參數(shù)資料
型號: ADM8845ACPZ
廠商: ANALOG DEVICES INC
元件分類: 顯示驅(qū)動器
英文描述: Charge Pump Driver for LCD White LED Backlights
中文描述: LED DISPLAY DRIVER, QCC16
封裝: 3 X 3 MM, 0.90 MM HEIGHT, LEAD FREE, LFCSP-16
文件頁數(shù): 10/18頁
文件大?。?/td> 341K
代理商: ADM8845ACPZ
ADM8845
Preliminary Technical Data
ADM8845 OPERATION
The ADM8845 charge pump driver for LCD white LED backlights implements a multiple gain charge pump (1x, 1.5x, 2x)to maintain the
correct voltage on the anodes of the LEDs over a 2.6V to 5.5V (li-ion) input supply voltage. The charge pump automatically switches
between 1x/1.5x/2x modes based on the input voltage, to maintain sufficient drive for the LED anodes, with V
CC
input voltages as low as
2.6V. It also includes regulation of the charge pump output voltage for supply voltages up to 5.5V. The ADM8845 six LEDs are arranged
into two groups; main and sub. The main display can be up to four LEDs (FB1 to FB4) and the sub display can be up to two LEDs (FB5
and FB6), see Figure 23. Two digital input control pins, CTRL1 and CTRL2, control the shutdown operation and the brightness of the
main and sub displays, see Table 4.
Rev. PrJ 06/04 | Page 10 of 18
CTRL1
0
0
1
1
CTRL2
0
1
0
1
Table 4. ADM8845 Digital Inputs Truth Table
LED Shutdown Operation
Sub Display Off / Main Display Off
Sub Display Off / Main Display On
Sub Display On / Main Display Off
Sub Display On / Main Display On
An external resistor R
SET
is connected between the I
SET
pin and GND, this resistor sets up a reference current I
SET
which is gained up by 120
internally within the ADM8845 to produce the I
LED
currents of up to 30mA/LED, (I
LED
= I
SET
* 120 and I
SET
= 1.18V /R
SET
). The ADM8845
uses six individual current sinks to individually sense each LED current with a maximum matching performance of 1%. This current
matching performance ensures uniform brightness across a color display.
The ADM8845 provides the option to control the brightness of the white LEDs with a digital PWM signal applied to CTRL1 and/or
CTRL2. The duty cycle of the applied PWM signal determines the brightness of the main and/or sub display backlight white LEDs. The
ADM8845 also allows the brightness of the white LEDs to be controlled using a DC voltage, refer to page 14, Figure 27Figure . Soft-start
circuitry limits the inrush current flow at power up. The ADM8845 is fabricated using CMOS technology for minimal power
consumption and is packaged in a 16-Lead Frame Chip Scale Package.
Charge Pump
1x/1.5x/2x mode
Control
Logic
VCC
C4
Osc
Vref
+
-
LED Current
Control
Circuit
Current Controlled Sinks
Iset
GND
ADM8845
Vout
FB2
FB3
FB4
FB5
FB6
FB1
C3
C1
C2
Rset
Current
Co1
Current
2
Current
3
Current
Control
4
Current
5
Current
Control
6
CTRL1
CTRL2
SUB
MAIN
Figure 23. ADM8845 FUNCTIONAL BLOCK DIAGRAM
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