GM6605
5.0A LOW DROPOUT
PRECISION REGULATOR
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
I
n microprocessor applications an output capacitor network of several tantalum and ceramic capacitors
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
regulator. The discharge current depends on the value of capacitor, output voltage, and rate at which V
IN
drops.
1N4002
1N4002
V
IN
V
OUT
V
IN
V
OUT
GM6605-3.3
C1
GND
C2
C1
GM6605-Ad
j
ADJ
C
ADJ
R1
C2
R2
(a) Fixed version
(b) Adjustable version
Figure 1. Protection Diode Scheme
for large Output Capacitors
GM6605
V2.04
7
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.
GAMMA [ GAMMA MICROELECTRONICS INC. ]
