7

GM6605

5.0A LOW DROPOUT

PRECISION REGULATOR

GM6605-3.3

GND

C2

C1

R2

R1

C1

GM6605-Adj

ADJ

C2

(a) Fixed version

(b) Adjustable version

1N4002

1N4002

Application Information

GM6605 series linear regulators provide fixed and adjustable output voltages at currents up to 5.0A.

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

The GM6605 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 output compensation capacitor helps to determine three main characteristics of a linear regulator's

performance: start-up delay, load transient response, and loop stability. The capacitor value and type is

based on cost, availability, size, and temperature constraints. A tantalum or aluminum electrolytic

capacitor is preferred, as a film or ceramic capacitor with almost zero ESR can cause instability. An

aluminum electrolytic capacitor is the least expensive type. But when the circuit operates at low

temperatures, both the value and ESR of the capacitor will vary widely. For optimum performance over

the full operating temperature range, a tantalum capacitor is the best. A 22µF tantalum capacitor will

work fine in most applications. But with high current regulators, such as GM6605 higher capacitance

values will improve the transient response and stability. Most applications for Gm6605 involve large

changes in load current, so the output capacitor must supply instantaneous load current. The ESR of

the output capacitor causes an immediate drop in output voltage given by:

V = I x ESR

in parallel is commonly used. This reduces overall ESR and minimizes the instantaneous output voltage

drop under transient load conditions. The output capacitor network should be placed as close to the

load as possible for the best results.

Protection Diodes

When large external capacitors are used with most linear regulators, it is wise to add protection diodes. If

the input voltage of the regulator is shorted, the output capacitor will discharge into the output of the

drops.

For GM6605, the discharge path is through a large junction, and protection diodes are normally not needed.

However, if the regulator is used with large output capacitance values and the input voltage is

instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown above

in Figure 1 is recommended.

Figure 1. Protection Diode Scheme

for large Output Capacitors