MAX11634 Datasheet, PDF (12/24 Pages) Maxim Integrated Products – 12-Bit, 300ksps ADCs with Differential

12-Bit, 300ksps ADCs with Differential
Track/Hold, and Internal Reference
Converter Operation
The MAX11634–MAX11637 ADCs use a fully differen-
tial, successive-approximation register (SAR) conver-
sion technique and an on-chip T/H block to convert
temperature and voltage signals into a 12-bit digital
result. Both single-ended and differential configurations
are supported, with a unipolar signal range for single-
ended mode and bipolar or unipolar ranges for differ-
ential mode.
Input Bandwidth
The ADC’s input-tracking circuitry has a 1MHz small-
signal bandwidth, so it is possible to digitize high-
speed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. Anti-alias prefiltering
of the input signals is necessary to avoid high-frequency
signals aliasing into the frequency band of interest.
Analog Input Protection
Internal ESD protection diodes clamp all pins to V_DD
and GND, allowing the inputs to swing from (GND -
0.3V) to (V_DD + 0.3V) without damage. However, for
accurate conversions near full scale, the inputs must
not exceed V_DD by more than 50mV or be lower than
GND by 50mV. If an off-channel analog input voltage
exceeds the supplies, limit the input current to 2mA.
3-Wire Serial Interface
The MAX11634–MAX11637 feature a serial interface
compatible with SPI/QSPI and MICROWIRE devices.
For SPI/QSPI, ensure the CPU serial interface runs in
master mode so it generates the serial clock signal.
Select the SCLK frequency of 10MHz or less, and set
clock polarity (CPOL) and phase (CPHA) in the µP con-
trol registers to the same value. The MAX11634–
MAX11637 operate with SCLK idling high or low, and
thus operate with CPOL = CPHA = 0 or CPOL = CPHA
= 1. Set CS low to latch input data at DIN on the rising
edge of SCLK. Output data at DOUT is updated on the
falling edge of SCLK. Bipolar true differential results are
available in two’s complement format, while all others
are in binary.
Serial communication always begins with an 8-bit input
data byte (MSB first) loaded from DIN. Use a second
byte, immediately following the setup byte, to write to
the unipolar mode or bipolar mode registers (see
Tables 1, 3, 4, and 5). A high-to-low transition on CS ini-
tiates the data input operation. The input data byte and
the subsequent data bytes are clocked from DIN into
the serial interface on the rising edge of SCLK.
Tables 1–7 detail the register descriptions. Bits 5 and 4,
CKSEL1 and CKSEL0, respectively, control the clock
modes in the setup register (see Table 3). Choose
between four different clock modes for various ways to
start a conversion and determine whether the acquisi-
tions are internally or externally timed. Select clock
mode 00 to configure CNVST/AIN7 to act as a conver-
sion start and use it to request the programmed, inter-
nally timed conversions without tying up the serial bus.
In clock mode 01, use CNVST to request conversions
one channel at a time, controlling the sampling speed
without tying up the serial bus. Request and start inter-
nally timed conversions through the serial interface by
writing to the conversion register in the default clock
mode 10. Use clock mode 11 with SCLK up to 4.8MHz
for externally timed acquisitions to achieve sampling
rates up to 300ksps. Clock mode 11 disables scanning
and averaging. See Figures 4–7 for timing specifica-
tions and how to begin a conversion.
These devices feature an active-low, end-of-conversion
output. EOC goes low when the ADC completes the last-
requested operation and is waiting for the next input
data byte (for clock modes 00 and 10). In clock mode
01, EOC goes low after the ADC completes each
requested operation. EOC goes high when CS or CNVST
goes low. EOC is always high in clock mode 11.
Single-Ended/Differential Input
The MAX11634–MAX11637 use a fully differential ADC
for all conversions. The analog inputs can be config-
ured for either differential or single-ended conversions
by writing to the setup register (see Table 3). Single-
ended conversions are internally referenced to GND
(see Figure 3).
In differential mode, the T/H samples the difference
between two analog inputs, eliminating common-mode
DC offsets and noise. IN+ and IN- are selected from the
following pairs: AIN0/AIN1, AIN2/AIN3, AIN4/AIN5, and
AIN6/AIN7. AIN0–AIN7 are available on the MAX11636/
MAX11637. AIN0–AIN3 are available on the MAX11634/
MAX11635. See Tables 2–5 for more details on config-
uring the inputs. For the inputs that can be configured
as CNVST or an analog input, only one can be used at
a time. For the inputs that can be configured as REF- or
an analog input, the REF- configuration excludes the
analog input.
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