DATA SHEET
AAT2822/2823/2824/2825
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
R8
R8
HF-PWM
R23
4.99k
adj
adj
R21
4.99k
R21
0
PWM
R22
28k
Connect WDIM to VIN
C25
0.1µF
1
2
3
18
17
16
15
14
13
WLX
PGND2
N/C
N/C
N/C
N/C
FB
1
2
3
18
17
16
15
14
13
WLX
PGND2
N/C
N/C
N/C
N/C
FB
AAT2822
FBN
WEN
DRVN
AAT2822
FBN
WEN
DRVN
COMP
COMP
Figure 4: PWM Dimming Control.
Figure 5: Low-Pass Filter PWM Dimming Control.
For applications requiring a PWM frequency higher than
1KHz, an external filter PWM is connected to the WFB pin
to control the dimming of the white LED. This low-pass
filter (R23/C25) integrates the high frequency PWM signal
to produce a DC dimming control as shown in Figure 5.
When the PWM duty cycle is adjusted, the DC voltage
across the ballast resistor (R8) changes, resulting in
change of the white LED current. Apply the KCL at the
feedback node (WFB). The voltage across the R8 resistor
can be expressed:
R21
R22
VR8 = 0.3V -
· (VC25 - 0.3V)
For minimum dimming, VR8 = 0V.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
18
202081B
• Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 2, 2012
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
