BD9870FPS_09 Datasheet, PDF (10/12 Pages) Rohm – Simple Step-down Switching Regulator with Built-in Power MOSFET

BD9870FPS
Technical Note
10.This IC is a monolithic IC which (as below) has P+ substrate and between
the 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 operationfaults and physical damage.
Accordingly, you must not use methods by which parasitic diodesoperate, such as applying a voltage that is lower than the
GND(P substrate)voltage toan input pin.
(PinA)
Resistance
(PinB)
B
C
Transistor (NPN)
E
P^＋
N
P
N
P substrate
P^＋
N
P^＋
N
N
P
N
P substrate
GND
P^＋
N
Parasitic diode
(PinA)
GND
Parasitic diode
(PinB)
Parasitic diode
B
GND
Simplified structure of a Bipolar IC
Other adjacent components
GND
C
E
GND
Parasitic diode
●Power Dissipation
（W）₅
4
③3.50W
①No heat sink
②2 layer PCB (Copper laminate area 15 mm×15mm)
③2 layer PCB (Copper laminate area 70 mm×70mm)
3
2
②1.85W
1
①0.80W
0
0
25
50
75 85 100
125
AMBIENT TEMPERATURE [Ta]
*When mounted on a 70mmx70mmx1.6mm board
150
（℃）
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10/11
2009.05 - Rev.A