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SM8135B

White LED Driver IC

Nippon Precision Circuits  

SM8135B

VOUT Output Circuit Mode Switching

The SM8135B output mode switches between 4 operating modes in response to the operating conditions. The

modes are: standby mode, ×1.0 mode (VIN through mode), ×1.5 mode (1.5-times charge pump boost), and

×2.0 mode (2.0-times charge pump boost). Specifically, the use of ×1.0 mode, ×1.5 mode, and ×2.0 mode

allows the VOUT output to be adjusted automatically to match drive LED characteristics. Switching between

×1.0 mode, ×1.5 mode, and ×2.0 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 SM8135B normal startup procedure (after VIN has been applied previously) is to switch from standby

mode to the ×1.0/×1.5/×2.0 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.

VIN High

VIN

EN Standby mode

(1)

Soft start time

ENABLE ON

(2)

Normal startup

(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 VIN supply voltage is applied when EN is HIGH level, startup commences after the power-ON reset

(POR) time (approximately 50µs) has elapsed.

VIN power source

(1)

Internal

power on

reset

Internal

enable

(CE)

POR time

typ: 50µs

(2)

Standby mode

Soft start time

(3)

1.5 mode

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

(1) VIN voltage rises when power is applied.

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

SEIKO NPC CORPORATION —7

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