SM8131B00B データシートの表示（PDF） - Nippon Precision Circuits

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SM8131B00B

White LED Driver IC

Nippon Precision Circuits  

SM8131B

EN input signal and LED drive current setting (startup)

An internal startup signal goes HIGH on the first rising edge of either EN1 or EN2, and LED drive current

starts after the soft-start time expires. The LED drive current control circuit sets the current by counting the

input pulses on EN, hence the EN input voltage must be switched HIGH → LOW → HIGH the required num-

ber of data steps to reduce the current setting. When the desired setting is reached, the EN input voltage should

be tied HIGH to maintain the setting. Note that the LED drive current does not flow when EN is LOW between

pulses, momentarily switching the group of LEDs OFF.

The EN data input circuit operates during the soft-start time when no LED drive current flows, hence the cur-

rent setting can be adjusted during the soft-start time and the LED drive circuit will then start at the desired cur-

rent setting. However, setting the current using EN signal pulses is possible only when the power-ON reset

ends after a rising edge on the VIN supply. Consequently, a delay of 1ms or greater should be allowed after

VIN is applied before starting the EN input signals.

EN1

input signal

12345

678

ILED

group A setting

1234

5

678

EN2

input signal

12345

ILED

group B setting

1234

5

EN input signal and LED drive current setting

I The LED drive current in group A (group B) is set by the number of EN1 (EN2) input signal rising-edge.

When either EN1 or EN2 input signal first rises, the internal enable signal CE goes HIGH, and the IC is

enabled. The LED drive current control circuit is disabled, and the LED drive current does not flow during

EN input signal LOW interval or at startup until after the soft-start time expires.

NIPPON PRECISION CIRCUITS INC.—7

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