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 rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD8400/AD8402/AD8403
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2002
1-/2-/4-Channel
Digital Potentiometers
FUNCTIONAL BLOCK DIAGRAM
8
8-BIT
LATCH
CK RS
8
8-BIT
LATCH
CK RS
8
8-BIT
LATCH
CK RS
8
8-BIT
LATCH
CK RS
SHDN
DAC
SELECT
A1, A0
1
10-BIT
SERIAL
LATCH
CK Q RS
D
RS
SDO
AD8403
V
DD
DGND
SDI
CLK
CS
8
2
3
2
4
RDAC1
SHDN
W1
A1
B1
AGND1
RDAC2
SHDN
W2
A2
B2
AGND2
RDAC3
SHDN
W3
A3
B3
AGND3
RDAC4
SHDN
W4
A4
B4
AGND4
FEATURES
256-Position
Replaces 1, 2, or 4 Potentiometers
1 k, 10 k, 50 k, 100 k
Power Shutdown—Less than 5 A
3-Wire SPI-Compatible Serial Data Input
10 MHz Update Data Loading Rate
2.7 V to 5.5 V Single-Supply Operation
Midscale Preset
APPLICATIONS
Mechanical Potentiometer Replacement
Programmable Filters, Delays, Time Constants
Volume Control, Panning
Line Impedance Matching
Power Supply Adjustment
GENERAL DESCRIPTION
The AD8400/AD8402/AD8403 provide a single, dual or quad
channel, 256 position digitally controlled variable resistor (VR) device.
These devices perform the same electronic adjustment function as
a potentiometer or variable resistor. The AD8400 contains a single
variable resistor in the compact SO-8 package. The AD8402 contains
two independent variable resistors in space-saving SO-14 surface-
mount packages. The AD8403 contains four independent variable
resistors in 24-lead PDIP, SOIC, and TSSOP packages. Each part
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
controlling serial input register. The resistance between the wiper and
either endpoint of the fixed resistor varies linearly with respect to the
digital code transferred into the VR latch. Each variable resistor
offers a completely programmable value of resistance, between the A
terminal and the wiper or the B terminal and the wiper. The fixed
A to B terminal resistance of 1 kΩ, 10 kΩ, 50 kΩ, or 100 kΩ has a ±1%
channel-to-channel matching tolerance with a nominal temperature
coefficient of 500 ppm/°C. A unique switching circuit minimizes the
high glitch inherent in traditional switched resistor designs avoiding
any make-before-break or break-before-make operation.
Each VR has its own VR latch that holds its programmed resistance
value. These VR latches are updated from an SPI compatible serial-
to-parallel shift register that is loaded from a standard 3-wire
serial-input digital interface. Ten data bits make up the data word
clocked into the serial input register. The data word is decoded where
the first two bits determine the address of the VR latch to be loaded,
the last eight bits are data. A serial data output pin at the opposite end
of the serial register allows simple daisy-chaining in multiple VR
applications without additional external decoding logic.
The reset (RS) pin forces the wiper to the midscale position by
loading 80
H
into the VR latch. The SHDN pin forces the resistor
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 SHDN is returned to logic high, the
previous latch settings put the wiper in the same resistance
setting prior to shutdown. The digital interface is still active in
shutdown so that code changes can be made that will produce
new wiper positions when the device is taken out of shutdown.
The AD8400 is available in both the SO-8 surface-mount and the
8-lead plastic DIP package.
The AD8402 is available in both surface mount (SO-14) and
14-lead plastic DIP packages, while the AD8403 is available in a
narrow body 24-lead plastic DIP and a 24-lead surface-mount
package. The AD8402/AD8403 are also offered in the 1.1 mm thin
TSSOP-14/TSSOP-24 packages for PCMCIA applications. All
parts are guaranteed to operate over the extended industrial tem-
perature range of –40°C to +125°C.
CODE – Decimal
100
75
50
25
00 64 128 192 255
R
WA
(D), R
WB
(D) – % of Nominal R
AB
R
WA
R
WB
Figure 1. RWA and RWB vs. Code
REV. C
–2–
AD8400/AD8402/AD8403–SPECIFICATIONS
(V
DD
= 3 V 10% or 5 V 10%, V
A
= V
DD
, V
B
= 0 V,
–40C ≤ T
A
≤ +125C unless otherwise noted.)
ELECTRICAL CHARACTERISTICS–10 k VERSION
Parameter Symbol Conditions Min Typ
1
Max Unit
DC CHARACTERISTICS RHEOSTAT MODE (Specifications Apply to All VRs)
Resistor Differential NL
2
R-DNL R
WB
, V
A
= No Connect –1±1/4 +1 LSB
Resistor Nonlinearity
2
R-INL R
WB
, V
A
= No Connect –2±1/2 +2 LSB
Nominal Resistance
3
R
AB
T
A
= 25°C, Model: AD840XYY10 8 10 12 kΩ
Resistance Tempco ∆R
AB
/∆TV
AB
= V
DD
, Wiper = No Connect 500 ppm/°C
Wiper Resistance R
W
I
W
= 1 V/R 50 100 Ω
Nominal Resistance Match ∆R/R
AB
CH 1 to 2, 3, or 4,
V
AB
= V
DD
, T
A
= 25°C 0.2 1 %
DC CHARACTERISTICS POTENTIOMETER DIVIDER Specifications Apply to All VRs
Resolution N 8 Bits
Integral Nonlinearity
4
INL –2±1/2 +2 LSB
Differential Nonlinearity
4
DNL V
DD
= 5 V –1±1/4 +1 LSB
DNL V
DD
= 3 V T
A
= 25°C–1±1/4 +1 LSB
DNL V
DD
= 3 V T
A
= –40°C, +85°C–1.5 ±1/2 +1.5 LSB
Voltage Divider Tempco ∆V
W
/∆T Code = 80
H
15 ppm/°C
Full-Scale Error V
WFSE
Code = FF
H
–4–2.8 0 LSB
Zero-Scale Error V
WZSE
Code = 00
H
0 1.3 2 LSB
RESISTOR TERMINALS
Voltage Range
5
V
A, B, W
0V
DD
V
Capacitance
6
Ax, Bx C
A, B
f = 1 MHz, Measured to GND, Code = 80
H
75 pF
Capacitance
6
Wx C
W
f = 1 MHz, Measured to GND, Code = 80
H
120 pF
Shutdown Current
7
I
A_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0 0.01 5 µA
Shutdown Wiper Resistance R
W_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0, V
DD
= 5 V 100 200 Ω
DIGITAL INPUTS AND OUTPUTS
Input Logic High V
IH
V
DD
= 5 V 2.4 V
Input Logic Low V
IL
V
DD
= 5 V 0.8 V
Input Logic High V
IH
V
DD
= 3 V 2.1 V
Input Logic Low V
IL
V
DD
= 3 V 0.6 V
Output Logic High V
OH
R
L
= 2.2 kΩ to V
DD
V
DD
– 0.1 V
Output Logic Low V
OL
I
OL
= 1.6 mA, V
DD
= 5 V 0.4 V
Input Current I
IL
V
IN
= 0 V or +5 V, V
DD
= 5 V ±1µA
Input Capacitance
6
C
IL
5pF
POWER SUPPLIES
Power Supply Range V
DD
Range 2.7 5.5 V
Supply Current (CMOS) I
DD
V
IH
= V
DD
or V
IL
= 0 V 0.01 5 µA
Supply Current (TTL)
8
I
DD
V
IH
= 2.4 V or 0.8 V, V
DD
= 5.5 V 0.9 4 mA
Power Dissipation (CMOS)
9
P
DISS
V
IH
= V
DD
or V
IL
= 0 V, V
DD
= 5.5 V 27.5 µW
Power Supply Sensitivity PSS V
DD
= 5 V ± 10% 0.0002 0.001 %/%
PSS V
DD
= 3 V ± 10% 0.006 0.03 %/%
DYNAMIC CHARACTERISTICS
6, 10
Bandwidth –3 dB BW_10K R = 10 kΩ600 kHz
Total Harmonic Distortion THD
W
V
A
= 1 V rms + 2 V dc, V
B
= 2 V dc, f = 1 kHz 0.003 %
V
W
Settling Time t
S
V
A
= V
DD
, V
B
= 0 V, ±1% Error Band 2 µs
Resistor Noise Voltage e
NWB
R
WB
= 5 kΩ, f = 1 kHz, RS = 0 9 nV/√Hz
Crosstalk
11
C
T
V
A
= V
DD
, V
B
= 0 V –65 dB
NOTES
11
Typicals represent average readings at 25°C and V
DD
= 5 V.
12
Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper
1
positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. See TPC 29 test circuit.
1
I
W
= 50 µA for V
DD
= 3 V and I
W
= 400 µA for V
DD
= 5 V for the 10 kΩ versions.
13
V
AB
= V
DD
, Wiper (V
W
) = No Connect.
14
INL and DNL are measured at V
W
with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. V
A
= V
DD
and V
B
= 0 V.
1
DNL Specification limits of ±1 LSB maximum are Guaranteed Monotonic operating conditions. See TPC 28 test circuit.
15
Resistor terminals A, B, W have no limitations on polarity with respect to each other.
16
Guaranteed by design and not subject to production test. Resistor-terminal capacitance tests are measured with 2.5 V bias on the measured terminal. The remaining
1
resistor terminals are left open circuit.
17
Measured at the Ax terminals. All Ax terminals are open circuited in shutdown mode.
18
Worst-case supply current consumed when input logic level at 2.4 V, standard characteristic of CMOS logic. See TPC 20 for a plot of I
DD
versus logic voltage.
19
P
DISS
is calculated from (I
DD
× V
DD
). CMOS logic level inputs result in minimum power dissipation.
10
All Dynamic Characteristics use V
DD
= 5 V.
11
Measured at a V
W
pin where an adjacent V
W
pin is making a full-scale voltage change.
Specifications subject to change without notice.
REV. C –3–
AD8400/AD8402/AD8403
SPECIFICATIONS
(V
DD
= 3 V 10% or 5 V 10%, V
A
= V
DD
, V
B
= 0 V, –40C ≤ T
A
≤ +125C unless otherwise noted.)
Parameter Symbol Conditions Min Typ
1
Max Unit
DC CHARACTERISTICS RHEOSTAT MODE (Specifications Apply to All VRs)
Resistor Differential NL
2
R-DNL R
WB
, V
A
= No Connect –1±1/4 +1 LSB
Resistor Nonlinearity
2
R-INL R
WB
, V
A
= No Connect –2±1/2 +2 LSB
Nominal Resistance
3
R
AB
T
A
= 25°C, Model: AD840XYY50 35 50 65 kΩ
R
AB
T
A
= 25°C, Model: AD840XYY100 70 100 130 kΩ
Resistance Tempco ∆R
AB
/∆TV
AB
= V
DD
, Wiper = No Connect 500 ppm/°C
Wiper Resistance R
W
I
W
= 1 V/R 53 100 Ω
Nominal Resistance Match ∆R/R
AB
CH 1 to 2, 3, or 4,
V
AB
= V
DD
, T
A
= 25°C 0.2 1 %
DC CHARACTERISTICS POTENTIOMETER DIVIDER (Specifications Apply to All VRs)
Resolution N 8 Bits
Integral Nonlinearity
4
INL –4±1 +4 LSB
Differential Nonlinearity
4
DNL V
DD
= 5 V –1±1/4 +1 LSB
DNL V
DD
= 3 V T
A
= 25°C–1±1/4 +1 LSB
DNL V
DD
= 3 V T
A
= –40°C, +85°C–1.5 ±1/2 +1.5 LSB
Voltage Divider Tempco ∆V
W
/∆T Code = 80
H
15 ppm/°C
Full-Scale Error V
WFSE
Code = FF
H
–1–0.25 0 LSB
Zero-Scale Error V
WZSE
Code = 00
H
0 +0.1 +1 LSB
RESISTOR TERMINALS
Voltage Range
5
V
A, B, W
0V
DD
V
Capacitance
6
Ax, Bx C
A, B
f = 1 MHz, Measured to GND, Code = 80
H
15 pF
Capacitance
6
Wx C
W
f = 1 MHz, Measured to GND, Code = 80
H
80 pF
Shutdown Current
7
I
A_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0 0.01 5 µA
Shutdown Wiper Resistance R
W_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0, V
DD
= 5 V 100 200 Ω
DIGITAL INPUTS AND OUTPUTS
Input Logic High V
IH
V
DD
= 5 V 2.4 V
Input Logic Low V
IL
V
DD
= 5 V 0.8 V
Input Logic High V
IH
V
DD
= 3 V 2.1 V
Input Logic Low V
IL
V
DD
= 3 V 0.6 V
Output Logic High V
OH
R
L
= 2.2 kΩ to V
DD
V
DD
– 0.1 V
Output Logic Low V
OL
I
OL
= 1.6 mA, V
DD
= 5 V 0.4 V
Input Current I
IL
V
IN
= 0 V or 5 V, V
DD
= 5 V ±1µA
Input Capacitance
6
C
IL
5pF
POWER SUPPLIES
Power Supply Range V
DD
Range 2.7 5.5 V
Supply Current (CMOS) I
DD
V
IH
= V
DD
or V
IL
= 0 V 0.01 5 µA
Supply Current (TTL)
8
I
DD
V
IH
= 2.4 V or 0.8 V, V
DD
= 5.5 V 0.9 4 mA
Power Dissipation (CMOS)
9
P
DISS
V
IH
= V
DD
or V
IL
= 0 V, V
DD
= 5.5 V 27.5 µW
Power Supply Sensitivity PSS V
DD
= 5 V ± 10% 0.0002 0.001 %/%
PSS V
DD
= 3 V ± 10% 0.006 0.03 %/%
DYNAMIC CHARACTERISTICS
6, 10
Bandwidth –3 dB BW_50K R = 50 kΩ125 kHz
BW_100K R = 100 kΩ71 kHz
Total Harmonic Distortion THD
W
V
A
= 1 V rms + 2 V dc, V
B
= 2 V dc, f = 1 kHz 0.003 %
V
W
Settling Time t
S
_50K V
A
= V
DD
, V
B
= 0 V, ±1% Error Band 9 µs
t
S
_100K V
A
= V
DD
, V
B
= 0 V, ±1% Error Band 18 µs
Resistor Noise Voltage e
NWB
_50K R
WB
= 25 kΩ, f = 1 kHz, RS = 0 20 nV/√Hz
e
NWB
_100K R
WB
= 50 kΩ, f = 1 kHz, RS = 0 29 nV/√Hz
Crosstalk
11
C
T
V
A
= V
DD
, V
B
= 0 V –65 dB
NOTES
11
Typicals represent average readings at 25°C and V
DD
= 5 V.
12
Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper
1
positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. See TPC 29 test circuit.
1
I
W
= V
DD
/R for V
DD
= 3 V or 5 V for the 50 kΩ and 100 kΩ versions.
13
V
AB
= V
DD
, Wiper (V
W
) = No Connect.
14
INL and DNL are measured at V
W
with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. V
A
= V
DD
and V
B
= 0 V.
1
DNL Specification limits of ±1 LSB maximum are Guaranteed Monotonic operating conditions. See TPC 28 test circuit.
15
Resistor terminals A, B, W have no limitations on polarity with respect to each other.
16
Guaranteed by design and not subject to production test. Resistor-terminal capacitance tests are measured with 2.5 V bias on the measured terminal. The remaining
1
resistor terminals are left open circuit.
17
Measured at the Ax terminals. All Ax terminals are open circuited in shutdown mode.
18
Worst-case supply current consumed when input logic level at 2.4 V, standard characteristic of CMOS logic. See TPC 20 for a plot of I
DD
versus logic voltage.
19
P
DISS
is calculated from (I
DD
× V
DD
). CMOS logic level inputs result in minimum power dissipation.
10
All Dynamic Characteristics use V
DD
= 5 V.
11
Measured at a V
W
pin where an adjacent V
W
pin is making a full-scale voltage change.
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS–50 k and 100 kVERSIONS
REV. C
–4–
AD8400/AD8402/AD8403–SPECIFICATIONS
(V
DD
= 3 V 10% or 5 V 10%, V
A
= V
DD
, V
B
= 0 V,
–40C ≤ T
A
≤ +125C unless otherwise noted.)
Parameter Symbol Conditions Min Typ
1
Max Unit
DC CHARACTERISTICS RHEOSTAT MODE Specifications Apply to All VRs
Resistor Differential NL
2
R-DNL R
WB
, V
A
= No Connect –5–1 +3 LSB
Resistor Nonlinearity
2
R-INL R
WB
, V
A
= No Connect –4±1.5 +4 LSB
Nominal Resistance
3
R
AB
T
A
= 25°C, Model: AD840XYY1 0.8 1.2 1.6 kΩ
Resistance Tempco ∆R
AB
/∆TV
AB
= V
DD
, Wiper = No Connect 700 ppm/°C
Wiper Resistance R
W
I
W
= 1 V/R
AB
53 100 Ω
Nominal Resistance Match ∆R/R
AB
CH 1 to 2, V
AB
= V
DD
, T
A
= 25°C 0.75 2 %
DC CHARACTERISTICS POTENTIOMETER DIVIDER Specifications Apply to All VRs
Resolution N 8 Bits
Integral Nonlinearity
4
INL –6±2 +6 LSB
Differential Nonlinearity
4
DNL V
DD
= 5 V –4–1.5 +2 LSB
DNL V
DD
= 3 V, T
A
= 25°C–5–2 +5 LSB
Voltage Divider Temperature Coefficent ∆V
W
/∆T Code = 80
H
25 ppm/°C
Full-Scale Error V
WFSE
Code = FF
H
–20 –12 0 LSB
Zero-Scale Error V
WZSE
Code = 00
H
0 6 10 LSB
RESISTOR TERMINALS
Voltage Range
5
V
A, B, W
0V
DD
V
Capacitance
6
Ax, Bx C
A, B
f = 1 MHz, Measured to GND, Code = 80
H
75 pF
Capacitance
6
Wx C
W
f = 1 MHz, Measured to GND, Code = 80
H
120 pF
Shutdown Supply Current
7
I
A_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0 0.01 5 µA
Shutdown Wiper Resistance R
W_SD
V
A
= V
DD
, V
B
= 0 V, SHDN = 0, V
DD
= 5 V 50 100 Ω
DIGITAL INPUTS AND OUTPUTS
Input Logic High V
IH
V
DD
= 5 V 2.4 V
Input Logic Low V
IL
V
DD
= 5 V 0.8 V
Input Logic High V
IH
V
DD
= 3 V 2.1 V
Input Logic Low V
IL
V
DD
= 3 V 0.6 V
Output Logic High V
OH
R
L
= 2.2 kΩ to V
DD
V
DD
– 0.1 V
Output Logic Low V
OL
I
OL
= 1.6 mA, V
DD
= 5 V 0.4 V
Input Current I
IL
V
IN
= 0 V or 5 V, V
DD
= 5 V ±1µA
Input Capacitance
6
C
IL
5pF
POWER SUPPLIES
Power Supply Range V
DD
Range 2.7 5.5 V
Supply Current (CMOS) I
DD
V
IH
= V
DD
or V
IL
= 0 V 0.01 5 µA
Supply Current (TTL)
8
I
DD
V
IH
= 2.4 V or 0.8 V, V
DD
= 5.5 V 0.9 4 mA
Power Dissipation (CMOS)
9
P
DISS
V
IH
= V
DD
or V
IL
= 0 V, V
DD
= 5.5 V 27.5 µW
Power Supply Sensitivity PSS ∆V
DD
= 5 V ± 10% 0.0035 0.008 %/%
PSS ∆V
DD
= 3 V ± 10% 0.05 0.13 %/%
DYNAMIC CHARACTERISTICS
6, 10
Bandwidth –3 dB BW_1K R = 1 kΩ5,000 kHz
Total Harmonic Distortion THD
W
V
A
= 1 V rms + 2 V dc, V
B
= 2 V dc, f = 1 kHz 0.015 %
V
W
Settling Time t
S
V
A
= V
DD
, V
B
= 0 V, ±1% Error Band 0.5 µs
Resistor Noise Voltage e
NWB
R
WB
= 500 Ω, f = 1 kHz, RS = 0 3 nV/√Hz
Crosstalk
11
C
T
V
A
= V
DD
, V
B
= 0 V –65 dB
NOTES
11
Typicals represent average readings at 25°C and V
DD
= 5 V.
12
Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper
1
positions. R-DNL measures the relative step change from ideal between successive tap positions. See TPC 29 test circuit.
1
I
W
= 500 µA for V
DD
= 3 V and I
W
= 2.5 mA for V
DD
= 5 V for 1 kΩ version.
13
V
AB
= V
DD
, Wiper (V
W
) = No Connect.
14
INL and DNL are measured at V
W
with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. V
A
= V
DD
and V
B
= 0 V.
DNL Specification limits of ±1 LSB maximum are Guaranteed Monotonic operating conditions. See TPC 28 test circuit.
15
Resistor terminals A, B, W have no limitations on polarity with respect to each other.
16
Guaranteed by design and not subject to production test. Resistor-terminal capacitance tests are measured with 2.5 V bias on the measured terminal. The remaining
resistor terminals are left open circuit.
17
Measured at the Ax terminals. All Ax terminals are open circuited in shutdown mode.
18
Worst-case supply current consumed when input logic level at 2.4 V, standard characteristic of CMOS logic. See TPC 20 for a plot of I
DD
versus logic voltage.
19
P
DISS
is calculated from (I
DD
× V
DD
). CMOS logic level inputs result in minimum power dissipation.
10
All Dynamic Characteristics use V
DD
= 5 V.
11
Measured at a V
W
pin where an adjacent V
W
pin is making a full-scale voltage change.
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS–1 k VERSION
REV. C –5–
AD8400/AD8402/AD8403
SPECIFICATIONS
(V
DD
= 3 V 10% or 5 V 10%, V
A
= V
DD
, V
B
= 0 V, –40C ≤ T
A
≤ +125C unless otherwise noted.)
DAC REGISTER LOAD
A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
1
0
1
0
1
0
VDD
0V
SDI
CLK
CS
VOUT
Figure 2a. Timing Diagram
1% ERROR BAND
1 %
t
CSH
t
CSS
t
DH
Ax OR DxAx OR Dx
t
PD_MIN
t
PD_MAX
A'x OR D'x A'x OR D'x
1
0
1
0
1
0
VDD
0V
SDI
(DATA IN)
CLK
CS
VOUT
1
0
SDO
(DATA OUT)
t
DS
t
CH
t
CS1
t
CL
t
S
t
CSW
Figure 2b. Detail Timing Diagram
1%
1% ERROR BAND
RS
1
0
V
DD
V
DD
/2
V
OUT
tRS
tS
Figure 2c. Reset Timing Diagram
ELECTRICAL CHARACTERISTICS–ALL VERSIONS
Parameter Symbol Conditions Min Typ
1
Max Unit
SWITCHING CHARACTERISTICS
2, 3
Input Clock Pulsewidth t
CH
, t
CL
Clock Level High or Low 10 ns
Data Setup Time t
DS
5ns
Data Hold Time t
DH
5ns
CLK to SDO Propagation Delay
4
t
PD
R
L
= 1 kΩ to 5 V, C
L
≤ 20 pF 1 25 ns
CS Setup Time t
CSS
10 ns
CS High Pulsewidth t
CSW
10 ns
Reset Pulsewidth t
RS
50 ns
CLK Fall to CS Rise Hold Time t
CSH
0ns
CS Rise to Clock Rise Setup t
CS1
10 ns
NOTES
1
Typicals represent average readings at 25°C and V
DD
= 5 V.
2
Guaranteed by design and not subject to production test. Resistor-terminal capacitance tests are measured with 2.5 V bias on the measured terminal. The remaining
resistor terminals are left open circuit.
3
See timing diagram for location of measured values. All input control voltages are specified with t
R
= t
F
= 1 ns (10% to 90% of V
DD
) and timed from a voltage level
of 1.6 V. Switching characteristics are measured using V
DD
= 3 V or 5 V. To avoid false clocking, a minimum input logic slew rate of 1 V/ µs should be maintained.
4
Propagation Delay depends on value of V
DD
, R
L
, and C
L
—see Applications section.
Specifications subject to change without notice.
REV. C
AD8400/AD8402/AD8403
–6–
ABSOLUTE MAXIMUM RATINGS*
(T
A
= 25°C, unless otherwise noted.)
V
DD
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +8 V
V
A
, V
B
, V
W
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, V
DD
A
X
– B
X
, A
X
– W
X
, B
X
– W
X
. . . . . . . . . . . . . . . . . . . . . ±20 mA
Digital Input and Output Voltage to GND . . . . . . . . 0 V, 7 V
Operating Temperature Range . . . . . . . . . . . –40°C to +85°C
Maximum Junction Temperature (T
J
max) . . . . . . . . . . 150°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . 300°C
Package Power Dissipation . . . . . . . . . . . . . (T
J
max – T
A
)/θ
JA
Thermal Resistance (θ
JA
)
P-DIP (N-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103°C/W
SOIC (SO-8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158°C/W
P-DIP (N-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83°C/W
P-DIP (N-24) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63°C/W
SOIC (SO-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . 120°C/W
SOIC (SOL-24) . . . . . . . . . . . . . . . . . . . . . . . . . . . 70°C/W
TSSOP-14 (RU-14) . . . . . . . . . . . . . . . . . . . . . . . 180°C/W
TSSOP-24 (RU-24) . . . . . . . . . . . . . . . . . . . . . . . 143°C/W
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
Table I. Serial Data Word Format
ADDR DATA
B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
MSB LSB MSB LSB
2
9
2
8
2
7
2
0
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although
the AD8400/AD8402/AD8403 features proprietary ESD protection circuitry, permanent damage
may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
REV. C
AD8400/AD8402/AD8403
–7–
Number of
Number of End-to-End Temperature Package Package Devices per Branding
Model Channels R
AB
(k) Range (C) Description Option*Container Information
AD8400AN10 1 10 –40 to +125 PDIP-8 N-8 50 8400A10
AD8400AR10 1 10 –40 to +125 SO-8 SO-8 98 8400A10
AD8402AN10 2 10 –40 to +125 PDIP-14 N-14 25 8400A10
AD8402AR10 2 10 –40 to +125 SO-14 SO-14 56 8400A10
AD8402ARU10 2 10 –40 to +125 TSSOP-14 RU-14 96 8400A10
AD8402ARU10-REEL 2 10 –40 to +125 TSSOP-14 RU-14 2,500 8400A10
AD8403AN10 4 10 –40 to +125 PDIP-24 N-24 15 8400A10
AD8403AR10 4 10 –40 to +125 SOIC-24 SOL-24 31 8400A10
AD8403ARU10 4 10 –40 to +125 TSSOP-24 RU-24 63 8400A10
AD8403ARU10-REEL 4 10 –40 to +125 TSSOP-24 RU-24 2,500 8400A10
AD8400AN50 1 50 –40 to +125 PDIP-8 N-8 50 8400A50
AD8400AR50 1 50 –40 to +125 SO-8 SO-8 98 8400A50
AD8402AN50 2 50 –40 to +125 PDIP-14 N-14 25 8400A50
AD8402AR50 2 50 –40 to +125 SO-14 SO-14 56 8400A50
AD8402ARU50 2 50 –40 to +125 TSSOP-14 RU-14 96 8400A50
AD8402ARU50-REEL 2 50 –40 to +125 TSSOP-14 RU-14 2,500 8400A50
AD8403AN50 4 50 –40 to +125 PDIP-24 N-24 15 8400A50
AD8403AR50 4 50 –40 to +125 SOIC-24 SOL-24 31 8400A50
AD8403ARU50 4 50 –40 to +125 TSSOP-24 RU-24 63 8400A50
AD8403ARU50-REEL 4 50 –40 to +125 TSSOP-24 RU-24 2,500 8400A50
AD8400AN100 1 100 –40 to +125 PDIP-8 N-8 50 8400A100
AD8400AR100 1 100 –40 to +125 SO-8 SO-8 98 8400A100
AD8402AN100 2 100 –40 to +125 PDIP-14 N-14 25 8400A100
AD8402AR100 2 100 –40 to +125 SO-14 SO-14 56 8400A100
AD8402ARU100 2 100 –40 to +125 TSSOP-14 RU-14 96 8400A100
AD8402ARU100-REEL 2 100 –40 to +125 TSSOP-14 RU-14 2,500 8400A100
AD8403AN100 4 100 –40 to +125 PDIP-24 N-24 15 8400A100
AD8403AR100 4 100 –40 to +125 SOIC-24 SOL-24 31 8400A100
AD8403ARU100 4 100 –40 to +125 TSSOP-24 RU-24 63 8400A100
AD8403ARU100-REEL 4 100 –40 to +125 TSSOP-24 RU-24 2,500 8400A100
AD8400AN1 1 1 –40 to +125 PDIP-8 N-8 50 8400A1
AD8400AR1 1 1 –40 to +125 SO-8 SO-8 98 8400A1
AD8402AN1 2 1 –40 to +125 PDIP-14 N-14 25 8400A1
AD8402AR1 2 1 –40 to +125 SO-14 SO-14 56 8400A1
AD8402ARU1 2 1 –40 to +125 TSSOP-14 RU-14 96 8400A1
AD8402ARU1-REEL 2 1 –40 to +125 TSSOP-14 RU-14 2,500 8400A1
AD8403AN1 4 1 –40 to +125 PDIP-24 N-24 15 8400A1
AD8403AR1 4 1 –40 to +125 SOIC-24 SOL-24 31 8400A1
AD8403ARU1 4 1 –40 to +125 TSSOP-24 RU-24 63 8400A1
AD8403ARU1-REEL 4 1 –40 to +125 TSSOP-24 RU-24 2,500 8400A1
*N = Plastic DIP; SO = Small Outline; RU = Thin Shrink SO.
The AD8400, AD8402, and AD8403 contain 720 transistors.
ORDERING GUIDE
REV. C
AD8400/AD8402/AD8403
–8–
AD8400 PIN FUNCTION DESCRIPTIONS
Pin Name Description
1 B1 Terminal B RDAC
2 GND Ground
3 CS Chip Select Input, Active Low. When CS
returns high, data in the serial input register
is loaded into the DAC register.
4 SDI Serial Data Input
5 CLK Serial Clock Input, Positive Edge Triggered.
6V
DD
Positive power supply, specified for operation
at both 3 V and 5 V.
7 W1 Wiper RDAC, Addr = 00
2
8 A1 Terminal A RDAC
AD8402 PIN FUNCTION DESCRIPTIONS
Pin Name Description
1 AGND Analog Ground*
2 B2 Terminal B RDAC #2
3 A2 Terminal A RDAC #2
4 W2 Wiper RDAC #2, Addr = 01
2
.
5 DGND Digital Ground*
6 SHDN Terminal A Open Circuit. Shutdown controls
Variable Resistors #1 and #2.
7 CS Chip Select Input, Active Low. When CS
returns high, data in the serial input register is
decoded based on the address bits and loaded
into the target DAC register.
8 SDI Serial Data Input
9 CLK Serial Clock Input, Positive Edge Triggered.
10 RS Active low reset to midscale; sets RDAC
registers to 80
H
.
11 V
DD
Positive power supply, specified for operation
at both 3 V and 5 V.
12 W1 Wiper RDAC #1, Addr = 00
2
.
13 A1 Terminal A RDAC #1
14 B1 Terminal B RDAC #1
*All AGNDs must be connected to DGND.
AD8403 PIN FUNCTION DESCRIPTIONS
Pin Name Description
1 AGND2 Analog Ground #2*
2 B2 Terminal B RDAC #2
3 A2 Terminal A RDAC #2
4 W2 Wiper RDAC #2, Addr = 01
2
.
5 AGND4 Analog Ground #4*
6 B4 Terminal B RDAC #4
7 A4 Terminal A RDAC #4
8 W4 Wiper RDAC #4, Addr = 11
2
.
9 DGND Digital Ground*
10 SHDN Active Low Input. Terminal A open circuit.
Shutdown controls Variable Resistors #1
through #4.
11 CS Chip Select Input, Active Low. When CS
returns high, data in the serial input register
is decoded based on the address bits and
loaded into the target DAC register.
12 SDI Serial Data Input
13 SDO Serial Data Output, Open Drain transistor
requires pull-up resistor.
14 CLK Serial Clock Input, Positive Edge Triggered
15 RS Active Low reset to midscale; sets RDAC
registers to 80
H
.
16 V
DD
Positive power supply, specified for
operation at both 3 V and 5 V.
17 AGND3 Analog Ground #3*
18 W3 Wiper RDAC #3, Addr = 10
2
19 A3 Terminal A RDAC #3
20 B3 Terminal B RDAC #3
21 AGND1 Analog Ground #1*
22 W1 Wiper RDAC #1, Addr = 00
2
23 A1 Terminal A RDAC #1
24 B1 Terminal B RDAC #1
*All AGNDs must be connected to DGND.
PIN CONFIGURATIONS
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
AD8400
B1
CLK
VDD
W1
A1
GND
CS
SDI
14
13
12
11
10
9
8
1
2
3
4
7
6
5
TOP VIEW
(Not to Scale)
AGND
VDD
W1
A1
B1
B2
A2
W2
AD8402
SDI
CLK
RS
DGND
SHDN
CS
13
16
15
14
24
23
22
21
20
19
18
17
TOP VIEW
(Not to Scale)
12
11
10
9
8
1
2
3
4
7
6
5
AD8403
AGND2
AGND1
W1
A1
B1
B2
A2
W2
W3
A3
B3
AGND4
B4
A4
W4
DGND
SHDN RS
VDD
AGND3
CS
SDI
CLK
SDO
W4
REV. C –9–
Typical Performance Characteristics–AD8400/AD8402/AD8403
CODE – Decimal
10
8
00 32 256
64 96 128 160 192 224
6
4
2
RESISTANCE – k
V
DD
= 3V OR 5V
R
AB
= 10k
R
WB
R
WA
TPC 1. Wiper to End Terminal
Resistance vs. Code
WIPER RESISTANCE –
FREQUENCY
60
48
0
40.0 42.5 65.045.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5
36
24
12
SS = 1205 UNITS
V
DD
= 4.5V
T
A
= 25C
TPC 4. 10 k
Ω
Wiper-Contact-
Resistance Histogram
WIPER RESISTANCE –
FREQUENCY
60
48
0
40.0 42.5 65.045.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5
36
24
12
SS = 184 UNITS
V
DD
= 4.5V
T
A
= 25C
TPC 7. 100 k
Ω
Wiper-Contact-
Resistance Histogram
IWB CURRENT – mA
5
4
007
145
3
2
1
23 6
80H
40H
20H
FFH
CODE = 10H
TA = 25C
VDD = 5V
VWB VOLTAGE – V
05H
TPC 2. Resistance Linearity vs.
Conduction Current
DIGITAL INPUT CODE – Decimal
1
0.5
–10 32 25664 96 128 160 192 224
0
–0.5
INL NONLINEARITY ERROR – LSB
T
A
= –40C
T
A
= +25C
T
A
= +85C
V
DD
= 5V
TPC 5. Potentiometer Divider
Nonlinearity Error vs. Code
TEMPERATURE – C
NOMINAL RESISTANCE – k
10
8
0
–75 –50 125
–25 0 25 50 75 100
6
4
2
RAB (END-TO-END)
RWB (WIPER-TO-END)
CODE = 80H
RAB = 10k
TPC 8. Nominal Resistance vs.
Temperature
DIGITAL INPUT CODE – Decimal
1
0.5
–10 32 25664 96 128 160 192 224
0
–0.5
V
DD
= 5V
T
A
= –40C
T
A
= +25C
T
A
= +85C
R-INL ERROR – LSB
TPC 3. Resistance Step Position
Nonlinearity Error vs. Code
WIPER RESISTANCE –
FREQUENCY
60
48
035 37 5539 41 43 45 47 49 51 53
36
24
12
SS = 184 UNITS
V
DD
= 4.5V
T
A
= 25C
TPC 6. 50 k
⍀
Wiper-Contact-
Resistance Histogram
CODE – Decimal
POTENTIOMETER MODE TEMPCO – ppm/C
70
60
–10 0 32 160
64 96 128
30
20
10
0
50
40
192 224 256
V
DD
= 5V
T
A
= –40C/+85C
V
A
= 2.00V
V
B
= 0V
TPC 9. DV
WB
/DT Potentiometer
Mode Tempco
REV. C
AD8400/AD8402/AD8403
–10–
FREQUENCY – Hz
6
0
–54
GAIN – dB
10 1M100 1k 10k 100k
–6
–12
–48
–18
–24
–30
–36
–42
CODE = FF
80
40
20
10
08
04
02
01
TA = +25C
SEE TEST CIRCUIT 7
TPC 12. 10 k
Ω
Gain vs. Frequency
FREQUENCY – Hz
GAIN – dB
0
–6
–48
1k 10k 1M
–30
–36
–42
–12
–24
–18
–54 100k
6CODE = FFH
80H
40H
20H
10H
08H
04H
02H
01H
TPC 15. 50 k
Ω
Gain vs. Frequency
vs. Code
FREQUENCY – Hz
GAIN – dB
0
–6
–48
1k 10k 1M
–30
–36
–42
–12
–24
–18
–54 100k
CODE = FF
H
6
80
H
40
H
20
H
10
H
08
H
04
H
02
H
01
H
TPC 18. 100 k
Ω
Gain vs. Frequency
vs. Code
CODE – Decimal
700
600
–1000 32 160
64 96 128
300
200
100
0
500
400
192 224 256
RHEOSTAT MODE TEMPCO – ppm/C
VDD = 5V
TA = –40C/+85C
VA = NO CONNECT
RWB MEASURED
TPC 10.
∆
R
WB
/
∆
T Rheostat Mode
Tempco
HOURS OF OPERATION AT 150C
0.75
0.50
–0.75
0 600
100 300 400
0.25
–0.25
–0.50
200 500
CODE = 80
H
V
DD
= 5V
SS = 158 UNITS
0
R
WB
RESISTANCE – %
AVG + 2 SIGMA
AVG
AVG – 2 SIGMA
TPC 13. Long-Term Drift
Accelerated by Burn-In
FREQUENCY – Hz
THD + NOISE – %
10
0.001
10 100k100 1k 10k
1
0.1
FILTER = 22kHz
V
DD
= 5V
T
A
= 25C
0.01
SEE TEST CIRCUIT 5
SEE TEST CIRCUIT 6
TPC 16. Total Harmonic Distortion
Plus Noise vs. Frequency
R
W
(20mV/DIV)
CS
(5V/DIV)
TIME 500ns/DIV
TPC 11. One Position Step Change at
Half-Scale (Code 7F
H
to 80
H
)
OUTPUT
INPUT
TIME 500
s/DIV
TPC 14. Large Signal Settling Time
V
OUT
(50mV/DIV)
TIME 200ns/DIV
TPC 17. Digital Feedthrough vs. Time
REV. C
AD8400/AD8402/AD8403
–11–
FREQUENCY – Hz
10 10k 1M
NORMALIZED GAIN FLATNESS – 0.1dB/DIV
100k100 1k
R = 10k
SEE TEST CIRCUIT 7
CODE = 80H
VDD = 5V
TA = 25C
R = 100k
R = 50k
TPC 19. Normalized Gain Flatness vs.
Frequency
FREQUENCY – Hz
GAIN – dB
0
–6
1k 10k 1M
–30
–36
–42
–12
–24
–18
100k
6
12
f
–3dB
= 125kHz, R = 50k
f
–3dB
= 700kHz, R = 10k
f
–3dB
= 71kHz, R = 100k
V
IN
= 100mV rms
V
DD
= 5V
R
L
= 1M
TPC 22. –3 dB Bandwidths
FREQUENCY – Hz
100k 2M
200k 1M
0
–10
–20
0
–45
–90
400k 4M 6M
PHASE – Degrees
10M
GAIN – dB
VDD = 5V
TA = 25C
WIPER SET AT
HALF-SCALE 80H
TPC 25. 1 k
Ω
Gain and Phase
vs. Frequency
DIGITAL INPUT VOLTAGE – V
IDD – SUPPLY CURRENT – mA
10
1
0.0105
1234
0.1
TA = 25C
VDD = 5V
VDD = 3V
TPC 20. Supply Current vs.
Digital Input Voltage
FREQUENCY – Hz
1k 1M 10M10k 100k
IDD – SUPPLY CURRENT – µA
1200
1000
800
600
400
200
0
TA = 25C
AB
C
D
A –
B –
C –
D –
VDD = 5.5V
CODE = 55H
VDD = 3.3V
CODE = 55H
VDD = 5.5V
CODE = FFH
VDD = 3.3V
CODE = FFH
TPC 23. Supply Current vs.
Clock Frequency
I
A
SHUTDOWN CURRENT – nA
100
1
–55 –35
10
V
DD
= 5V
–15 5 25 45 65 85 105 125
TEMPERATURE – C
TPC 26. Shutdown Current vs.
Temperature
FREQUENCY – Hz
PSRR – dB
80
0
100 1M1k 10k 100k
60
40
VDD = +5V DC 1V p-p AC
TA = 25C
CODE = 80H
CL = 10pF
VA = 4V, VB = 0V
20
SEE TEST CIRCUIT 4
TPC 21. Power Supply Rejection
vs. Frequency
V
BIAS
– V
R
ON
–
160
0
140
80
60
40
20
120
100
01 6
2345
T
A
= 25C
V
DD
= 2.7V
V
DD
= 5.5V
SEE TEST CIRCUIT 3
TPC 24. AD8403 Incremental Wiper
ON Resistance vs. V
DD
TEMPERATURE – C
I
DD
– SUPPLY CURRENT – A
1
0.1
0.001
–55 –35 125
–155 25456585105
0.01
LOGIC INPUT
VOLTAGE = 0, V
DD
V
DD
= 5.5V
V
DD
= 3.3V
TPC 27. Supply Current vs.
Temperature
REV. C
AD8400/AD8402/AD8403
–12–
V+
DUT
V
MS
A
B
W
V+ = V
DD
1LSB = V+/256
Test Circuit 1. Potentiometer Divider Nonlinearity
Error (INL, DNL)
DUT
V
MS
A
B
W
NO CONNECT
I
W
Test Circuit 2. Resistor Position Nonlinearity
Error (Rheostat Operation; R-INL, R-DNL)
IMS
VW2 – [VW1 + IW (RAW II RBW)]
IW
V+ VDD
WHERE VW1 = VMS WHEN IW = 0
AND VW2 = VMS WHEN IW = 1/R
V+
DUT
VMS
A
B
WVW
IW = 1V/RNOMINAL
RW = ––––––––––––––––––––––––––
Test Circuit 3. Wiper Resistance
PSRR (dB) = 20LOG
(
–––––
)
PSS (%/%) = –––––––
∆V
MS
∆V
DD
∆V
MS
%
∆V
DD
%
V+ = V
DD
10%
V+
V
MS
A
B
W
V
DD
V
A
~
Test Circuit 4. Power Supply Sensitivity (PSS, PSRR)
TEST CIRCUITS
AB
V
IN
2.5V DC
OP279
5V
V
OUT
~
DUT
W
OFFSET
GND
Test Circuit 5. Inverting Programmable Gain
~
AB
V
IN
2.5V
OP279
5V
V
OUT
DUT
W
OFFSET
GND
Test Circuit 6. Noninverting Programmable Gain
~
B
A
VIN
2.5V
+15V
VOUT
DUT W
–15V
OFFSET
GND
OP42
Test Circuit 7. Gain vs. Frequency
DUT
I
SW
B
W
V
BIAS
R
SW
=0.1V
I
SW
CODE = ØØ
H
0.1V
A = NC
+
–
Test Circuit 8. Incremental ON Resistance
REV. C
AD8400/AD8402/AD8403
–13–
OPERATION
The AD8400/AD8402/AD8403 provide a single, dual, and quad
channel, 256-position digitally controlled variable resistor (VR)
device. Changing the programmed VR settings is accomplished by
clocking in a 10-bit serial data word into the SDI (Serial Data Input)
pin. The format of this data word is two address bits, MSB first,
followed by eight data bits, MSB first. Table I provides the serial
register data word format. The AD8400/AD8402/AD8403 has the
following address assignments for the ADDR decode, which
determines the location of VR latch receiving the serial register
data in Bits B7 through B0:
VR A A#=×+ +12 01
(1)
The single-channel AD8400 requires A1 = A0 = 0. The dual-
channel AD8402 requires A1 = 0. VR settings can be changed
one at a time in random sequence. The serial clock running at
10 MHz makes it possible to load all four VRs in under 4 µs
(10 × 4 × 100 ns) for the AD8403. The exact timing requirements
are shown in Figures 2a, 2b, and 2c.
The AD8402/AD8403 resets to midscale by asserting the RS
pin, simplifying initial conditions at power up. Both parts have a
power shutdown SHDN pin that places the VR in a zero power
consumption state where terminals Ax are open circuited and the
wiper Wx is connected to Bx resulting in only leakage currents
being consumed in the VR structure. In shutdown mode the VR
latch settings are maintained so that returning to operational mode
from power shutdown, the VR settings return to their previous
resistance values. The digital interface is still active in shutdown,
except that SDO is deactivated. Code changes in the registers can
be made that will produce new wiper positions when the device is
taken out of shutdown.
D7
D6
D5
D4
D3
D2
D1
D0
RDAC
LATCH
AND
DECODER
Ax
Wx
Bx
R
S
= R
NOMINAL
/256
R
S
R
S
R
S
R
S
SHDN
Figure 3. AD8402/AD8403 Equivalent VR (RDAC) Circuit
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the VR (RDAC) between terminals A and
B is available with values of 1 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ. The
final digits of the part number determine the nominal resistance
value, e.g., 10 kΩ = 10; 100 kΩ = 100. The nominal resistance
(R
AB
) of the VR has 256 contact points accessed by the wiper
terminal, plus the B terminal contact. The 8-bit data word in the
RDAC latch is decoded to select one of the 256 possible settings.
The wiper’s first connection starts at the B terminal for data 00
H
.
This B terminal connection has a wiper contact resistance of 50 Ω.
The second connection (10 kΩ part) is the first tap point located
at 89 Ω [= R
AB
(nominal resistance)/256 + R
W
= 39 Ω + 50 Ω] for
data 01
H
. The third connection is the next tap point representing
78 + 50 = 128 Ω for data 02
H
. Each LSB data value increase
moves the wiper up the resistor ladder until the last tap point is
reached at 10,011 Ω. The wiper does not directly connect to the
B terminal. See Figure 3 for a simplified diagram of the equiva-
lent RDAC circuit.
The AD8400 contains one RDAC, the AD8402 contains two
independent RDACs, and the AD8403 contains four independent
RDACs. The general transfer equation that determines the digi-
tally programmed output resistance between Wx and Bx is:
RDx Dx R R
WB AB W
()
=
()
×+/ 256
(2)
where Dx is the data contained in the 8-bit RDAC# latch, and
R
AB
is the nominal end-to-end resistance.
For example, when V
B
= 0 V and when the A terminal is open
circuit, the following output resistance values will be set for the
following RDAC latch codes (applies to 10 kΩ potentiometers):
DR
WB
(Dec) () Output State
255 10,011 Full Scale
128 5,050 Midscale (RS = 0 Condition)
1891 LSB
0 50 Zero-Scale (Wiper Contact Resistance)
Note in the zero-scale condition a finite wiper resistance of 50 Ω
is present. Care should be taken to limit the current flow between
W and B in this state to a maximum value of 5 mA to avoid
degradation or possible destruction of the internal switch contact.
Like the mechanical potentiometer the RDAC replaces, it is totally
symmetrical. The resistance between the wiper W and terminal
A also produces a digitally controlled complementary resistance
R
WA
. When these terminals are used, the B terminal can be tied
to the wiper or left floating. Setting the resistance value for R
WA
starts at a maximum value of resistance and decreases as the data
loaded in the RDAC latch is increased in value. The general transfer
equation for this operation is:
RD D R R
WA XX
AB W
()
=−
()
×+256 256
(3)
REV. C
AD8400/AD8402/AD8403
–14–
where Dx is the data contained in the 8-bit RDAC# latch, and
R
AB
is the nominal end-to-end resistance. For example, when
V
A
= 0 V and B terminal is open circuit, the following output
resistance values will be set for the following RDAC latch codes
(applies to 10 kΩ potentiometers):
DR
WA
(Dec) () Output State
255 89 Full Scale
128 5,050 Midscale (RS = 0 Condition)
1 10,011 1 LSB
0 10,050 Zero Scale
The typical distribution of R
AB
from channel to channel matches
within ±1%. However, device-to-device matching is process lot-
dependent, having a ±20% variation. The change in R
AB
with
temperature has a positive 500 ppm/°C temperature coefficient.
The wiper-to-end-terminal resistance temperature coefficient has
the best performance over the 10% to 100% of adjustment range
where the internal wiper contact switches do not contribute any
significant temperature related errors. The graph in TPC 10 shows
the performance of R
WB
tempco versus code: using the trimmer with
codes below 32 results in the larger temperature coefficients plotted.
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates an output voltage
proportional to the input voltage applied to a given terminal.
For example, connecting A terminal to 5 V and B terminal to
ground produces an output voltage at the wiper starting at zero
volts up to 1 LSB less than 5 V. Each LSB of voltage is equal to
the voltage applied across terminal AB divided by the 256
position resolution of the potentiometer divider. The general
equation defining the output voltage with respect to ground for
any given input voltage applied to terminals AB is:
VD D V V
WXX AB B
()
=×+256
(4)
Operation of the digital potentiometer in the divider mode results
in more accurate operation over temperature. Here the output
voltage is dependent on the ratio of the internal resistors, not
the absolute value; therefore, the temperature drift improves to
15 ppm/°C.
At the lower wiper position settings, the potentiometer divider
temperature coefficient increases due to the contributions of the
CMOS switch wiper resistance becoming an appreciable portion of
the total resistance from Terminal B to the wiper. See TPC 9 for
a plot of potentiometer tempco performance versus code setting.
DIGITAL INTERFACING
The AD8400/AD8402/AD8403 contain a standard SPI compat-
ible three-wire serial input control interface. The three inputs
are clock (CLK), CS and serial data input (SDI). The positive-
edge sensitive CLK input requires clean transitions to avoid
clocking incorrect data into the serial input register. For best
results use logic transitions faster than 1 V/µs. Standard logic
families work well. If mechanical switches are used for product
evaluation, they should be debounced by a flip-flop or other
suitable means. The Figure 4 block diagrams show more detail
of the internal digital circuitry. When CS is taken active low, the
clock loads data into the 10-bit serial register on each positive
clock edge (see Table II).
RDAC
LATCH
#1
GND
A1
W1
B1
VDD
AD8400
CS
CLK
8
D7
D0
EN
ADDR
DEC
A1
A0
SDI DI
SER
REG
D0
D7
10-BIT
a.
RDAC
LATCH
#1
R
AGND
RS
A1
W1
B1
VDD
AD8402
CS
CLK D7
D0
RDAC
LATCH
#2
R
A4
W4
B4
D7
D0
EN
ADDR
DEC
A1
A0
SDI DI
10-BIT
SER
REG
D0
SHDN
DGND
D7
8
b.
RDAC
LATCH
#1
R
AGND
RS
A1
W1
B1
VDD
AD8403
CS
CLK
SDO
D7
D0
RDAC
LATCH
#4
R
A4
W4
B4
D7
D0
EN
ADDR
DEC
A1
A0
D7
SDI
DO
DI
SER
REG
D0
SHDN
DGND
8
c.
Figure 4. Block Diagrams
REV. C
AD8400/AD8402/AD8403
–15–
Table II. Input Logic Control Truth Table
CLK CS RS SHDN Register Activity
L L H H No SR effect, enables SDO pin.
P L H H Shift one bit in from the SDI pin.
The tenth previously entered bit is
shifted out of the SDO pin.
X P H H Load SR data into RDAC latch
based on A1, A0 decode (Table III).
X H H H No Operation
X X L H Sets all RDAC latches to midscale,
wiper centered, and SDO latch
cleared.
X H P H Latches all RDAC latches to 80
H
.
X H H L Open circuits all resistor
A-terminals, connects W to B,
turns off SDO output transistor.
NOTE: P = positive edge, X = don’t care, SR = shift register.
The serial data-output (SDO) pin contains an open drain n-channel
FET. This output requires a pull-up resistor in order to transfer data
to the next package’s SDI pin. The pull-up resistor termination
voltage may be larger than the V
DD
supply (but less than max
V
DD
of 8 V) of the AD8403 SDO output device, e.g., the AD8403
could operate at V
DD
= 3.3 V and the pull-up for interface to the
next device could be set at 5 V. This allows for daisy-chaining
several RDACs from a single processor serial data line. The
clock period needs to be increased when using a pull-up resistor
to the SDI pin of the following device in the series. Capacitive
loading at the daisy-chain node SDO–SDI between devices must
be accounted for to successfully transfer data. When daisy chaining
is used, the CS should be kept low until all the bits of every package
are clocked into their respective serial registers ensuring that the
address bits and data bits are in the proper decoding location.
This would require 20 bits of address and data complying to the
word format provided in Table I if two AD8403 four-channel
RDACs are daisy-chained. Note, only the AD8403 has a SDO
pin. During shutdown SHDN the SDO output pin is forced to
the off (logic high) state to disable power dissipation in the pull-up
resistor. See Figure 6 for equivalent SDO output circuit schematic.
The data setup and data hold times in the specification table
determine the data valid time requirements. The last 10 bits of
the data word entered into the serial register are held when CS
returns high. At the same time CS goes high it gates the address
decoder, which enables one of the two (AD8402) or four (AD8403)
positive edge triggered RDAC latches. See Figure 5 detail and
Table III Address Decode Table.
Table III. Address Decode Table
A1 A0 Latch Decoded
0 0 RDAC#1
0 1 RDAC#2
1 0 RDAC#3 AD8403 Only
1 1 RDAC#4 AD8403 Only
ADDR
DECODE
RDAC 1
RDAC 2
RDAC 4
SERIAL
REGISTER
AD8403
SDI
CLK
CS
Figure 5. Equivalent Input Control Logic
The target RDAC latch is loaded with the last eight bits of the
serial data word completing one DAC update. In the case of the
AD8403 four separate 10-bit data words must be clocked in to
change all four VR settings.
SERIAL
REGISTER
SDI
CK RS
DQ
SHDN
CS
CLK
RS
SDO
Figure 6. Detail SDO Output Schematic of the AD8403
All digital pins are protected with a series input resistor and
parallel Zener ESD structure shown in Figure 7a. This structure
applies to digital pins CS, SDI, SDO, RS, SHDN, CLK. The
digital input ESD protection allows for mixed power supply
applications where 5 V CMOS logic can be used to drive an
AD8400/AD8402 or AD8403 operating from a 3 V power supply.
The analog pins A, B, and W are protected with a 20 Ω series
resistor and parallel Zener. (see Figure 7b).
1k
DIGITAL
PINS LOGIC
Figure 7a. Equivalent ESD Protection Circuits
20
A, B, W
Figure 7b. Equivalent ESD Protection Circuit
(Analog Pins)
C
W
120pF
AB
C
A
C
B
W
CA = 90.4pF ( ) + 30pF
DW
256
RDAC
10k
C
B
= 90.4pF (1 – ) + 30pF
DW
256
Figure 8. RDAC Circuit Simulation Model for
RDAC =10 k
Ω
REV. C
AD8400/AD8402/AD8403
–16–
The ac characteristics of the RDACs are dominated by the internal
parasitic capacitances and the external capacitive loads. The –3dB
bandwidth of the AD8403AN10 (10 kΩ resistor) measures 600 kHz
at half scale as a potentiometer divider. TPC 22 provides the large
signal BODE plot characteristics of the three available resistor
versions 10 kΩ, 50 kΩ, and 100 kΩ. The gain flatness versus
frequency graph, TPC 25, predicts filter applications performance.
A parasitic simulation model has been developed, and is shown
in Figure 8. Listing I provides a macro model net list for the
10 kΩ RDAC:
Listing I. Macro Model Net List for RDAC
.PARAM DW=255, RDAC=10E3
*
.SUBCKT DPOT (A,W,)
*
CA A 0 {DW/256*90.4E-12+30E-12}
RAW A W {(1-DW/256)*RDAC+50}
CW W 0 120E-12
RBW W B {DW/256*RDAC+50}
CB B 0 {(1-DW/256)*90.4E-12+30E-12}
*
.ENDS DPOT
The total harmonic distortion plus noise (THD+N) is measured
at 0.003% in an inverting op amp circuit using an offset ground
and a rail-to-rail OP279 amplifier, Test Circuit 5. Thermal noise is
primarily Johnson noise, typically 9 nV/√Hz for the 10 kΩ version
at f = 1 kHz. For the 100 kΩ device, thermal noise becomes
29 nV/√Hz. Channel-to-channel crosstalk measures less than
–65 dB at f = 100 kHz. To achieve this isolation, the extra ground
pins provided on the package to segregate the individual RDACs
must be connected to circuit ground. AGND and DGND pins
should be at the same voltage potential. Any unused potentio-
meters in a package should be connected to ground. Power
supply rejection is typically –35 dB at 10 kHz (care is needed to
minimize power supply ripple in high accuracy applications).
APPLICATIONS
The digital potentiometer (RDAC) allows many of the applications
of trimming potentiometers to be replaced by a solid-state solu-
tion offering compact size and freedom from vibration, shock and
open contact problems encountered in hostile environments.
A
major advantage of the digital potentiometer is its programma-
bility. Any settings can be saved for later recall in system memory.
The two major configurations of the RDAC include the
potentiometer divider (basic 3-terminal application) and the
rheostat (2-terminal configuration) connections shown in Test
Circuits 1 and 2 (see page 11).
Certain boundary conditions must be satisfied for proper AD8400/
AD8402/AD8403 operation. First, all analog signals must remain
within the 0 to V
DD
range used to operate the single-supply
AD8400/AD8402/AD8403 products. For standard potentiometer
divider applications, the wiper output can be used directly. For
low resistance loads, buffer the wiper with a suitable rail-to-rail
op amp such as the OP291 or the OP279. Second, for ac signals
and bipolar dc adjustment applications, a virtual ground will
generally be needed. Whatever method is used to create the
virtual ground, the result must provide the necessary sink and
source current for all connected loads, including adequate bypass
capacitance. Test Circuit 5 (see page 11) shows one channel of
the AD8402 connected in an inverting programmable gain
amplifier circuit. The virtual ground is set at 2.5 V, which allows
the circuit output to span a ±2.5 volt range with respect to virtual
ground. The rail-to-rail amplifier capability is necessary for the
widest output swing. As the wiper is adjusted from its midscale
reset position (80
H
) toward the A terminal (code FF
H
), the voltage
gain of the circuit is increased in successfully larger increments.
Alternatively, as the wiper is adjusted toward the B terminal
(code 00
H
), the signal becomes attenuated. The plot in Figure 9
shows the wiper settings for a 100:1 range of voltage gain (V/V).
Note the ±10 dB of pseudo-logarithmic gain around 0 dB (1 V/V).
This circuit is mainly useful for gain adjustments in the range of
0.14 V/V to 4 V/V; beyond this range the step sizes become very
large and the resistance of the driving circuit can become a
significant term in the gain equation.
INVERTING GAIN – V/V
256
128
0
0.1 1.0 10
96
64
32
160
192
224
DIGITAL CODE – Decimal
Figure 9. Inverting Programmable Gain Plot
REV. C
AD8400/AD8402/AD8403
–17–
ACTIVE FILTER
One of the standard circuits used to generate a low-pass, high-
pass, or band-pass filter is the state variable active filter. The
digital potentiometer allows full programmability of the frequency,
gain and Q of the filter outputs. Figure 10 shows the filter circuit
using a 2.5 V virtual ground, which allows a ±2.5 V
P
input and
output swing. RDAC2 and 3 set the LP, HP, and BP cutoff and
center frequencies, respectively. These variable resistors should
be programmed with the same data (as with ganged potentiom-
eters) to maintain the best circuit Q. Figure 11 shows the measured
filter response at the band-pass output as a function of the RDAC2
and RDAC3 settings which produce a range of center frequencies
from 2 kHz to 20 kHz. The filter gain response at the band-pass
output is shown in Figure 12. At a center frequency of 2 kHz, the
gain is adjusted over a –20 dB to +20 dB range determined by
RDAC1. Circuit Q is adjusted by RDAC4. For more detailed
reading on the state variable active filter, see Analog Devices’
application note, AN-318.
A1
RDAC1
VIN
B
A2
A3
A4
RDAC4
B
10k
10k
OP279 2
RDAC2
RDAC3
B
B
0.01F
0.01F
BAND-
PASS
HIGH-
PASS
LOW-
PASS
Figure 10. Programmable State Variable Active Filter
FREQUENCY – Hz
40
20
–80 20 100k100 1k 10k
0
–20
–40
–60
200k
AMPLITUDE – dB
–0.16 20.0000 k
A
Figure 11. Programmed Center Frequency Band-Pass
Response
FREQUENCY – Hz
40
20
–8020 100k100 1k 10k
0
–20
–40
–60
200k
AMPLITUDE – dB
–19.01 2.00000 k
A
Figure 12. Programmed Amplitude Band-Pass Response
REV. C
AD8400/AD8402/AD8403
–18–
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic DIP
(N-8)
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.022 (0.558)
0.014 (0.356)
0.160 (4.06)
0.115 (2.93)
0.070 (1.77)
0.045 (1.15)
0.130
(3.30)
MIN
8
14
5
PIN 1
0.280 (7.11)
0.240 (6.10)
0.100 (2.54)
BSC
0.430 (10.92)
0.348 (8.84)
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.325 (8.25)
0.300 (7.62)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
O
NLY AND ARE N
O
T APPR
O
PRIATE F
O
R
US
E IN DE
S
I
G
N
8-Lead SOIC
(R-8)
0.1968 (5.00)
0.1890 (4.80)
85
41
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0500
(1.27)
BSC
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8°
0°
0.0196 (0.50)
0.0099 (0.25)x 45°
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
14-Lead Plastic DIP Package
(N-14)
14
17
8
PIN 1
0.795 (20.19)
0.725 (18.42)
0.280 (7.11)
0.240 (6.10)
0.100 (2.54)
BSC
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.210 (5.33)
MAX
0.022 (0.558)
0.014 (0.356)
0.160 (4.06)
0.115 (2.93)
0.070 (1.77)
0.045 (1.15)
0.130
(3.30)
MIN
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.325 (8.25)
0.300 (7.62)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. C
AD8400/AD8402/AD8403
–19–
14-Lead Narrow Body SOIC Package
(SO-14)
14 8
71
0.2440 (6.20)
0.2284 (5.80)
0.1574 (4.00)
0.1497 (3.80)
PIN 1
0.3444 (8.75)
0.3367 (8.55)
0.050 (1.27)
BSC
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.0688 (1.75)
0.0532 (1.35)
8
0
0.0196 (0.50)
0.0099 (0.25) 45
0.0500 (1.27)
0.0160 (0.41)
0.0099 (0.25)
0.0075 (0.19)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
14-Lead TSSOP
(RU-14)
14 8
71
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
0.201 (5.10)
0.193 (4.90)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0256
(0.65)
BSC
0.0433 (1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8
0
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
24-Lead Narrow Body Plastic DIP Package
(N-24)
24
112
13
PIN 1
1.275 (32.30)
1.125 (28.60)
0.280 (7.11)
0.240 (6.10)
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
0.325 (8.25)
0.300 (7.62)
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.022 (0.558)
0.014 (0.356)
0.200 (5.05)
0.125 (3.18)
0.150
(3.81)
MIN
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. C
–20–
C01092–0–2/02(C)
PRINTED IN U.S.A.
AD8400/AD8402/AD8403
OUTLINE DIMENSIONS (continued)
Dimensions shown in inches and (mm).
24-Lead SOIC Package
(SOL-24)
0.0125 (0.32)
0.0091 (0.23)
8
0
0.0291 (0.74)
0.0098 (0.25) 45
0.0500 (1.27)
0.0157 (0.40)
SEATING
PLANE
0.0118 (0.30)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
0.1043 (2.65)
0.0926 (2.35)
0.0500
(1.27)
BSC
24 13
12
1
0.4193 (10.65)
0.3937 (10.00)
0.2992 (7.60)
0.2914 (7.40)
PIN 1
0.6141 (15.60)
0.5985 (15.20)
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
24-Lead Thin Surface-Mount TSSOP Package
(RU-24)
24 13
121
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
0.311 (7.90)
0.303 (7.70)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0256 (0.65)
BSC
0.0433 (1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8
0
CONTROLLING DIMENSIONS ARE IN MILLIMETERS, INCH DIMENSIONS
ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE
ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
Revision History
Location Page
Data Sheet changed from REV. B to REV. C.
Addition of new Figure 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Edits to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Edits to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Edits to TPCs 1, 8, 12, 16, 20, 24, 35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Edits to PROGRAMMING THE VARIABLE RESISTOR section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12