MAX11626_1110 Datasheet, PDF (12/22 Pages) Maxim Integrated Products – 12-Bit, 300ksps ADCs with FIFO and Internal Reference

12-Bit, 300ksps ADCs
with FIFO and Internal Reference
Converter Operation
The MAX11626–MAX11629/MAX11632/MAX11633
ADCs use a successive-approximation register (SAR)
conversion technique and an on-chip T/H block to con-
vert voltage signals into a 12-bit digital result. This sin-
gle-ended configuration supports unipolar signal
ranges.
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 MAX11626–MAX11629/MAX11632/MAX11633 fea-
ture 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 control registers to the same value.
The MAX11626–MAX11629/MAX11632/MAX11633 oper-
ate 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. Results are output in binary format.
Serial communication always begins with an 8-bit input
data byte (MSB first) loaded from DIN. A high-to-low
transition on CS initiates 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 1–5 detail the register descrip-
tions. 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 vari-
ous ways to start a conversion and determine whether
the acquisitions are internally or externally timed. Select
clock mode 00 to configure CNVST/AIN_ to act as a
conversion start and use it to request the programmed,
internally timed conversions without tying up the serial
bus. In clock mode 01, use CNVST to request conver-
sions one channel at a time, controlling the sampling
speed without tying up the serial bus. Request and
start internally 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 specifications 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 Inputs
The single-ended analog input conversion modes can
be configured by writing to the setup register (see
Table 3). Single-ended conversions are internally refer-
enced to GND (see Figure 3).
AIN0–AIN3 are available on the MAX11626–MAX11629/
MAX11632/MAX11633. AIN4–AIN7 are only available on
the MAX11628–MAX11633. AIN8–AIN15 are only avail-
able on the MAX11632/MAX11633. See Tables 2–5 for
more details on configuring the inputs. For the inputs
that can be configured as CNVST or an analog input,
only one can be used at a time.
Unipolar
The MAX11626–MAX11629/MAX11632/MAX11633
always operate in unipolar mode. The analog inputs are
internally referenced to GND with a full-scale input
range from 0 to V_REF.
AIN0-AIN15
HOLD
GND
REF
GND
DAC
CIN+
CIN-
HOLD
V_DD/2
Figure 3. Equivalent Input Circuit
COMPARATOR
+
-
HOLD
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