SM8136A

SEIKO NPC CORPORATION —6

The SM8136A output mode switches between 3 operating modes in response to the operating conditions. The

modes are: standby mode,

×1.0 mode (VIN through mode), and ×1.5 mode (1.5-times charge pump boost). The

VOUT output switches automatically between these modes in response to the drive LED characteristics and the

overall power consumption. Switching from

×1.0 mode to ×1.5 mode is controlled automatically by an internal

circuit. The operating mode cannot be specified by an external control signal.

Startup: Internal Reset Time and Soft Start Time

The SM8136A normal startup procedure (after VIN has been applied previously) is to switch from standby

mode to the

×1.0/×1.5 operating modes when the EN enable input goes HIGH. The soft start time (described

on the following page) begins after switching to the operating mode using EN.

(1) VIN is HIGH, EN is LOW (standby mode)

(2) Switches to an operating mode when EN goes HIGH (soft start time begins)

If the use at EN = VIN when power is applied, the startup commences after the power-ON reset (POR) time

(approximately 50

µs) has elapsed.

(1) When using at EN = VIN, rising time from 0.3V to 2.7V should set < 50

µs.

(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 ris-

ing 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.

Normal startup

Internal reset operation when power is applied (power-ON reset)

Soft start time

VIN

EN

VIN High

ENABLE ON

(1)

(2)

Standby mode

EN = VIN

1.5 mode

Internal

power on

reset

Internal

enable

(CE)

POR time

typ: 50

µs

(2)

(3)

Soft start time

Standby mode

(1)

< 50

µs

0.3V

2.7V