SM8131B

NIPPON PRECISION CIRCUITS INC.—9

The SM8131B switches between 3 output states: power-save mode (standby state),

×1.0 mode (VIN through

mode), and

×1.5 mode (×1.5 charge pump boost). This automatically adjusts the VOUT output to match the

drive LED characteristics and reduces the total power dissipation. Switching to and from

×1.0 and ×1.5 mode

occurs automatically in an internal circuit, and cannot be controlled using an external input.

Power-ON internal reset time

The SM8131B switches from standby condition (power-save mode) to normal operating condition (

×1.0/×1.5

mode) on the first rising edge of either EN1 or EN2. Note that if the VIN supply voltage is applied when EN1

or EN2 is HIGH, startup occurs after the internal power-ON reset time (approximately 50

µs) expires. At star-

tup, operation commences in

×1.5 mode for a fixed interval during the soft-start time in order to determine

whether a LED is connected to each DIN pin.

(1) VIN voltage rises when power is applied.

(2) Power-ON reset (POR) circuit resets internal circuits approximately 50

µs after the power is applied.

(3) If EN1 or EN2 is HIGH when power is applied, the internal circuits start operating when the internal “CE”

signal rising edge occurs after the power-ON reset time. If EN1 and EN2 are LOW when power is applied,

the “CE” rising edge occurs simultaneously with the first rising edge.

(1) If the EN signals are input after POR time is expired, the soft start time begin from the first EN input rising

edge. The current setting can be adjusted during the soft-start time.

(2) LED current starts flow immediately before the soft start time expires.

Power-ON reset operation

Soft start time and LED current

power source

Power save

mode

1.5 mode

Power on

reset output

Internal

enable (CE)

POR time

typ: 50

µs

(1)

(2)

(3)

Soft start time

EN1

input signal

LED current

(1)

(2)

Dimming pulses enable

EN1

LED ON

typ: 1.3ms

Soft start time