AP3156

HIGH EFFICIENCY 1X/1.5X/2X CHARGE PUMP

FOR WHITE LED APPLICATIONS

AP3156 Rev. 1

9 of 15

SEPTEMBER 2009

www.diodes.com

Functional Description

The AP3156 is a tri-mode high efficiency six-channel charge

pump (1x, 1.5x or 2x) device intended for white LED backlight

applications.

An internal comparator circuit compares the

voltage at each constant current sink input against a reference

voltage.

To ensure maximum power efficiency, the most

appropriate switching mode (1x, 1.5x, 2x) is automatically

selected.

The AP3156 requires only four external components: two 1µF

The each output channel of the AP3156 can drive six

individual LEDs with a maximum current of 25mA per channel.

These can be paralleled to give a total output current of

150mA.

Constant Current Output Level Settings

The constant current level for the outputs is set via the Serial

Digital Interface and has a logarithmic variance. This results in

the LED brightness varying linearly when the settings in the

scale are traversed. Because the inputs D1 to D6 are true

independent constant current sinks, the voltage observed on

any single given input will be determined by the difference

being driven.

Since the constant current levels for the AP3156 are

programmable, no PWM (pulse width modulation) or additional

control circuitry is needed to control LED brightness. With its

high-speed serial interface (>1MHz data rate), the LED current

drive of the AP3156 can be changed successively to brighten

or dim LEDs in smooth transitions or in abrupt steps, giving the

user complete programmability and real-time control of LED

brightness.

There are 32 current level settings separated from one another

by approximately 0.5dB (see Constant Current Programming

Level table). Code 1 is full-scale current, and Code 31 is full

scale attenuated roughly 15dB. Code 32 is reserved as a “no

current” setting.

Constant Current Programming Levels (mA)

Data

20mA Max

25mA Max

1

20

25

2

18.9

23.6

3

17.8

22.3

4

16.8

21.0

5

15.9

19.9

6

15.0

18.7

7

14.2

17.7

8

13.4

16.7

9

12.6

15.8

10

11.9

14.9

11

11.2

14.1

12

10.6

13.3

13

10.0

12.5

14

9.5

11.8

15

8.9

11.2

16

8.4

10.5

17

8.0

10.0

18

7.5

9.4

19

7.1

8.9

20

6.7

8.4

21

6.3

7.9

22

6.0

7.5

23

5.6

7.0

24

5.3

6.7

25

5.0

6.3

26

4.7

5.9

27

4.5

5.6

28

4.2

5.3

29

4.0

5.0

30

3.8

4.7

31

3.6

4.4

32

0

0

Low Current Output Level Setting

The AP3156 has a distinct Low Current mode with ultra-low

quiescent current. For drive currents of 2mA or less, the device

operates with significantly reduced quiescent current.

Low Current Programming Levels (mA)

Data

Current (mA)

1

2

2

1

3

0.5

4

0.05

5

0

Serial Digital Interface

SDI is a general purpose 1-wire digital interface designed to

transport digital controls for power management ICs such as

AP3156.

The current levels of the six channels can be

configured either together, individually or specific grouping.

Up to 32 current levels are allowed. A generic system

controller can easily support the SDI protocol via bit-banging

over its general purpose I/Os.

The

SDI

protocol

is

simple

yet

flexible

enough

to

accommodate different switching clock frequencies. Any

sequence of negative-edged pulses of 63 or less (see

interpreted by the AP3156 as a channel configuration event.

In future, the number of pulses can be extended to support

additional commands.