AP3154

120mA HIGH EFFICIENCY WHITE LED DRIVER

AP3154 Rev. 2

FEBRUARY 2009

www.diodes.com

Functional Description

General Functional Description

The AP3154 is designed for white LED 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 (x1, x1.5,

x2) is automatically selected.

In applications, only four external components are required: two

AP3154 drives up to four white LEDs with a maximum current of

30mA each.

A total of 120mA is provided to the four channels.

Through SDI, the current into each channel can be configured in

accordance to specific protocol and pre-defined values.

Maximum output current can be set to one of the four possible

scales: 2mA, 14mA, 20mA, 30mA. Among these, the ‘2mA’

setting is called “low current mode”. This would be useful for

applications which require very low operating current, e.g.

transmissive LCD panels.

For each maximum output current scale, there are 16 current

level settings separated from one another by approximately

1dB. While level-16 corresponds to maximum current output,

level-1 corresponds to zero output current. As the current level

varies logarithmically, intensity of the LED changes in a linear

fashion.

The current level at the individual channels is configured via SDI

which supports data rate up to 10MHz.

It allows the main

controller in the system to be offloaded to perform more

mission-critical functions.

Serial Digital Interface

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

transport digital controls for power management ICs such as

AP3154.

The current levels of the four channels can be

configured either together or individually.

Up to 16 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 table 1),

a channel configuration event. In the future, the number of

pulses can be extended to support additional commands.

In addition to the SDI protocol, dimming control can also be

achieved by presenting a timing-specific PWM signaling at the

SDI pin.

Number

of Falling

Edges

Command Description

1

Current level step up (1 up to level 16)

2

Current level step down (16 down to level 1)

3

Current level set to 16 (maximum current level)

4

Current level set to 1 (minimum current level)

5

All 4 Channels in dimming control

6

CH2, CH3 and CH4 in dimming control

7

CH1 and CH2 in dimming control

8

CH3 and CH4 in dimming control

9

CH1 in dimming control

10

CH2 in dimming control

11

CH3 in dimming control

12

CH4 in dimming control

13

Low-Current Mode (Maximum Current set to 2mA)

14

Maximum Current set to 14mA (All channels)

15

Maximum Current set to 20mA (All channels)

16

Maximum Current set to 30mA (All channels)

17

10% Up Spread Spectrum Control Enable/Disable

18

Switching Frequency set to 0.6Mhz

19

Switching Frequency set to 1.2Mhz

20

Switching Frequency set to 1.8Mhz

21~62

Reserved

63

PWM Dimming Control Enable/Disable

Dimming Control Current Level Setting

AP3154 supports four maximum output current scales including

maximum current scale, there are 16 current level settings

separated from one another by appromimately 1dB (see table 2).

By default, maximum current scale is set to 20mA and dimming

control current level is set to maximum (level 16).

Through SDI, certain channels or all four channels can be

selected, and dimming control level for these channels can be set

to maximum (level 16), minimum (level1), up from minimum to

maximum or down from maximum to minimum (see table 1).

Dimming

Control

Current

Levels

(20mA)

(30mA)

(14mA)

Low-Current

(2mA)

16

20.0

30.0

14.0

2.0

15

17.8

26.7

12.5

1.78

14

15.9

23.8

11.1

1.59

13

14.3

21.4

10.0

1.43

12

12.7

19.0

8.9

1.27

11

11.1

16.7

7.8

1.11

10

10.2

15.2

7.1

1.02

9

8.9

13.3

6.2

0.89

8

7.9

11.9

5.6

0.79

7

7.0

10.5

4.9

0.70

6

6.3

9.5

4.4

0.63

5

5.7

8.6

4.0

0.57

4

5.1

7.6

3.5

0.51

3

4.4

6.7

3.1

0.44

2

4.1

6.2

2.9

0.41

1

0.05

0.05

0.05

0.05

Table 2: Dimming Control Current Level