BD9745EKN Datasheet, PDF (17/22 Pages) Rohm – Silicon Monolithic Integrated Circuit

○APPLICATION INFORMATION
17/21
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
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)
ｂ：A battery input to VCC, or external power supply input to VCC.（Fig－5）
The ERRCOMP circuit that adjust CH1 output voltage on UVLO condition, switches Lx1 NMOS ON/OFF to compare INV1 and soft-start output.
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)
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.
STB1
　ｔ
Within 1msec
VCC
2.6V
　ｔ
0
Fig－5
● ERRCOMP: To compare SS and INV1
SS
STB1
UVLO and UDSEL ⇒ ON
INV1
0.8V
-
ON/OFF
+
ERRCOMP
Start-Up
OSC
Pch
DRIVER
-
+
+
ERRAMP
Current mode
Control Block
UVLO ⇒ ON
Nch
DRIVER
STB,UVLO
Fig - 6 CH1 Block diagram: Start up circuit
Hx1
Lx1
PGND12
UDSEL pin of
Step-down short to VBAT
VCC
UDSEL
VBAT
CH1 Step up
/down
Current mode
control
Pch
DRIVER
PVCC
Nch
DRIVER
Hx1
RB551V-30
BG
C
CTL
Lx1 ^L
PGND12
PVCC
VBAT pin connect
to VCC,PVCC line
C
R
UNREG
Vo1
(Feed Back 1ch)
5.0V
A parameter of C-R
Capacitance[uF] Resistance[Ω]
10
1～10
4.7
2.2～10
1
10
Fig – 7. Recommended application circuit of CH1
REV. D