Datasheet
Detailed Description
The MAX1236–MAX1239 analog-to-digital converters
(ADCs) use successive-approximation conversion tech-
niques and fully differential input track/hold (T/H) cir-
cuitry to capture and convert an analog signal to a
serial 12-bit digital output. The MAX1236/MAX1237 are
4-channel ADCs, and the MAX1238/MAX1239 are 12-
channel ADCs. These devices feature a high-speed, 2-
wire serial interface supporting data rates up to 1.7MHz.
Figure 2 shows the simplified internal structure for the
MAX1238/MAX1239.
Power Supply
The MAX1236–MAX1239 operates from a single supply
and consumes 670µA (typ) at sampling rates up to
94.4ksps. The MAX1237/MAX1239 feature a 2.048V
internal reference and the MAX1236/MAX1238 feature
a 4.096V internal reference. All devices can be config-
ured for use with an external reference from 1V to V
DD
.
Analog Input and Track/Hold
The MAX1236–MAX1239 analog-input architecture con-
tains an analog-input multiplexer (mux), a fully differen-
tial track-and-hold (T/H) capacitor, T/H switches, a
comparator, and a fully differential switched capacitive
digital-to-analog converter (DAC) (Figure 4).
In single-ended mode, the analog input multiplexer con-
nects C
T/H
between the analog input selected by
CS[3:0] (see the
Configuration/Setup Bytes (Write Cycle)
section) and GND (Table 3). In differential mode, the
analog-input multiplexer connects C
T/H
to the “+” and “-”
analog inputs selected by CS[3:0] (Table 4).
During the acquisition interval, the T/H switches are in
the track position and C
T/H
charges to the analog input
MAX1236–MAX1239
2.7V to 3.6V and 4.5V to 5.5V, Low-Power,
4-/12-Channel, 2-Wire Serial, 12-Bit ADCs
_______________________________________________________________________________________ 9
ANALOG
INPUT
MUX
AIN1
AIN11/REF
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
AIN9
AIN10
AIN0
SCL
SDA
INPUT SHIFT REGISTER
SETUP REGISTER
CONFIGURATION REGISTER
CONTROL
LOGIC
REFERENCE
4.096V (MAX1238)
2.048V (MAX1239)
INTERNAL
OSCILLATOR
OUTPUT SHIFT
REGISTER
AND RAM
REF
T/H
12-BIT
ADC
V
DD
GND
MAX1238
MAX1239
Figure 2. MAX1238/MAX1239 Simplified Functional Diagram
V
DD
I
OL
I
OH
V
OUT
400pF
SDA
Figure 3. Load Circuit