BD9540EFV Datasheet, PDF (16/18 Pages) Rohm – 2ch Switching Regulators for Desktop PC

BD9540EFV
Technical Note
(11) Regarding input pins of the IC
This monolithic IC contains P+ isolation and P substrate layers between adjacent elements in order to keep them
isolated. PN junctions are formed at the intersection of these P layers with the N layers of other elements, creating
parasitic diodes and/or transistors. For example (refer to the figure below):
 When GND > Pin A and GND > Pin B, the PN junction operates as a parasitic diode
 When GND > Pin B, the PN junction operates as a parasitic transistor
Parasitic diodes occur inevitably in the structure of the IC, and the operation of these parasitic diodes can result in
mutual interference among circuits, operational faults, or physical damage. Accordingly, conditions that cause these
diodes to operate, such as applying a voltage lower than the GND voltage to an input pin (and thus to the P substrate)
should be avoided.
Pin A
N
N ^P+
Parasitic element
Resistor
Pin A
P
P⁺ _N
P substrate
GND
Transistor (NPN)
Pin B _C B
Pin B
E
Parasitic
element
N _P+
Parasitic element
N
P
P⁺ _N
P substrate
GND
GND
B
C
E
Parasitic
element
GND
Other adjacent elements
Example of IC structure
(12)Ground Wiring Pattern
When using both small-signal and large-current GND traces, the two ground traces should be routed separately but
connected to a single ground potential within the application in order to avoid variations in the small-signal ground
caused by large currents. Also ensure that the GND traces of external components do not cause variations on GND
voltage.
●Power Dissipation
5.0
④4.70W
4.0
③3.30W
3.0
2.0 _②1.85W
①1.45W
1.0
①Mounted on board 70mm×70mm×1.6mm glass-epoxy PCB, 1 layer
No copper foil area. θj-a=86.2℃/W
②Mounted on board 70mm×70mm×1.6mm glass-epoxy PCB, 2 layers,
Copper foil area : 15mm×15mm, θj-a=67.6℃/W
③Mounted on board 70mm×70mm×1.6mm glass-epoxy PCB, 2 layers,
Copper foil area :: 70mm×70mm, θj-a=37.9℃/W
④Mounted on board 70mm×70mm×1.6mm glass-epoxy PCB, 4 layers,
Copper foil area :: 70mm×70mm, θj-a=26.6℃/W
0
0
25
50
75
100 125
150
Ambient temperature :Ta [℃]
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2009.04 - Rev.B