R1218K021A RICOH [RICOH electronics devices division], R1218K021A Datasheet - Page 6

• Manufacturer Part Number: R1218K021A
• Description: Step-up DC/DC converter for White LED Backlight
• Manufacturer: RICOH [RICOH electronics devices division]

6
•
•
TYPICAL APPLICATIONS
R1218x
LED Current setting
LED current can be set with feedback resister(R1)
I
LED Dimming Control, Softstart
(1) LED dimming control by PWM signal to CE pin
1µF
C1
LED
=0.2 / R1
LED dimming control is possible by forcing PWM signal to CE pin.
When the power-on or start up with CE pin, softstart function works, however, after that, if the CE pin is set
as "L" and set CE pin "H" again during the shutdown delay time, softstart function is disabled and starts up
fast to normal mode, therefore 200Hz to 5kHz PWM signal is standard. By the CE pin input, LED turns on
and off. Average LED current varies depending on the duty cycle of CE input. Too high frequency PWM
signal is not effective because of its delay.
V
CE
GND
IN
L1
22µH
R1218x041A
V
V
L
OUT
X
FB
Dimming controle by CE pin input
R1
10Ω
C2
0.22µF
CE
V
C1
1µF
FB
V
CE
GND
IN
R1
L1
22µH
R1218x062A
V
V
L
OUT
X
FB
R1
10Ω
C2
0.22µF