MCP1726-0802ESLASHMF datasheet(19/32 Pages) MICROCHIP

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 2005-2014 Microchip Technology Inc.

DS20001936D-page 19

MCP1726

The maximum power dissipation capability for a

package

can

calculated

given

the

junction-to-ambient

thermal

resistance

and

the

maximum ambient temperature for the application. The

following equation 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

are calculated in the following example. The power

dissipation as a result of ground current is small

enough to be neglected.

5.3.1

POWER DISSIPATION EXAMPLE

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

JA) 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.

DMAX



JMA X



AMAX



–





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

PD(MAX) = Maximum device power dissipation

TJ(MAX) = Maximum continuous junction

temperature

TA(MAX) = Maximum ambient temperature

JA = Thermal resistance from

junction-to-ambient

JRISE



DMAX







TJ(RISE) = Rise in device junction temperature

over the ambient temperature

PD(MAX) = Maximum device power dissipation

JA = Thermal resistance from

junction-to-ambient

JRISE



TJ = Junction temperature

TJ(RISE) = Rise in device junction temperature

over the ambient temperature

TA = Ambient temperature

Package

Package Type = 3x3 DFN

Input Voltage

VIN = 3.3V ± 10%

LDO Output Voltage and Current

VOUT =2.5V

IOUT =1.0A

Maximum Ambient Temperature

TA(MAX) =70°C

Internal Power Dissipation

PLDO(MAX) =[VIN(MAX) –VOUT(MIN)]x IOUT(MAX)

PLDO = [(3.3V x 1.1) – (0.975 x 2.5V)]

x1.0A

PLDO = 1.192W

TJ(RISE) =PTOTAL xRJA

TJ(RISE) = 1.192W x 64.0°C/W

TJ(RISE) = 76.3°C

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