Datasheet

8-Channel, 1.5 MSPS, 12-Bit and 10-Bit
Parallel ADCs with a Sequencer
Data Sheet
AD7938/AD7939
Rev. C
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FEATURES
Throughput rate: 1.5 MSPS
Specified for V
DD
of 2.7 V to 5.25 V
Power consumption
6 mW maximum at 1.5 MSPS with 3 V supplies
13.5 mW maximum at 1.5 MSPS with 5 V supplies
8 analog input channels with a sequencer
Software-configurable analog inputs
8-channel single-ended inputs
4-channel fully differential inputs
4-channel pseudo differential inputs
7-channel pseudo differential inputs
Accurate on-chip 2.5 V reference
±0.2% maximum @ 25°C, 25 ppm/°C maximum
69 dB SINAD at 50 kHz input frequency
No pipeline delays
High speed parallel interface—word/byte modes
Full shutdown mode: 2 µA maximum
32-lead LFCSP and TQFP packages
FUNCTIONAL BLOCK DIAGRAM
03715-001
V
IN
7
T/H
PARALLEL INTERFACE/CONTROL REGISTER
SEQUENCER
12-/10-BIT
SAR ADC
AND
CONTROL
I/P
MUX
2.5V
VREF
DB0 DB11
V
DRIVE
V
DD
AD7938/AD7939
V
IN
0
AGND
V
REFIN/
V
REFOUT
CLKIN
BUSY
CONVST
CS DGND
RD
WR W/B
Figure 1.
GENERAL DESCRIPTION
The AD7938/AD7939 are 12-bit and 10-bit, high speed, low
power, successive approximation (SAR) analog-to-digital
converters (ADCs). The parts operate from a single 2.7 V to
5.25 V power supply and feature throughput rates up to
1.5 MSPS. The parts contain a low noise, wide bandwidth,
differential track-and-hold amplifier that can handle input
frequencies up to 50 MHz.
The AD7938/AD7939 feature eight analog input channels with
a channel sequencer that allows a preprogrammed selection of
channels to be converted sequentially. These parts can operate
with either single-ended, fully differential, or pseudo
differential analog inputs.
The conversion process and data acquisition are controlled
using standard control inputs that allow easy interfacing with
microprocessors and DSPs. The input signal is sampled on the
falling edge of
CONVST
and the conversion is also initiated at
this point.
The AD7938/AD7939 have an accurate on-chip 2.5 V reference
that can be used as the reference source for the analog-to-digital
conversion. Alternatively, this pin can be overdriven to provide
an external reference.
These parts use advanced design techniques to achieve very
low power dissipation at high throughput rates. They also
feature flexible power management options. An on-chip control
register allows the user to set up different operating conditions,
including analog input range and configuration, output coding,
power management, and channel sequencing.
PRODUCT HIGHLIGHTS
1. High throughput with low power consumption.
2. Eight analog inputs with a channel sequencer.
3. Accurate on-chip 2.5 V reference.
4. Single-ended, pseudo differential, or fully differential
analog inputs that are software selectable.
5. Single-supply operation with V
DRIVE
function. The V
DRIVE
function allows the parallel interface to connect directly to
3 V or 5 V processor systems independent of V
DD
.
6. No pipeline delay.
7. Accurate control of the sampling instant via a
CONVST
input and once-off conversion control.
Table 1. Related Devices
Device No. of Bits No. of Channels Speed
AD7933/AD7934 12/10 4 1.5 MSPS
AD7938-6 12 8 625 kSPS
AD7934-6 12 4 625 kSPS