R1218X Datasheet, PDF (6/14 Pages) RICOH electronics devices division – Step-up DC/DC converter for Whilte LED Backlight

R1218X
VFB Voltage, Oscillator Frequency, Maximum Duty OVP Detector Threshold, OVP Released Voltage
Test Circuit
Test Circuit
V_IN
L_X
V_IN
LX
CE
GND
V ^FB
CE
GND
V ^OUT
V ^FB
TYPICAL APPLICATIONS
R1218X041A
L1
22uH
C1
1uF
V_IN L_X
CE
V
OUT
R1218X062A
L1
22uH
C2
0.22uF
C1
1uF
VIN
CE
LX
V_OUT
GND V_FB
R1
10Ω
GND VFB
C2
0.22uF
R1
10Ω
• LED Current setting
LED current can be set with feedback resister(R1)
ILED=VFB/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.
(2)Dimming control by DC voltage
LED dimming control is also possible by using the DC voltage to VFB pin. LED current is adjustable by DC voltage and
resisters, R1 and R2 in the figure 4.
ILED=(DC-0.2)/R2-0.2/R1
(3)Dimming control by feedback voltage and filtered PWM signal
LED dimming control is also possible by using the feedback voltage and filtered PWM signal. LED current is adjustable
according to the "H" level (VH) and "L" level(VL) of PWM signal and resisters, R1, R2, R3, and R4 in the figure5.Duty
6