SM8135A

SEIKO NPC CORPORATION —13

The mode reset operation when in

×2.0 mode performs boost mode switching between ×2.0 mode and ×1.5

mode. Mode switching directly from

×2.0 mode to ×1.0 mode does not occur.

(1) Mode switches from

×2.0 to ×1.5 mode on the rising edge of the mode reset signal.

(2) A 200

µs (max) mode hold time begins after switching to ×1.5 mode. LED drive current insufficient state is

detected but the mode is not switched during this interval.

(3) LED drive current insufficient signal is ignored during the mode hold time, but normal mode switching

operation resumes when the mode hold time elapses.

The mode reset function periodically tests the boost mode to try to maximize the duration of operation in the

higher efficiency

×1.0 and ×1.5 modes in order to extend battery drive time.

Thermal Shutdown Circuit (Overtemperature Protection Circuit)

The SM8135A features a thermal shutdown circuit that operates whenever the IC temperature exceeds approx-

imately 170

ature falls below approximately 150°C.

Switching from

×2.0 mode to ×1.5 mode due to mode reset signal

Mode hold

(L: hold)

Mode reset

1.0sec/cycle

min 80

µs

max 200

µs

ignore

4.9V

2.0 mode

1.5 mode

2.0 mode