MP3021 – 1X, 1.5X, 2X AUTO-ADJUST CHARGE PUMP WLED BACKLIGHT DRIVER

MP3021 Rev. 1.0

www.MonolithicPower.com

8

11/21/2007

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© 2007 MPS. All Rights Reserved.

0

On/Off

Bit

1-bit

1-bit

2-bits

2-bits

5-bits

HC/LC

Bit

LED Sel

Bits

Mode

Bits

Brightness

Bits

123456789

10

<0> OFF

<1> ON

<0> High Current

<1> Low Current

<23>

<00> All On

<11> 1 LED On

<10> 2 LEDs On

<01> 3 LEDs On

<45>

<00> BL Only

<10> Not Allowed

<01> Not Allowed

<11> Not Allowed

<678910>

<00000> 1 x Max Brightness / 32

<10000> 2 x Max Brightness / 32

<01000> 3 x Max Brightness / 32

<11000> 4 x Max Brightness / 32

.

.

.

.

.

.

<11111> Max Brightness

Figure 3—Control Register

Control Register Definition

The control register is as follows:

• Bit 0 is the enable bit and determines

whether the part is active or in shutdown

• Bit 1 allows the part to be put into a low

current mode

• Bits 2-3 control which backlight WLED pins

are active

• Bits 4-5 control the mode [BL=backlight].

Always set B4B5 = <00>

• Bits 6-10 control the brightness. Step size

and max brightness depend on R1 and Bit1.

Bit 6 is the LSB.

• Default is all “0” and the register is reset

only upon power up.

Shutdown

Setting the DATA-bit low [DATA:0] causes

shutdown. During shutdown, the charge-pump

output is switched to VSS through a weak path.

The supply current will be less than 1µA in

shutdown.

Soft-Start

During startup and mode switching, an internal

soft-start prevents excessive input current thus

preventing excessive loading of the battery or

input power source.

Setting the Backlight LED Current

The full-scale backlight LED regulation current is

set through the resistor R1 (refer to the typical

application circuit on page 1). The voltage across

R1 is fixed at 1.25V, and the internal current

desired full-scale LED current according to the

equation:

MAX

I

1mA

k

125

R1

×

Ω

=

values for R1 are greater than 4.17kΩ.

The exact LED current between 0 and the max

set by R1 is determined by the brightness code

and the HC/LC bit.

The HC/LC bit allows for fine control at low

current settings. The following table and graph

exhibit the possible settings for a R1 of 4.17kΩ.