SM8132A

NIPPON PRECISION CIRCUITS INC.—10

The SM8132A 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 SM8132A switches from standby condition (power-save mode) to normal operating condition (

×1.0/×1.5

mode) on the first rising edge of EN. Note that if the VIN supply voltage is applied when EN is HIGH, startup

occurs after the internal power-ON reset time (approximately 50

µs) expires. At startup, 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 EN 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 EN is 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

EN

input signal

LED current

(1)

(2)

Dimming pulses enable

LED ON

typ: 1.3ms

Soft start time

EN