BD7957FS-E2 Datasheet, PDF (13/17 Pages) Rohm – Simple Step-down Switching Regulators with Built-in Power MOSFET

BD9701FP/CP-V5/T/T-V5,BD9703FP/CP-V5/T/T-V5,BD9702CP-V5/T/T-V5 Technical Note
8. IC pin input
This IC is a monolithic IC which (as below) has P+ substrate and betweenthe various pin. A P-N junction is formed from
this P layer of each pin. For example the relation between each potential is as follows. (When GND > PinB and GND >
PinA, the P-N junction operates as a parasitic diode.) Parasitic diodes can occur inevitably in the structure of the IC. The
operation of parasitic diodes can result in mutual interference among circuits as well as operation faults and physical
damage. Accordingly, you must not use methods by which parasitic diodes operate, such as applying a voltage that is
lower than the GND(P substrate)voltage to an input pin.
(PinA)
Resistance
(PinB)
Transistor (NPN)
B
ï¼£
E
P^＋
N
P
N
P substrate
P^＋
ï¼®
P^＋
N
N
P
N
P substrate
GND
P^＋
N
Parasitic diode
GND
Parasitic diode
ＧＮＤ
(PinB)
(PinA)
B
Parasitic diode
GND
Other adjacent components
C
E
GND
Parasitic diode
Fig.34 Simplified structure of a Bipolar IC
9. Common impedance
Power supply and ground wiring should reflect consideration of the need to lower common impedance and minimize ripple
as much as possible (by making wiring as short and thick as possible or rejecting ripple by incorporating inductance and
capacitance).
10. Pin short and mistake fitting
Do not short-circuit between OUT pin and VCC pin, OUT pin and GND pin,
or VCC pin and GND pin. When soldering the IC on circuit board,
please be unusually cautious about theorientation and the position of the IC.
Bypass diode
Back current prevention diode
VCC
Output Pin
Fig.35
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13/16
2009.04- Rev.B