32-Position Manual Up/Down Control
Potentiometer
AD5228
Rev. A
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infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
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Tel: 781.329.4700 www.analog.com
Fax: 781.326.8703© 2004–2009Analog Devices, Inc. All rights reserved.
FEATURES
32-position digital potentiometer
10 kΩ, 50 kΩ, 100 kΩ end-to-end terminal resistance
Simple manual up/down control
Self-contained, requires only 2 pushbutton tactile switches
Built-in adaptive debouncer
Discrete step-up/step-down control
Autoscan up/down control with 4 steps per second
Pin-selectable zero-scale/midscale preset
Low potentiometer mode tempco, 5 ppm/°C
Low rheostat mode tempco, 35 ppm/°C
Digital control compatible
Ultralow power, IDD = 0.4 μA typ and 3 μA max
Low operating voltage, 2.7 V to 5.5 V
Automotive temperature range, −40°C to +105°C
Compact thin SOT-23-8 (2.9 mm × 3 mm) Pb-free package
APPLICATIONS
Mechanical potentiometer and trimmer replacements
LCD backlight, contrast, and brightness controls
Digital volume control
Portable device-level adjustments
Electronic front panel-level controls
Programmable power supply
GENERAL DESCRIPTION
The AD5228 is Analog Devices’ latest 32-step-up/step-down
control digital potentiometer emulating mechanical potenti-
ometer operation1. Its simple up/down control interface allows
manual control with just two external pushbutton tactile
switches. The AD5228 is designed with a built-in adaptive
debouncer that ignores invalid bounces due to contact bounce
commonly found in mechanical switches. The debouncer is
adaptive, accommodating a variety of pushbutton tactile
switches that generally have less than 10 ms of bounce time
during contact closures. When choosing the switch, the user
should consult the timing specification of the switch to ensure
its suitability in an AD5228 application.
1 The terms digital potentiometer and RDAC are used interchangeably.
FUNCTIONAL BLOCK DIAGRAM
04422-0-001
UP/DOWN
CONTROL
LOGIC
DISCRETE
STEP/AUTO
SCAN DETECT
ADAPTIVE
DEBOUNCER ZERO- OR MID-
SCALE PRESET
AD5228
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
R1 R2
D
E
C
O
D
EA
W
B
V
DD
PRE GND
PU
PD
Figure 1.
The AD5228 can increment or decrement the resistance in
discrete steps or in autoscan mode. When the PU or PD button
is pressed briefly (no longer than 0.6 s), the resistance of the
AD5228 changes by one step. When the PU or PD button is
held continuously for more than a second, the device activates
the autoscan mode and changes four resistance steps per
second.
The AD5228 can also be controlled digitally; its up/down
features simplify microcontroller usage. The AD5228 is available
in a compact thin SOT-23-8 (TSOT-8) package. The part is
guaranteed to operate over the automotive temperature range of
−40°C to +105°C.
The AD5228’s simple interface, small footprint, and very low
cost enable it to replace mechanical potentiometers and
trimmers with typically 3× improved resolution, solid-state
reliability, and faster adjustment, resulting in considerable cost
saving in end users’ systems.
Users who consider EEMEM potentiometers should refer to the
recommendations in the Applications section.
Table 1. Truth Table
PU PD Operation1
0 0 RWB Decrement
0 1 RWB Increment
1 0 RWB Decrement
1 1 RWB Does Not Change
1RWA increments if RWB decrements and vice versa.
AD5228
Rev. A | Page 2 of 20
TABLE OF CONTENTS
Electrical Characteristics ................................................................. 3
Interface Timing Diagrams ......................................................... 4
Absolute Maximum Ratings ............................................................ 5
ESD Caution .................................................................................. 5
Pin Configuration and Function Descriptions ............................. 6
Typical Performance Characteristics ............................................. 7
Theory of Operation ...................................................................... 11
Programming the Digital Potentiometers ............................... 12
Controlling Inputs ...................................................................... 13
Terminal Voltage Operation Range ......................................... 13
Power-Up and Power-Down Sequences .................................. 14
Layout and Power Supply Biasing ............................................ 14
Applications ..................................................................................... 15
Manual Adjustable LED Driver ................................................ 15
Adjustable Current Source for LED Driver ............................ 15
Automatic LCD Panel Backlight Control ................................ 16
Audio Amplifier with Volume Control ................................... 16
Constant Bias with Supply to Retain Resistance Setting ...... 17
Outline Dimensions ....................................................................... 18
Ordering Guide .......................................................................... 18
REVISION HISTORY
4/09—Rev. 0 to Rev. A
Changes to Table 2………………………………………………3
4/04—Revision 0: Initial Version
AD5228
Rev. A | Page 3 of 20
ELECTRICAL CHARACTERISTICS
10 kΩ, 50 kΩ, 100 kΩ versions: VDD = 3 V ± 10% or 5 V ± 10%, VA = VDD, VB = 0 V, −40°C < TA < +105°C, unless otherwise noted.
Table 2.
Parameter Symbol Conditions Min Typ1Max Unit
DC CHARACTERISTICS, RHEOSTAT MODE
Resistor Differential Nonlinearity2R-DNL RWB, A terminal = no connect −0.5 ±0.05 +0.5 LSB
Resistor Integral Nonlinearity2
R-INL RWB, A terminal = no connect −0.5 ±0.1 +0.5 LSB
Nominal Resistor Tolerance3∆RAB/RAB −20 +20 %
Resistance Temperature Coefficient (∆RAB/RAB) × 104/∆T 35 ppm/°C
Wiper Resistance RW V
DD = 2.7 V 100 250 Ω
V
DD = 2.8 V to 5.5 V 50 200 Ω
DC CHARACTERISTICS, POTENTIOMETER DIVIDER MODE
(Specifications apply to all RDACs)
Resolution N 5 Bits
Integral Nonlinearity3
INL −0.5 ±0.05 +0.5 LSB
Differential Nonlinearity3, 5
DNL −0.5 ±0.05 +0.5 LSB
Voltage Divider Temperature Coefficient (∆VW/VW) × 104/∆T Midscale 5 ppm/°C
Full-Scale Error VWFSE ≥+15 steps from midscale −1 .2 −0.5 0 LSB
Zero-Scale Error VWZSE ≤−16 steps from midscale 0 0.3 0.6 LSB
RESISTOR TERMINALS
Voltage Range6VA, B, W With respect to GND 0 VDD V
Capacitance4 A, B CA, B f = 1 MHz, measured to GND 140 pF
Capacitance4 W CW f = 1 MHz, measured to GND 150 pF
Common-Mode Leakage ICM V
A = VB = VW 1 nA
PU, PD INPUTS
Input High VIH VDD = 5 V 2.4 5.5 V
Input Low VIL VDD = 5 V 0 0.8 V
Input Current II V
IN = 0 V or 5 V ±1 μA
Input Capacitance4
CI 5 pF
POWER SUPPLIES
Power Supply Range VDD VDD = 5 V, PU = PD = VDD 2.7 5.5 V
Supply Standby Current IDD_STBY 0.4 3 μA
Supply Active Current7IDD_ACT VDD = 5 V, PU or PD = 0 V 50 110 μA
Power Dissipation7, 8
PDISS V
DD = 5 V 17 μW
Power Supply Sensitivity PSSR VDD = 5 V ± 10% 0.01 0.05 %/%
Footnotes on next page.
AD5228
Rev. A | Page 4 of 20
Parameter Symbol Conditions Min Typ1Max Unit
DYNAMIC CHARACTERISTICS 4, 9, 10, 11
Built-in Debounce and Settling Time 12 tDB 6 ms
PU Low Pulse Width tPU 12 ms
PD Low Pulse Width tPD 12 ms
PU High Repetitive Pulse Width tPU_REP 1 μs
PD High Repetitive Pulse Width tPD_REP 1 μs
Autoscan Start Time tAS_START PU or PD = 0 V 0.6 0.8 1.2 s
Autoscan Time tAS PU or PD = 0 V 0.16 0.25 0.38 s
Bandwidth –3 dB BW_10 RAB = 10 kΩ, midscale 460 kHz
BW_50 RAB = 50 kΩ, midscale 100 kHz
BW_100 RAB = 100 kΩ, midscale 50 kHz
Total Harmonic Distortion THD VA = 1 V rms, RAB = 10 kΩ,
VB = 0 V dc, f = 1 kHz
0.05 %
Resistor Noise Voltage eN_WB R
WB = 5 kΩ, f = 1 kHz 14 nV/√Hz
1 Typicals represent average readings at 25°C, VDD = 5 V.
2 Resistor 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.
3 INL and DNL are measured at VW with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. VA = VDD and VB = 0 V.
4 Guaranteed by design and not subject to production test.
5 DNL specification limits of ±1 LSB maximum are guaranteed monotonic operating conditions.
6 Resistor Terminals A, B, and W have no limitations on polarity with respect to each other.
7 PU and PD have 100 kΩ internal pull-up resistors, IDD_ACT = VDD/100 kΩ + IOSC (internal oscillator operating current) when PU or PD is connected to ground.
8 PDISS is calculated based on IDD_STBY × VDD only. IDD_ACT duration should be short. Users should not hold PU or PD pin to ground longer than necessary to elevate power
dissipation.
9 Bandwidth, 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.
10 All dynamic characteristics use VDD = 5 V.
11 Note that all input control voltages are specified with tR = tF = 1 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. Switching characteristics are measured
using VDD = 5 V.
12 The debouncer keeps monitoring the logic-low level once PU is connected to ground. Once the signal lasts longer than 11 ms, the debouncer assumes the last
bounce is met and allows the AD5228 to increment by one step. If the PU signal remains at low and reaches tAS_START, the AD5528 increments again, see Figure 7. Similar
characteristics apply to PD operation.
INTERFACE TIMING DIAGRAMS
04422-0-006
R
WB
PU
t
DB
t
PD
t
PD_REP
04422-0-004
R
WB
PU t
PU
t
PU_REP
t
DB
Figure 2. Increment RWB in Discrete Steps
Figure 4. Decrement RWB in Discrete Steps
04422-0-007
R
WB
PD
t
DB
t
AS
t
AS_START
04422-0-005
R
WB
PU
t
DB
t
AS
t
AS_START
Figure 5. Decrement RWB in Autoscan Mode
Figure 3. Increment RWB in Autoscan Mode
AD5228
Rev. A | Page 5 of 20
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Rating
VDD to GND −0.3 V, +7 V
VA, VB, VW to GND 0 V, VDD
PU, PD, PRE Voltage to GND 0 V, VDD
Maximum Current
IWB, IWA Pulsed ±20 mA
IWB Continuous (RWB ≤ 5 kΩ, A open)1±1 mA
IWA Continuous (RWA ≤ 5 kΩ, B open)1
±1 mA
IAB Continuous
(RAB = 10 kΩ/50 kΩ/100 kΩ)1
±500 μA/±100 μA/
±50 μA
Operating Temperature Range −40°C to +105°C
Maximum Junction Temperature
(TJmax)
150°C
Storage Temperature −65°C to +150°C
Lead Temperature
(Soldering, 10 s – 30 s)
245°C
Thermal Resistance2 θJA 230°C/W
1 Maximum terminal current is bounded by the maximum applied voltage
across any two of the A, B, and W terminals at a given resistance, the
maximum current handling of the switches, and the maximum power
dissipation of the package. VDD = 5 V.
2 Package power dissipation = (TJmax – TA) / θJA.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only and functional operation of the device at these or
any other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD 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 this product 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.
AD5228
Rev. A | Page 6 of 20
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
04422-0-003
AD5228
PU
1
PD
2
A
3
GND
4
V
DD
PRE
B
W
8
7
6
5
Figure 6. SOT-23-8 Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 PU Push-Up Pin.
Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to VDD.
2 PD Push-Down Pin.
Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to VDD.
3 A Resistor Terminal A. GND ≤VA ≤ VDD.
4 GND Common Ground.
5 W Wiper Terminal W. GND ≤ VW ≤ VDD.
6 B Resistor Terminal B. GND ≤ VB ≤ VDD.
7 PRE Power-On Preset. Output = midscale if PRE = GND; output = zero scale if PRE = VDD. Do not let the PRE pin float.
No pull-up resistor is needed.
8 VDD Positive Power Supply, 2.7 V to 5.5 V.
AD5228
Rev. A | Page 7 of 20
TYPICAL PERFORMANCE CHARACTERISTICS
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
032282420161284
04422-0-008
CODE (Decimal)
RHEOSTAT MODE INL (LSB)
T
A
= 25°C
5.5V
2.7V
Figure 7. R-INL vs. Code vs. Supply Voltages
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
032282420161284
04422-0-009
CODE (Decimal)
RHEOSTAT MODE INL (LSB)
V
DD
= 5.5V
–40°C
+25°C
+85°C
+105°C
Figure 8. R-INL vs. Code vs. Temperature, VDD = 5 V
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
032282420161284
04422-0-010
CODE (Decimal)
RHEOSTAT MODE DNL (LSB)
T
A
= 25°C
5.5V
2.7V
Figure 9. R-DNL vs. Code vs. Supply Voltages
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
03282420161284
04422-0-011
CODE (Decimal)
RHEOSTAT MODE DNL (LSB)
2
V
DD
= 5.5V
–40°C
+25°C
+85°C
+105°C
Figure 10. R-DNL vs. Code vs. Temperature, VDD = 5 V
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
03282420161284
04422-0-012
CODE (Decimal)
POTENTIOMETER MODE INL (LSB)
2
T
A
= 25°C
5.5V
2.7V
Figure 11. INL vs. Code vs. Supply Voltages
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
03282420161284
04422-0-013
CODE (Decimal)
POTENTIOMETER MODE INL (LSB)
2
V
DD
= 5.5V
–40°C
+25°C
+85°C
+105°C
Figure 12. INL vs. Code, VDD = 5 V
AD5228
Rev. A | Page 8 of 20
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
032282420161284
04422-0-014
CODE (Decimal)
POTENTIOMETER MODE DNL (LSB)
T
A
= 25°C
5.5V
2.7V
Figure 13. DNL vs. Code vs. Supply Voltages
0.10
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
032282420161284
04422-0-015
CODE (Decimal)
POTENTIOMETER MODE DNL (LSB)
V
DD
= 5.5V
–40°C
+25°C
+85°C
+105°C
Figure 14. DNL vs. Code, VDD = 5 V
–
0.50
–0.90
–0.85
–0.80
–0.75
–0.70
–0.65
–0.60
–0.55
–40 –20 0 20 40 60 10080
04422-0-016
TEMPERATURE (°C)
FSE (LSB)
V
DD
= 5.5V
V
DD
= 2.7V
Figure 15. Full-Scale Error vs. Temperature
0.40
0.45
0.50
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
–40 –20 0 20 40 60 10080
04422-0-017
TEMPERATURE (°C)
ZSE (LSB)
V
DD
= 5.5V
V
DD
= 2.7V
Figure 16. Zero-Scale Error vs. Temperature
1
0.1
–40 –20 0 20 40 60 10080
04422-0-018
TEMPERATURE (°C)
SUPPLY STANDBY CURRENT (
μ
A)
V
DD
= 5.5V
I
DD_ACT
= 50μA TYP
Figure 17. Supply Current vs. Temperature
120
0
20
40
60
80
100
–40 –20 0 20 40 60 10080
04422-0-019
TEMPERATURE (°C)
NOMINAL RESISTANCE R
AB
(kΩ)
V
DD
= 5.5V
R
AB
= 100kΩ
R
AB
= 50kΩ
R
AB
= 10kΩ
Figure 18. Nominal Resistance vs. Temperature
AD5228
Rev. A | Page 9 of 20
120
0
20
40
60
80
100
–40 –20 0 20 40 60 10080
04422-0-020
TEMPERATURE (°C)
WIPER RESISTANCE, R
W
(Ω)
V
DD
= 2.7V
V
DD
= 5.5V
Figure 19. Wiper Resistance vs. Temperature
150
–30
0
30
60
90
120
0 4 8 121620242832
04422-0-021
CODE (Decimal)
RHEOSTAT MODE TEMPCO,
Δ
R
WB
/
Δ
T (ppm/°C)
10kΩ
50kΩ
100kΩ
V
DD
= 5.5V
A = OPEN
Figure 20. Rheostat Mode Tempco ΔRWB/ΔT vs. Code
20
–20
–15
–10
–5
0
5
10
15
0 4 8 12 16 20 24 28 32
04422-0-022
CODE (Decimal)
POTENTIOMETER MODE TEMPCO,
Δ
VWB/
Δ
T (ppm/
°
C)
10kΩ
50kΩ
100kΩ
V
DD
= V
A
= 5.5V
V
B
= 0V
Figure 21. Potentiometer Mode Tempco ΔVWB/ΔT vs. Code
6
–54
–48
–42
–36
–30
–24
–18
–12
–6
0
1k 10k 1M
START 1 000.000Hz STOP 1 000 000.000Hz
REF LEVEL
0dB
/
DI
V
6.0dB MARKE
R
MAG (A/R) 469 390.941H
z
–8.966dB
100k
04422-0-050
GAIN (dB)
T
A
= 25°C
V
DD
= 5.5V
V
A
= 50mV rms
16 STEPS
8 STEPS
4 STEPS
2 STEPS
1 STEP
Figure 22. Gain vs. Frequency vs. Code, RAB = 10 kΩ
6
–54
–48
–42
–36
–30
–24
–18
–12
–6
0
1k 10k 1M
START 1 000.000Hz STOP 1 000 000.000Hz
REF LEVEL
0dB
/
DI
V
6.0dB MARKE
R
MAG (A/R) 97 525.233H
z
–9.089dB
100k
04422-0-051
GAIN (dB)
T
A
= 25°C
V
DD
= 5.5V
V
A
= 50mV rms
16 STEPS
8 STEPS
4 STEPS
2 STEPS
1 STEP
Figure 23. Gain vs. Frequency vs. Code, RAB = 50 kΩ
6
–54
–48
–42
–36
–30
–24
–18
–12
–6
0
1k 10k 1M
START 1 000.000Hz STOP 1 000 000.000Hz
REF LEVEL
0dB
/
DI
V
6.0dB MARKE
R
MAG (A/R) 51 404.427H
z
–9.123dB
100k
04422-0-052
GAIN (dB)
T
A
= 25°C
V
DD
= 5.5V
V
A
= 50mV rms
16 STEPS
8 STEPS
4 STEPS
2 STEPS
1 STEP
Figure 24. Gain vs. Frequency vs. Code, RAB = 100 kΩ
AD5228
Rev. A | Page 10 of 20
0
–60
–40
–20
100 1k 10k 100k 1M
04422-0-026
FREQUENCY (Hz)
PSRR (dB)
STEP = MIDSCALE, V
A
= V
DD
, V
B
= 0V
V
DD
= 3V DC
±
10% p-p AC
V
DD
= 5V DC
±
10% p-p AC
04422-0-029
CH1 5.00V CH2 200mV M2.00ms A CH1 2.80V
VW
1
2
PU
T 800.000ms
VDD = 5V
VA = 5V
VB = 0V
Figure 28. Autoscan Increment
Figure 25. PSRR
1.2
0
0.2
0.4
0.6
0.8
1.0
03282420161284
04422-0-030
CODE (Decimal)
THEORETICAL I
WB_MAX
(mA)
04422-0-027
CH1 5.00V CH2 100mV M2.00ms A CH1 3.00V
VW
2
1
PU
T 3.92000ms
Δ: 8.32ms Δ: 4.00mV
@: 8.24ms @: 378mV
VDD = 5V
VA = 5V
VB = 0V
2
RAB = 50k
Ω
RAB = 10k
Ω
RAB = 100k
Ω
VA = OPEN
TA = 25
°
C
Figure 29. Maximum IWB vs. Code
Figure 26. Basic Increment
04422-0-028
CH1 5.00V CH2 100mV M2.00ms A CH1 2.60V
VW
1
2
PU
T 59.8000ms
VDD = 5V
VA = 5V
VB = 0V
Figure 27. Repetitive Increment
AD5228
Rev. A | Page 11 of 20
THEORY OF OPERATION
The AD5228 is a 32-position manual up/down digitally con-
trolled potentiometer with selectable power-on preset. The
AD5228 presets to midscale when the PRE pin is tied to ground
and to zero-scale when PRE is tied to VDD. Floating the PRE pin
is not allowed. The step-up and step-down operations require
the activation of the PU (push-up) and PD (push-down) pins.
These pins have 100 kΩ internal pull-up resistors that the PU
and PD activate at logic low. The common practice is to apply
external pushbuttons (tactile switches) as shown in . Figure 30
04422-0-031
UP/DOWN
CONTROL
LOGIC
DISCRETE
STEP/AUTO
SCAN DETECT
ADAPTIVE
DEBOUNCER ZERO- OR MID-
SCALE PRESET
AD5228
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
R1 R2
D
E
C
O
D
EA
W
B
VDD
PRE GND
PU
PD
Figure 30. Typical Pushbutton Interface
Because of the bounce mechanism commonly found in the
switches during contact closures, a single pushbutton press
usually generates numerous bounces during contact closure.
Note that the term pushbutton refers specifically to a
pushbutton tactile switch or a similar switch that has 10 ms or
less bounce time during contact closure. Figure 31 shows the
characteristics of one such switch, the KRS-3550 tactile switch.
Figure 32 and Figure 33 show close ups of the initial bounces
and end bounces, respectively.
04422-0-032
CH1 1.00V M40.0ms A CH1 2.38V
1
T 20.40%
Figure 31. Typical Tactile Switch Characteristics
04422-0-033
CH1 1.00V M100μs A CH1 2.38V
1
T 20.20%
Figure 32. Close-Up of Initial Bounces
04422-0-034
CH1 1.00V M10.0μs A CH1 2.38V
1
T 20.20%
Figure 33. Close-Up of Final Bounces
The following paragraphs describes the PU incrementing
operation. Similar characteristics apply to the PD decrementing
operation.
The AD5228 features an adaptive debouncer that monitors the
duration of the logic-low level of PU signal between bounces. If
the PU logic-low level signal duration is shorter than 7 ms, the
debouncer ignores it as an invalid incrementing command.
Whenever the logic-low level of PU signal lasts longer than
11 ms, the debouncer assumes that the last bounce is met and
therefore increments RWB by one step.
Repeatedly pressing the PU button for fast adjustment without
missing steps is allowed, provided that each press is not shorter
than tPU, which is 12 ms (see ). As a point of reference,
an advanced video game player can press a pushbutton switch
in 40 ms.
Figure 2
AD5228
Rev. A | Page 12 of 20
If the PU button is held for longer than 1 second, continuously
holding it activates autoscan mode such that the AD5228
increments by four RWB steps per second (see ). Figure 3
Whenever the maximum RWB (= RAB) is reached, RWB stops
incrementing regardless of the state of the PU pin. Any continu-
ous holding of the PU pin to logic-low simply elevates the supply
current.
When both PU and PD buttons are pressed, RWB decrements
until it stops at zero scale.
All the preceding descriptions apply to PD operation. Due to
the tolerance of the internal RC oscillator, all the timing
information given previously is based on the typical values,
which can vary ±30%.
The AD5228 debouncer is carefully designed to handle common
pushbutton tactile switches. Other switches that have excessive
bounces and duration are not suitable to use in conjunction
with the AD5228.
04422-0-035
B
W
A
D0
D2
D1
D4
D3
RS
RS
=
RAB/32
RW
RS
RS
RS
RDAC
UP/DOWN
CTRL AND
DECODE
Figure 34. AD5228 Equivalent RDAC Circuit
PROGRAMMING THE DIGITAL POTENTIOMETERS
Rheostat Operation
If only the W-to-B or W-to-A terminals are used as variable
resistors, the unused terminal can be opened or shorted with W.
Such operation is called rheostat mode and is shown in Figure 35.
04422-0-036
A
W
B
A
W
B
A
W
B
Figure 35. Rheostat Mode Configuration
The end-to-end resistance, RAB, has 32 contact points accessed
by the wiper terminal, plus the B terminal contact if RWB is used.
Pushing the PU pin discretely increments RWB by one step. The
total resistance becomes RS + RW as shown in . The
change of RWB can be determined by the number of discrete
Figure 34
PU
executions provided that its maximum setting is not reached
during operation. ∆RWB can, therefore, be approximated as
⎟
⎠
⎞
⎜
⎝
⎛++=Δ W
AB
WB R
R
PUR 32 (1)
⎟
⎠
⎞
⎜
⎝
⎛+−=Δ W
AB
WB R
R
PDR 32 (2)
where:
PU is the number of push-up executions.
PD is the number of push-down executions.
RAB is the end-to-end resistance.
RW is the wiper resistance contributed by the on-resistance of
the internal switch.
Similar to the mechanical potentiometer, the resistance of the
RDAC between the Wiper W and Terminal A also produces a
complementary resistance, RWA . When these terminals are used,
the B terminal can be opened or shorted to W. RWA can also be
approximated if its maximum and minimum settings are not
reached.
(
)
⎟
⎠
⎞
⎜
⎝
⎛+−−=Δ W
AB
WA R
R
PUR 32
32 3)
(
)
⎟
⎠
⎞
⎜
⎝
⎛+−+=Δ W
AB
WA R
R
PDR 32
32 (4)
Note that Equations 1 to 4 do not apply when PU and PD = 0
execution.
Because in the lowest end of the resistor string, a finite wiper
resistance is present, care should be taken to limit the current
flow between W and B in this state to a maximum pulse current
of no more than 20 mA. Otherwise, degradation or possible
destruction of the internal switches can occur.
The typical distribution of the resistance tolerance from device
to device is process lot dependent, and ±20% tolerance is possible.
AD5228
Rev. A | Page 13 of 20
Potentiometer Mode Operation
If all three terminals are used, the operation is called potenti-
ometer mode. The most common configuration is the voltage
divider operation as shown in Figure 36.
04422-0-037
A
W
B
V
I
V
C
Figure 36. Potentiometer Mode Configuration
The change of VWB is known provided that the AD5228
maximum or minimum scale has not been reached during
operation. If the effect of wiper resistance is ignored, the
transfer functions can be simplified as
AWB V
PU
V32
+=Δ (5)
AWB V
PD
V32
+=Δ (6)
Unlike in rheostat mode operation where the absolute tolerance
is high, potentiometer mode operation yields an almost ratio-
metric function of PU/32 or PD/32 with a relatively small error
contributed by the RW term. The tolerance effect is, therefore,
almost canceled. Although the thin film step resistor RS and
CMOS switch resistance, RW, have very different temperature
coefficients, the ratiometric adjustment also reduces the overall
temperature coefficient effect to 5 ppm/°C except at low value
codes where RW dominates.
Potentiometer mode operations include an op amp input and
feedback resistors network and other voltage scaling applications.
The A, W, and B terminals can be input or output terminals and
have no polarity constraint provided that |VAB|, |VWA |, and |VWB|
do not exceed VDD-to-GND.
CONTROLLING INPUTS
All PU and PD inputs are protected with a Zener ESD structure
as shown in . Figure 37
04422-0-038
V
DD
PU
100kΩDECODE
AND
DEBOUNCE
CKT
Figure 37. Equivalent ESD Protection in PU and PD Pins
PU and PD pins are usually connected to pushbutton tactile
switches for manual operation, but the AD5228 can also be
controlled digitally. It is recommended to add external
MOSFETs or transistors that simplify the logic controls.
04422-0-039
UP/DOWN
CONTROL
LOGIC
DISCRETE
STEP/AUTO
SCAN DETECT
ADAPTIVE
DEBOUNCER ZERO- OR MID-
SCALE PRESET
AD5228
R1 R2
D
E
C
O
D
EA
W
B
V
DD
PRE GND
PU
PD
DOWN
N2
2N7002
UP
N1
2N7002
Figure 38. Digital Control with External MOSFETs
TERMINAL VOLTAGE OPERATION RANGE
The AD5228 is designed with internal ESD diodes for
protection. These diodes also set the voltage boundary of the
terminal operating voltages. Positive signals present on
Terminal A, B, or W that exceed VDD are clamped by the
forward-biased diode. There is no polarity constraint between
VA, VW, and VB, but they cannot be higher than VDD or lower
than GND.
0
4422-0-040
V
DD
GND
A
W
B
Figure 39. Maximum Terminal Voltages Set by VDD and GND
AD5228
Rev. A | Page 14 of 20
LAYOUT AND POWER SUPPLY BIASING
POWER-UP AND POWER-DOWN SEQUENCES
It is always a good practice to use compact, minimum lead
length layout design. The leads to the input should be as direct
as possible with a minimum conductor length. Ground paths
should have low resistance and low inductance. It is also good
practice to bypass the power supplies with quality capacitors.
Low ESR (equivalent series resistance) 1 μF to 10 μF tantalum
or electrolytic capacitors should be applied at the supplies to
minimize any transient disturbance and to filter low frequency
ripple. Figure 39 illustrates the basic supply bypassing configu-
ration for the AD5228.
Because of the ESD protection diodes that limit the voltage
compliance at Terminals A, B, and W (Figure 39), it is
important to power on VDD before applying any voltage to
Terminals A, B, and W. Otherwise, the diodes are forward-
biased such that VDD is powered on unintentionally and can
affect other parts of the circuit. Similarly, VDD should be
powered down last. The ideal power-on sequence is in the
following order: GND, VDD, and VA/B/W. The order of powering
VA, VB, and VW is not important as long as they are powered on
after VDD. The states of the PU and PD pins can be logic high or
floating, but they should not be logic low during power-on.
04422-0-041
V
DD
V
DD
+
GND
AD5228
C2
10μFC1
0.1μF
Figure 40. Power Supply Bypassing
AD5228
Rev. A | Page 15 of 20
APPLICATIONS
MANUAL ADJUSTABLE LED DRIVER
The AD5228 can be used in many electronics-level adjustments
such as LED drivers for LCD panel backlight controls. Figure 41
shows a manually adjustable LED driver. The AD5228 sets the
voltage across the white LED D1 for the brightness control.
Since U2 handles up to 250 mA, a typical white LED with VF of
3.5 V requires a resistor, R1, to limit U2 current. This circuit is
simple but not power efficient. The U2 shutdown pin can be
toggled with a PWM signal to conserve power.
04422-0-042
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
AW
B
10kΩ
V
DD
GNDPRE
PU
PD
U1
AD5228
C1
1μFC2
0.1μF
5V
U2
AD8591
+
–V+
V– SD
5V C3
0.1μF
R1
6ΩWHITE
LED
D1
PWM
Figure 41. Low Cost Adjustable LED Driver
ADJUSTABLE CURRENT SOURCE FOR LED DRIVER
Because LED brightness is a function of current rather than of
forward voltage, an adjustable current source is preferred as
shown in Figure 42. The load current can be found as the VWB
of the AD5228 divided by RSET.
SET
WB
D1 R
V
I= (7)
The U1 ADP3333ARM-1.5 is a 1.5 V LDO that is lifted above
or lowered below 0 V. When VWB of the AD5228 is at its
minimum, there is no current through D1, so the GND pin of U1
is at –1.5 V if U3 is biased with the dual supplies. As a result,
some of the U2 low resistance steps have no effect on the output
until the U1 GND pin is lifted above 0 V. When VWB of the
AD5228 is at its maximum, VOUT becomes VL + VAB, so the U1
supply voltage must be biased with adequate headroom. Similarly,
PWM signal can be applied at the U1 shutdown pin for power
efficiency.
04422-0-043
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
A
W
B
10kΩ
R1
418kΩ
V
DD
GND
PRE
PU
PD
U2
AD5228
5V
5V
U3
AD8591
+
–
V+
V–
5V
PWM
V
IN
V
OUT
GND
U1
ADP3333
ARM-1.5
SD
R
SET
0.1Ω
VL
ID
D1
Figure 42. Adjustable Current Source for LED Driver
ADJUSTABLE HIGH POWER LED DRIVER
The previous circuit works well for a single LED. Figure 43
shows a circuit that can drive three to four high power LEDs.
The ADP1610 is an adjustable boost regulator that provides the
voltage headroom and current for the LEDs. The AD5228 and
the op amp form an average gain of 12 feedback network that
servos the RSET voltage and the ADP1610 FB pin 1.2 V band gap
reference voltage. As the loop is set, the voltage across RSET is
regulated around 0.1 V and adjusted by the digital
potentiometer.
SET
R
LED R
V
ISET
= (8)
RSET should be small enough to conserve power but large enough
to limit maximum LED current. R3 should also be used in par-
allel with AD5228 to limit the LED current within an achievable
range. A wider current adjustment range is possible by lowering
the R2 to R1 ratio as well as changing R3 accordingly.
04422-0-044
SS RT GND
IN
U2
ADP1610
SW
FB
PWM
1.2V
SD
COMP
C
SS
10nF
C
C
390pF
R
C
100kΩ
L1
10μF
D1 C3
10μF
R4
13.5kΩ
D2
D3
D4
V
OUT
C2
10μF
5V
+
–
AD8541
U1
L1–SLF6025-100M1R0
D1–MBR0520LT1
U3
V+
V–
5V
C8
0.1μF
U1
AD5228
BA
10kΩ
R3
200Ω
WR1
100Ω
R2
1.1kΩ
R
SET
0.25Ω
Figure 43. Adjustable Current Source for LEDs in Series
AD5228
Rev. A | Page 16 of 20
AUTOMATIC LCD PANEL BACKLIGHT CONTROL
With the addition of a photocell sensor, an automatic brightness
control can be achieved. As shown in Figure 44, the resistance
of the photocell changes linearly but inversely with the light
output. The brighter the light output, the lower the photocell
resistance and vice versa. The AD5228 sets the voltage level that
is gained up by U2 to drive N1 to a desirable brightness. With
the photocell acting as the variable feedback resistor, the change
in the light output changes the R2 resistance, therefore causing
U2 to drive N1 accordingly to regulate the output. This simple
low cost implementation of an LED controller can compensate
for the temperature and aging effects typically found in high
power LEDs. Similarly, for power efficiency, a PWM signal can
be applied at the gate of N2 to switch the LED on and off
without noticeable effect.
04422-0-045
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
AW
B
10kΩ
V
DD
GNDPRE
PU
PD
U1
AD5228
C1
1μFC2
0.1μF
5V
U2
AD8531
+
–V+
V–
5V C3
0.1μF
R1
1kΩ
R3
4.75kΩ
R2
5V
PWM
N2
2N7002
N1
2N7002
WHITE
LED
D1
5V
PHOTOCELL
Figure 44. Automatic LCD Panel Backlight Control
AUDIO AMPLIFIER WITH VOLUME CONTROL
The AD5228 and SSM2211 can form a 1.5 W audio amplifier
with volume control that has adequate power and quality for
portable devices such as PDAs and cell phones. The SSM2211
can drive a single speaker differentially between Pins 5 and 8
without any output capacitor. The high-pass cutoff frequency is
fH1 = 1/(2 × π × R1 × C1). The SSM2211 can also drive two
speakers as shown in Figure 45. However, the speakers must be
configured in single-ended mode, and output coupling capacitors
are needed to block the dc current. The output capacitor and
the speaker load form an additional high-pass cutoff frequency
as fH2 = 1/(2 × π × R5 × C3). As a result, C3 and C4 must be
large to make the frequency as low as fH1.
04422-0-046
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
AW
B
10kΩ
V
DD
PRE
GND
PU
PD
U1
AUDIO_INPUT
U3
AD8591
+
–
R4
10kΩ
R3
10kΩ
5V
C6
10μFC7
0.1μF
5V
±
2.5V p-p
C1
1μFR1
10kΩ
C2
0.1μF
U2
SSM2211
+
–V+
6
4
3
2718
5
V–
5V
C5
0.1μF
R6
8Ω
R5
8Ω
C3
470μF
C44
470μF
R2
10kΩ
Figure 45. Audio Amplifier with Volume Control
AD5228
Rev. A | Page 17 of 20
3.50
3.40
3.41
3.42
3.43
3.44
3.45
3.46
3.47
3.48
3.49
02468101
04422-0-048
DAYS
BATTERY VOLTAGE (V)
CONSTANT BIAS WITH SUPPLY TO
RETAIN RESISTANCE SETTING
2
TA = 25°C
Users who consider EEMEM potentiometers but cannot justify
the additional cost and programming for their designs can
consider constantly biasing the AD5228 with the supply to
retain the resistance setting as shown in Figure 46. The AD5228
is designed specifically with low power to allow power conser-
vation even in battery-operated systems. As shown in Figure 47,
a similar low power digital potentiometer is biased with a 3.4 V
450 mA/hour Li-Ion cell phone battery. The measurement shows
that the device drains negligible power. Constantly biasing the
potentiometer is a practical approach because most of the
portable devices do not require detachable batteries for charging.
Although the resistance setting of the AD5228 is lost when the
battery needs to be replaced, this event occurs so infrequently
that the inconvenience is minimal for most applications.
Figure 47. Battery Consumption Measurement
04422-0-047
V
DD
AD5228
U1
GND
V
DD
U2
GND
COMPONENT X
V
DD
U3
GND
COMPONENT Y
GND
V
DD
BATTERY OR
SYSTEM POWER
SW1
+
–
Figure 46. Constant Bias AD5228 for Resistance Retention
AD5228
Rev. A | Page 18 of 20
OUTLINE DIMENSIONS
13
56
2
8
4
7
2.90 BSC
PIN 1
INDICATOR
1.60 BSC
1.95
BSC
0.65 BSC
0.38
0.22
0.10 MAX
*0.90
0.87
0.84
SEATING
PLANE
*1.00 MAX 0.20
0.08 0.60
0.45
0.30
8°
4°
0°
2.80 BSC
*COMPLIANT TO JEDEC STANDARDS MO-193-BA WITH
THE EXCEPTION OF PACKAGE HEIGHT AND THICKNESS.
Figure 48. 8-Lead Small Outline Transistor Package [TSOT]
(UJ-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 RAB (kΩ) Temperature Range Package Description Package Option Ordering Quantity Branding
AD5228BUJZ102-RL7 10 −40°C to +105°C 8-Lead TSOT UJ-8 3000 D3K
AD5228BUJZ102-R2 10 −40°C to +105°C 8-Lead TSOT UJ-8 250 D3K
AD5228BUJZ502-RL7 50 −40°C to +105°C 8-Lead TSOT UJ-8 3000 D3L
AD5228BUJZ502-R2 50 −40°C to +105°C 8-Lead TSOT UJ-8 250 D3L
AD5228BUJZ1002-RL7 100 −40°C to +105°C 8-Lead TSOT UJ-8 3000 D3M
AD5228BUJZ1002-R2 100 −40°C to +105°C 8-Lead TSOT UJ-8 250 D3M
EVAL-AD5228EBZ 10 Evaluation Board 1
1 The end-to-end resistance RAB is available in 10 kΩ, 50 kΩ, and 100 kΩ. The final three characters of the part number determine the nominal resistance value, for
example,10 kΩ = 10.
2 Z = RoHS Compliant Part.
AD5228
Rev. A | Page 19 of 20
NOTES
AD5228
Rev. A | Page 20 of 20
NOTES
© 2004–2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04422–0–4/09(A)
