R1218K021A RICOH [RICOH electronics devices division], R1218K021A Datasheet - Page 7

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

(2) Dimming control by DC voltage
(3) Dimming control by feedback voltage and filtered PWM signal
C3 should be set large enough to regard the PWM signal as adjustable DC voltage by the filter. In this method,
higher frequency control than the frequency against the CE pin can be used for dimming control.
For example, if the frequency is 40kHz, 0.1µF or more capacitor is our recommendation value as C3.
For example, supposed that the PWM signal level is set as 2.5V/0V, to adjust the LED current range from 0mA
to 20mA by the duty cycle, our recommendation external components values are, R1=10Ω, R2=5.1kΩ,
R3=51kΩ, R4=5.1kΩ or around.
LED dimming control is also possible by using the DC voltage to V
voltage and resisters, R1 and R2 in the following figure.
I
LED dimming control is also possible by using the feedback voltage and filtered PWM signal.
LED current is adjustable according to the "H" level (V
maximum LED current and minimum LED current as in the next formulas.
I
I
LED
LEDMIN
LEDMAX
=(DC − 0.2) / R2 − 0.2 / R1
R1, R2, R3, and R4 in the figure5. Duty=0% to 100% PWM signal duty cycle can be used up to the
=(0.2 − R2 × (V
=(0.2 − R2 × (V
H
L
− 0.2) / (R3 + R4)) / R1
− 0.2) / (R3 + R4)) / R1
Dimming controle by filtered PWM signal
Dimming control by DC voltage
V
FB
V
FB
C3
R3
R2
R4
R1
H
) and "L" level(V
R2
R1
DC
FB
pin. LED current is adjustable by DC
V
V
L
) of PWM signal and resisters,
H
L
R1218x
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