SM8131B Datasheet, PDF (7/21 Pages) Nippon Precision Circuits Inc – The SM8131B is a charge pump DC/DC converter that switches between 1 and 1.5 automatically.

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