AAT2848

High-Current Charge Pump For Backlight Display and Flash Applications

ChargePump

TM

PRODUCT DATASHEET

2848.2008.05.1.0

11

www .analogictech.com

FENS

Data

(%)

(Ω)

FENS

Data

(%)

(Ω)

1

100

14.3k

(206mA

Max)

946

14.3k

(206mA

Max)

294

10

40

387

11

34

481

12

27

573

13

20

667

14

13

760

15

6

853

16

3

FENS Data (#)

0

40

80

120

160

200

240

13

5

7

9

11

13

15

Figure 2: FL1-FL2 Current Control Profile.

AAT2848 exhibits flexible timing in that data can be

clocked-in at speeds ranging from 15kHz to higher than

1MHz.

both the BENS pin and at the FENS pin. For setting the

backlight current level, data applied at the AAT2848’s

BENS input is decoded into 32 different levels. For set-

ting the flash current level, data applied at the AAT2848’s

FENS input is decoded into 16 different levels. After data

is supplied, the BENS and the FENS inputs pins are held

high to latch the data.

Once the data at BENS or FENS has been held in the

grammed backlight or flash current becomes active and

the internal backlight and flash data registers are

latched. To adjust the backlight and/or flash current lev-

els once programmed, the requisite number of rising

edges corresponding to the desired code must be applied

at the BENS or the FENS pin.

The AAT2848 features separate control interfaces for

backlight and flash current control. The backlight current

features 32 current steps, each step as a percentage of

the maximum backlight current set by the BSET resistor.

The flash has 16 current level settings; again, each step

as a percentage of the maximum flash current set by the

FSET resistor.

Flash Timeout Functionality

The AAT2848 contains an internal flash mode operation

timeout safety circuit. The purpose of this timeout circuit

is to prevent any thermal damage to the flash white LED

when flash mode operation is unable to be disabled by

the embedded microprocessor/microcontroller.

Flash

mode operation is initiated by strobing the FENS pin low-

to-high, this also initiates the flash timer circuit which

can be programmed via an external capacitor at the

FLTMR pin. The flash timeout period can be calculated

using the following equation:

example, for a 0.33μF capacitor:

Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s

To disable the flash timer, connect the FLTMR pin to

AGND.

When both the BENS and the FENS inputs are strobed

enters shutdown mode and draws less than 1μA from

cleared to zero when in shutdown.

Backlight/Flash LED Current Setting

The maximum backlight and flash LED currents are set,

or programmed, with external resistors. The backlight

following equation:

R

300

I

BLED