MCP1726 datasheet(19/30 Pages) MICROCHIP

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DS21936B-page 19

MCP1726

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. The following equation

can be used to determine the package maximum inter-

nal 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 dissi-

pation 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 ther-

mal 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 Appli-

cation” (DS00792), for more information regarding this

subject.

DMAX

()

JMAX

() 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

JRISE

()

DMAX

()

TJ(RISE) = Rise in device junction

temperature over the ambient

temperature

PD(MAX) = Maximum device power

dissipation

θJA = 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 = 3X3DFN

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))

x 1.0A

PLDO = 1.192 Watts

TJ(RISE) =PTOTAL x RθJA

TJRISE = 1.192 W x 41.0° C/W

TJRISE =48.8°C

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