MICROWIRE (Figure 8a and 8b), set CPOL = CPHA = 0. Two 8-bit readings are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clocks falling edge and is clocked into the µP on SCLKs rising edge. The first 8-bit data stream contains the first 8-bits of DOUT starting with the MSB. The sec­ond 8-bit data stream contains the remaining two result bits (B1, B0) and two trailing sub-bits (S1, S0). DOUT then goes high impedance.
QSPI Interface
Using the high-speed QSPI interface (Figure 9a) with CPOL = 0 and CPHA = 0, the MAX1086–MAX1089 support a maximum f
SCLK
of 8MHz. One 8- to16-bit reading is necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clocks falling edge and is clocked into the µP on
SCLKs rising edge. The first 10 bits are the data and the next two bits are sub-bits (S1, S0). DOUT then goes high impedance (Figure 9b).
PIC16 and SSP Module and
PIC17 Interface
The MAX1086–MAX1089 are compatible with a PIC16/PIC17 microcontroller (µC), using the synchro­nous serial port (SSP) module
To establish SPI communication, connect the controller as shown in Figure 10a and configure the PIC16/PIC17 as system master. This is done by initializing its syn­chronous serial port control register (SSPCON) and synchronous serial port status register (SSPSTAT) to the bit patterns shown in Tables 1 and 2.
In SPI mode, the PIC16/PIC17 µCs allow eight bits of data to be synchronously transmitted and received simultaneously. Two consecutive 8-bit readings (Figure 10b) are necessary to obtain the entire 10-bit result from the ADC. DOUT data transitions on the serial clocks falling edge and is clocked into the µC on SCLKs rising edge. The first 8-bit data stream contains
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
______________________________________________________________________________________ 11
Figure 8a. SPI Connections Figure 8b. MICROWIRE Connections
Table 1. Detailed SSPCON Register Content
SPI
SCK
MISO
I/O
V
DD
SS
CNVST
SCLK
DOUT
MAX1086– MAX1089
I/O
SK
SI
MICROWIRE
CNVST
SCLK
DOUT
MAX1086– MAX1089
CONTROL BIT
WCOL Bit 7 X Write Collision Detection Bit
SSPOV Bit 6 X Receive Overflow Detect Bit
SSPEN Bit 5 1
CKP Bit 4 0 Clock Polarity Select Bit. CKP = 0 for SPI master mode selection.
SSPM3 Bit 3 0
SSPM2 Bit 2 0
SSPM1 Bit 1 0
SSPM0 Bit 0 1
X = Dont care
MAX1086–MAX1089
SETTINGS
SYNCHRONOUS SERIAL PORT CONTROL REGISTER (SSPCON)
Synchronous Serial Port Enable Bit. 0: Disables serial port and configures these pins as I/O port pins. 1: Enables serial port and configures SCK, SDO and SCI pins as serial port pins.
Synchronous Serial Port Mode Select Bit. Sets SPI master mode and selects
= f
OSC
/ 16.
f
CLK
MAX1086–MAX1089
the first eight data bits starting with the MSB. The sec­ond 8-bit data stream contains the remaining bits, D1 through D0, and the two sub-bits S1 and S0.
Layout, Grounding, and Bypassing
For best performance, use printed circuit (PC) boards. Wire-wrap configurations are not recommended since the layout should ensure proper separation of analog
and digital traces. Do not run analog and digital lines parallel to each other, and do not lay out digital signal paths underneath the ADC package. Use separate analog and digital PC board ground sections with only one starpoint (Figure 11), connecting the two ground systems (analog and digital). For lowest-noise opera­tion, ensure the ground return to the star ground’s power supply is low impedance and as short as possi­ble. Route digital signals far away from sensitive analog and reference inputs.
High-frequency noise in the power supply (VDD) may degrade the performance of the ADCs fast comparator. Bypass V
DD
to the star ground with a 0.1µF capacitor, located as close as possible to the MAX1086–MAX1089s power supply pin. Minimize capacitor lead length for best supply-noise rejection. Add an attenuation resistor (5) if the power supply is extremely noisy.
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
12 ______________________________________________________________________________________
Figure 9a. QSPI Connections
Table 2. Detailed SSPSTAT Register Content
Figure 8c. SPI/MICROWIRE Interface Timing Sequence (CPOL = CPHA = 0)
CNVST
1ST BYTE READ
2ND BYTE READ
SCLK
DOUT
B9
B8 B7 B6 B5
MSB
SAMPLING INSTANT
418
B4
B3 B2 B1
CNVST
SCLK
DOUT
MAX1086– MAX1089
QSPI
SCK
MISO
CS
V
DD
SS
B0
LSB
S1 S0
12
HIGH-Z
16
CONTROL BIT
SMP Bit 7 0
CKE Bit 6 1 SPI Clock Edge Select Bit. Data will be transmitted on the rising edge of the serial clock.
D/A
P Bit 4 X Stop Bit
S Bit 3 X
R/W
UA Bit 1 X
BF Bit 0 X
X = Dont care
MAX1086–MAX1089
SETTINGS
SPI Data Input Sample Phase. Input data is sampled at the middle of the data output time.
Bit 5 X Data Address Bit
Start Bit
Bit 2 X
Read/Write Bit Information
Update Address
Buffer Full Status Bit
SYNCHRONOUS SERIAL STATUS REGISTER (SSPSTAT)
Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values on an actual transfer function from a straight line. This straight line can be either a best-straight-line fit or a line drawn between the endpoints of the transfer function, once offset and gain errors have been nullified. The sta­tic linearity parameters for the MAX1086–MAX1089 are measured using the endpoint method.
Differential Nonlinearity
Differential nonlinearity (DNL) is the difference between an actual step-width and the ideal value of 1LSB. A DNL error specification of less than 1LSB guarantees no missing codes and a monotonic transfer function.
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
______________________________________________________________________________________ 13
Figure 9b. QSPI Interface Timing Sequence (CPOL = CPHA = 0)
Figure 10a. SPI Interface Connection for a PIC16/PIC17 Controller
Figure 10b. SPI Interface Timing with PIC16/PIC17 in Master Mode (CKE = 1, CKP = 0, SMP = 0, SSPM3 - SSPM0 = 0001)
CNVST
SCLK
DOUT
B9
B8 B7 B6 B5
MSB
SAMPLING INSTANT
418
B4
B3 B2 B1
V
DD
SCLK
DOUT
CNVST
SCK
SDI
I/O
PIC16/PIC17
V
DD
MAX1086– MAX1089
GND GND
16
B0
LSB
S1 S0
12
HIGH-Z
CNVST
SCLK
DOUT
B9
B8 B7 B6 B5
MSB
SAMPLING INSTANT
1ST BYTE READ
418
B4
B3 B2 B1
B0
LSB
S1 S0
2ND BYTE READ
12
HIGH-Z
16
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and 1-Channel True-Differential ADCs in SOT23
14 ______________________________________________________________________________________
Aperture Definitions
Aperture jitter (tAJ) is the sample-to-sample variation in the time between the samples. Aperture delay (tAD) is the time between the rising edge of the sampling clock and the instant when an actual sample is taken.
Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital sam­ples, signal-to-noise ratio (SNR) is the ratio of full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to­digital noise is caused by quantization error only and results directly from the ADCs resolution (N-bits):
SNR = (6.02
N + 1.76)dB
In reality, there are other noise sources besides quanti­zation noise: thermal noise, reference noise, clock jitter, etc. SNR is computed by taking the ratio of the RMS signal to the RMS noise, which includes all spectral components minus the fundamental, the first five har­monics, and the DC offset.
Signal-to-Noise Plus Distortion
Signal-to-noise plus distortion (SINAD) is the ratio of the fundamental input frequencys RMS amplitude to RMS equivalent of all other ADC output signals.
SINAD (dB) = 20 log (Signal
RMS
/ Noise
RMS
)
Effective Number of Bits
Effective number of bits (ENOB) indicates the global accuracy of an ADC at a specific input frequency and sampling rate. An ideal ADCs error consists of quanti­zation noise only. With an input range equal to the full­scale range of the ADC, calculate the effective number of bits as follows:
ENOB = (SINAD - 1.76) / 6.02
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS sum of the first five harmonics of the input signal to the fundamental itself. This is expressed as:
where V1is the fundamental amplitude, and V2through V5are the amplitudes of the 2nd- through 5th-order har­monics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of RMS amplitude of the fundamental (maximum signal compo­nent) to the RMS value of the next largest distortion component.
Chip Information
TRANSISTOR COUNT: 6922
PROCESS: BiCMOS
Figure 11. Power-Supply and Grounding Connections
SUPPLIES
+3V OR +5V
R* = 5
0.1µF
V
DD
*OPTIONAL
GND
MAX1086–
MAX1089
V
LOGIC
= +5V/+3V
CIRCUITRY
GND
DGND+5V/+3V
DIGITAL
20
THD VVVV V +++
2
2
log /
2
3
2
4
2
5
1
MAX1086–MAX1089
150ksps, 10-Bit, 2-Channel Single-Ended, and
1-Channel True-Differential ADCs in SOT23
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15
© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
SOT23, 8L.EPS
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