1A Low-Voltage Low-Dropout Regulator
LM37101/37102
APPLICATION INFORMATION
The LM37101/2 is a high-performance low-dropout voltage regulator suitable for moderate to high-current
voltage regulator applications. Its 630mV dropout voltage at full load and over temperature makes it
especially valuable in battery-powered systems and as high-efficiency noise filters in post-regulator
applications. Unlike older NPN-pass transistor de-signs, where the minimum dropout voltage is limited by the
base-to-emitter voltage drop and collector-to-emitter saturation voltage, dropout performance of the PNP
output of these devices is limited only by the low VCE saturation voltage. A trade-off for the low dropout
voltage is a varying base drive requirement.
The LM37101/2 regulator is fully protected from damage due to fault conditions. Linear current limiting is
provided. Output current during overload conditions is constant. Thermal shutdown disables the device when
the die temperature exceeds the maximum safe operating temperature. Transient protection allows device
(and load) survival even when the input voltage spikes above and below nominal. The output structure of
these regulators allows voltages in excess of the desired output voltage to be applied without reverse current
flow.
Output Capacitor
The LM37101/2 requires an output capacitor to maintain stability and improve transient response. Proper
capacitor selection is important to ensure proper operation. The LM37101/2 output capacitor selection is
dependent upon the ESR (equivalent series resistance) of the output capacitor to maintain stability. When
the output capacitor is 10μF or greater, the output capacitor should have an ESR less than 2Ω. This will
improve transient response as well as promote stability. Ultra-low ESR capacitors (<100mΩ), such as
ceramic chip capacitors, may promote the instability. These very low ESR levels may cause an oscillation
and/or underdamped transient response. A low ESR solid tantalum capacitor works extremely well and
provides a good transient response and the stability over the temperature range. Aluminum electrolytes can
also be used, as long as the capacitor ESR is <2Ω. The value of the output capacitor can be increased
without limit. Higher capacitance values help one to improve transient response and ripple rejection and
reduce an output noise.
Input Capacitor
An input capacitor of 1μF or greater is recommended when the device is more than 4 inches away from the
bulk ac supply capacitance or when the supply is a battery. In the case of ceramic chip capacitor, 10uF
capacitance is recommended. Larger values will help to improve ripple rejection by bypassing the input to
the regulator, further improving the integrity of the output voltage.
Error Flag
The LM37101 features an error flag (FLG), which monitors the output voltage and signals an error condition
when this voltage drops 5% below its expected value. The error flag is an open-collector output that pulls low
under fault conditions and may sink up to 10mA. Low output voltage signifies a number of possible problems,
including an over current fault (the device is in current limit) or low input voltage. The flag output is inoperative
during over temperature conditions. A pull-up resistor from FLG to either VIN or VOUT is required for proper
operation. For information regarding the minimum and maximum values of pull-up resistance, refer to the
graph in the typical characteristics section of the data sheet.
Nov. 2011 – R1.1
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HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
