Input Capacitor
The error flag is an open-collector output that can
sink 10mA during a fault condition. Low output
voltage can be caused by a number of problems,
including an overcurrent fault (device in current limit)
or low input voltage. The flag is inoperative during
overtemperature shutdown. When the error flag is
not used, it is best to leave it open. The flag pin can
be tied directly to pin 4, the output pin.
An input capacitor of 1µF or greater is recommended
when the device is more than 4 inches away from the
bulk as supply capacitance, or when the supply is a
battery. Small surfacemount ceramic chip capacitors
can be used for the bypassing. Larger values will help
to improve ripple rejection by bypassing the input to the
regulator, further improving the integrity of the output
voltage.
Enable Input
Transient Response and 3.3V to 2.5V and 2.5V to
1.8V Conversions
The GM66300 series version features an enable
input for on/off control of the device. Its shutdown
state draws "zero" current. The enable input is
TTL/CMOS compatible for simple logic interface, but
can be connected to up to 20V. When enabled, it
draws approximately 15µA.
The GM66300 series has excellent transient response
to variations in input voltage and load current. The
device has been designed to respond quickly to load
current variations and input voltage variations. Large
output capacitors are not required to obtain this
performance. A standard 47µF output capacitor,
preferably tantalum, is all that is required. Larger
values improve performance even further.
By virtue of its low-dropout voltage, this device does
not saturate into dropout as readily as similar NPN-
based designs. When converting from 3.3V to 2.5V or
2.5V to 1.8V, the NPN-based regulators are already
operating in dropout, with typical dropout requirements
of 1.2V or greater. To convert down to 2.5V without
operating in dropout, NPN-based regulators require an
input voltage of 3.7V at the very least.
The GM66300 series regulator will provides excellent
performance with an input as low as 3.0V or 2.5V
respectively. This gives the PNP-based regulators a
distinct advantage over older, NPN-based linear
regulators. A typical NPN regulator does not have the
headroom to do this conversion.
Minimum Load Current
The GM66300 series regulator is specified between
finite loads. If the output current is too small, leakage
currents dominate and the output voltage rises. A
10mA minimum load current is necessary for proper
regulation.
Error Flag
The GM66300 series version features an error flag
circuit which monitors the output voltage and signals
an error condition when the voltage 5% below the
nominal output voltage.
7
GAMMA [ GAMMA MICROELECTRONICS INC. ]
