Datasheet AD5228 Datasheet (Analog Devices)

32-Position Manual Up/Down Control

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, I 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 potentiometer operation 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 term s digital potentiometer and RDAC are used interchangeably.

= 0.4 µA typ and 3 µA max

DD

1

. Its simple up/down control interface allows

Potentiometer

AD5228

FUNCTIONAL BLOCK DIAGRAM

D

UP/DOWN CONTROL

LOGIC

DISCRETE

STEP/AUTO

SCAN DETECT

ADAPTIVE

DEBOUNCER

Figure 1.

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

V

DD

R1 R2

PU

PD

The AD5228 can increment or decrement the resistance in discrete steps or in autoscan mode. When the

is pressed briefly (no longer than 0.6 s), the resistance of the AD5228 changes by one step. When the

PU

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

Operation1

PD

0 0 RWB Decrement 0 1 RWB Increment 1 0 RWB Decrement 1 1 RWB Does Not Change

1

RWA increments if RWB decrements and vice versa.

AD5228

E C O D E

ZERO- OR MID-

SCALE PRESET

PRE GND

or PD button

PU

A

W

B

or PD button is held

04422-0-001

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 that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

AD5228

TABLE OF CONTENTS

Electrical Characteristics ................................................................. 3

Power-Up and Power-Down Sequences.................................. 14

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

REVISION HISTORY

Revision 0: Initial Version

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

Rev. 0 | Page 2 of 20

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

Nominal Resistor Tolerance3 ∆RAB/RAB −20 +20 %

Resistance Temperature Coefficient (∆RAB/RAB) × 104/∆T 35 ppm/°C

Wiper Resistance RW V

V

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 Nonlinearity

3, 5

DNL −0.5 ±0.05 +0.5 LSB

Voltage Divider Temperature Coefficient (∆VW/VW) × 104/∆T Midscale 5 ppm/°C

Full-Scale Error V

Zero-Scale Error V

≥+15 steps from midscale −1 −0.5 0 LSB

WFSE

≤−16 steps from midscale 0 0.3 0.5 LSB

WZSE

RESISTOR TERMINALS

Voltage Range6 V

Capacitance4 A, B C

With respect to GND 0 VDD V

A, B, W

f = 1 MHz, measured to GND 140 pF

A, B

Capacitance4 W CW f = 1 MHz, measured to GND 150 pF

Common-Mode Leakage ICM V

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

Input Capacitance4 C

5 pF

I

POWER SUPPLIES

Power Supply Range VDD

Supply Standby Current I

Supply Active Current7 I

Power Dissipation

7, 8

P

0.4 3 µA

DD_STBY

DD_ACT

V

DISS

Power Supply Sensitivity PSSR VDD = 5 V ± 10% 0.01 0.05 %/%

Footnotes on next page.

= 2.7 V 100 200 Ω

DD

= 5.5 V 50 Ω

DD

= VB = VW 1 nA

A

= 0 V or 5 V ±1 µA

IN

= 5 V, PU = PD = VDD

V

DD

= 5 V, PU or PD = 0 V

V

DD

= 5 V 17 µW

DD

2.7 5.5 V

50 110 µA

Rev. 0 | Page 3 of 20

AD5228

Parameter Symbol Conditions Min Typ1 Max Unit

DD_STBY

4, 9, 10, 11

6 ms

DB

t

12 ms

PU

t

12 ms

PD

t

1 µs

PU_REP

t

1 µs

PD_REP

0.6 0.8 1.2 s

0.16 0.25 0.38 s

0.05 %

nV/√Hz

× VDD only. I

AS_START

R

N_WB

= VDD/100 kΩ + I

DD_ACT

duration should be short. Users should not hold PU or PD pin to ground longer than necessary to elevate power

DD_ACT

(internal oscillator operating current) when PU or PD is connected to ground.

OSC

or PD = 0 V

PU

or PD = 0 V

PU

= 1 V rms, RAB = 10 kΩ,

V

A

V

= 0 V dc, f = 1 kHz

B

= 5 kΩ, f = 1 kHz 14

WB

, the AD5528 increments again, see Figure 7. Similar

AS_START

DYNAMIC CHARACTERISTICS

Built-in Debounce and Settling Time 12 t

PU Low Pulse Width

PD Low Pulse Width

PU High Repetitive Pulse Width

PD High Repetitive Pulse Width

Autoscan Start Time t

Autoscan Time tAS

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

Resistor Noise Voltage e

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, I

8

P

is calculated based on I

DISS

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 t characteristics apply to PD operation.

INTERFACE TIMING DIAGRAMS

t

PU

R

WB

PU

R

WB

PU

t

PU_REP

t

DB

Figure 2. Increment R

t

AS_START

t

DB

t

AS

Figure 3. Increment R

in Discrete Steps

WB

in Autoscan Mode

WB

04422-0-004

04422-0-005

Rev. 0 | Page 4 of 20

t

PU

R

WB

PD

t

PD_REP

t

DB

Figure 4. Decrement R

in Discrete Steps

WB

04422-0-006

PD

t

AS_START

t

R

WB

DB

Figure 5. Decrement R

t

AS

04422-0-007

in Autoscan Mode

WB

AD5228

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

VDD to GND −0.3 V, +7 V VA, VB, VW to GND 0 V, VDD

0 V, V

PU, PD, PRE Voltage to GND

DD

Maximum Current

IWB, IWA Pulsed ±20 mA IWB Continuous (R

≤ 5 kΩ, A open)1 ±1 mA

WB

IWA Continuous (RWA ≤ 5 kΩ, B open)1 ±1 mA IAB Continuous

= 10 kΩ/50 kΩ/100 kΩ)1

(R

AB

±500 µA/±100 µA/

±50 µA Operating Temperature Range −40°C to +105°C Maximum Junction Temperature

(T

max)

J

150°C

Storage Temperature −65°C to +150°C Lead Temperature

245°C (Soldering, 10 s – 30 s)

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.

Rev. 0 | Page 5 of 20

AD5228

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

PU

1

PD

2

A

3 4

GND

Figure 6. SOT-23-8 Pin Configuration

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1

Push-Up Pin.

PU

Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to V

2

Push-Down Pin.

PD

Connect to the external pushbutton. Active low. A 100 kΩ pull-up resistor is connected to V 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 = V

No pull-up resistor is needed. 8 VDD Positive Power Supply, 2.7 V to 5.5 V.

AD5228

V

8

DD

PRE

7

B

6 5

W

04422-0-003

.

DD

.

DD

. Do not let the PRE pin float.

DD

Rev. 0 | Page 6 of 20

AD5228

TYPICAL PERFORMANCE CHARACTERISTICS

0.10

0.08

0.06

0.04

0.02

0

–0.02

–0.04

RHEOSTAT MODE INL (LSB)

–0.06

–0.08

–0.10

032282420161284

CODE (Decimal)

Figure 7. R-INL vs. Code vs. Supply Voltages

0.10

0.08

0.06

0.04

0.02

0

–0.02

–0.04

RHEOSTAT MODE INL (LSB)

–0.06

–0.08

–0.10

032282420161284

CODE (Decimal)

Figure 8. R-INL vs. Code vs. Temperature, V

0.10

0.08

0.06

–0.02

–0.04

RHEOSTAT MODE DNL (LSB)

–0.06

–0.08

–0.10

0.04

0.02

0

032282420161284

2.7V

CODE (Decimal)

Figure 9. R-DNL vs. Code vs. Supply Voltages

2.7V

5.5V

TA = 25°C

–40°C +25°C +85°C +105°C

VDD = 5.5V

= 5 V

DD

TA = 25°C

04422-0-008

04422-0-009

04422-0-010

0.10

0.08

0.06

0.04

0.02

0

–0.02

–0.04

RHEOSTAT MODE DNL (LSB)

–0.06

–0.08

–0.10

032282420161284

CODE (Decimal)

Figure 10. R-DNL vs. Code vs. Temperature, V

0.10

0.08

0.06

0.04

–0.02

–0.04

–0.06

POTENTIOMETER MODE INL (LSB)

–0.08

–0.10

0.02

0

5.5V

032282420161284

CODE (Decimal)

Figure 11. INL vs. Code vs. Supply Voltages

0.10

0.08

0.06

0.04

0.02

0

–0.02

–0.04

–0.06

POTENTIOMETER MODE INL (LSB)

–0.08

–0.10

032282420161284

CODE (Decimal)

Figure 12. INL vs. Code, V

DD

= 5 V

–40°C +25°C +85°C +105°C

VDD = 5.5V

= 5 V

DD

TA = 25°C

2.7V

–40°C +25°C +85°C +105°C

VDD = 5.5V

04422-0-011

04422-0-012

04422-0-013

Rev. 0 | Page 7 of 20

AD5228

–

0.10

0.08

0.06

–0.02

–0.04

–0.06

POTENTIOMETER MODE DNL (LSB)

–0.08

–0.10

–0.02

–0.04

–0.06

POTENTIOMETER MODE DNL (LSB)

–0.08

–0.10

–0.55

–0.60

–0.65

–0.70

FSE (LSB)

–0.75

–0.80

–0.85

–0.90

0.04

0.02

0

0.10

0.08

0.06

0.04

0.02

0

0.50

5.5V

032282420161284

CODE (Decimal)

Figure 13. DNL vs. Code vs. Supply Voltages

032282420161284

CODE (Decimal)

Figure 14. DNL vs. Code, V

VDD = 5.5V

= 2.7V

V

DD

–40 –20 0 20 40 60 10080

TEMPERATURE (°C)

Figure 15. Full-Scale Error vs. Temperature

DD

= 5 V

TA = 25°C

–40°C +25°C +85°C +105°C

VDD = 5.5V

2.7V

04422-0-014

04422-0-015

04422-0-016

0.50

0.45

0.40 = 2.7V

0.35

0.30

0.25

ZSE (LSB)

0.20

0.15

0.10

0.05

0

–40 –20 0 20 40 60 10080

V

DD

VDD = 5.5V

TEMPERATURE (°C)

Figure 16. Zero-Scale Error vs. Temperature

1

A)

µ

SUPPLY STANDBY CURRENT (

0.1 –40 –20 0 20 40 60 10080

TEMPERATURE (°C)

Figure 17. Supply Current vs. Temperature

120

100

(kΩ)

AB

80

60

40

NOMINAL RESISTANCE R

20

0

–40 –20 0 20 40 60 10080

RAB = 100kΩ

R

= 50kΩ

AB

R

= 10kΩ

AB

TEMPERATURE (°C)

Figure 18. Nominal Resistance vs. Temperature

VDD = 5.5V I

DD_ACT

VDD = 5.5V

04422-0-017

= 50µA TYP

04422-0-018

04422-0-019

Rev. 0 | Page 8 of 20

AD5228

/DIV

R

z

/DIV

R

z

/DIV

R

z

120

VDD = 2.7V

100

(Ω)

W

80

60

V

= 5.5V

DD

40

WIPER RESISTANCE, R

20

0

–40 –20 0 20 40 60 10080

TEMPERATURE (°C)

Figure 19. Wiper Resistance vs. Temperature

150

120

T (ppm/°C)

∆

/

WB

90

R

∆

60

30

0

RHEOSTAT MODE TEMPCO,

–30

0 4 8 121620242832

CODE (Decimal)

Figure 20. Rheostat Mode Tempco ∆R

/∆T vs. Code

WB

20

C)

°

15

T (ppm/

∆

/

10

WB

V

∆

5

0

–5

–10

–15

POTENTIOMETER MODE TEMPCO,

–20

0 4 8 12 16 20 24 28 32

CODE (Decimal)

VDD = VA = 5.5V

= 0V

V

B

10kΩ 50kΩ 100kΩ

VDD = 5.5V A = OPEN

10kΩ 50kΩ 100kΩ

04422-0-020

04422-0-021

04422-0-022

REF LEVEL 0dB

6

6.0dB

0

–6

–12

–18

–24

GAIN (dB)

–30

16 STEPS

8 STEPS

4 STEPS

2 STEPS

1 STEP

MARKE MAG (A/R)

TA = 25°C V

DD

= 50mV rms

V

A

–36

–42

–48

–54

1k 10k 1M

START 1 000.000Hz STOP 1 000 000.000Hz

Figure 22. Gain vs. Frequency vs. Code, R

100k

= 10 kΩ

AB

REF LEVEL 0dB

6

6.0dB

0

–6

–12

–18

–24

GAIN (dB)

–30

16 STEPS

8 STEPS

4 STEPS

2 STEPS

1 STEP

–36

–42

–48

–54

1k 10k 1M

START 1 000.000Hz STOP 1 000 000.000Hz

Figure 23. Gain vs. Frequency vs. Code, R

MARKE MAG (A/R)

100k

TA = 25°C V

DD

= 50mV rms

V

A

= 50 kΩ

AB

REF LEVEL 0dB

6

6.0dB

0

–6

–12

–18

–24

GAIN (dB)

–30

16 STEPS

8 STEPS

4 STEPS

2 STEPS

1 STEP

–36

–42

–48

–54

1k 10k 1M

START 1 000.000Hz STOP 1 000 000.000Hz

MARKE MAG (A/R)

100k

TA = 25°C V

DD

= 50mV rms

V

A

469 390.941H –8.966dB

= 5.5V

97 525.233H –9.089dB

= 5.5V

51 404.427H –9.123dB

= 5.5V

04422-0-050

04422-0-051

04422-0-052

Figure 21. Potentiometer Mode Tempco ∆V

/∆T vs. Code

WB

Figure 24. Gain vs. Frequency vs. Code, R

= 100 kΩ

AB

Rev. 0 | Page 9 of 20

AD5228

0

–20

STEP = MIDSCALE, VA = VDD, VB = 0V

PU

1

VDD= 5V DC±10% p-p AC

PSRR (dB)

VDD= 3V DC±10% p-p AC

–40

–60

100 1k 10k 100k 1M

FREQUENCY (Hz)

Figure 25. PSRR

∆: 8.32ms ∆: 4.00mV

@: 8.24ms @: 378mV

1

VDD = 5V

= 5V

V

A

= 0V

V

B

2

CH1 5.00V CH2 100mV M2.00ms A CH1 3.00V

T 3.92000ms

Figure 26. Basic Increment

PU

V

W

04422-0-027

04422-0-026

VDD = 5V V

A

V

2

CH1 5.00V CH2 200mV M2.00ms A CH1 2.80V

T 800.000ms

B

Figure 28. Autoscan Increment

1.2

1.0

(mA)

0.8

WB_MAX

0.6

0.4

THEORETICAL I

0.2

0

032282420161284

RAB = 50k

RAB = 100k

Ω

Figure 29. Maximum I

Ω

CODE (Decimal)

RAB = 10k

vs. Code

WB

= 5V = 0V

VA = OPEN T

= 25°C

A

Ω

V

W

04422-0-029

04422-0-030

1

VDD = 5V

= 5V

V

2

CH1 5.00V CH2 100mV M2.00ms A CH1 2.60V

T 59.8000ms

A

= 0V

V

B

Figure 27. Repetitive Increment

PU

V

W

04422-0-028

Rev. 0 | Page 10 of 20

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 V is not allowed. The step-up and step-down operations require the activation of the

(push-up) and PD (push-down) pins.

PU These pins have 100 kΩ internal pull-up resistors that the and

activate at logic low. The common practice is to apply

PD

external pushbuttons (tactile switches) as shown in Figure 30.

UP/DOWN CONTROL

LOGIC

DISCRETE

STEP/AUTO

SCAN DETECT

ADAPTIVE

DEBOUNCER

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

V

DD

R1 R2

PU

PD

Figure 30. Typical Pushbutton Interface

. Floating the PRE pin

DD

D

AD5228

E C O D E

ZERO- OR MID-

SCALE PRESET

PRE GND

PU

A

W

B

04422-0-031

1

CH1 1.00V M100µs A CH1 2.38V

T 20.20%

Figure 32. Close-Up of Initial Bounces

04422-0-033

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.

1

CH1 1.00V M40.0ms A CH1 2.38V

T 20.40%

Figure 31. Typical Tactile Switch Characteristics

04422-0-032

1

CH1 1.00V M10.0µs A CH1 2.38V

T 20.20%

04422-0-034

Figure 33. Close-Up of Final Bounces

The following paragraphs describes the PU incrementing operation. Similar characteristics apply to the

decrementing

PD

operation.

The AD5228 features an adaptive debouncer that monitors the duration of the logic-low level of

logic-low level signal duration is shorter than 7 ms, the

the

PU

signal between bounces. If

PU

debouncer ignores it as an invalid incrementing command. Whenever the logic-low level of

signal lasts longer than

PU 11 ms, the debouncer assumes that the last bounce is met and therefore increments R

Repeatedly pressing the

by one step.

WB

button for fast adjustment without

PU

missing steps is allowed, provided that each press is not shorter

, which is 12 ms (see Figure 2). As a point of reference,

than t

PU

an advanced video game player can press a pushbutton switch in 40 ms.

Rev. 0 | Page 11 of 20

AD5228

(

If the PU button is held for longer than 1 second, continuously holding it activates autoscan mode such that the AD5228

increments by four R

Whenever the maximum R incrementing regardless of the state of the

ous holding of the current.

When both

and PD buttons are pressed, RWB decrements

PU

until it stops at zero scale.

All the preceding descriptions apply 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.

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.

Figure 35. Rheostat Mode Configuration

steps per second (see Figure 3).

WB

(= RAB) is reached, RWB stops

WB

pin. Any continu-

PU

pin to logic-low simply elevates the supply

PU

operation. Due to

PD

A

R

S

D0

R

D1 D2 D3 D4

RDAC

UP/DOWN

CTRL AND

DECODE

A

B

S

R

S

W

R

W

R

S

R

=

RAB/32

S

A

W

B

04422-0-035

A

W

B

04422-0-036

The end-to-end resistance, RAB, has 32 contact points accessed by the wiper terminal, plus the B terminal contact if R Pushing the

total resistance becomes R change of R

pin discretely increments RWB by one step. The

PU

+ RW as shown in Figure 34. The

S

can be determined by the number of discrete PU

WB

is used.

WB

executions provided that its maximum setting is not reached during operation. ∆R

WB

can, therefore, be approximated as

WB

R

⎛

AB

PUR

⎜

32

⎝

R

⎛

AB

PDR

⎜

32

⎝

⎞

++=∆

R

(1)

⎟

W

⎠

⎞

+−=∆

R

(2)

⎟

W

⎠

where:

is the number of push-up executions.

PU

is the number of push-down executions.

PD

is the end-to-end resistance.

R

AB

is the wiper resistance contributed by the on-resistance of

R

W

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, R the B terminal can be opened or shorted to W. R

. When these terminals are used,

WA

can also be

WA

approximated if its maximum and minimum settings are not reached.

WA

⎛

32

⎜ ⎝

⎛

32

⎜ ⎝

R

AB

)

PUR

32

R

AB

)

PDR

32

Note that Equations 1 to 4 do not apply when

⎞

R

+−−=∆

3)

⎟

W

⎠

⎞

R

+−+=∆

(4)

⎟

W

⎠

and PD = 0

PU

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.

Rev. 0 | Page 12 of 20

AD5228

Potentiometer Mode Operation

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.

V

I

A

V

C

W

B

04422-0-037

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

PU

V

+=∆ (5)

AWB

32

PD

V

+=∆ (6)

AWB

32

Unlike in rheostat mode operation where the absolute tolerance is high, potentiometer mode operation yields an almost ratiometric function of

contributed by the R almost canceled. Although the thin film step resistor R CMOS switch resistance, R

/32 or PD/32 with a relatively small error

PU

term. The tolerance effect is, therefore,

W

S

, have very different temperature

W

and

coefficients, the ratiometric adjustment also reduces the overall temperature coefficient effect to 5 ppm/°C except at low value codes where R

dominates.

W

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 |V do not exceed V

-to-GND.

DD

|, |VWA|, and |VWB|

AB

CONTROLLING INPUTS

All PU and PD inputs are protected with a Zener ESD structure as shown in Figure 37.

V

DD

100kΩ

PU

Figure 37. Equivalent ESD Protection in

and PD pins are usually connected to pushbutton tactile

PU

DECODE

AND

DEBOUNCE

CKT

04422-0-038

PU

and PD Pins

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.

D

AD5228

E C O D E

ZERO- OR MID-

SCALE PRESET

PRE GND

A

W

B

UP

2N7002

UP/DOWN

V

DD

R1 R2

PU

N1

PD

N2

DOWN

2N7002

CONTROL

LOGIC

DISCRETE

STEP/AUTO

SCAN DETECT

ADAPTIVE

DEBOUNCER

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 Ter mi n al A, B , o r W t h at e xc e ed V forward-biased diode. There is no polarity constraint between

, VW, and VB, but they cannot be higher than VDD or lower

V

A

than GND.

are clamped by the

DD

V

DD

04422-0-039

Rev. 0 | Page 13 of 20

A W B

GND

4422-0-040

Figure 39. Maximum Terminal Voltages Set by V

and GND

DD

AD5228

POWER-UP AND POWER-DOWN SEQUENCES

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 V and W. Otherwise, the diodes are forward-biased such that V is powered on unintentionally and can affect other parts of the circuit. Similarly, V power-on sequence is in the following order: GND, V

. The order of powering VA, VB, and VW is not important

V

A/B/W

as long as they are powered on after V and

pins can be logic high or floating, but they should not

PD

be logic low during power-on.

before applying any voltage to Terminals A, B,

DD

should be powered down last. The ideal

DD

, and

DD

. The states of the PU

DD

LAYOUT AND POWER SUPPLY BIASING

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

V

DD

+

C2 10µFC10.1µF

Figure 40. Power Supply Bypassing

V

DD

GND

04422-0-041

Rev. 0 | Page 14 of 20

AD5228

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 V

F

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.

5V

C1 1µFC20.1µF

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

V

PU

PD

U1

AD5228

DD

A

W

10kΩ

B

GNDPRE

Figure 41. Low Cost Adjustable LED Driver

5V

V+

–

U2

AD8591

+

V–

C3

0.1µF

PWM

R1

SD

6Ω

WHITE LED D1

04422-0-042

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 V the AD5228 divided by R

V

WB

I =

D1

(7)

R

SET

.

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 V maximum, V

becomes VL + VAB, so the U1 supply voltage

OUT

of the AD5228 is at its

WB

must be biased with adequate headroom. Similarly, PWM signal can be applied at the U1 shutdown pin for power efficiency.

V

5V

INVOUT

U1

ADP3333

ARM-1.5

PWM

SD

GND

5V

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

V PRE

PU

PD

DD

Figure 42. Adjustable Current Source for LED Driver

GND

U2

AD5228

B

W

10kΩ A

R1 418kΩ

5V

V+

U3

AD8591

V–

R

SET

0.1Ω

–

+

VL

D1

of

WB

ID

04422-0-043

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 R reference voltage. As the loop is set, the voltage across R regulated around 0.1 V and adjusted by the digital potentiometer.

I

LED

should be small enough to conserve power but large enough

R

SET

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.

5V

C2

10µF

L1–SLF6025-100M1R0 D1–MBR0520LT1

voltage and the ADP1610 FB pin 1.2 V band gap

SET

is

SET

V

R

SET

(8)

=

R

SET

13.5kΩ

R4

PWM

1.2V R

C

100kΩ

C

390pF

C8

0.1µF

U1

R2

1.1kΩ

IN

U2

ADP1610

SD FB

COMP SS RT GND

V+

C

SS

10nF

5V

SW

U3

+

AD8541

–

V–

L1 10µF

D1

U1

AD5228

W

BA

10kΩ

R3

200Ω

C3 10µF

R

0.25Ω

R1

100Ω

SET

V

OUT

D2

D3

D4

Figure 43. Adjustable Current Source for LEDs in Series

04422-0-044

Rev. 0 | Page 15 of 20

AD5228

±

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.

C1 1µFC20.1µF

PUSH-UP BUTTON

PUSH-DOWN

BUTTON

5V

R2

R1

PHOTOCELL

1kΩ

PU

PD

5V

U1

AD5228

V

DD

A

W

10kΩ B

GNDPRE

5V

V+

–

U2

AD8531

+

V–

C3

0.1µF

PWM

R3

4.75kΩ

N2

Figure 44. Automatic LCD Panel Backlight Control

N1

2N7002

5V

WHITE LED

D1

2N7002

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

= 1/(2 × π × R1 × C1). The SSM2211 can also drive two

f

H1

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

= 1/(2 × π × R5 × C3). As a result, C3 and C4 must be

as f

H2

large to make the frequency as low as f

AUDIO_INPUT

5V

C6

10µFC70.1µF

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

5V

R3

10kΩ

R4

10kΩ

04422-0-045

2.5V p-p

U1

V

DD

PRE

A

1µF

W

10kΩ B

GND

–

U3

AD8591

+

PU

PD

Figure 45. Audio Amplifier with Volume Control

.

H1

R2

10kΩ

C5

5V

0.1µF

C1

R1

10kΩ

4

–

V+

U2

SSM2211

3

V–

+

7

2

C2

0.1µF

C3

470µF

6

1

5

8

C44

470µF

R5 8Ω

R6 8Ω

04422-0-046

Rev. 0 | Page 16 of 20

AD5228

V

CONSTANT BIAS WITH SUPPLY TO RETAIN RESISTANCE SETTING

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.

DD

SW1

U1

AD5228

V

DD

+

U2

V

DD

COMPONENT X

U3

V

DD

COMPONENT Y

3.50

3.49

3.48

3.47

3.46

3.45

3.44

3.43

BATTERY VOLTAGE (V)

3.42

3.41

3.40 024681012

DAYS

TA = 25°C

Figure 47. Battery Consumption Measurement

04422-0-048

BATTERY OR

GND

SYSTEM POWER

–

GND

04422-0-047

Figure 46. Constant Bias AD5228 for Resistance Retention

Rev. 0 | Page 17 of 20

AD5228

OUTLINE DIMENSIONS

2.90 BSC

847

1.60 BSC

PIN 1

0.90

0.87

0.84

0.10 MAX

1 3562

1.95 BSC

0.38

0.22

COMPLIANT TO JEDEC STANDARDS MO-193BA

2.80 BSC

0.65 BSC

1.00MAX 0.20

SEATING PLANE

0.08 8° 4° 0°

0.60

0.45

0.30

Figure 48. 8-Lead Small Outline Transistor Package TSOT-8 [Thin SOT-23-8]

(UJ-8)

Dimensions shown in millimeters

ORDERING GUIDE

Full Container

Model1 RAB (kΩ) Temperature Range Package Code Package Description

AD5228BUJZ102-RL7 10 −40°C to +105°C UJ TSOT-8 3000 D3K AD5228BUJZ102-R2 10 −40°C to +105°C UJ TSOT-8 250 D3K AD5228BUJZ502-RL7 50 −40°C to +105°C UJ TSOT-8 3000 D3L AD5228BUJZ502-R2 50 −40°C to +105°C UJ TSOT-8 250 D3L AD5228BUJZ1002-RL7 100 −40°C to +105°C UJ TSOT-8 3000 D3M AD5228BUJZ1002-R2 100 −40°C to +105°C UJ TSOT-8 250 D3M AD5228EVAL 10 Evaluation Board 1

1

The end-to-end resistance R

example,10 kΩ = 10.

2

Z = Pb-free part.

is available in 10 kΩ, 50 kΩ, and 100 kΩ. The final three characters of the part number determine the nominal resistance value, for

AB

Quantity

Branding

Rev. 0 | Page 18 of 20

AD5228

NOTES

Rev. 0 | Page 19 of 20

AD5228

NOTES

D04422–0–4/04(0)

Rev. 0 | Page 20 of 20

Datasheet AD5228 Datasheet (Analog Devices)

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

APPLICATIONS

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM

ELECTRICAL CHARACTERISTICS

INTERFACE TIMING DIAGRAMS

ABSOLUTE MAXIMUM RATINGS

ESD CAUTION

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS

THEORY OF OPERATION

PROGRAMMING THE DIGITAL POTENTIOMETERS

Rheostat Operation

Potentiometer Mode Operation

CONTROLLING INPUTS

TERMINAL VOLTAGE OPERATION RANGE

POWER-UP AND POWER-DOWN SEQUENCES

LAYOUT AND POWER SUPPLY BIASING

APPLICATIONS

MANUAL ADJUSTABLE LED DRIVER

ADJUSTABLE CURRENT SOURCE FOR LED DRIVER

ADJUSTABLE HIGH POWER LED DRIVER

AUTOMATIC LCD PANEL BACKLIGHT CONTROL

AUDIO AMPLIFIER WITH VOLUME CONTROL

CONSTANT BIAS WITH SUPPLY TO RETAIN RESISTANCE SETTING

OUTLINE DIMENSIONS

ORDERING GUIDE