MIC39300 datasheet(12/24 Pages) MICROCHIP

12 / 24 page

MIC39300/01/02

DS20006017B-page 12



2018 - 2022 Microchip Technology Inc. and its subsidiaries

4.0

APPLICATION INFORMATION

The MIC39300/1/2 are high-performance, low-dropout

voltage regulators suitable for moderate to high-current

voltage regulator applications. Its 550 mV 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 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. Microchip’s Super βeta PNP

process reduces this drive requirement to only 2% to

5% of the load current.

The MIC39300/1/2 regulators are 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.

4.1

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:

• Maximum ambient temperature (TA)

• Output Current (IOUT)

• Output Voltage (VOUT)

• Input Voltage (VIN)

• Ground Current (IGND)

Calculate the power dissipation of the regulator from

these numbers and the device parameters from this

data sheet, where the ground current is taken from the

data sheet.

EQUATION 4-1:

The heat sink thermal resistance is determined by:

EQUATION 4-2:

The heat sink may be 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 Microchip’s

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 1.0 μF 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.

FIGURE 4-1:

Capacitor Requirements.

4.2

Output Capacitor

The MIC39300/1/2 requires an output capacitor to

maintain stability and improve transient response.

Proper capacitor selection is important to ensure

proper operation. The MIC39300/1/2 output capacitor

selection is dependent upon the ESR (equivalent

series resistance) of the output capacitor to maintain

stability. When the output capacitor is 47 µF or greater,

the output capacitor should have less than 1Ω 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

VIN VOUT

–





IOUT VIN IGND



SA

TJ MAX





–

--------------------------------

JC CS





–

Where:

TJ(MAX) ≤

125°C

θCS

Between 0°C/W and 2°C/W

MIC39300-x.x

OUT

GND

CIN

COUT

VIN

VOUT

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