BD9285F Datasheet, PDF (26/39 Pages) Rohm – Boost 1channel white LED driver For large LCDs

BD9285F
●3.7. Timing chart
3.7.1 starting up 1 (STB inputs and PWM signal succeeds)
Datasheet
VCC
7.5V
STB
PWM1
andPWM2
TC54
V5UVLO
SS
2.5V
3.0V
1.1V
2.4V
2.5V
1.1V
GATE
FAILB
OFF
STANDBY
SS
(*1)
(*2)
(*3)
Normal
OFF
SS
(Reset)
STANDBY
(*4) (*5)
(*1)…TC54 starts up if STB turns from L to H. The pin SS is not charged in the state that the PWM signal is not input, the boost
is not started.
(*2)…The charge of the pin SS starts by the positive edge of PWM=L to H, and the soft start starts. The GATE pulse outputs
only during PWM=H. And as the SS is less than 1.1V, the pulse does not output. The pin SS continues charging in spite of
the assertion of PWM and OVP.
(*3)…The soft start interval will end if the voltage of the pin SS, Vss reaches to 3.0V. By this time, BD9285 boost Vout where the
set LED current flows. It is started to monitor the abnormal detection of SCP and OPEN.
(*4)…As STB=L, instantaneously the boost operation is stopped. (GATE=L, SS=L) On the other hand, the discharge circuit
works in the interval “STB=L and V5UVLO=H”. Please refer to the time chart in the section 3.7.3 for details.
(*5)…As STB=H again, the boost operation restarts by the next PWM=L to H. It is the same operation as the timing of (*1).
Please refer to the section 3.4.1 for the setting of soft start external capacitance.
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TSZ02201-0F1F0C100030-1-2
11.Jul.2012 Rev.001