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2010/3/2

GM66300 Series

3.0A ULTRA LOW DROPOUT VOLTAGE

REGULATORS

Typical Application Circuits

The GM66300/01/02 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 a high-efficiency noise filter in post-regulator applications.

Unlike older NPN-pass transistor designs, 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.

Super beta PNP process reduces this drive requirement to only 2% to 5% of the load current.

The GM66300/01/02 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.

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Thermal design

Linear regulators are simple to use. The most complicated design parameters to consider are thermal

characteristics.

Thermal design requires four application-specific parameters:

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Calculate the power dissipation of the regulator from these numbers and the device parameters from this

datasheet, where the ground current is taken from data sheet

The heat sink thermal resistance is determined by:

The heat sink may by significantly reduced in applications where the minimum input voltage is known and is

large compared with the dropout voltage. Use a series input resistor to drop excessive voltage and distribute the

heat between this resistor and the regulator. The low dropout properties of Super βeta PNP regulators allow

significant reductions in regulator power dissipation and the associated heat sink without compromising

performance. When this technique is employed, a capacitor of at least 1.0µF is needed directly between the

input and regulator ground. Refer to Application Note 9 for further details and examples on thermal design and

heat sink specification.

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Output Capacitor

The GM66300/1/2 requires an output capacitor to maintain stability and improve transient response. Proper

capacitor selection is important to ensure proper operation. The GM66300/1/2 output capacitor selection is

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

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

transient response as well as promote stability. Ultra-low ESR capacitors, such as ceramic 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 ≤1Ω.

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.