1A Low-Voltage Low-Dropout Regulator
APPLICATION INFORMATION
LM39100/39101/39102
The LM39100/1/2 is a high-performance low-dropout voltage regulator suitable for moderate to high-current
voltage regulator applications. Its 630mV dropout voltage at full loadand 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 thebase-to-emitter voltage drop
and collector-to-emitter satura-tion voltage, dropout performance of the PNP output of these devices is limited only
by the low V
CE
saturation voltage.A trade-off for the low dropout voltage is a varying base drive requirement.
The LM39100/1/2 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. Tran-sient 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 LM39100/1/2 requires an output capacitor to maintain stability and improve transient response. Proper capacitor
selection is important to ensure proper operation. The LM39100/1/2 output capacitor selection is dependent upon
the ESR (equivalent series resistance) of the output capacitor to maintain stability. When the output capacitor is 10µF
orgreater, 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 ce-ramic chip capacitors, may promote 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 good transient response and stability over temperature.
Aluminum electrolytics can also be used, as long as the ESR of the capacitor is <2Ω.The value of the output
capacitor can be increased without limit. Higher capacitance values help to improve transient response and ripple
rejection and reduce output noise.
Input Capacitor
An input capacitor of 1µF or greater is recommended whenthe device is more than 4 inches away from the bulk ac
supply capacitance or when the supply is a battery. Small, surfacemount, ceramic chip capacitors can be used for
bypassing. 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 LM39101 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 isan open-collector output that pulls low under fault
conditions and may sink up to 10mA. Low output voltage signifies anumber of possible problems, including an
overcurrent fault(the device is in current limit) or low input voltage. The flag output is inoperative during
overtemperature conditions. Apull-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.
Enable Input
The LM39101 and LM39102 versions feature an active-high enable input (EN) that allows on-off control of the
regulator. Current drain reduces to “zero” when the device is shutdown, with only micro amperes of leakage current.
The EN input has TTL/CMOS compatible thresholds for simple logic interfacing. EN may be directly tied to VIN and
pulled upto the maximum supply voltage
Transient Response and 3.3V to 2.5V or 2.5V to 1.8V Conversion
The LM39100/1/2 has excellent transient response to varia-tions 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.
By virtue of its low-dropout voltage, this device does not saturate into dropout as readily as similar NPN-based de-
signs. When converting from 3.3V to 2.5V or 2.5V to 1.8V, the NPN based regulators are already operating in
dropout, withtypical dropout requirements of 1.2V or greater. To convertdown to 2.5V or 1.8V without operating in
dropout, NPN-based regulators require an input voltage of 3.7V at the veryleast. The LM39100 regulator will provide
excellent perfor-mance with an input as low as 3.0V or 2.5V respectively. This gives the PNP based regulators a
distinct advantage overolder, NPN based linear regulators.
HTC
7
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
