BA78□□Series,BA78M□□Series
Technical Note
11/12
www.rohm.com
2012.03 - Rev.C
© 2012 ROHM Co., Ltd. All rights reserved.
●Notes for use
(1) Absolute Maximum Ratings
While utmost care is taken to quality control of this product, any application that may exceed some of the absolute
maximum ratings including the voltage applied and the operating temperature range may result in breakage. If broken,
short-mode or open-mode may not be identified. So if it is expected to encounter with special mode that may exceed the
absolute maximum ratings, it is requested to take necessary safety measures physically including insertion of fuses.
(2) Ground voltage
Make setting of the potential of the GND terminal so that it will be maintained at the minimum in any operating state.
Furthermore, check to be sure no terminals are at a potential lower than the GND voltage including an actual electric transient.
(3) Thermal design
When you do the kind of use which exceeds Pd, It may be happened to deteriorating IC original quality such as decrease
of electric current ability with chip temperature rise. Do not exceed the power dissipation (Pd) of the package specification
rating under actual operation, and please design enough temperature margins.
(4) Short-circuiting between terminals, and mismounting
When mounting to pc board, care must be taken to avoid mistake in its orientation and alignment. Failure to do so may
result in IC breakdown. Short-circuiting due to foreign matters entered between output terminals, or between output and
power supply or GND may also cause breakdown.
(5) Operation in Strong electromagnetic field
Be noted that using the IC in the strong electromagnetic radiation can cause operation failures.
(6) Inspection with the IC set to a pc board
If a capacitor must be connected to the pin of lower impedance during inspection with the IC set to a pc board, the
capacitor must be discharged after each process to avoid stress to the IC. For electrostatic protection, provide proper
grounding to assembling processes with special care taken in handling and storage. When connecting to jigs in the
inspection process, be sure to turn OFF the power supply before it is connected and removed.
(7) Input to IC terminals
This is a monolithic IC with P
+
isolation between P-substrate and each element as illustrated below. This P-layer and the
N-layer of each element form a P-N junction, and various parasitic element are formed.
If a resistor is joined to a transistor terminal as shown in Fig 28.
○P-N junction works as a parasitic diode if the following relationship is satisfied;
GND>Terminal A (at resistor side), or GND>Terminal B (at transistor side); and
○if GND>Terminal B (at NPN transistor side),
a parasitic NPN transistor is activated by N-layer of other element adjacent to the above-mentioned parasitic diode.
The structure of the IC inevitably forms parasitic elements, the activation of which may cause interference among circuits,
and/or malfunctions contributing to breakdown. It is therefore requested to take care not to use the device in such
manner that the voltage lower than GND (at P-substrate) may be applied to the input terminal, which may result in
activation of parasitic elements.
(8) Ground wiring pattern
If small-signal GND and large-current GND are provided, It will be recommended to separate the large-current GND
pattern from the small-signal GND pattern and establish a single ground at the reference point of the set PCB so that
resistance to the wiring pattern and voltage fluctuations due to a large current will cause no fluctuations in voltages of the
small-signal GND. Pay attention not to cause fluctuations in the GND wiring pattern of external parts as well.
(9) Thermal shutdown circuit
A temperature control circuit is built in the IC to prevent the damage due to overheat.Therefore, the output is turned off
when the thermal circuit works and is turned on when the temperature goes down to the specified level.
But, built-in the IC a temperature control circuit to protect itself, and avoid the design used the thermal protection.
(10) Over current protection circuit
The over-current protection circuits are built in at output, according to their respective current outputs and prevent the IC
from being damaged when the load is short-circuited or over-current. But, these protection circuits are effective for
preventing destruction by unexpected accident. When it’s in continuous protection circuit moving period don’t use please.
And for ability, because this chip has minus characteristic, be careful for heat plan.
(11) There is a possibility to damage an internal circuit or the element when Vin and the voltage of each terminal reverse in the
application. For instance, Vin is short-circuited to GND etc. with the charge charged to an external capacitor. Please use
the capacitor of the output terminal with 1000μF or less. Moreover, the Vin series is recommended to insert the diode of
the by-pass the diode of the backflow prevention or between each terminal and Vin.
Fig.27 Bypass Diode Fig.28
Simplified structure of monorisic IC
VCC
Output terminal
Bypass diode
Backflow prevention diode
P substrate
Pin A
aras
c
element
Resistor
N
N N
P
+
P
+
P
GND
Parasitic element
Pin A
P substrate
Transistor (NPN)
N
N
P
+
P
+
P
GND
Parasitic element
Pin B
C
B
E
N
GND
Pin B
Other adjacent elements
E
B C
GND
aras
c
element
