؎15 V Operation
Digital Potentiometer
a
AD7376*
FUNCTIO NAL BLO CK D IAGRAM
FEATURES
128 Position
Potentiom eter Replacem ent
10 k⍀, 50 k⍀, 100 k⍀, 1 M⍀
Pow er Shutdow n: Less than 1 A
3-Wire SPI Com patible Serial Data Input
+5 V to +30 V Single Supply Operation
؎5 V to ؎15 V Dual Supply Operation
Midscale Preset
AD7376
V
DD
SDO
SDI
Q
A
W
B
7-BIT
SERIAL
REGISTER
7
7
7-BIT
LATCH
D
CK
R
SHDN
V
SS
CLK
CS
APPLICATIONS
Mechanical Potentiom eter Replacem ent
Instrum entation: Gain, Offset Adjustm ent
Program m able Voltage-to-Current Conversion
Program m able Filters, Delays, Tim e Constants
Line Im pedance Matching
GND
SHDN
RS
to an end-to-end open circuit condition on the A terminal and
shorts the wiper to the B terminal, achieving a microwatt power
shutdown state. When shutdown is returned to logic high, the
previous latch settings put the wiper in the same resistance
setting prior to shutdown as long as power to VDD is not re-
moved. T he digital interface is still active in shutdown so that
code changes can be made that will produce a new wiper posi-
tion when the device is taken out of shutdown.
Pow er Supply Adjustm ent
GENERAL D ESCRIP TIO N
T he AD7376 provides a single channel, 128-position digitally-
controlled variable resistor (VR) device. T his device performs the
same electronic adjustment function as a potentiometer or vari-
able resistor. T hese products were optimized for instrument and
test equipment applications where a combination of high voltage
with a choice between bandwidth or power dissipation are avail-
able as a result of the wide selection of end-to-end terminal resis-
tance values. T he AD7376 contains a fixed resistor with a wiper
contact that taps the fixed resistor value at a point determined by
a digital code loaded into the SPI-compatible serial-input regis-
ter. T he resistance between the wiper and either endpoint of the
fixed resistor varies linearly with respect to the digital code trans-
ferred into the VR latch. T he variable resistor offers a completely
programmable value of resistance between the A terminal and the
wiper or the B terminal and the wiper. T he fixed A to B terminal
resistance of 10 kΩ, 50 kΩ, 100 kΩ or 1 MΩ has a nominal tem-
perature coefficient of –300 ppm/°C.
T he AD7376 is available in both surface mount (SOL-16) and
the 14-lead plastic DIP package. For ultracompact solutions
selected models are available in the thin T SSOP package. All
parts are guaranteed to operate over the extended industrial
temperature range of –40°C to +85°C. For operation at lower
supply voltages (+3 V to +5 V), see the AD8400/AD8402/
AD8403 products.
1
SDI
(DATA IN)
D
D
X
X
0
tDS
tDH
1
0
SDO
(DATA OUT)
D'
D'
X
X
tPD_MAX
tCH
1
0
tCS1
CLK
T he VR has its own VR latch which holds its programmed resis-
tance value. T he VR latch is updated from an internal serial-to-
parallel shift register which is loaded from a standard 3-wire
serial-input digital interface. Seven data bits make up the data
word clocked into the serial data input register (SDI). Only the
last seven bits of the data word loaded are transferred into the
7-bit VR latch when the CS strobe is returned to logic high. A
serial data output pin (SDO) at the opposite end of the serial
register allows simple daisy-chaining in multiple VR applications
without additional external decoding logic.
tCSH0
tCL
tCSH
tCSS
1
tCSW
tS
CS
0
V
DD
0V
V
OUT
؎1 LSB ERROR BAND
؎1 LSB
Figure 1. Detail Tim ing Diagram
T he reset (RS) pin forces the wiper to the midscale position by
loading 40H into the VR latch. T he SHDN pin forces the resistor
T he last seven data bits clocked into the serial input register will
be transferred to the VR 7-bit latch when CS returns to logic
high. Extra data bits are ignored.
*Patent Number: 5495245
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 781/ 329-4700
Fax: 781/ 326-8703
World Wide Web Site: http:/ / w w w .analog.com
© Analog Devices, Inc., 1997
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