MIC79050 datasheet(16/28 Pages) MICROCHIP

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MIC79050

DS20005771B-page 16



2017 - 2022 Microchip Technology Inc. and its subsidiaries.

ΔT is calculated by taking the maximum junction

temperature and subtracting the maximum ambient

operating temperature.

For example, if the maximum ambient temperature is

+40°C, the ΔT is determined as follows:

EQUATION 5-1:

Using Figure 5-12, the minimum amount of required

copper can be determined based on the required

power dissipation. Power dissipation in a linear

regulator is calculated as follows:

EQUATION 5-2:

For example, using the charging circuit in Figure 5-10,

assume the input is a fixed 5V and the output is pulled

down to 4.2V at a charge current of 500 mA. The power

dissipation in the MIC79050 is calculated as follows:

EQUATION 5-3:

From Figure 5-12, the minimum amount of copper

required to operate this application at a ΔT of +85°C is

less than 50 mm2.

5.10.2

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 5-13, 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 +40°C and the power dissipation is as

above, 0.46W, the curve in Figure 5-13 shows that the

required area of copper is 50 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 5-13:

Copper Area vs. Power

SOIC Power Dissipation (TA).

5.10.3

POWER MSOP-8 THERMAL

CHARACTERISTICS

The power MSOP-8 package follows the same idea as

the power SOIC-8 package, using four ground leads

with the die-attach paddle to create a single-piece

electrical and thermal conductor, reducing thermal

resistance and increasing power dissipation capability.

The same method of determining the heat sink area

used for the power SOIC-8 can be applied directly to

the power MSOP-8. The same two curves showing

power dissipation versus copper area are reproduced

for the power-MSOP-8 and they can be applied

identically.

5.10.4

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 5-15, 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 +25°C and the power dissipation is 1W,

the curve in Figure 5-15 shows that the required area

of copper is 500 mm2, when using the power MSOP-8.



125C

40C 85C

–

VIN VOUT

–





IOUT VIN IGND



5V 4.2V

–





0.5A 5V 0.012A 0.460W



100

200

300

400

500

600

700

900

0.25 0.50 0.75 1.00 1.25 1.50

POWER DISSIPATION (W)

85°C

50°C

25°C

= 125°C

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