ADM8845 Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

componentes Descripción

Fabricante

ADM8845

Charge Pump Driver for LCD White LED Backlights

Analog Devices 

ADM8845

DRIVING FOUR BACKLIGHT WHITE LEDS AND FLASH LEDS

The ADM8845 also can be configured to power four backlight

white LEDs and a camera flash, packaged into one package. FB1

to FB4 power the backlight light, FB5 and FB6 powers the two

of the flash LEDs, and the third is powered an external current

mirror to control the current flowing through the third flash LED

(see Figure 33). All the backlight white LEDs have 15 mA/LED,

and the flash current is 20 mA/LED. The total load on the

ADM8845 charge pump is 120 mA; the maximum load on

the ADM8845 charge pump is 180 mA (see Figure 21).

CTRL1 controls the flash on/off, and CTRL2 controls the back-

light on/off and brightness control. Because the RSET resistor sets

the current that each of the six current control blocks can sink,

a PWM signal is used to change the current in the backlight

from 20 mA to 5 mA/LED. The CTRL2 duty cycle is 15/20 to

give 15 mA/backlight LED.

C1

C2

1µF 1µF

VCC

C4

4.7µF

ADM8845

CHARGE PUMP

1×/1.5×/2× MODE

CTRL1

CTRL2

CONTROL

LOGIC

OSC

VREF

ISET

RSET

7.32kΩ

LED

CURRENT

CONTROL

CIRCUIT

VOUT

C3

2.2µF

FB1

FB2

FB3

FB4

FB5

FB6

BACK-

LIGHT

15mA/LED

CURRENT CONTROLLED SINKS

GND

Figure 33. Driving Four Backlight LEDs and Flash LED

FLASH

20mA/LED

CURRENT

CONTROL 7

R

Rev. 0 | Page 16 of 20

Share Link: