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BD9486F

1ch Boost up type White LED Driver for large LCD

ROHM Semiconductor 

BD9486F

●3.5.Timing Chart

3.5.1 PWM Start up 1 (Input PWM Signal After Input STB Signal)

VCC

7.5V

STB

PWM

REG50

SS

GATE

RT

2.6V

3.7V

0.4V

2.0V

Datasheet

0.4V

STATE

OFF

STANDBY

SS

Normal

STANDBY SS

(*1) (*2)

(*3)

(*4)

(*5) (*6)

Figure 32. PWM Start up 1 (Input PWM Signal After Input STB Signal)

(*1)…REG50 starts up when STB is changed from Low to High. In the state where the PWM signal is not inputted, SS terminal

is not charged and DCDC doesn’t start to boost, either.

(*2)…When REG50 is more than 2.6V, the reset signal is released.

(*3)…The charge of the pin SS starts at the positive edge of PWM=L to H, and the soft start starts. The GATE pulse outputs only

during the corresponding PWM=H. And while the SS is less than 0.4V, the pulse does not output. The pin SS continues

charging in spite of the assertion of PWM or OVP level.

(*4)…The soft start interval will end if the voltage of the pin SS, Vss reaches 3.7V. By this time, it boosts VOUT to the voltage

where the set LED current flows. The abnormal detection of FBMAX starts to be monitored.

(*5)…As STB=L, the boost operation is stopped instantaneously. (Discharge operation continues in the state of STB=L and

REGUVLO=L. Please refer to section 3.5.3)

(*6)…In this diagram, before the charge period is completed, STB is changed to High again. As STB=H again, the boost

operation restarts the next PWM=H. It is the same operation as the timing of (*2). (For capacitance setting of SS terminal,

please refer to section 3.2.1.

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