BD9845FV Datasheet, PDF (13/16 Pages) Rohm – Single/Dual-output High-frequency Step-down Switching Regulator(Controller type)

BD9845FV
Technical Note
5) About board layout
In order to make full use of IC performance, fully investigate the items below in addition to general precautions.
・ Each output of OCP+/OCP- is such a sensitive circuit. When wiring is routed around, it is easily subjected to noise.
Try to make the wiring as short as possible.
・ Switching of large current is likely to generate noise. Try to make the large current route (VIN, Rsense, FET, L, Di,
and Cout) as thick and short as possible, and try to apply one-point grounding for GND. OUT terminal is also a
switching line, and it must be wired along a distance as short as possible. (When multi-layer board is used, shielding
by intermediate layer also seems to be effective.)
・ C_CT and C_VREF are reference of all, and must be wired along the shortest distance to GND of IC stabilized to be
protected against external influence.
・ Also be careful not to allow common impedance to sense family GND.
6) PIN processing of channel unused
VREF
VREF
VCC VCC
VREF DT SS INV FB
1 14 13 12 11
OCP- OCP+ VCC OUT
987 6
Fig.43
When only one channel is used, process unused channels as shown above.
●I/O equivalent circuit diagram
2pin(CT)
VREF
VREF VREF ^{VREF VREF}
14pin (DT)
VREF
VREF
CT
DT
12pin (INV)
VREF VREF
INV
11pin (FB)
VREF
VREF
FB
13pin (SS)
VREF
VREF
VCC
SS
VREF
9pin (OCP-)
VCC
VCC
OCP-
5pin (C5V)
VCC
VCC
VCC
VCC
C5V
6pin (OUT)
VCC
VCC
OUT
C5V
C5V
8pin (OCP+)
VCC
VCC
OCP+
4pin (STB)
VCC
STB
10pin (SEL)
VCC
C5V
C5V
1pin (VREF)
VCC
VCC
SEL
VREF
C5V
C5V
3pin (GND) , 7pin (VCC)
VCC
GND
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13/15
2009.05 - Rev.A