8-Channel, 1.5 MSPS, 12-Bit and 10-Bit
Parallel ADCs with a Sequencer
Data Sheet
AD7938/AD7939
FEATURES
FUNCTIONAL BLOCK DIAGRAM
V
AGND
DD
Throughput rate: 1.5 MSPS
Specified for VDD of 2.7 V to 5.25 V
Power consumption
AD7938/AD7939
V
REFIN/
V
REFOUT
2.5V
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
VREF
V
0
IN
IN
CLKIN
CONVST
BUSY
12-/10-BIT
SAR ADC
AND
I/P
MUX
T/H
CONTROL
V
7
4-channel fully differential inputs
4-channel pseudo differential inputs
7-channel pseudo differential inputs
Accurate on-chip 2.5 V reference
SEQUENCER
V
PARALLEL INTERFACE/CONTROL REGISTER
DRIVE
0.2% maximum @ 25°C, 25 ppm/°C maximum
69 dB SINAD 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: 2 µA maximum
32-lead LFCSP and TQFP packages
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.
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
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.
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 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
3 V or 5 V processor systems independent of VDD
6. No pipeline delay.
.
CONVST
falling edge of
this point.
and the conversion is also initiated at
CONVST
7. Accurate control of the sampling instant via a
input and once-off conversion control.
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.
Table 1. Related Devices
Device
No. of Bits
No. of Channels
Speed
AD7933/AD7934 12/10
4
8
4
1.5 MSPS
625 kSPS
625 kSPS
AD7938-6
AD7934-6
12
12
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rightsof third parties that may result fromits use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks andregisteredtrademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2004–2011 Analog Devices, Inc. All rights reserved.
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