bd9745ekn ROHM Co. Ltd., bd9745ekn Datasheet - Page 17

• Manufacturer Part Number: bd9745ekn
• Description: 7-channel Switching Regulator Controller For Digital Camera
• Manufacturer: ROHM Co. Ltd.

○ APPLICATION INFORMATION
１.) CH1 Start up sequence.
Using step up function in CH1, please take below measure to prevent operation faults and destruction on start-up.
ａ：CH1 output input to VCC
ｂ：A battery input to VCC, or external power supply input to VCC.（Fig－5）
It must be put schottky Di between Lx1 and Hx1 to clamp Lx1 voltage the input of VBAT pin must short to VCC line and input through C-R filter.
(Ref Fig-7)
The ERRCOMP circuit that adjust CH1 output voltage on UVLO condition, switches Lx1 NMOS ON/OFF to compare INV1 and soft-start output.
As a rule, VCC voltage is applied before applying STB voltage, or applied at the same time. At the worst, when VCC voltage is applied late
from STB, UVLO function must be canceled within 1msec from applying STB voltage.
In this circuit, if it is late to switch from start up OSC to main current mode control, it is possible that the output voltage is overshot (Ref, Fig－6)
INV1
Current mode
CH1 Step up
/down
control
0.8V
SS
STB,UVLO
+
-
+
+
-
● ERRCOMP: To compare SS and INV1
STB1
DRIVER
PVCC
DRIVER
Pch
Nch
ERRCOMP
Fig – 7. Recommended application circuit of CH1
ERRAMP
Fig - 6 CH1 Block diagram: Start up circuit
CTL
BG
ON/OFF
STB1
VCC
2.6V
PVCC
Hx1
Lx1
UDSEL
VBAT
VCC
0
PGND12
RB551V-30
Current mode
Control Block
Within 1msec
L
Start-Up
Fig－5
OSC
C
REV. D
UVLO and UDSEL ⇒ ON
UNREG
C
ｔ
ｔ
UVLO ⇒ ON
R
UDSEL pin of
Step-down short to VBAT
Capacitance[uF]
A parameter of C-R
4.7
10
1
Vo1
(Feed Back 1ch)
VBAT pin connect
to VCC,PVCC line
DRIVER
DRIVER
Nch
Pch
Resistance[Ω]
2.2～10
5.0V
1～10
10
PGND12
Hx1
Lx1
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