The linear dimming can be implemented by applying a

control voltage from 0mV to the 250mV to the LIN_D

pin. This control voltage overrides the internally set 250mV

threshold level of the ISEN pin and programs the output

current accordingly.

For example, a potentiometer

connected between Vcc and ground can program the

control voltage at the ISEN pin.

Applying a control

voltage higher then 250mV will not change the output

current setting. When higher current is desired, select a

smaller sense resistor.

The PWM dimming scheme can be implemented by

applying an external PWM signal to the PWM_D pin.

The PWM signal can be generated by a microcontroller

or a pulse generator with a duty cycle proportional to the

amount of desired light output. This signal enables and

disables the converter modulating the LED current in

the PWM fashion. In this mode LED current can be in

one of the two states, zero or the nominal current set by

the current sense resistor. It is not possible to use this

methode to achive everage brightness levels higher then

the one set by the current sense threshold level of the

FC9910. By using the PWM control methode of the

FC9910, the l ight output can be adjusted between zero

and 100%. the accuracy of the PWM dimming methode

is limited only by the minimum gate pulse width, which

is a fraction of a percent of the low frequency duty cycle.

The operating frequency of the oscillator is programmed

between 25 and 300kHz using an external resistor

connected to the connected to the Rosc pin.

Fosc = 25000/(Rosc[kΩ] +22) [kHz]

FC9910B

2013. 05. 08

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Revision No : 0

Application Information (Continued)

5. Programming Operating Frequency

33% PWM Ratio at 500Hz Dimming

95% PWM Ratio at 500Hz Dimming

0.4% PWM Ratio at 500Hz Dimming