BD9285F ROHM [Rohm], BD9285F Datasheet - Page 17

• Manufacturer Part Number: BD9285F
• Description: Boost 1channel white LED driver For large LCDs
• Manufacturer: ROHM [Rohm]

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© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
BD9285F
●3.4.2 how to shutdown and set TC54 capacitance
●3.4.3 The LED current setting
This IC is equipped the discharge function when shutdown is operated.
○ ○ ○ ○ Explanation of shutdown sequence
① When STB=L, DC/DC and TC54 are stop.
② When STB=L, TC54UVLO=H, the DIMOUT logic asserts the PWM logic. The voltage of TC54 (5.4V) will decrease by
the constant current -10uA and is discharged to 2.4V.
③ VOUT will be discharged and ILED decresing.
④ When the voltage of TC54 pin is under 2.4V(typ.), the IC will shutdown.
○ ○ ○ ○ The setting method of TC54 external capacitance
Please use below formula to calculate the shutdown time TOFF.
As shown the above, the PWM signal is required even after STB=L.
The discharge interval of VOUT is the longest in the minimum PWM duty. Please set the Creg value with a enough timing
margin from the end of the VOUT discharge to shutdown.
○ ○ ○ ○ the relationship between RISET and ILED current
[setting example]
If ILED current is 400mA as ADIM is 1.5V, we can calculate R
LED current can be adjusted by setting the resistance R
to ISENSE pin.
Without DC dimming
With DC dimming
R
ISENSE
ADIM
I
R
R
LED
ISENSE
ISENSE
T
OFF
[
A
[
V
]
Figure 23. the shutdown waveform and circuit
]
I
C
ADIM
3
LED
I
1
[ 5 .
0
REG
LED
[ 5 .
[ 4 .
[
V
A
V
[
10
[
A
]
F
A
[
]
]
]
V
[
]
]
[
]
uA
[
]
. 3
. 3
17/36
]
75
[ 0
]
ISENSE
[
V
]
ISENSE
]
which connects
[
Sec
as below.
]
Figure 24. the example of LED
current setting
TSZ02201-0F1F0C100030-1-2
Error AMP
-
+
+
3.5V
11.Jul.2012 Rev.001
DIMOUT
ADIM
FB
ISENSE
Datasheet
Vout
R
ISENSE