MCP1725 datasheet(21/32 Pages) MICROCHIP

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DS22026A-page 21

MCP1725

The maximum power dissipation capability for a

package can be calculated given the junction-to-

ambient thermal resistance and the maximum ambient

temperature for the application. Equation 5-4 can be

used to determine the package maximum internal

power dissipation.

EQUATION 5-4:

EQUATION 5-5:

EQUATION 5-6:

5.3

Typical Application

Internal power dissipation, junction temperature rise,

junction temperature and maximum power dissipation

is calculated in the following example. The power

dissipation as a result of ground current is small

enough to be neglected.

EXAMPLE 5-1:

POWER DISSIPATION

EXAMPLE

5.3.1

DEVICE JUNCTION TEMPERATURE

RISE

The internal junction temperature rise is a function of

internal power dissipation and the thermal resistance

from junction-to-ambient for the application. The

thermal resistance from junction-to-ambient (R

θJA) is

derived from an EIA/JEDEC standard for measuring

thermal resistance for small surface-mount packages.

The EIA/JEDEC specification is JESD51-7 “High

Effective Thermal Conductivity Test Board for Leaded

Surface-Mount Packages”. The standard describes the

test method and board specifications for measuring the

thermal resistance from junction to ambient. The actual

thermal resistance for a particular application can vary

depending on many factors such as copper area and

thickness. Refer to AN792, “A Method to Determine

How Much Power a SOT23 Can Dissipate in an

Application” (DS00792), for more information regarding

this subject.

PDMAX

()

TJMAX

()

TAMAX

()

–

()

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

PD(MAX) = Maximum device power dissipation

TJ(MAX) = maximum continuous junction

temperature

TA(MAX) = maximum ambient temperature

θJA = Thermal resistance from junction to

ambient

TJRISE

()

PDMAX

()

TJ(RISE) = Rise in device junction temperature

over the ambient temperature

PD(MAX) = Maximum device power dissipation

θJA = Thermal resistance from junction to

ambient

TJRISE

()

TJ = Junction temperature

TJ(RISE) = Rise in device junction temperature

over the ambient temperature

TA = Ambient temperature

Package

Type

2x3 DFN

Input Voltage

VIN

=3.3V ± 5%

LDO Output Voltage and Current

VOUT

=2.5V

IOUT

=0.5A

Maximum Ambient Temperature

TA(MAX)

60°C

Internal Power Dissipation

PLDO(MAX)

=(VIN(MAX) – VOUT(MIN)) x

IOUT(MAX)

PLDO

((3.3V x 1.05) – (2.5V x 0.975))

x 0.5A

PLDO

0.51 Watts

TJ(RISE) =PTOTAL x RθJA

TJRISE = 0.51 W x 76.0° C/W

TJRISE =38.8°C

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