8-Channel, 1.5 MSPS, 12-Bit and 10-Bit
Parallel ADCs with a Sequencer
Preliminary Technical Data
AD7938/AD7939
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Fast throughput rate: 1.5 MSPS
Specified for VDD of 2.7 V to 5.25 V
Low power
V
AGND
DD
AD7938/AD7939
V
REFIN/
V
REFOUT
2.5V
8 mW max at 1.5 MSPS with 3 V supplies
16 mW max 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
Wide input bandwidth
VREF
V
V
0
IN
IN
CLKIN
12-/10-BIT
SAR ADC
AND
I/P
CONVST
T/H
MUX
CONTROL
BUSY
7
SEQUENCER
V
PARALLEL INTERFACE/CONTROL REGISTER
DRIVE
70 dB SNR at 50 kHz input frequency
No pipeline delays
DB0 DB11
CS RD WR W/B
DGND
High speed parallel interface—word/byte modes
Full shutdown mode: 1 µA max
32-lead LFCSP and TQFP package
Figure 1.
conversion. Alternatively, this pin can be overdriven to provide
an external reference.
GENERAL DESCRIPTION
The AD7938/AD7939 are 12-bit and 10-bit, high speed, low
power, successive approximation (SAR) 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 20 MHz.
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.
The AD7938/AD7939 feature eight analog input channels with
a channel sequencer that allow a preprogrammed selection of
channels to be converted sequentially. These parts can operate
with either single-ended, fully differential, or pseudo-
differential analog inputs.
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. Software configurable analog inputs. Single-ended, pseudo-
differential, or fully differential analog inputs that are
software selectable.
5. Single-supply operation with VDRIVE function. The VDRIVE
function allows the parallel interface to connect directly to
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
and the conversion is also initiated at
CONVST
this point.
3 V, or 5 V processor systems independent of VDD
6. No pipeline delay.
.
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
7. Accurate control of the sampling instant via a
CONVST
input and once off conversion control.
Rev. PrN
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