Technical Note
7/9
BD3570FP/HFP, BD3571FP/HFP, BD3572FP/HFP, BD3573FP/HFP
BD3574FP/HFP, BD3575FP/HFP
www.rohm.com
2011.03 - Rev.B
© 2011 ROHM Co., Ltd. All rights reserved.
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.
Fig. 26 Example of a Simple Monolithic IC Architecture
8) Ground wiring patterns
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.
9) SW Pin
Do not apply the voltage to SW pin when the V
CC is not applied.
And when the V
CC is applied, the voltage of SW pin must not exceed VCC.
10) Thermal shutdown circuit (TSD)
This IC incorporates a built-in thermal shutdown circuit for the protection from thermal destruction. The IC should be used
within the specified power dissipation range. However, in the event that the IC continues to be operated in excess of its
power dissipation limits, the attendant rise in the chip's temperature T
j will trigger the thermal shutdown circuit to turn off
all output power elements. The circuit automatically resets once the chip's temperature T
j drops.
The thermal shutdown circuit operates if the IC is under conditions in express of the absolute maximum ratings. Never
design sets on the premise of using the thermal shutdown circuit. (See Fig. 8)
11) Overcurrent protection circuit (OCP)
The IC incorporates a built-in overcurrent protection circuit that operates according to the output current capacity. This
circuit serves to protect the IC from damage when the load is shorted. The protection circuit is designed to limit current
flow by not latching in the event of a large and instantaneous current flow originating from a large capacitor or other
component. These protection circuits are effective in preventing damage due to sudden and unexpected accidents.
However, the IC should not be used in applications characterized by the continuous operation or transitioning of the
protection circuits. At the time of thermal designing, keep in mind that the current capability has negative characteristics to
temperatures. (See Fig. 3)
GND
N
P
NN
P+
P+
Parasitic elemen
or transistor
P
substr
(Pin B
C
B
E
Transistor (NPN)
(Pin A)
GND
N
P
N
N
P+
P+
Resistor
Parasitic element
P
Parasitic elements
(Pin A)
Parasitic element o
transistor
(Pin B
GND
C
B
E
