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SM8122A

White LED Driver IC

Nippon Precision Circuits  

SM8122A

OVP (Over Voltage Protection)

SM8122A is always monitoring the VOUT terminal voltage in order to protect itself from the stress of VOUT

over voltage. If SM8122A detects the VOUT over voltage, it immediately stop the switching of the inductor

drive transistor. After the VOUT terminal voltage decreases below the release voltage, SM8122A restarts

switching the inductor drive transistor. The over voltage is set as approximately 30.5V, the release voltage is

approximately 28.5V.

30.5V

28.5V

Over voltage

detection

Over voltage

detection

Over voltage

detection release

Over voltage

detection release

SW Tr = OFF

SW Tr

Switching

SW Tr = OFF

Selecting the Current-setting Resistor (R1)

The SM8122A control stabilizes the voltage on pin FB (0.5V typ.). Hence, the current-setting resistor R1 con-

nected between FB and VSS sets the LED current ILED, where the resistance R1 is given by the following

equation.

R1 = 0.5 / ILED

FB VFB=0.5V

ILED=0.5/R1

R1=0.5/ILED

NIPPON PRECISION CIRCUITS INC.—6

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