Technical Note

9/11

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2011.03 - Rev.C

© 2011 ROHM Co., Ltd. All rights reserved.

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Other Points of Caution

1) Protection Circuits

Over-current Protection Circuit

A built-in over-current protection circuit corresponding to the current capacity prevents the destruction of the IC when there

are load shorts. This protection circuit is a “7”-shaped current control circuit that is designed such that the current is restricted

and does not latch even when a large current momentarily flows through the system with a high-capacitance capacitor.

However, while this protection circuit is effective for the prevention of destruction due to unexpected accidents, it is not

suitable for continuous operation or transient use. Please be aware when creating thermal designs that the overcurrent

protection circuit has negative current capacity characteristics with regard to temperature (Refer to Figs.4 and 16).

Thermal Shutdown Circuit (Thermal Protection)

This system has a built-in temperature protection circuit for the purpose of protecting the IC from thermal damage.

As shown above, this must be used within the range of acceptable loss, but if the acceptable loss happens to be

continuously exceeded, the chip temperature Tj increases, causing the temperature protection circuit to operate.

When the thermal shutdown circuit operates, the operation of the circuit is suspended. The circuit resumes operation

immediately after the chip temperature Tj decreases, so the output repeats the ON and OFF states (Please refer to

Figs.12 and 24 for the temperatures at which the temperature protection circuit operates).

There are cases in which the IC is destroyed due to thermal runaway when it is left in the overloaded state. Be sure to

avoid leaving the IC in the overloaded state.

Reverse Current

In order to prevent the destruction of the IC when a reverse current flows through the IC, it is recommended that a diode

be placed between the Vcc and Vo and a pathway be created so that the current can escape (Refer to Fig.35).

Fig. 36:Bypass diode

2) This IC is bipolar IC that has a P-board (substrate) and P+ isolation layer between each devise, as shown in Fig.36. A P-N

junction is formed between this P-layer and the N-layer of each device, and the P-N junction operates as a parasitic diode

when the electric potential relationship is GND> Terminal A, GND> Terminal B, while it operates as a parasitic transistor

when the electric potential relationship is Terminal B GND> Terminal A. Parasitic devices are structurally inevitable in the

IC. The operation of parasitic devices induces mutual interference between circuits, causing malfunctions and eventually

the destruction of the IC. It is necessary to be careful not to use the IC in ways that would cause parasitic elements to

operate. For example, applying a voltage that is lower than the GND (P-board) to the input terminal.

Fig. 37: Example of the basic structure of a bipolar IC

OUT

Vcc

CTL

GND

Reverse current

(Pin A)

GND

N

P+

Resistor

Parasitic element

P

N

P

P+

N

(Pin A)

Parasitic element

or transistor

(Pin B)

GND

C

B

E

Parasitic element

GND

GND

N

P

N

P+

P+

Parasitic element

or transistor

(Pin B)

B

E

Transistor (NPN)

N

P

N

GND

C