Micrel, Inc.
MIC37139
Transient Response and 3.3V to 2.5V, 2.5V to 1.8V
or1.65V, or 2.5V to 1.5V Conversions
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 MIC37139 regulator will provide excellent
performance with an input as low as 3.0V or 2.25V,
respectively. This gives the PNP-based regulators a
distinct advantage over older, NPN-based linear
regulators.
The MIC37139 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 10µF output capacitor, preferably tantalum, is
all that is required. Larger values help to improve
performance even further.
Minimum Load Current
The MIC37139 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 operation.
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, 2.5V to
1.8V or 1.65V, or 2.5V to 1.5V, the NPN-based
regulators are already operating in dropout, with typical
M9999-110209
November 2009
9
MICREL [ MICREL SEMICONDUCTOR ]
