32-Position Manual Up/Down Control
Potentiometer
AD5228
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
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 potentiometer 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.
D
E
C
O
D
E
UP/DOWN
CONTROL
LOGIC
VDD
R1
R2
AD5228
A
W
DISCRETE
STEP/AUTO
SCAN DETECT
B
PUSH-UP
BUTTON
PU
PD
ADAPTIVE
DEBOUNCER
ZERO- OR MIDSCALE PRESET
PUSH-DOWN
BUTTON
PRE
04422-0-001
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
Temperature range, −40°C to +105°C
Compact thin SOT-23-8 (2.9 mm × 3 mm) Pb-free package
GND
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 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
0
0
1
1
PD
0
1
0
1
Operation1
RWB Decrement
RWB Increment
RWB Decrement
RWB Does Not Change
RWA increments if RWB decrements and vice versa.
1
1
The terms digital potentiometer and RDAC are used interchangeably.
Rev. B
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Technical Support
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AD5228
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Terminal Voltage Operation Range ......................................... 13
Applications ....................................................................................... 1
Power-Up and Power-Down Sequences .................................. 14
General Description ......................................................................... 1
Layout and Power Supply Biasing ............................................ 14
Revision History ............................................................................... 2
Applications..................................................................................... 15
Electrical Characteristics ................................................................. 3
Manual Adjustable LED Driver ................................................ 15
Interface Timing Diagrams ......................................................... 4
Adjustable Current Source for LED Driver ............................ 15
Absolute Maximum Ratings............................................................ 5
Adjustable High Power LED Driver ........................................ 15
ESD Caution .................................................................................. 5
Automatic LCD Panel Backlight Control................................ 16
Pin Configuration and Function Descriptions ............................. 6
Audio Amplifier with Volume Control ................................... 16
Typical Performance Characteristics ............................................. 7
Constant Bias with Supply to Retain Resistance Setting ...... 17
Theory of Operation ...................................................................... 11
Outline Dimensions ....................................................................... 18
Programming the Digital Potentiometers ............................... 12
Ordering Guide .......................................................................... 18
Controlling Inputs ...................................................................... 13
REVISION HISTORY
6/15—Rev. A to Rev. B
Changes to Features Section and General Description Section .... 1
Changes to Ordering Guide ........................................................... 18
4/09—Rev. 0 to Rev. A
Changes to Table 2………………………………………………3
4/04—Revision 0: Initial Version
Rev. B | Page 2 of 18
Data Sheet
AD5228
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
Typ1
Max
Unit
DC CHARACTERISTICS, RHEOSTAT MODE
Resistor Differential Nonlinearity2
R-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
+20
%
Nominal Resistor Tolerance
3
∆RAB/RAB
−20
4
Resistance Temperature Coefficient
(∆RAB/RAB) × 10 /∆T
Wiper Resistance
RW
35
ppm/°C
VDD = 2.7 V
100
250
Ω
VDD = 2.8 V to 5.5 V
50
200
Ω
5
Bits
−0.5
±0.05
+0.5
LSB
−0.5
±0.05
+0.5
LSB
DC CHARACTERISTICS, POTENTIOMETER DIVIDER MODE
(Specifications apply to all RDACs)
Resolution
N
Integral Nonlinearity3
INL
Differential Nonlinearity3, 5
DNL
Voltage Divider Temperature Coefficient
4
(∆VW/VW) × 10 /∆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
VA, B, W
With respect to GND
0
VDD
V
Capacitance 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 = V W
1
nA
Input High
VIH
VDD = 5 V
2.4
5.5
V
Input Low
VIL
VDD = 5 V
0
0.8
V
Input Current
II
VIN = 0 V or 5 V
Input Capacitance4
CI
RESISTOR TERMINALS
Voltage Range6
4
PU, PD INPUTS
±1
5
μA
pF
POWER SUPPLIES
Power Supply Range
VDD
Supply Standby Current
Supply Active Current
7
7, 8
VDD = 5 V, PU = PD = VDD
IDD_STBY
IDD_ACT
VDD = 5 V, PU or PD = 0 V
Power Dissipation
PDISS
VDD = 5 V
Power Supply Sensitivity
PSSR
VDD = 5 V ± 10%
Footnotes on next page.
Rev. B | Page 3 of 18
2.7
5.5
V
0.4
3
μA
50
110
μA
17
μW
0.01
0.05
%/%
AD5228
Data Sheet
Parameter
Symbol
DYNAMIC CHARACTERISTICS 4, 9, 10, 11
Built-in Debounce and Settling Time 12
PU Low Pulse Width
PD Low Pulse Width
PU High Repetitive Pulse Width
PD High Repetitive Pulse Width
Autoscan Start Time
Autoscan Time
Bandwidth –3 dB
Total Harmonic Distortion
tDB
tPU
tPD
tPU_REP
tPD_REP
tAS_START
tAS
BW_10
BW_50
BW_100
THD
Resistor Noise Voltage
eN_WB
Conditions
Min
6
12
12
1
1
0.6
0.16
PU or PD = 0 V
PU or PD = 0 V
RAB = 10 kΩ, midscale
RAB = 50 kΩ, midscale
RAB = 100 kΩ, midscale
VA = 1 V rms, RAB = 10 kΩ,
VB = 0 V dc, f = 1 kHz
RWB = 5 kΩ, f = 1 kHz
Typ1
0.8
0.25
460
100
50
0.05
Max
1.2
0.38
14
Unit
ms
ms
ms
μs
μs
s
s
kHz
kHz
kHz
%
nV/√Hz
1
Typicals represent average readings at 25°C, VDD = 5 V.
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.
2
INTERFACE TIMING DIAGRAMS
tPD
tPU_REP
PU
tDB
RWB
tPD_REP
tDB
04422-0-006
04422-0-004
tPU
PU
RWB
Figure 2. Increment RWB in Discrete Steps
Figure 4. Decrement RWB in Discrete Steps
RWB
tAS
tDB
04422-0-005
tAS_START
tAS_START
tDB
tAS
RWB
Figure 3. Increment RWB in Autoscan Mode
Figure 5. Decrement RWB in Autoscan Mode
Rev. B | Page 4 of 18
04422-0-007
PD
PU
Data Sheet
AD5228
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter
VDD to GND
VA, VB, VW to GND
PU, PD, PRE Voltage to GND
Maximum Current
IWB, IWA Pulsed
IWB Continuous (RWB ≤ 5 kΩ, A open)1
IWA Continuous (RWA ≤ 5 kΩ, B open)1
IAB Continuous
(RAB = 10 kΩ/50 kΩ/100 kΩ)1
Operating Temperature Range
Maximum Junction Temperature
(TJmax)
Storage Temperature
Lead Temperature
(Soldering, 10 s – 30 s)
Thermal Resistance2 θJA
Rating
−0.3 V, +7 V
0 V, VDD
0 V, VDD
±20 mA
±1 mA
±1 mA
±500 μA/±100 μA/
±50 μA
−40°C to +105°C
150°C
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
ESD CAUTION
−65°C to +150°C
245°C
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.
Rev. B | Page 5 of 18
AD5228
Data Sheet
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
8
VDD
PD 2
7
PRE
6
B
5
W
A 3
GND 4
AD5228
04422-0-003
PU 1
Figure 6. SOT-23-8 Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
1
Mnemonic
PU
2
PD
3
4
5
6
7
A
GND
W
B
PRE
8
VDD
Description
Push-Up Pin.
Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to VDD.
Push-Down Pin.
Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to VDD.
Resistor Terminal A. GND ≤VA ≤ VDD.
Common Ground.
Wiper Terminal W. GND ≤ VW ≤ VDD.
Resistor Terminal B. GND ≤ VB ≤ VDD.
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.
Positive Power Supply, 2.7 V to 5.5 V.
Rev. B | Page 6 of 18
Data Sheet
AD5228
TYPICAL PERFORMANCE CHARACTERISTICS
0.10
0.10
TA = 25C
RHEOSTAT MODE DNL (LSB)
5.5V
0.04
2.7V
0.02
0
–0.02
–0.04
–0.06
04422-0-008
–0.08
0
4
8
12
16
20
CODE (Decimal)
24
28
0.06
0.04
0.02
0
–0.02
–0.04
–0.06
–0.08
–0.10
32
Figure 7. R-INL vs. Code vs. Supply Voltages
8
12
16
20
CODE (Decimal)
24
TA = 25C
0.04
0.02
0
–0.02
–0.04
04422-0-009
–0.06
–0.08
0
4
8
12
16
20
CODE (Decimal)
24
28
0.06
2.7V
0.04
0.02
5.5V
0
–0.02
–0.04
–0.06
–0.08
–0.10
32
0
Figure 8. R-INL vs. Code vs. Temperature, VDD = 5 V
4
8
12
16
20
CODE (Decimal)
24
28
32
Figure 11. INL vs. Code vs. Supply Voltages
0.10
0.10
–40C
+25C
+85C
+105C
VDD = 5.5V
TA = 25C
0.08
0.04
2.7V
5.5V
0.02
0
–0.02
–0.04
04422-0-010
–0.06
–0.08
0
4
8
12
16
20
CODE (Decimal)
24
28
32
0.06
0.04
0.02
0
–0.02
–0.04
–0.06
04422-0-013
0.06
POTENTIOMETER MODE INL (LSB)
0.08
RHEOSTAT MODE DNL (LSB)
32
0.08
POTENTIOMETER MODE INL (LSB)
0.06
–0.10
28
0.10
–40C
+25C
+85C
+105C
VDD = 5.5V
0.08
RHEOSTAT MODE INL (LSB)
4
Figure 10. R-DNL vs. Code vs. Temperature, VDD = 5 V
0.10
–0.10
0
04422-0-012
RHEOSTAT MODE INL (LSB)
0.06
–0.10
–40C
+25C
+85C
+105C
VDD = 5.5V
0.08
04422-0-011
0.08
–0.08
–0.10
Figure 9. R-DNL vs. Code vs. Supply Voltages
0
4
8
12
16
20
CODE (Decimal)
24
Figure 12. INL vs. Code, VDD = 5 V
Rev. B | Page 7 of 18
28
32
AD5228
Data Sheet
0.50
0.10
0.08
0.45
0.06
0.40
0.04
ZSE (LSB)
0.02
0
–0.02
–0.04
0.30
0.25
VDD = 5.5V
0.20
0.15
2.7V
–0.08
0
4
8
12
16
20
CODE (Decimal)
24
28
0.05
0
–40
32
Figure 13. DNL vs. Code vs. Supply Voltages
0
80
100
0.02
0
–0.02
–0.04
04422-0-015
–0.06
4
8
12
16
20
CODE (Decimal)
24
28
0.1
–40
32
Figure 14. DNL vs. Code, VDD = 5 V
–20
0
80
100
Figure 17. Supply Current vs. Temperature
–0.50
120
RAB = 100k
NOMINAL RESISTANCE RAB (k)
–0.55
–0.60
–0.65
VDD = 5.5V
–0.70
–0.75
VDD = 2.7V
04422-0-016
–0.80
–0.85
–0.90
–40
20
40
60
TEMPERATURE (C)
–20
0
20
40
60
TEMPERATURE (C)
80
80
60
Figure 15. Full-Scale Error vs. Temperature
RAB = 50k
40
20
0
–40
100
VDD = 5.5V
100
04422-0-019
0
04422-0-018
0.04
SUPPLY STANDBY CURRENT (A)
0.06
VDD = 5.5V
IDD_ACT = 50A TYP
–0.08
FSE (LSB)
20
40
60
TEMPERATURE (C)
1
–40C
+25C
+85C
+105C
VDD = 5.5V
0.08
POTENTIOMETER MODE DNL (LSB)
–20
Figure 16. Zero-Scale Error vs. Temperature
0.10
–0.10
04422-0-017
0.10
–0.06
–0.10
VDD = 2.7V
0.35
5.5V
04422-0-014
POTENTIOMETER MODE DNL (LSB)
TA = 25C
RAB = 10k
–20
0
20
40
60
TEMPERATURE (C)
80
Figure 18. Nominal Resistance vs. Temperature
Rev. B | Page 8 of 18
100
Data Sheet
AD5228
120
6
REF LEVEL
0dB
MARKER 469 390.941Hz
MAG (A/R) –8.966dB
/DIV
6.0dB
TA = 25C
VDD = 5.5V
VA = 50mV rms
VDD = 2.7V
0
16 STEPS
–6
8 STEPS
80
–12
4 STEPS
GAIN (dB)
60
VDD = 5.5V
40
–18
2 STEPS
–24
1 STEP
–30
–36
0
–40
04422-0-020
20
–20
0
20
40
60
TEMPERATURE (C)
80
–42
04422-0-050
WIPER RESISTANCE, RW ()
100
–48
100
–54
1k
100k
10k
START 1 000.000Hz
Figure 19. Wiper Resistance vs. Temperature
Figure 22. Gain vs. Frequency vs. Code, RAB = 10 kΩ
10k
50k
100k
VDD = 5.5V
A = OPEN
120
6
REF LEVEL
0dB
MARKER 97 525.233Hz
MAG (A/R) –9.089dB
/DIV
6.0dB
TA = 25C
VDD = 5.5V
VA = 50mV rms
0
16 STEPS
–6
90
8 STEPS
GAIN (dB)
–12
60
30
4 STEPS
–18
2 STEPS
–24
1 STEP
–30
–36
–30
0
4
8
12
16
20
CODE (Decimal)
24
28
–42
04422-0-051
0
04422-0-021
RHEOSTAT MODE TEMPCO, RWB/T (ppm/C)
150
–48
32
–54
1k
100k
10k
START 1 000.000Hz
Figure 20. Rheostat Mode Tempco ΔRWB/ΔT vs. Code
20
10k
50k
100k
VDD = VA = 5.5V
VB = 0V
15
10
6
REF LEVEL
0dB
MARKER 51 404.427Hz
MAG (A/R) –9.123dB
/DIV
6.0dB
TA = 25C
VDD = 5.5V
VA = 50mV rms
0
16 STEPS
–6
8 STEPS
–12
GAIN (dB)
5
0
–5
–10
4 STEPS
–18
2 STEPS
–24
1 STEP
–30
–36
–42
0
4
8
12
16
20
CODE (Decimal)
24
28
04422-0-052
–15
–20
1M
STOP 1 000 000.000Hz
Figure 23. Gain vs. Frequency vs. Code, RAB = 50 kΩ
04422-0-022
POTENTIOMETER MODE TEMPCO, VWB/T (ppm/C)
1M
STOP 1 000 000.000Hz
–48
32
–54
1k
START 1 000.000Hz
Figure 21. Potentiometer Mode Tempco ΔVWB/ΔT vs. Code
10k
100k
1M
STOP 1 000 000.000Hz
Figure 24. Gain vs. Frequency vs. Code, RAB = 100 kΩ
Rev. B | Page 9 of 18
AD5228
Data Sheet
0
STEP = MIDSCALE, VA = VDD, VB = 0V
PU
1
PSRR (dB)
–20
VDD = 5V DC 10% p-p AC
VW
VDD = 3V DC 10% p-p AC
–40
1k
10k
FREQUENCY (Hz)
100k
04422-0-029
04422-0-026
–60
100
VDD = 5V
VA = 5V
VB = 0V
2
CH1 5.00V
1M
CH2 200mV
M2.00ms
A CH1
T
800.000ms
2.80V
Figure 28. Autoscan Increment
Figure 25. PSRR
1.2
: 8.32ms : 4.00mV
VA = OPEN
TA = 25C
@: 8.24ms @: 378mV
VW
VDD = 5V
VA = 5V
VB = 0V
THEORETICAL IWB_MAX (mA)
PU
1
1.0
CH1 5.00V
CH2 100mV
M2.00ms
A CH1
T
3.92000ms
0
4
8
04422-0-030
12
16
20
CODE (Decimal)
24
Figure 29. Maximum IWB vs. Code
PU
VW
VDD = 5V
VA = 5V
VB = 0V
04422-0-028
CH2 100mV
0.4
0
3.00V
1
CH1 5.00V
RAB = 50k
RAB = 100k
Figure 26. Basic Increment
2
0.6
0.2
04422-0-027
2
RAB = 10k
0.8
M2.00ms
A CH1
T
59.8000ms
2.60V
Figure 27. Repetitive Increment
Rev. B | Page 10 of 18
28
32
Data Sheet
AD5228
THEORY OF OPERATION
The AD5228 is a 32-position manual up/down digitally controlled 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.
R1
R2
D
E
C
O
D
E
04422-0-033
UP/DOWN
CONTROL
LOGIC
VDD
1
AD5228
CH1 1.00V
A
M100s
T 20.20%
A CH1
2.38V
Figure 32. Close-Up of Initial Bounces
W
DISCRETE
STEP/AUTO
SCAN DETECT
B
PUSH-UP
BUTTON
PU
ADAPTIVE
DEBOUNCER
ZERO- OR MIDSCALE PRESET
04422-0-031
PD
PUSH-DOWN
BUTTON
PRE
GND
Figure 30. Typical Pushbutton Interface
1
04422-0-034
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.
CH1 1.00V
M10.0s
T 20.20%
A CH1
2.38V
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.
04422-0-032
1
CH1 1.00V
M40.0ms
T 20.40%
A CH1
2.38V
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 Figure 2). As a point of reference,
an advanced video game player can press a pushbutton switch
in 40 ms.
Figure 31. Typical Tactile Switch Characteristics
Rev. B | Page 11 of 18
AD5228
Data Sheet
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 continuous holding of the PU pin to logic-low simply elevates the supply
current.
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 Figure 34. The
change of RWB can be determined by the number of discrete PU
executions provided that its maximum setting is not reached
during operation. ∆RWB can, therefore, be approximated as
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.
A
RS
RS
RS = RAB/32
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.
W
B
A
W
B
W
B
04422-0-036
A
3)
(4)
R
RWA 32 PD AB RW
32
Figure 34. AD5228 Equivalent RDAC Circuit
A
R
RWA 32 PU AB RW
32
04422-0-035
B
(2)
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.
W
RS
R
RWB PD AB RW
32
where:
RW
RDAC
UP/DOWN
CTRL AND
DECODE
(1)
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.
RS
D0
D1
D2
D3
D4
R
RWB PU AB RW
32
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.
Figure 35. Rheostat Mode Configuration
Rev. B | Page 12 of 18
Data Sheet
AD5228
Potentiometer Mode Operation
CONTROLLING INPUTS
If all three terminals are used, the operation is called potentiometer mode. The most common configuration is the voltage
divider operation as shown in Figure 36.
All PU and PD inputs are protected with a Zener ESD structure
as shown in Figure 37.
VI
VDD
A
Figure 36. Potentiometer Mode Configuration
Figure 37. Equivalent ESD Protection in PU and PD Pins
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
VWB
PU
VA
32
PD
VA
32
(5)
(6)
R1
Unlike in rheostat mode operation where the absolute tolerance
is high, potentiometer mode operation yields an almost ratiometric 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.
D
E
C
O
D
E
UP/DOWN
CONTROL
LOGIC
VDD
R2
AD5228
A
W
DISCRETE
STEP/AUTO
SCAN DETECT
B
PU
N1
UP
2N7002
PD
ADAPTIVE
DEBOUNCER
ZERO- OR MIDSCALE PRESET
N2
DOWN
PRE
GND
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.
VDD
A
W
B
GND
Figure 39. Maximum Terminal Voltages Set by VDD and GND
Rev. B | Page 13 of 18
04422-0-039
VWB
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.
04422-0-040
B
DECODE
AND
DEBOUNCE
CKT
PU
04422-0-037
W
04422-0-038
100k
VC
AD5228
Data Sheet
POWER-UP AND POWER-DOWN SEQUENCES
LAYOUT AND POWER SUPPLY BIASING
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 forwardbiased 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.
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 configuration for the AD5228.
AD5228
VDD
+
C2
10F
C1
0.1F
VDD
04422-0-041
GND
Figure 40. Power Supply Bypassing
Rev. B | Page 14 of 18
Data Sheet
AD5228
APPLICATIONS
MANUAL ADJUSTABLE LED DRIVER
ADJUSTABLE HIGH POWER 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.
C2
0.1F
V+
U1
AD5228
VDD
PUSH-UP
BUTTON
PD
I LED
–
U2
AD8591
R1
SD 6
W
+
10k
PU
PUSH-DOWN
BUTTON
A
C3
0.1F
B
PRE
PWM
GND
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.
I D1
VWB
R SET
VIN
5V
C2
10F
R4
13.5k
U2
IN
L1
10F
ADP1610
PWM
SD
1.2V
FB
COMP
RC
100k
CC
390pF
SS
VOUT
SW
D1
C3
10F
RT GND
D2
CSS
10nF
D3
C8
5V
0.1F
D4
U3
V+
+
AD8541
U1
RSET
0.25
–
U1
V–
L1–SLF6025-100M1R0
D1–MBR0520LT1
AD5228
R2
1.1k
W
B
A
R1
100
10k
VOUT
U1
AD5228
ARM-1.5
SD
GND
R3
200
U2
ADP3333
5V
Figure 43. Adjustable Current Source for LEDs in Series
VDD
PRE
B
PUSH-UP
BUTTON
W
10k
A
PU
PD
PUSH-DOWN
BUTTON
GND
RSET
0.1
R1
418k
5V
V+
–
U3
AD8591
V–
+
VL
D1
ID
04422-0-043
PWM
(8)
RSET
(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.
5V
VRSET
RSET should be small enough to conserve power but large enough
to limit maximum LED current. R3 should also be used in parallel 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.
WHITE
LED
D1
V–
04422-0-042
C1
1F
5V
Figure 42. Adjustable Current Source for LED Driver
Rev. B | Page 15 of 18
04422-0-044
5V
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.
AD5228
Data Sheet
AUTOMATIC LCD PANEL BACKLIGHT CONTROL
AUDIO AMPLIFIER WITH VOLUME 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.
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.
5V
5V
C6
10F
R2
10k
U1
VDD
C7
0.1F
C5 5V
0.1F
PRE
C3
470F
R2
R1
1k
D1
PHOTOCELL
5V
5V
PUSH-UP
BUTTON
WHITE
LED
C3
0.1F
A
PD
C2
0.1F
PUSH-UP
BUTTON
U1
AD5228
VDD
PUSH-DOWN
BUTTON
R3
4.75k
U2
N1
2N7002
W
5V
+
V–
R3
10k
B
PRE
N2
GND
B
–
6
V+
U2
5
+
V–
8
1
7
C2
0.1F
–
2N7002
Rev. B | Page 16 of 18
R6
8
U3
R4
10k
Figure 44. Automatic LCD Panel Backlight Control
C44
470F
AD8591
+
PWM
R5
8
SSM2211
3
GND
2
AD8531
10k
PU
PD
A
V+
–
04422-0-045
C1
1F
4
10k
PU
PUSH-DOWN
BUTTON
W
C1 R1
1F 10k
Figure 45. Audio Amplifier with Volume Control
04422-0-046
5V
2.5V p-p
AUDIO_INPUT
Data Sheet
AD5228
VDD
U1
SW1
BATTERY OR
SYSTEM POWER
VDD
U3
VDD
VDD
COMPONENT X
COMPONENT Y
GND
GND
+
GND
–
GND
Figure 46. Constant Bias AD5228 for Resistance Retention
3.50
TA = 25C
3.49
3.48
BATTERY VOLTAGE (V)
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 conservation 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.
U2
AD5228
04422-0-047
CONSTANT BIAS WITH SUPPLY TO
RETAIN RESISTANCE SETTING
3.47
3.46
3.45
3.44
3.43
04422-0-048
3.42
3.41
3.40
0
2
4
6
DAYS
8
10
Figure 47. Battery Consumption Measurement
Rev. B | Page 17 of 18
12
AD5228
Data Sheet
OUTLINE DIMENSIONS
2.90 BSC
8
7
6
5
1
2
3
4
2.80 BSC
1.60 BSC
PIN 1
INDICATOR
0.65 BSC
1.95
BSC
*0.90
0.87
0.84
*1.00 MAX
0.10 MAX
0.38
0.22
0.20
0.08
SEATING
PLANE
8°
4°
0°
0.60
0.45
0.30
*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, 2
AD5228BUJZ10-RL7
AD5228BUJZ10-R2
AD5228BUJZ50-RL7
AD5228BUJZ100-RL7
AD5228BUJZ100-R2
EVAL-AD5228DBZ
1
2
RAB (kΩ)
10
10
50
100
100
10
Temperature Range
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
−40°C to +105°C
Package Description
8-Lead TSOT
8-Lead TSOT
8-Lead TSOT
8-Lead TSOT
8-Lead TSOT
Evaluation Board
Package Option
UJ-8
UJ-8
UJ-8
UJ-8
UJ-8
Ordering Quantity
3000
250
3000
3000
250
1
Branding
D3K
D3K
D3L
D3M
D3M
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.
Z = RoHS Compliant Part.
©2004–2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D04422-0-6/15(B)
Rev. B | Page 18 of 18
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