Voltage Regulators

AN78xx/AN78xxF Series

9

I Usage Notes

1. Cautions for a basic circuit

is long, it is likely to oscillate in output. A capacitor of 0.1

µF to

0.47

µF should be connected near an input pin.

connect an electrolytic capacitor of 10

µF to 100µF to improve a

transitional response of output voltage.

residual voltage at the output capacitor Co even after switching

off the supply power because a current is likely to flow into an

output pin of the IC and damage the IC.

2. Other caution items

1) Short-circuit between the input pin and GND pin

If the input pin is short-circuitted to GND or is cut

off when a large capacitance capacitor has been con-

nected to the IC's load, a voltage of a capacitor con-

nected to an output pin is applied between input/out-

put of the IC and this likely results in damage of the

IC. It is necessary, therefore, to connect a diode, as

shown in figure 2, to counter the reverse bias between

input/output pins.

2) Floating of GND pin

If a GND pin is made floating in an operating mode, an unstabilized input voltage is outputted. In this case, a

thermal protection circuit inside the IC does not normally operate. In this state, if the load is short-circuited or

overloaded, it is likely to damage the IC.

I Application Circuit Examples

1. Current bootstrap circuit

I Basic Regulator Circuit

Input

Output

AN78xx

AN78xxF

Common

13

2

0.33

µF

0.1

µF

3

Ω

AN78xx

AN78xxF

AN78xx

AN78xxF

13

2

1

3

2

Figure 1

1

3

2

In

GND

Out

Output

Figure 2

1

3

2

+

−

2. Adjustable output regulator