MIC5237 datasheet(8/18 Pages) MICROCHIP

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MIC5237

DS20006095B-page 8



2018 - 2022 Microchip Technology Inc. and its subsidiaries

4.0

APPLICATION INFORMATION

The MIC5237 is intended for general purpose use and

can be implemented in a wide variety of applications

where 500 mA of output current is needed. It is

available in several voltage options for ease-of-use.

For voltage options that are not available on the

MIC5237, consult the MIC5209 for a 500 mA

adjustable LDO regulator, or the MIC5219 for

applications that require only short-duration peak

output current.

4.1

Input Capacitor

A 1 µF capacitor should be placed from IN to GND if

there is more than 10 inches of wire between the input

and the ac filter capacitor or if a battery is used as the

input.

4.2

Output Capacitor

An output capacitor is required between OUT and GND

to prevent oscillation. 1 µF minimum is recommended

for standard applications. Larger values improve the

regulator’s transient response. The output capacitor

value may be increased without limit.

The output capacitor should have an ESR (equivalent

series resistance) of about 5Ω or less and a resonant

frequency above 1 MHz. Ultra low-ESR capacitors can

cause low-amplitude oscillations and/or under-damped

transient response. Most tantalum or aluminum

electrolytic capacitors are adequate; film types will

work, but are more expensive. Because many

aluminum electrolytics have electrolytes that freeze at

about –30°C, solid tantalums are recommended for

operation below –25°C.

At lower values of output current, less output

capacitance is needed for output stability. The

capacitor can be reduced to 0.47 µF for current below

10 mA or 0.33 µF for currents below 1 mA.

For 2.5V applications a 22 µF output capacitor is

recommended to reduce startup voltage overshoot.

4.3

No-Load Stability

The MIC5237 will remain stable and in regulation with

no load (other than the internal voltage divider) unlike

many other voltage regulators. This is especially

important in CMOS RAM keep-alive applications.

4.4

Thermal Considerations

Proper thermal design can be accomplished with some

basic design criteria and some simple equations. The

following information is required to implement a

regulator design.

• VIN = Input Voltage

• VOUT = Output Voltage

• IOUT = Output Current

• TA = Ambient Operating Temperature

• IGND = Ground Current

The regulator ground current, IGND, can be measured

or read from the data sheet. Assuming the worst case

scenario is good design procedure, and the

corresponding ground current number can be obtained

from the data sheet. First, calculate the power

dissipation of the device. This example uses the

MIC5237-5.0YT, a 13V input, and 500 mA output

current, which results in 20 mA of ground current, worst

case. The power dissipation is the sum of two power

calculations: voltage drop × output current and input

voltage × ground current.

EQUATION 4-1:

EQUATION 4-2:

From this number, the heat sink thermal resistance is

determined using the regulator’s maximum operating

junction temperature (TJ(max)) and the ambient

temperature (TA) along with the power dissipation

number already calculated.

• TJMAX = 125°C

• θJC = Junction-to-Case Thermal Resistance

• θCS = Case-to-Sink Thermal Resistance

• θJA = Junction-to-Ambient Thermal Resistance

• θSA = Sink-to-Ambient Thermal Resistance

To determine the heat sink thermal resistance, the

junction-to-case thermal resistance of the device must

be used along with the case-to-heat sink thermal

resistance. These numbers show the heat sink thermal

resistance required at TA = 25°C that does not exceed

the maximum operating junction temperature.

EQUATION 4-3:

VIN VOUT

–





IOUT







VIN IGND







13V 5V

–





500mA







13V 20mA







4.260W

JA

TJ MAX





–

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