MIC5212 datasheet(10/18 Pages) MICROCHIP

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MIC5212

DS20005774B-page 10



2017 - 2022 Microchip Technology Inc. and its subsidiaries

during operation of the device. To prevent this

maximum junction temperature from being exceeded,

the appropriate ground plane heat sink must be used.

FIGURE 4-2:

Copper Area vs. Power-SO

Power Dissipation (ΔTJA).

Figure 4-2 shows copper area versus power

dissipation with each trace corresponding to a different

temperature rise above ambient.

From these curves, the minimum area of copper

necessary for the part to operate safely can be

determined. The maximum allowable temperature rise

must be calculated to determine operation along which

curve.

EQUATION 4-1:

For example, the maximum ambient temperature is

50°C, the ΔT is determined as shown in Equation 4-2.

EQUATION 4-2:

Using Figure 4-2, the minimum amount of required

copper can be determined based on the required

power dissipation.

Power dissipation in a linear regulator is calculated as

shown in Equation 4-3.

EQUATION 4-3:

With a common 5V input, a 3.3V, 300 mA output on

LDO 1 and a 2.5V, 150 mA output on LDO 2, power

dissipation is as follows:

EQUATION 4-4:

From Figure 4-2, the minimum amount of copper

required to operate this application at a ΔT of 75°C is

500 mm2.

4.4.2

QUICK METHOD

Determine the power dissipation requirements for the

design along with the maximum ambient temperature

at which the device will be operated. Refer to

Figure 4-3, which shows safe operating curves for

three different ambient temperatures: 25°C, 50°C and

85°C. From these curves, the minimum amount of

copper can be determined by knowing the maximum

power dissipation required. If the maximum ambient

temperature is 50°C and the power dissipation is as

above, 920 mW, the curve in Figure 4-3 shows that the

required area of copper is 500 mm2.

The θJA of this package is ideally 63°C/W, but it will

vary depending upon the availability of copper ground

plane to which it is attached.

FIGURE 4-3:

Copper Area vs. Power-SO

Power Dissipation (TA).

Where:

TJ(max)

= 125°C

TA(max)

= Maximum ambient operating

temperature

ΔT

125°C – 50°C

ΔT

75°C

100

200

300

400

500

600

700

800

900

0.25 0.50 0.75 1.00 1.25 1.50

POWER DISSIPATION (W)



TJ max





TA max





–

VIN1 VOUT1

–





IOUT1



VIN1

IGND1



VIN2 VOUT2

–





IOUT2 VIIN2



IGND2



0.919W

5V 3.3V

–





300mA



5mA



5V 2.5V

–





150mA



1.8mA



100

200

300

400

500

600

700

800

900

0.25 0.50 0.75 1.00 1.25 1.50

POWER DISSIPATION (W)

°C

°C 25°C

= 125

°C

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