7

GM6603

3.0A LOW DROPOUT

PRECISION REGULATOR

R2

R1

ADJ

150

μF

1N4002

10

μF

Application Information

GM6603 series linear regulators provide fixed and adjustable output voltages at currents up to 3.0A.

These regulators are protected against over-current conditions and include thermal shutdown protection.

The GM6603 has a composite PNP-NPN output transistor and require an output capacitor for stability.

A detailed procedure for selecting this capacitor is as below:

Stability Considerations

The circuit design used in the GM6603 series requires the use of an output capacitor as part of the device

frequency compensation. The addition of 150µF aluminum electrolytic or a 22µF solid tantalum on the output

will ensure stability for all operating conditions.

When the adjustment terminal is bypassed with a capacitor to improve the ripple rejection, the requirement

for an output capacitor increases. The value of 22µF tantalum or 150µF aluminum covers all cases of

bypassing the adjustment terminal. Without bypassing the adjustment terminal smaller capacitors can be

used with equally good results.

To ensure good transient response with heavy load current changes capacitor values on the order of 100µF

are used in the output of many regulators. To further improve stability and transient response of these

devices larger values of output capacitor can be used.

Protection Diodes

Unlike older regulators, the GM6603 family does not need any protection diodes between the adjustment pin

and the output and from the output to the input to prevent over stressing the die. Internal resistors are

limiting the internal current paths on the GM6603 adjustment pin, therefore even with capacitors on the

adjustment pin no protection diode is needed to ensure device safety under short-circuit conditions.

Microsecond surge currents of 50A to 100A can be handled by the internal diode between the input and

output pins of the device. In normal operations it is difficult to get those values of surge currents even with

the use of large output capacitances. If high value output capacitors are used, such as 1000µF to 5000µF at

the input pin, is instantaneously shorted to ground, damage can occur. A diode from output to input is

recommended, when a crowbar circuit at the input of the GM6603 is used. Normal power supply cycling or

even plugging and unplugging in the system will not generate current large enough to do any damage.

The adjustment pin can be driven on a transient basis ±25V, with respect to the output without any device

degradation. As with any IC regulator, none the protection circuitry will be functional and the internal

transistors will break down if the maximum input to output voltage differential is exceeded.

Ripple Rejection

The ripple rejection values are measured with the adjustment pin bypassed. The impedance of the adjust pin

capacitor at the ripple frequency should be less than the value of R1 (normally 100. to 120.) for a proper

bypassing and ripple rejection approaching the values shown. The size of the required adjust pin capacitor is

a function of the input ripple frequency. If R1=100. at 120Hz the adjust pin capacitor should be 25µF. At

10kHz only 0.22µF is needed. The ripple rejection will be a function of output voltage, in circuits without an

adjust pin bypass capacitor. The output ripple will increase directly as a ratio of the output voltage to the

Diodes between the input and output are

not usually needed.