LM39300(2011) Ver la hoja de datos (PDF) - HTC Korea

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LM39300
(Rev.:2011)

3A Low-Voltage Low-Dropout Regulator

HTC Korea 

3A Low-Voltage Low-Dropout Regulator LM39300/39301/39302

APPLICATION INFORMATION

The LM39300/1 is a high-performance low-dropout voltage regulator suitable for moderate to high-current

voltage regulator applications. Its 500mV dropout voltage at full load makes it especially valuable in battery-

powered systems and as a high-efficiency noise filter in post-regulator applications. Unlike older NPN-pass

transistor designs, where the mini-mum 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 LM39300/1/2 regulator is fully protected from damage due to fault conditions. Current limiting is provided.

This limiting is linear 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 LM39300/1/2 requires an output capacitor to maintain stability and improve transient response. Proper

capacitor selection is important to ensure proper operation. The LM39300/1/2 output capacitor selection is

dependent upon the ESR (equivalent series resistance) of the output capacitor to maintain stability. When the

output capacitor is 47uF or greater, the output capacitor should have less than 1 of ESR. This will improve

transient response as well as promote stability. Ultralow ESR capacitors, such as ceramic chip capacitors may

promote instability. These very low ESR levels may cause an oscillation and/or under damped transient

response. A low-ESR solid tantalum capacitor works extremely well and provides good transient response and

stability over temperature. Aluminum electrolytic can also be used, as long as the ESR of the capacitor is <

1.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 1uF 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. Small, surface-mount, 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.

Minimum Load Current

The LM39300/1/2 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.

Transient Response and 3.3V to 2.5V Conversion

The LM39300/1/2 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 47uF 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

Feb. 2011 - Rev. 1.1

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HTC

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