GM6603
3.0A LOW DROPOUT
PRECISION REGULATOR
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.
1N4002
V
IN
GM6603-Ad
j
ADJ
R1
V
OUT
C
OUT
150µF
C
ADJ
10µF
R2
Diodes between the input and output are
not usually needed.
GM6603
V1.00
6
Ripple Rejectiopn
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
reference voltage (V
OUT
/ V
REF
).
GAMMA [ GAMMA MICROELECTRONICS INC. ]
