The MAX1132/MAX1133 are 200ksps, 16-bit ADCs.
These serially interfaced ADCs connect directly to
SPI™, QSPI™, and MICROWIRE™ devices without
external logic. They combine an input scaling network,
internal track/hold, clock, a +4.096V reference, and
three general-purpose digital output pins (for external
multiplexer or PGA control) in a 20-pin SSOP package.
The excellent dynamic performance (SINAD ≥ 85dB),
high-speed (200ksps), and low power (7.5mA) of these
ADCs, make them ideal for applications such as industrial process control, instrumentation, and medical
applications. The MAX1132 accepts input signals of 0
to +12V (unipolar) or ±12V (bipolar), while the
MAX1133 accepts input signals of 0 to +4.096V (unipolar) or ±4.096V (bipolar). Operating from a single
+4.75V to +5.25V analog supply and a +4.75V to
+5.25V digital supply, power-down modes reduce
current consumption to 1mA at 10ksps and further
reduce supply current to less than 20µA at slower data
rates. A serial strobe output (SSTRB) allows direct connection to the TMS320 family of digital signal processors. The MAX1132/MAX1133 user can select either the
internal clock, or an external serial-interface clock for
the ADC to perform analog-to-digital conversions.
The MAX1132/MAX1133 feature internal calibration circuitry to correct linearity and offset errors. On-demand
calibration allows the user to optimize performance.
Three user-programmable logic outputs are provided
for the control of an 8-channel mux or a PGA.
Applications
Industrial Process Control
Industrial I/O Modules
Data-Acquisition Systems
Medical Instruments
Portable and Battery-Powered Equipment
Features
♦ 200ksps (Bipolar) and 150ksps (Unipolar)
Sampling ADC
♦ 16-Bits, No Missing Codes
♦ 1.5LSB INL Guaranteed
♦ 85dB (min) SINAD
♦ +5V Single-Supply Operation
♦ Low-Power Operation, 7.5mA (Unipolar Mode)
♦ 2.5µA Shutdown Mode
♦ Software-Configurable Unipolar and Bipolar Input
Ranges
0 to +12V and ±12V (MAX1132)
0 to +4.096V and ±4.096V (MAX1133)
Internal or External Reference
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.
AVDDto AGND, DVDDto DGND .............................-0.3V to +6V
AGND to DGND.....................................................-0.3V to +0.3V
AIN to AGND.....................................................................±16.5V
REFADJ, CREF, REF to AGND.................-0.3V to (AV
DD
+ 0.3V)
Digital Inputs to DGND.............................................-0.3V to +6V
Digital Outputs to DGND .........................-0.3V to (DV
Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the gain error and offset
error have been nulled.
Note 3: Offset nulled.
Note 4: Conversion time is defined as the number of clock cycles multiplied by the clock period, clock has 50% duty cycle.
Includes the acquisition time.
Note 5: ADC performance is limited by the converter’s noise floor, typically 300µVp-p.
Note 6: When an external reference has a different voltage than the specified typical value, the full scale of the ADC will scale
proportionally.
Note 7: Electrical characteristics are guaranteed from AV
DD(MIN)
= DV
DD(MIN)
to AV
DD(MAX)
= DV
DD(MAX)
. For operations beyond
this range, see the Typical Operating Characteristics. For guaranteed specifications beyond the limits, contact the factory.
Note 8: Defined as the change in positive full scale caused by a ±5% variation in the nominal supply voltage.
TIMING CHARACTERISTICS (Figures 5 and 6)
(AVDD= DVDD= +5V ±5%, TA= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Acquisition Timet
DIN to SCLK Setupt
DIN to SCLK Holdt
SCLK to DOUT Validt
CS Fall to DOUT Enablet
CS Rise to DOUT Disablet
CS to SCLK Rise Setupt
CS to SCLK Rise Holdt
SCLK High Pulse Widtht
SCLK Low Pulse Widtht
SCLK Fall to SSTRBt
CS Fall to SSTRB Enablet
CS Rise to SSTRB Disablet
SSTRB Rise to SCLK Riset
RST Pulse Widtht
ACQ
DS
DH
DO
DV
TR
CSS
CSH
CH
CL
SSTRB
SDV
STR
SCK
RS
C
LOAD
C
LOAD
C
LOAD
C
LOAD
C
LOAD
Internal clock mode0ns
= 50pF80ns
= 50pF80ns
= 50pF80ns
= 50pF, external clock mode80ns
= 50pF, external clock mode80ns
1.14µs
50ns
0ns
70ns
100ns
0ns
80ns
80ns
208ns
MAX1132/MAX1133
16-Bit ADC, 200ksps, 5V Single-Supply
with Reference
bipolar input, external REF = +4.096V, 0.22µF bypassing on REFADJ, 2.2µF on REF, 1µF on CREF, T
A
= 25°C, unless otherwise noted.)
0
0.1100101
SFDR PLOT
120
MAX1132 toc10
FREQUENCY (kHz)
AMPLITUDE (dB)
100
80
60
40
10
20
30
110
90
70
50
f
SAMPLE
= 200kHz
-110
0.1100101
THD PLOT
0
MAX1132 toc11
FREQUENCY (kHz)
AMPLITUDE (dB)
-10
-30
-50
-70
-100
-90
-80
-20
-40
-60
f
SAMPLE
= 200kHz
Pin Description
PINNAMEFUNCTION
Reference Buffer Output/ADC Reference Input. Reference voltage for analog-to-digital conversion. In
1REF
internal reference mode, the reference buffer provides a +4.096V nominal output, externally adjustable at
REFADJ. In external reference mode, disable the internal buffer by pulling REFADJ to AV
AGND with a 2.2µF capacitor when using the internal reference.
. Bypass to
DD
2REFADJ
Bandgap Reference Output/Bandgap Reference Buffer Input. Bypass to AGND with 0.22µF. When using an
external reference, connect REFADJ to AV
to disable the internal bandgap reference.
DD
3AGNDAnalog Ground. This is the primary analog ground (Star Ground).
4AVDDAnalog Supply. 5V ±5%. Bypass AVDD to AGND (pin 3) with a 0.1µF capacitor.
5DGNDDigital Ground
6SHDNShutdown Control Input. Drive SHDN low to put the ADC in shutdown mode.
7P2User-Programmable Output 2
8P1User-Programmable Output 1
9P0User-Programmable Output 0
Serial Strobe Output. In internal clock mode, SSTRB goes low when the ADC begins a conversion and goes
10SSTRB
11DOUT
high when the conversion is finished. In external clock mode, SSTRB pulses high for one clock period
before the MSB decision. It is high impedance when CS is high in external clock mode.
Serial Data Output. MSB first, straight binary format for unipolar input, two’s complement for bipolar input.
Each bit is clocked out of DOUT at the falling edge of SCLK.
12RSTReset Inp ut. D r i ve RST l ow to p ut the d evi ce i n the p ow er - on d efaul t m od e. S ee the P ow er - O n Reset secti on.
MAX1132/MAX1133
Detailed Description
The MAX1132/MAX1133 analog-to-digital converters
(ADCs) use a successive-approximation technique and
input track/hold (T/H) circuitry to convert an analog signal to a 16-bit digital output. The MAX1132/MAX1133
easily interfaces to microprocessors (µPs). The data
bits can be read either during the conversion in external clock mode or after the conversion in internal clock
mode.
In addition to a 16-bit ADC, the MAX1132/MAX1133
include an input scaler, an internal digital microcontroller, calibration circuitry, an internal clock generator,
and an internal bandgap reference. The input scaler for
the MAX1132 enables conversion of input signals ranging from 0 to +12V (unipolar input) or ±12V (bipolar
input). The MAX1133 accepts 0 to +4.096V (unipolar
input) or ±4.096V (bipolar input). Input range selection
is software controlled.
Calibration
To minimize linearity, offset, and gain errors, the
MAX1132/MAX1133 have on-demand software calibration. Initiate calibration by writing a Control-Byte with bit
M1 = 0, and bit M0 = 1 (see Table 1). Select internal or
external clock for calibration by setting the INT/EXT bit
in the Control Byte. Calibrate the MAX1132/MAX1133
with the clock used for performing conversions.
Offsets resulting from synchronous noise (such as the
conversion clock) are canceled by the MAX1132/
MAX1133’s calibration circuitry. However, because the
magnitude of the offset produced by a synchronous
signal depends on the signal’s shape, recalibration
may be appropriate if the shape or relative timing of the
clock or other digital signals change, as might occur if
more than one clock signal or frequency is used.
Input Scaler
The MAX1132/MAX1133 have an input scaler which
allows conversion of true bipolar input voltages while
operating from a single +5V supply. The input scaler
attenuates and shifts the input as necessary to map the
external input range to the input range of the internal
DAC. The MAX1132 analog input range is 0 to +12V
(unipolar) or ±12V (bipolar). The MAX1133 analog input
range is 0 to +4.096V (unipolar) or ±4.096V (bipolar).
Unipolar and bipolar mode selection is configured with
bit 6 of the serial Control Byte.
Figure 1 shows the equivalent input circuit of the
MAX1132/MAX1133. The resistor network on the analog
input provides ±16.5V fault protection. This circuit limits
the current going into or out of the pin to less than 2mA.
The overvoltage protection is active, even if the device
is in a power-down mode, or if AVDD= 0.
Digital Interface
The digital interface pins consist of SHDN, RST, SSTRB,
DOUT, SCLK, DIN and CS. Bringing SHDN low, places
the MAX1132/MAX1133 in its 2.5µA shutdown mode. A
logic low on RST halts the MAX1132/MAX1133 operation and returns the part to its power-on reset state.
In external clock mode, SSTRB is is low and pulses
high for one clock cycle at the start of conversion. In
internal clock mode, SSTRB goes low at the start of the
conversion and goes high to indicate the conversion is
finished.
16-Bit ADC, 200ksps, 5V Single-Supply
with Reference
Serial Data Clock Input. Serial data on DIN is loaded on the rising edge of SCLK, and serial data is updated
on DOUT on the falling edge of SCLK. In external clock mode, SCLK sets the conversion speed.
15DV
16DINSerial Data Input. Serial data on DIN is latched on the rising edge of SCLK.
17CS
18CREFReference Buffer Bypass. Bypass CREF to AGND (pin 3) with 1µF.
19AGNDAnalog Ground. Connect pin 19 to pin 3.
20AINAnalog Input
Digital Supply. 5V ±5%. Bypass DVDD to DGND (pin 14) with a 0.1µF capacitor.
DD
Chip-Select Input. Drive CS low to enable the serial interface. When CS is high, DOUT is high impedance.
In external clock mode, SSTRB is high impedance when CS is high.
The DIN input accepts Control Byte data which is
clocked in on each rising edge of SCLK. After CS goes
low or after a conversion or calibration completes, the
first logic “1” clocked into DIN is interpreted as the
START bit, the MSB of the 8-bit Control Byte.
The SCLK input is the serial data transfer clock which
clocks data in and out of the MAX1132/MAX1133.
SCLK also drives the A/D conversion steps in external
clock mode (see Internal and External Clock Modes
section).
DOUT is the serial output of the conversion result.
DOUT is updated on the falling edge of SCLK. DOUT is
high-impedance when CS is high.
CS must be low for the MAX1132/MAX1133 to accept a
Control Byte. The serial interface is disabled when CS
is high.
User-Programmable Outputs
The MAX1132/MAX1133 have three user-programmable outputs, P0, P1 and P2. The power-on default state
for the programmable outputs is zero. These are pushpull CMOS outputs suitable for driving a multiplexer, a
PGA, or other signal preconditioning circuitry. The userprogrammable outputs are controlled by bits 0, 1, and
2 of the Control Byte (Table 2).
The user-programmable outputs are set to zero during
power-on reset (POR) or when RST goes low. During
hardware or software shutdown P0, P1, and P2 are
unchanged and remain low-impedance.
Starting a Conversion
Start a conversion by clocking a Control Byte into the
device’s internal shift register. With CS low, each rising
edge on SCLK clocks a bit from DIN into the
MAX1132/MAX1133’s internal shift register. After CS
goes low or after a conversion or calibration completes,
the first arriving logic “1” is defined as the start bit of
the Control Byte. Until this first start bit arrives, any
number of logic “0” bits can be clocked into DIN with
no effect. If at any time during acquisition or conversion,
CS is brought high and then low again, the part is
placed into a state where it can recognize a new start
bit. If a new start bit occurs before the current conversion is complete, the conversion is aborted and a new
acquisition is initiated.
Internal and External Clock Modes
The MAX1132/MAX1133 may use either the external
serial clock or the internal clock to perform the successive-approximation conversion. In both clock modes,
the external clock shifts data in and out of the
MAX1132/MAX1133. Bit 5 (INT/EXT) of the Control Byte
programs the clock mode.
External Clock
In external clock mode, the external clock not only
shifts data in and out, but it also drives the ADC conversion steps. In short acquisition mode, SSTRB pulses
high for one clock period after the seventh falling edge
of SCLK following the start bit. The MSB of the conversion is available at DOUT on the eighth falling edge of
SCLK (Figure 2).
In long acquisition mode, when using external clock,
SSTRB pulses high for one clock period after the fifteenth falling edge of SCLK following the start bit. The
MSB of the conversion is available at DOUT on the sixteenth falling edge of SCLK (Figure 3).
In external clock mode, SSTRB is high-impedance
when CS is high. In external clock mode, CS is normally
held low during the entire conversion. If CS goes high
during the conversion, SCLK is ignored until CS goes
low. This allows external clock mode to be used with 8bit bytes.
Internal Clock
In internal clock mode, the MAX1132/MAX1133 generates its own conversion clock. This frees the microprocessor from the burden of running the SAR conversion clock, and allows the conversion results to be read
back at the processor’s convenience, at any clock rate
up to 8MHz.
SSTRB goes low at the start of the conversion and goes
high when the conversion is complete. SSTRB will be
7 (MSB)STARTThe first logic “1” bit, after CS goes low, defines the beginning of the Control Byte
1 = unipolar, 0 = bipolar. Selects unipolar or bipolar conversion mode. In unipolar mode, analog
6UNI/BIP
input signals from 0 to +12V (MAX1132) or 0 to V
mode analog input signals from -12V to +12V (MAX1132) or -V
converted.
5INT/EXTSelects the internal or external conversion clock. 1 = Internal, 0 = External.
4M1
M1M0MODE
0024 External clocks per conversion (short acquisition mode)
3M0
01Start Calibration. Starts internal calibration.
10Software power-down mode
1132 External clocks per conversion (long acquisition mode)
1
0(LSB)
2
P2
P1
P0
These three bits are stored in a port register and output to pins P2, P1, P0 for use in addressing
a mux or PGA. These three bits are updated in the port register simultaneously when a new
Control Byte is written.
(MAX1133) can be converted. In bipolar
REF
REF
to +V
(MAX1133) can be
REF
OUTPUT
PIN
PROGRAMMED
THROUGH
CONTROL BYTE
P2Bit 20
P1Bit 10
P0Bit 00
CS
t
ACQ
SCLK
UNI/
INT/
BIP
EXT
ACQUISITIONCONVERSIONIDLEIDLE
DIN
SSTRB
DOUT
A/D
STAT E
START
POWER-ON
OR RST
DEFAULT
41812
M1 M0
P2
P1P0
B15
MSB
DESCRIPTION
U ser - p r og r am m ab l e outp uts fol l ow the state of the C ontr ol Byte’ s thr ee LS Bs
and ar e up d ated si m ul taneousl y w hen a new C ontr ol Byte i s w r i tten. O utp uts
ar e p ush- p ul l . In har d w ar e and softw ar e shutd ow n, these outp uts ar e
unchang ed and r em ai n l ow - i m p ed ance.
15
B12 B11B14 B13
B10
B9B4
2124
B2B3B1
B0
LSB
FILLED WITH
ZEROS
low for a maximum of 6µs, during which time SCLK
should remain low for best noise performance. An internal register stores data when the conversion is in
progress. SCLK clocks the data out of the internal storage register at any time after the conversion is complete.
The MSB of the conversion is available at DOUT when
SSTRB goes high. The subsequent 15 falling edges on
SCLK shift the remaining bits out of the internal storage
register (Figure 4). CS does not need to be held low
once a conversion is started.
When internal clock mode is selected, SSTRB does not
go into a high-impedance state when CS goes high.
Figure 5 shows the SSTRB timing in internal clock
mode. In internal clock mode, data can be shifted in to
the MAX1132/MAX1133 at clock rates up to 4.8MHz,
provided that the minimum acquisition time, t
ACQ
, is
kept above 1.14µs in bipolar mode and 1.82µs in
unipolar mode. Data can be clocked out at 8MHz.
Output Data
The output data format is straight binary for unipolar
conversions and two’s complement in bipolar mode. In
both modes the MSB is shifted out of the MAX1132/
MAX1133 first.
Data Framing
The falling edge of CS does NOT start a conversion on
the MAX1132/MAX1133. The first logic high clocked into
DIN is interpreted as a start bit and defines the first bit of
the Control Byte. A conversion starts on the falling edge
of SCLK, after the seventh bit of the Control Byte (the P1
bit) is clocked into DIN. The start bit is defined as:
The first high bit clocked into DIN with CS low anytime the converter is idle, e.g., after AV
DD
is
applied, or as the first high bit clocked into DIN
after CS is pulsed high, then low.
OR
If a falling edge on CS forces a start bit before the
conversion or calibration is complete, then the
current operation will be terminated and a new
one started.
Applications Information
Power-On Reset
When power is first applied to the MAX1132/MAX1133
or if RST is pulsed low, the internal calibration registers
are set to their default values. The user-programmable
registers (P0, P1, and P2) are low, and the device is
configured for bipolar mode with internal clocking.
Calibration
To compensate the MAX1132/MAX1133 for temperature
drift and other variations, they should be periodically
calibrated. After any change in ambient temperature
more than 10°C the device should be recalibrated. A
100mV change in supply voltage or any change in the
reference voltage should be followed by a calibration.
Calibration corrects for errors in gain, offset, integral
nonlinearity, and differential nonlinearity. The MAX1132/
MAX1133 should be calibrated after power-up or the
assertion of reset. Make sure the power supplies and
the reference voltage have fully settled prior to initiating
the calibration sequence.
Initiate calibration by setting M1 = 0 and M0 = 1 in the
Control-Byte. In internal clock mode, SSTRB goes low at
NOTE: FOR BEST NOISE PERFORMANCE, KEEP SCLK LOW DURING CONVERSION.
t
SSTRB
t
SCK
t
SSTRB
t
CSS
t
STR
SCLK
P1 CLOCKED IN
the beginning of calibration and goes high to signal the
end of calibration, approximately 80,000 clock cycles
later. In external clock mode, SSTRB goes high at the
beginning of calibration and goes low to signal the end
of calibration. Calibration should be performed in the
same clock mode as will be used for conversions.
Reference
The MAX1132/MAX1133 can be used with an internal
or external reference. An external reference can be
connected directly at the REF pin or at the REFADJ pin.
CREF is an internal reference node and must be
bypassed with a 1µF capacitor when using either the
internal or an external reference.
Internal Reference
When using the MAX1132/MAX1133’s internal reference, place a 0.22µF ceramic capacitor from REFADJ
to AGND and place a 2.2µF capacitor from REF to
AGND. Fine adjustments can be made to the internal
reference voltage by sinking or sourcing current at
REFADJ. The input impedance of REFADJ is nominally
9kΩ. The internal reference voltage is adjustable to
±1.5% with the circuit of Figure 7.
External reference
An external reference can be placed at either the input
(REFADJ) or the output (REF) of the MAX1132/
MAX1133’s internal buffer amplifier.
When connecting an external reference to REFADJ, the
input impedance is typically 9kΩ. Using the buffered
REFADJ input makes buffering of the external reference
unnecessary, however, the internal buffer output must
be bypassed at REF with a 2.2µF capacitor.
When connecting an external reference at REF,
REFADJ must be connected to AVDD. Then the input
impedance at REF is a minimum of 164kΩ for DC currents. During conversion, an external reference at REF
must deliver 250µA DC load current and have an output impedance of 10Ω or less. If the reference has a
higher output impedance or is noisy, bypass it at the
REF pin with a 4.7µF capacitor.
Analog Input
The MAX1132/MAX1133 use a capacitive DAC that
provides an inherent track/hold function. Drive AIN with
a source impedance less than 10Ω. Any signal conditioning circuitry must settle with 16-bit accuracy in less
than 500ns. Limit the input bandwidth to less than half
the sampling frequency to eliminate aliasing. The
MAX1132/MAX1133 has a complex input impedance
which varies from unipolar to bipolar mode (Figure 1).
Input Range
The analog input range in unipolar mode is 0 to +12V
for the MAX1132, and 0 to +4.096V for the MAX1133. In
bipolar mode, the analog input can be -12V to +12V for
the MAX1132, and -4.096V to +4.096V for the
MAX1133. Unipolar and bipolar mode is programmed
with the UNI/BIP bit of the Control Byte. When using a
reference other than the MAX1132/MAX1133’s internal
+4.096V reference, the full-scale input range will vary
accordingly. The full-scale input range depends on the
voltage at REF and the sampling mode selected (Tables
3 and 4).
Input Acquisition and Settling
Clocking in a Control Byte starts input acquisition. In
bipolar mode the main capacitor array starts acquiring
the input as soon as a start bit is recognized. If unipolar
mode is selected by the second DIN bit, the part will
immediately switch to unipolar sampling mode and
acquire a sample.
Acquisition can be extended by eight clock cycles by
setting M1 = 1, M0 = 1 (long acquisition mode). The
sampling instant in short acquisition completes on the
falling edge of the sixth clock cycle after the start bit
(Figure 2).
Acquisition is 5.5 clock cycles in short acquisition
mode and 13.5 clock cycles in long acquisition mode.
Short acquisition mode is 24 clock cycles per conversion. Using the external clock to run the conversion
process limits unipolar conversion speed to 125ksps
instead of 200ksps in bipolar mode. The input resistance in unipolar mode is larger than that of bipolar
mode (Figure1). The RC time constant in unipolar mode
is larger than that of bipolar mode, reducing the maximum conversion rate in 24 external clock mode. Long
acquisition mode with external clock allows both unipolar and bipolar sampling of 150ksps (4.8MHz/32 clock
cycles) by adding eight extra clock cycles to the conversion.
Most applications require an input buffer amplifier. If
the input signal is multiplexed, the input channel should
be switched immediately after acquistion, rather than
near the end of or after a conversion. This allows more
time for the input buffer amplifier to respond to a large
step-change in input signal. The input amplifier must
have a high enough slew-rate to complete the required
output voltage change before the beginning of the
acquisition time. At the beginning of acquisition, the
capacitive DAC is connected to the amplifier output,
causing some output disturbance. Ensure that the sampled voltage has settled to within the required limits
before the end of the acquisition time. If the frequency
of interest is low, AIN can be bypassed with a large
enough capacitor to charge the capacitive DAC with
very little change in voltage. However, for AC use, AIN
must be driven by a wideband buffer (at least 10MHz),
which must be stable with the DACs capacitive load (in
parallel with any AIN bypass capacitor used) and also
settle quickly (Figures 8 or 9).
Digital Noise
Digital noise can couple to AIN and REF. The conversion clock (SCLK) and other digital signals that are
active during input acquisition contribute noise to the
conversion result. If the noise signal is synchronous to
the sampling interval, an effective input offset is produced. Asynchronous signals produce random noise
on the input, whose high-frequency components may
be aliased into the frequency band of interest. Minimize
noise by presenting a low impedance (at the frequencies contained in the noise signal) at the inputs. This
requires bypassing AIN to AGND, or buffering the input
with an amplifier that has a small-signal bandwidth of
several MHz, or preferably both. AIN has a bandwidth
of about 4MHz.
Offsets resulting from synchronous noise (such as the
conversion clock) are canceled by the MAX1132/
MAX1133’s calibration scheme. The magnitude of the
offset produced by a synchronous signal depends on
the signal’s shape. Recalibration may be appropriate if
the shape or relative timing of the clock or other digital
signals change, as might occur if more than one clock
signal or frequency is used.
Distortion
Avoid degrading dynamic performance by choosing an
amplifier with distortion much less than the MAX1132/
MAX1133’s THD (-90dB) at frequencies of interest. If
the chosen amplifier has insufficient common-mode
rejection, which results in degraded THD performance,
use the inverting configuration to eliminate errors from
common-mode voltage. Low temperature-coefficient
resistors reduce linearity errors caused by resistance
changes due to self-heating. To reduce linearity errors
due to finite amplifier gain, use an amplifier circuit with
sufficient loop gain at the frequencies of interest.
DC Accuracy
If DC accuracy is important, choose a buffer with an
offset much less than the MAX1132/MAX1133’s maximum offset (±6mV), or whose offset can be trimmed
while maintaining good stability over the required temperature range.
16-Bit ADC, 200ksps, 5V Single-Supply
with Reference
Table 4. Bipolar Full Scale, Zero Scale, and Negative Scale
PARTREFERENCEZERO SCALEFULL SCALE
MAX1132
MAX1133
PARTREFERENCE
MAX1132
MAX1133
Internal-12V0+12V
External-12(V
Internal-4.096V0+4.096V
External-V
Internal0+12V
External0+12(V
Internal0+4.096V
External0+V
NEGATIVE FULL
SCALE
/4.096)0+12(V
REF
REF
ZERO SCALEFULL SCALE
0+V
REF
/4.096)
REF
REF
/4.096)
REF
Operating Modes and Serial Interfaces
The MAX1132/MAX1133 are fully compatible with
MICROWIRE and SPI/QSPI devices. MICROWIRE and
SPI/QSPI both transmit a byte and receive a byte at the
same time. The simplest software interface requires
only three 8-bit transfers to perform a conversion (one
8-bit transfer to configure the ADC, and two more 8-bit
transfers to clock out the 16-bit conversion result).
Short Acquisition Mode (24 SCLK)
Configure short acquisition by setting M1 = 0 and M0 =
0. In short acquisition mode, the acquisition time is 5.5
clock cycles. The total period is 24 clock cycles per
conversion.
Mode 2 Long Acquisition Mode (32 SCLK)
Configure long acquisition by setting M1 = 1 and M0 =
1. In long acquisition mode, the acquisition time is 13.5
clock cycles. The total period is 32 clock cycles per
conversion.
Calibration Mode
A calibration is initiated through the serial interface by
setting M1 = 0, M0 = 1. Calibration can be done in
either internal or external clock mode, though it is desirable that the part be calibrated in the same mode in
which it will be used to do conversions. The part will
remain in calibration mode for approximately 80,000
clock cycles unless the calibration is aborted.
Calibration is halted if RST or SHDN goes low, or if a
valid start condition occurs.
Software Shutdown
A software power-down is initiated by setting M1 = 1,
M0 = 0. After the conversion completes, the part shuts
down. It reawakens upon receiving a new start bit.
Conversions initiated with M1 = 1 and M0 = 0 (shutdown) use the acquisition mode selected for the previous conversion.
Shutdown Mode
The MAX1132/MAX1133 may be shut down by pulling
SHDN low or by asserting software shutdown. In addition to lowering power dissipation to 13µW, considerable power can be saved by shutting down the
converter for short periods (duration will be affected by
REF startup time with internal reference) between conversions. There is no need to perform a calibration after
the converter has been shut down, unless the time in
Figure 9. ±5V Buffer for AC/DC Use Has ±3.5V Swing
IN
510
Ω
+5V
0.1µF
2
MAX410
3
IN
7
6
4
0.1µF
-5V
2
MAX427
3
+15V
-15V
1k
Ω
0.1µF
7
6
4
0.1µF
100pF
ELANTEC
20
EL2003
Ω
0.0033µF
AIN
22
Ω
AIN
0.1µF
MAX1132/MAX1133
shutdown is long enough that the supply voltage or
ambient temperature may have changed.
Supplies, Layout, Grounding
and Bypassing
For best system performance, use separate analog and
digital ground planes. The two ground planes should
be tied together at the MAX1132/MAX1133. Use pins 3
and 14 as the primary AGND and DGND, respectively.
If the analog and digital supplies come from the same
source, isolate the digital supply from the analog with a
low value resistor (10Ω).
The MAX1132/MAX1133 are not sensitive to the order
of AVDDand DVDDsequencing. Either supply can be
present in the absence of the other. Do not apply an
external reference voltage until after both AV
DD
and
DVDDare present.
Be sure that digital return currents do not pass through
the analog ground. All return current paths must be
low-impedance. A 5mA current flowing through a PC
board ground trace impedance of only 0.05Ω creates
an error voltage of about 250µV, or about 2LSBs error
with a ±4V full-scale system. The board layout should
ensure as much as possible that digital and analog signal lines are kept separate. Do not run analog and digital lines parallel to one another. If you must cross one
with the other, do so at right angles.
The ADC is sensitive to high-frequency noise on the
AVDDpower supply. Bypass this supply to the analog
ground plane with 0.1µF. If the main supply is not adequately bypassed, add an additional 1µF or 10µF lowESR capacitor in parallel with the primary bypass
capacitor.
Transfer Function
Figures 10 and 11 show the MAX1132/MAX1133’s
transfer functions. In unipolar mode, the output data is
binary format and in bipolar mode it is two’s complement.
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 end points of the transfer function,
once offset and gain errors have been nullified. INL for
the MAX1132/MAX1133 is 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.
Aperture Jitter
Aperture jitter (tAJ) is the sample-to-sample variation in
the time between the samples.
Aperture Delay
Aperture delay (tAD) is the time between the falling
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 analogto-digital 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, including thermal noise, reference noise,
clock jitter, etc. Therefore, SNR is calculated 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 frequency’s RMS amplitude to
the 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:
16-Bit ADC, 200ksps, 5V Single-Supply
with Reference
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.
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 ____________________ 19