a
FEATURES
128-Position, 2-Channel
Potentiometer Replacement
10 k⍀, 50 k⍀, 100 k⍀, 1 M⍀
Very Low Power: 40 A Max
ⴞ2.7 V Dual Supply Operation or
2.7 V to 5.5 V Single Supply Operation
Increment/Decrement Count Control
APPLICATIONS
Stereo Channel Audio Level Control
Mechanical Potentiometer Replacement
Remote Incremental Adjustment Applications
Instrumentation: Gain, Offset Adjustment
Programmable Voltage-to-Current Conversion
Line Impedance Matching
GENERAL DESCRIPTION
The AD5222 provides a dual channel, 128-position, digitally
controlled variable-resistor (VR) device. This device performs
the same electronic adjustment function as a potentiometer or
variable resistor. These products were optimized for instrument
and test equipment push-button applications. Choices between
bandwidth or power dissipation are available as a result of the
wide selection of end-to-end terminal resistance values.
The AD5222 contains two fixed resistors with wiper contacts that
tap the fixed resistor value at a point determined by a digitally
controlled up/down counter. The resistance between the wiper
and either end point of the fixed resistor provides a constant
resistance step size that is equal to the end-to-end resistance
divided by the number of positions (e.g., R STEP = 10 kΩ/128 =
78 Ω). The variable resistor offers a true adjustable value of
resistance, between Terminal A and the wiper, or Terminal B
and the wiper. The fixed A-to-B terminal resistance of 10 kΩ,
50 kΩ, 100 kΩ, or 1 MΩ has a nominal temperature coefficient
of –35 ppm/°C.
The chip select CS, count CLK and U/D direction control inputs
set the variable resistor position. The MODE determines whether
both VRs are incremented together or independently. With
MODE at logic zero, both wipers are incremented UP or DOWN
without changing the relative settings between the wipers. Also,
the relative ratio between the wipers is preserved if either wiper
reaches the end of the resistor array. In the independent MODE
(Logic 1) only the VR determined by the DACSEL pin is changed.
DACSEL (Logic 0) changes RDAC 1. These inputs, which control the internal up/down counter, can be easily generated with
Increment/Decrement
Dual Digital Potentiometer
AD5222
FUNCTIONAL BLOCK DIAGRAM
VDD
AD5222
A1
UP/DOWN
COUNTER
U/D
DECODE
W1
B1
POR
CS
MODE
DACSEL
CLK
DAC
SELECT
AND
ENABLE
A2
UP/DOWN
COUNTER
DECODE
W2
B2
GND
VSS
mechanical or push-button switches (or other contact closure
devices). This simple digital interface eliminates the need for
microcontrollers in front panel interface designs.
The AD5222 is available in the surface-mount (SO-14) package.
For ultracompact solutions, selected models are available in the
thin TSSOP-14 package. All parts are guaranteed to operate
over the extended industrial temperature range of –40°C to
+85°C. For 3-wire, SPI-compatible interface applications, see
the AD5203/AD5204/AD5206, AD7376, and AD8400/AD8402/
AD8403 products.
5V
VDD
CS
U/D
U/D
CLK
A1
W1
B1
INCREMENT
A2
DACSEL
W2
MODE
B2
GND
VSS
Figure 1. Typical Push-Button Control Application
REV. 0
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1999
V ⴞ 10% or 5 V ⴞ 10%, V
AD5222–SPECIFICATIONS (Vunless= 3otherwise
noted.)
DD
Parameter
Symbol
SS
= 0 V, VA = +VDD, VB = 0 V, –40ⴗC < TA < +85ⴗC,
Condition
DC CHARACTERISTICS RHEOSTAT MODE (Specifications Apply to All VRs)
R-DNL
RWB, VA = NC
Resistor Differential NL2
Resistor Nonlinearity2
R-INL
RWB, VA = NC
Nominal Resistor Tolerance
∆R
VAB = VDD, Wiper = No Connect, T A = 25°C
Resistance Temperature Coefficient
RAB/∆T
VAB = VDD, Wiper = No Connect
Wiper Resistance3
RW
IW = VDD /R, VDD = 3 V or 5 V
Nominal Resistance Match
∆R/RO
CH 1 to 2, V AB = VDD, TA = 25°C
DC CHARACTERISTICS POTENTIOMETER DIVIDER MODE (Specifications Apply to All VRs)
Resolution
N
INL
RAB = 10 kΩ, 50 kΩ, or 100 kΩ
Integral Nonlinearity4
INL
RAB = 1 MΩ
Differential Nonlinearity4
DNL
Voltage Divider Temperature Coefficient ∆VW /∆T
Code = 40H
Full-Scale Error
VWFSE
Code = 7F H
Zero-Scale Error
VWZSE
Code = 00H
RESISTOR TERMINALS
Voltage Range 5
Capacitance6 A, B
Capacitance6 W
Common-Mode Leakage
VA, B, W
CA, B
CW
ICM
DIGITAL INPUTS AND OUTPUTS
Input Logic High
Input Logic Low
Input Current
Input Capacitance6
VIH
VIL
IIL
CIL
VDD = 5 V/3 V
VDD = 5 V/3 V
VIN = 0 V or 5 V
POWER SUPPLIES
Power Single-Supply Range
Power Dual-Supply Range
Positive Supply Current
Negative Supply Current
Power Dissipation 7
Power Supply Sensitivity
VDD RANGE
VDD/SS RANGE
IDD
ISS
PDISS
PSS
VSS = 0 V
BW_10K
BW_50K
BW_100K
BW_1M
THDW
tS
eN_WB
RAB = 10 kΩ, Code = 40 H
RAB = 50 kΩ, Code = 40 H
RAB = 100 kΩ, Code = 40H
RAB = 500 kΩ, Code = 40H
VA = 1 V rms + 2 V dc, VB = 2 V dc, f = 1 kHz
RAB = 10 kΩ, ± 1 LSB Error Band
RWB = 5 kΩ, f = 1 kHz
DYNAMIC CHARACTERISTICS6, 8, 9
Bandwidth –3 dB
Total Harmonic Distortion
VW Settling Time
Resistor Noise Voltage
Min
Typ1 Max
Unit
–1
–1
–30
± 1/4 +1
± 0.4 +1
+30
–35
45
100
0.2 1
LSB
LSB
%
ppm/°C
Ω
%
± 1/4
± 1/2
± 1/4
20
–0.5
0.5
Bits
LSB
LSB
LSB
ppm/°C
LSB
LSB
7
–1
–2
–1
–1
0
VSS
f = 1 MHz, Measured to GND, Code = 40 H
f = 1 MHz, Measured to GND, Code = 40 H
VA = V B = V W
+0
1
VDD
45
60
1
2.4/2.1
5
2.7
± 2.3
VIH = 5 V or VIL = 0 V
VSS = –2.5 V, VDD = +2.7 V
VIH = 5 V or VIL = 0 V, VDD = 5 V
INTERFACE TIMING CHARACTERISTICS (Applies to All Parts) 6, 10
Input Clock Pulsewidth
tCH, t CL
Clock Level High or Low
CS to CLK Setup Time
tCSS
CS Rise to CLK Hold Time
tCSH
U/D to Clock Fall Setup Time
tUDS
U/D to Clock Fall Hold Time
tUDH
DACSEL to Clock Fall Setup Time
tDSS
DACSEL to Clock Fall Hold Time
tDSH
MODE to Clock Fall Setup Time
tMDS
MODE to Clock Fall Hold Time
tMDH
+1
+2
+1
30
20
20
10
30
20
30
20
40
V
pF
pF
nA
V
0.8/0.6 V
±1
µA
pF
5.5
± 2.7
15
40
15
40
150 400
0.002 0.05
V
V
µA
µA
µW
%/%
1000
180
78
7
0.005
2
14
kHz
kHz
kHz
kHz
%
µs
nV√Hz
ns
ns
ns
ns
ns
ns
ns
ns
ns
NOTES
1Typicals represent average readings at 25°C, V
DD = 5 V.
2Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions.
R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. See Figure 22 test circuit.
3Wiper resistance is not measured on the R
AB = 1 MΩ models.
4INL and DNL are measured at V with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. V = V
W
A
DD and VB = 0 V. DNL
specification limits of ±1 LSB maximum are guaranteed monotonic operating conditions. See Figure 21 test circuit.
5Resistor Terminals A, B, W have no limitations on polarity with respect to each other.
6Guaranteed by design and not subject to production test.
7P
DISS is calculated from (I DD × V DD). CMOS logic level inputs result in minimum power dissipation.
8Bandwidth, noise and settling time are dependent on the terminal resistance value chosen. The lowest R value results in the fastest settling time and highest bandwidth.
The highest R value results in the minimum overall power consumption.
9All dynamic characteristics use V
DD = 5 V.
10See timing diagram for location of measured values. All input control voltages are specified with t = t = 2.5 ns (10% to 90% of +3 V) and timed from a voltage level
R
F
of 1.5 V. Switching characteristics are measured using both V DD = 5 V or V DD = 3 V.
Specifications subject to change without notice.
–2–
REV. 0
AD5222
ABSOLUTE MAXIMUM RATINGS
ORDERING GUIDE
(TA = 25°C, unless otherwise noted)
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +7 V
VSS to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, –5 V
VDD to VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V
VA, VB, V W to GND . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, VDD
AX – BX , AX – WX , BX – WX . . . . . . . . . . . . . . . . . . . ± 20 mA
Digital Input Voltage to GND . . . . . . . . . . . . 0 V, VDD + 0.3 V
Operating Temperature Range . . . . . . . . . . . –40°C to +85°C
Maximum Junction Temperature (TJ max) . . . . . . . . . . 150°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . 300°C
Package Power Dissipation . . . . . . . . . . . . . (TJ max – TA)/θJA
Thermal Resistance θJA,
SOIC (SO-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158°C/W
TSSOP-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206°C/W
Model
Kilo
Package
Package
Ohms Temperature Description Option
AD5222BR10
AD5222BRU10
AD5222BR50
AD5222BRU50
AD5222BR100
AD5222BRU100
AD5222BR1M
AD5222BRU1M
10
10
50
50
100
100
1,000
1,000
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
–40°C/+85°C
SO-14
TSSOP-14
SO-14
TSSOP-14
SO-14
TSSOP-14
SO-14
TSSOP-14
R-14
RU-14
R-14
RU-14
R-14
RU-14
R-14
RU-14
The AD5222 die size is 56 mil × 60 mil, 3360 sq. mil; 1.4224 mm × 1.524 mm,
2.1677 sq. mm. Contains 1503 transistors. Patent Number 5495245 applies.
PIN FUNCTION DESCRIPTIONS
Pin Name
CS
tCSS
tCH
tCL
tCSH
CLK
tUDS
tUDH
U/D
1
2
3
4
tDSS
tDSH
DACSEL
tMDS
tMDH
MODE
Figure 2. Detail Timing Diagram
5
6
7
8
9
10
Truth Table
CS
CLK
U/D
Operation
L
L
H
t
t
X
H
L
X
Wiper Increment Toward Terminal A
Wiper Decrement Toward Terminal B
Wiper Position Fixed
Common Mode (MODE = 0) moves both wipers together either
UP or DOWN the resistor array without changing the relative
distance between the wipers. Also, the distance between both
wipers is preserved if either reaches the end of the array. Independent Mode (MODE = 1) allows user to control each RDAC
individually: DACSEL = 0 sets RDAC1; DACSEL = 1: sets
RDAC2.
11
12
13
14
Description
B1
A1
W1
VSS
B Terminal RDAC #1.
A Terminal RDAC #1.
Wiper RDAC #1, DACSEL = 0.
Negative Power Supply. Specified for operation
at both 0 V or –2.7 V (Sum of |VDD | + |VSS |
< 5.5 V).
W2
Wiper RDAC #2, DACSEL = 1.
A2
A Terminal RDAC #2.
B2
B Terminal RDAC #2.
GND
Ground.
MODE
Common MODE = 0, Independent MODE = 1.
DACSEL DAC Select determines which wiper is incremented in the Independent MODE = 1.
DACSEL = 0 sets RDAC1, DACSEL = 1 sets
RDAC2.
U/D
UP/DOWN Direction Control.
CLK
Serial Clock Input, Negative Edge Triggered.
CS
Chip Select Input, Active Low. When CS is
high, the UP/DOWN counter is disabled.
VDD
Positive Power Supply. Specified for operation
at both +3 V or +5 V. (Sum of |VDD | + |VSS |
< 5.5 V).
PIN CONFIGURATION
B1 1
14 VDD
A1 2
13 CS
12 CLK
TOP VIEW
11 U/D
(Not to Scale)
W2 5
10 DACSEL
W1 3
AD5222
VSS 4
A2 6
9 MODE
B2 7
8 GND
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 AD5222 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.
REV. 0
–3–
WARNING!
ESD SENSITIVE DEVICE
AD5222–Typical Performance Characteristics
100
0.25
0.15
50
TA = +258C
0.10
0.05
0
–0.05
TA = +858C
–0.10
25
–0.15
RWB
0
32
64
CODE – Decimal
96
–0.25
128
0
Figure 3. Wiper-To-End Terminal Resistance vs. Code
20H
3
50kV VERSION
05H
2.5
2
02H
1.5
RAB = 10kV
VDD = 5V
TA = 258C
1
0.5
112
128
1
2
3
4
IWA CURRENT – mA
5
6
10kV VERSION
0.4
0.2
0
–0.2
100kV VERSION
1MV VERSION
–0.4
–0.6
–0.8
–1.0
7
0
Figure 4. Resistance Linearity vs. Conduction Current
16
32
48
64
80
CODE – Decimal
96
112
128
Figure 7. R-INL Resistance Nonlinearity Error vs. Code
0.6
180
150
96
0.6
08H
3.5
0
48
64
80
CODE – Decimal
VDD/VSS = 2.7V/0V
TA = 258C
0.8
10H
4
0
32
1.0
3FH
4.5
16
Figure 6. R-DNL Relative Resistance Step Position
Change vs. Code
R-INL ERROR – LSB
5
VDD = +15V
VSS = –15V
RAB = 50kV
–0.20
RWA
0
VWB VOLTAGE – V
TA = –558C
75
R-DNL ERROR – LSB
PERCENT OF NOMINAL
END-TO-END RESISTANCE – % RAB
0.20
SS = 600 UNITS
VDD = 2.7V
TA = 258C
VDD/VSS = 2.7V/0V
TA = 258C
0.4
10kV VERSION
0.2
50kV VERSION
INL – LSB
FREQUENCY
120
90
0
–0.2
–0.4
60
100kV VERSION
–0.6
30
1MV VERSION
–0.8
0
40 41 42 44 45 47 48 50 51 53 54 56 57 59 60
WIPER RESISTANCE – V
–1.0
0
16
32
48
64
80
CODE – Decimal
96
112
128
Figure 8. Potentiometer Divider INL Error vs. Code
Figure 5. Wiper Contact Resistance
–4–
REV. 0
AD5222
9
VDD/VSS = 2.7V/0V
TA = 258C
1MV VERSION
60
10kV VERSION
50
40
3
50kV VERSION
20
10
–3
A
OP42
W
–6
50kV
1MV
–9
0
–12
–10
–15
–20
–18
B
100kV
0
16
32
48
64
80
CODE – Decimal
96
112
BW 10kV
50kV
100kV
1MV
–21
100
–30
128
Figure 9. ⌬VWB /⌬T Potentiometer Mode Tempco
1k
764kHz
132kHz
64kHz
6.6kHz
10k
FREQUENCY – Hz
1M
100k
Figure 12. Gain vs. Frequency vs. RAB
10
120
FILTER = 22kHz
VDD = 62.7V
VIN = 1V rms
TA = 258C
VDD/VSS = 2.7V/0V
TA = 258C
100
RHEOSTAT MODE TEMPCO – ppm/8C
10kV
0
100kV VERSION
30
VDD = +2.7V
VSS = –2.7V
DATA = 40H
VA = 50mV rms
VB = 0V
6
GAIN – dB
POTENTIOMETER MODE TEMPCO – ppm/8C
70
100kV VERSION
80
1.0
THD + NOISE – %
60
50kV VERSION
40
20
0
–20
–60
SEE TEST CIRCUIT FIGURE 25
0.01
10kV VERSION
–40
0.1
SEE TEST CIRCUIT FIGURE 26
1MV VERSION
0.001
–80
0
16
32
48
64
80
CODE – Decimal
96
112
10
128
Figure 10. ⌬RWB /⌬T Rheostat Mode Tempco
100
1k
FREQUENCY – Hz
10k
100k
Figure 13. Total Harmonic Distortion Plus Noise vs.
Frequency
0
NORMALIZED GAIN FLATNESS – 0.1dB/DIV
CODE = 3FH
20H
–10
GAIN - dB
10H
–20
08H
04H
–30
02H
01H
–40
TA = 258C
SEE TEST CIRCUIT FIGURE 32
–50
10
100
1k
10k
100k
FREQUENCY – Hz
1M
10M
10kV
100kV
SEE TEST CIRUIT 27
VDD = 2.7V
VSS = –2.7V
VA = 50mV rms
VB = 0V
DATA = 40H
50kV
A
W
OP42
B
10
Figure 11. 10 kΩ Gain vs. Frequency vs. Code
REV. 0
1MV
100
1k
10k
FREQUENCY – Hz
100k
1M
Figure 14. Normalized Gain Flatness vs. Frequency
–5–
AD5222
1200
10
800
SUPPLY CURRENT – mA
1000
IDD – SUPPLY CURRENT – mA
TA = 258C
A – VDD = 5.5V
CODE = 15H
B – VDD = 3.3V
CODE = 15H
C – VDD = 5.5V
CODE = 3FH
D – VDD = 3.3V
CODE = 3FH
600
A
B
400
VDD = 5.5V
VA = 5.5V
1
VDD/VSS = 62.5V
VA = 2.5V
0.1
0.01
200
C
D
0
10k
1
100k
FREQUENCY – Hz
0.001
10M
1M
VDD = 2.7V
VA = 2.7V
0
Figure 15. IDD , ISS Supply Current vs. Clock Frequency
1
2
3
4
INPUT LOGIC VOLTAGE – V
5
6
Figure 18. Supply Current vs. Input Logic Voltage
100
TA = 258C
SWITCH RESISTANCE – V
90
VDD = 2.7V
VA = 2.7V
VB = 0V
VDD/VSS = 2.7V/0V
80
70
VW
20mV/DIV
60
50
VDD/VSS = 62.7V
40
2V/DIV
30
CLK
VDD/VSS = 5.5V/0V
20
10
–3
–2
–1
0
1
2
3
COMMON MODE – Volts
4
5
6
Figure 16. Incremental Wiper Contact Resistance vs.
VDD / V SS
Figure 19. Midscale Transition 3FH to 40H
1
SUPPLY CURRENT – mA
LOGIC = 0V OR VDD
VDD = 2.7V
VA = 2.7V
VB = 0V
0.1
VWA
VWB
20mV/DIV
VDD = 5.5V OR VDD/VSS = 62.7V
0.01
VDD = 2.7V
CLK
2V/DIV
0.001
–40
–15
10
35
TEMPERATURE – 8C
60
85
Figure 17. Supply Current vs. Temperature
Figure 20. Stereo Step Transition, Mode = 0
–6–
REV. 0
Parametric Test Circuits–AD5222
A
V+ = VDD
1LSB = V+/128
DUT
A
W
V+
DUT B
+5V
W
VIN
OP279
B
VOUT
+
VMS
–5V
Figure 25. Inverting Programmable Gain Test Circuit
Figure 21. Potentiometer Divider Nonlinearity Error Test
Circuit (INL, DNL)
+5V
NO CONNECT
DUT
A
W
OP279
W
VIN
IW
VOUT
–5V
B
A
DUT
B
VMS
Figure 22. Resistor Position Nonlinearity Error (Rheostat
Operation; R-INL, R-DNL)
DUT
A
W
VMS2
Figure 26. Noninverting Programmable Gain Test Circuit
+15V
A
IW = VDD /R NOMINAL
W
VIN
VW
DUT
B
OP42
VOUT
B
VMS1
RW = [VMS1 – V MS2]/IW
–15V
Figure 27. Gain vs. Frequency Test Circuit
Figure 23. Wiper Resistance Test Circuit
VA
V+ = VDD ± 10%
V+
~
VDD
A
B
PSRR (dB) = 20 LOG
W
VMS
DVMS%
PSS (%/%) = –––––––
DVDD%
DV
CODE = 00H
W
MS
( –––––
)
DVDD
B
ISW
0.1V
0 TO VDD
Figure 28. Incremental ON Resistance Test Circuit
Figure 24. Power Supply Sensitivity Test Circuit (PSS,
PSRR)
REV. 0
RSW = 0.1V
ISW
DUT
–7–
AD5222
OPERATION
U/D
The AD5222 provides a 128-position, digitally-controlled, variable
resistor (VR) device. Changing the VR settings is accomplished
by pulsing the CLK pin while CS is active low. The U/D (UP/
DOWN) control input pin controls the direction of the increment.
When the wiper hits the end of the resistor (Terminal A or B)
additional CLK pulses no longer change the wiper setting. The
wiper position is immediately decoded by the wiper decode logic
changing the wiper resistance. Appropriate debounce circuitry is
required when push-button switches are used to control the
count sequence and direction of count. The exact timing requirements are shown in Figure 2. The AD5222 powers ON in a
centered wiper position, exhibiting nearly equal resistances of
RWA and R WB.
RDAC 1
U/D
COUNTER
DACSEL
MODE
RDAC 2
U/D
COUNTER
CS
CLK
VDD
AD5222
A1
UP/DOWN
COUNTER
U/D
DECODE
Figure 30. Detailed Digital Logic Interface Circuit
W1
All digital inputs (CS, U/D, CLK, MODE, DACSEL) are
protected with a series input resistor and parallel Zener ESD
structure shown in Figure 31. All potentiometer terminal pins
(A, B, W) are protected from ESD as shown in Figure 32.
B1
POR
CS
MODE
DACSEL
CLK
DAC
SELECT
AND
ENABLE
A2
UP/DOWN
COUNTER
DECODE
GND
W2
1kV
LOGIC
B2
VSS
VSS
Figure 31. Equivalent ESD Protection Digital Pins
Figure 29. Block Diagram
20V
A, B, W
DIGITAL INTERFACING OPERATION
VSS
The AD5222 contains a push-button controllable interface. The
active inputs are clock (CLK), CS and up/down (U/D). While
the MODE, and DACSEL pins control common updates or
individual updates. The negative-edge sensitive CLK input
requires clean transitions to avoid clocking multiple pulses into
the internal UP/DOWN counter register, Figure 30. Standard
logic families work well. If mechanical switches are used for
product evaluation a flip-flop or other suitable means should
debounce them. When CS is taken active low, the clock begins
to increment or decrement the internal up/down counter, dependent upon the state of the U/D control pin. The UP/DOWN
counter value (D) starts at 40H at system power ON. Each new
CLK pulse will increment the value of the internal counter by
1 LSB until the full-scale value of 7FH is reached, as long as the
U/D pin is logic high. If the U/D pin is taken to logic low, the
counter will count down, stopping at code 00H (zero-scale).
Additional clock pulses on the CLK pin are ignored when the
wiper is at either the 00H position or the 7F H position. The
detailed digital logic interface circuitry is shown in Figure 30.
Figure 32. Equivalent ESD Protection Analog Pins
RS
D0
D1
D2
D3
D4
D5
D6
A
RS
RS
W
RDAC
UP/DOWN
CNTR
&
DECODE
RS
B
RS = RNOMINAL/128
Figure 33. AD5222 Equivalent RDAC Circuit
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AD5222
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between Terminals A and
B are available with values of 10 kΩ, 50 kΩ, 100 kΩ, and 1 MΩ
The final three characters of the part number determine the
nominal resistance value, e.g., 10 kΩ = 10; 50 kΩ = 50; 100 kΩ
= 100; 1 MΩ = 1M. The nominal resistance (RAB ) of the VR
has 128 contact points accessed by the wiper terminal, plus the
B terminal contact. At power ON, the resistance from the wiper
to either end Terminal A or B is approximately equal. Pulsing
the CLK pin will increase the resistance from the wiper W to
Terminal B by one unit of RS resistance, see Figure 33. The
resistance RWB is determined by the number of pulses applied to
the clock pin. Each segment of the internal resistor string has a
nominal resistance value of RS = RAB/128, which becomes 78 Ω
in the case of the 10 kΩ AD5222BR10 product. Care should be
taken to limit the current flow between W and B in the direct
contact state (RWB code = 0) to a maximum value of 20 mA to
avoid degradation or possible destruction of the internal switch
contact.
Like the mechanical potentiometer the RDAC replaces, it is
totally symmetrical (see Figure 3). The resistance between the
wiper W and Terminal A also produces a digitally controlled
resistance RWA. When these terminals are used the B-terminal
should be tied to the wiper.
The RBA temperature coefficient increases as the wiper is programmed near the B-terminal due to the larger percentage
contribution of the wiper contact switch resistance, which has a
0.5%/°C temperature coefficient. Figures 9 and 10 show the
effect of the wiper contact resistance as a function of code setting.
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 which can be
any value starting at zero volts up to 1 LSB less than 5 V. Each
LSB of voltage is equal to the voltage applied across Terminals
AB divided by the 128-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:
VW(D) = D/128 × VAB + VB
D represents the current contents of the internal up/down counter.
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 drift improves to 20 ppm/°C.
The typical part-to-part distribution of R BA is process-lotdependent having a ± 30% variation. The change in RBA with
temperature has a –35 ppm/°C temperature coefficient.
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(1)
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AD5222
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
14-Lead Narrow Body SOIC
(R-14)
0.201 (5.10)
0.193 (4.90)
0.3444 (8.75)
0.3367 (8.55)
0.1574 (4.00)
0.1497 (3.80)
PIN 1
C3715–8–10/99
14-Lead TSSOP
(RU-14)
14
8
1
7
0.050 (1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.2440 (6.20)
0.2284 (5.80)
14
8
0.177 (4.50)
0.169 (4.30)
0.256 (6.50)
0.246 (6.25)
0.0196 (0.50)
3 458
0.0099 (0.25)
1
7
PIN 1
88
0.0192 (0.49) SEATING
08 0.0500 (1.27)
0.0099 (0.25)
0.0138 (0.35) PLANE
0.0160 (0.41)
0.0075 (0.19)
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
0.0256
(0.65)
BSC
0.0433 (1.10)
MAX
0.0118 (0.30)
0.0075 (0.19)
0.0079 (0.20)
0.0035 (0.090)
88
08
0.028 (0.70)
0.020 (0.50)
PRINTED IN U.S.A.
0.0098 (0.25)
0.0040 (0.10)
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