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): 14/18頁
文件大小: 341K
代理商: ADM8845ACPZ
ADM8845
Preliminary Technical Data
ADM8845 LED BRIGHTNESS CONTROL USING A
PWM SIGNAL APPLIED TO V
PWM
Adding two external resistors and a capacitor as shown on
Figure 26, can also be used to achieve PWM brightness control.
This PWM brightness control method can be used instead of
CTRL1 and/or CTRL2 digital PWM brightness control. With
this configuration, CTRL1 and CTRL2 digital logic pins can be
used to control shutdown of the white LEDs, while V
PWM
can be
used to control the brightness of all the white LEDs. By applying
a high-frequency PWM signal (Amplitude 0V to 2.5V) to drive
an R-C-R filter on the I
SET
pin of the ADM8845. A 0% PWM
duty cycle corresponds to 20mA/LED, while a 100% PWM duty
cycle corresponds to a 0mA/LED. At PWM frequencies above
5kHz, C5 may be reduced. Refer to Figure 26, ADM8845 PWM
Brightness Control Using Filtered-PWM Signal. The amplitude
of the PWM signal must be 0 V and 2.5 V only, in order to have
20mA flowing in each LED.
Rev. PrJ 06/04 | Page 14 of 18
#8#####9 ,)04
###:##:#%##!1#1,4(
#######:#
#########
-#8#
#8#
####-#8#
#8#
6
;<6
##.
#8#=
#8#".>
#8#".>#
#8#.>
Figure 26. ADM8845 PWM Brightness Control Using Filtered-
PWM Signal
ADM8845 LED BRIGHTNESS CONTROL USING A
DC VOLTAGE APPLIED TO V
BRIGHT
Adding one resistor as shown in figure 27 , this configuration
can also be used to achieve brightness control of the white LEDs
using a DC voltage applied to the V
BRIGHT
node. Figure 28 shows
an application example of LED Brightness control using a DC
Voltage with a amplitude of 0V to 2.5V, applied to V
BRIGHT
.
6
7
#8#>
#8#.>
##.
Figure 27. ADM8845 PWM Brightness Control Using a DC
Voltage applied to VBRIGHT
The equation for I
LED
is:
I
SET
= [(1/R
SET
+ 1/R)(V
SET
)] – [(1/R)(V
BRIGHT
)]
I
LED
= 120*I
SET
Where R = 15k Ohm, V
SET
= voltage at I
SET
pin (1.18V)
7
.
.
.
".
.
Figure 28. ADM8845 PWM Brightness Control Application
Diagram Using a DC Voltage applied to V
BRIGHT
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