R1218N021A Datasheet, PDF (6/21 Pages) RICOH electronics devices division – Step-up DC/DC converter for White LED Backlight

R1218x
TYPICAL APPLICATIONS
R1218x041A
L1
22µH
C1
1µF
VIN
LX
CE
VOUT
GND
VFB
R1
10Ω
C2
C1
0.22µF
1µF
R1218x062A
L1
22µH
VIN
CE
LX
VOUT
GND
VFB
R1
10Ω
C2
0.22µF
• LED Current setting
LED current can be set with feedback resister(R1)
ILED=0.2 / R1
• LED Dimming Control, Softstart
(1) LED dimming control by PWM signal to CE pin
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.
CE
VFB
R1
Dimming controle by CE pin input
6