XC9116B02A Ver la hoja de datos (PDF) - TOREX SEMICONDUCTOR

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XC9116B02A

Step-Up DC/DC Converter-Backlight LED Driver

TOREX SEMICONDUCTOR 

XC9116

Series

■APPLICATION INFORMATION

<Dimming Control>

1. Applying PWM signal to the CE pin

The XC9116 repeats on/off operations by a PWM signal applied to the CE pin. The magnitude of LED current, ILED, when

the diode is on, is determined by RLED. The magnitude is zero when the diode is off. The average of LED current is

proportional to the positive duty ratio of the PWM signal.

The frequency of the PWM signal can be controlled to the optimum value between 100Hz and 10kHz. With regard to the

amplitude of the PWM signal, the high level should be higher than the "H" voltage of CE, VCEH, and the low level, lower

than the "L" voltage of CE, VCEL.

20μs / div

20μs / div

4 series

200μs / div

200μs / div

2. Step-Wise Regulation of LED Current

In some applications, it may be necessary to incorporate step-wise regulation of LED current, ILED. Step-wise regulation

of LED illumination is achieved by connecting a switch element SW1 in parallel with RLED and in series with RLED1 and

turning SW1 on and off, as shown below. Choose a resistance of RLED so that the minimum necessary current is gained

when switch element SW1 is off. The resistance of RLED1 should be such that a desired increase of current passed

through the LED is gained when the switch element is on.

L

SD

VIN

Ex.) Current ILED = 5mA and 15mA

RLED = 200mV / 5mA = 40 Ω

RLED1 = 200mV / (15mA – 5mA) = 20 Ω

ILED

VIN

Lx

CIN

ON/OFF

CE

FB

VSS

RLED

CL

RLED1

signal

SW1

Figure : Circuit using Step-wise Regulation of LED Current

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