BD6761FS,BD6762FV

Technical Note

21/22

www.rohm.com

2010.06 - Rev.A

© 2010 ROHM Co., Ltd. All rights reserved.

(12) Regarding input pin of the IC

This monolithic IC contains P+ isolation and P substrate layers between adjacent elements in order to keep them

isolated.

P/N junctions are formed at the intersection of these P layers with the N layers of other elements to create a variety of

parasitic elements.

For example, when a resistor and transistor are connected to pins as shown in Fig. 14,

○ the P/N junction functions as a parasitic diode

when GND > (Pin A) for the resistor or GND > (Pin B) for the transistor (NPN).

○ Similarly, when GND > (Pin B) for the transistor (NPN), the parasitic diode described above combines

with the N layer of other adjacent elements to operate as a parasitic NPN transistor.

The formation of parasitic elements as a result of the relationships of the potentials of different pins is an inevitable result

of the IC's architecture. The operation of parasitic elements can cause interference with circuit operation as well as IC

malfunction and damage. For these reasons, it is necessary to use caution so that the IC is not used in a way that will

trigger the operation of parasitic elements, such as by the application of voltages lower than the GND (P substrate)

voltage to input pins.

(13) Ground Circuit Pattern

When using both small signal and large current GND patterns, it is recommended to isolate the two ground patterns,

placing a single ground point at the application's reference point so that the pattern wiring resistance and voltage

variations caused by large currents do not cause variations in the small signal ground voltage. Be careful not to change

the GND wiring pattern of any external parts, either.

Fig. 14 Mimetic Diagram of Parasitic Element

Resistor

Transistor (NPN)

N

N

N

P

+

P

+

P

P substrate

GND

Parasitic element

Pin A

N

N

P

+

P

+

P

P substrate

GND

Parasitic element

Pin B

C

B

E

N

GND

Pin A

Parasitic

element

Pin B

Other adjacent elements

E

B

C

GND

Parasitic

element