BD9285F Datasheet, PDF (32/39 Pages) Rohm – Boost 1channel white LED driver For large LCDs

BD9285F
3.7.7 LED OPEN detection
Datasheet
STB
PWM1and
PWM2
0.1V
0.1V
0.1V
ISENSE
GATE
・・・・・
・・・・・
①② ③ ④
CPcountor
4096count
3.0V
SS
1.1V
1.1V
DIMOUT
FAILB
STATE OFF
SS
STANDBY
(*1) (*2)
NORMAL
CP COUNTOR
RESET
SS
(*3)
(*4)
(off)
latch
STANDBY
off
(*5) (*6)
(*7)
(*1)…During starting up, even if the normality, ISENSE<0.1V because of the low Vout. Therefore the OPEN detection will be
masked for the soft start period.
(*2)…In the same way, as PWM=L, ISENSE<0.1V because of DIMOUT=L. OPEN will be masked, too.
(*3)…Though the OPEN is detected if ISENSE<0.1V as the PWM=H, it is not judged immediately to abnormal state. The
behavior of GATE, FAILB keeps the normal operation.
(*4)…The CP counter will start if the OPEN detection continues 4 clock of the GATE frequency. To detect the OPEN state
continuously, it compulsorily becomes DIMOUT=H regardless of the PWM logic.
(*5)…When the OPEN detection continues up to 4649 count with the CP counter, IC will be latched off. At this time, it asserts
GATE=L, DIMOUT=L, FAILB=L for the first time.
(*6)…The latch off state can be reset by the STB=L.
(*7)…It normally starts by STB=L to H, in this figure.
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TSZ02201-0F1F0C100030-1-2
11.Jul.2012 Rev.001