MCP1727 datasheet(20/32 Pages) MICROCHIP

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MCP1727

DS21999B-page 20

5.0

APPLICATION CIRCUITS/

ISSUES

5.1

Typical Application

The MCP1727 is used for applications that require high

LDO output current and a power good output.

FIGURE 5-1:

Typical Application Circuit.

5.1.1

APPLICATION CONDITIONS

5.2

Power Calculations

5.2.1

POWER DISSIPATION

The internal power dissipation within the MCP1727 is a

function of input voltage, output voltage, output current

and quiescent current. Equation 5-1 can be used to

calculate the internal power dissipation for the LDO.

EQUATION 5-1:

In addition to the LDO pass element power dissipation,

there is power dissipation within the MCP1727 as a

result of quiescent or ground current. The power

dissipation as a result of the ground current can be

calculated using the following equation:

EQUATION 5-2:

The total power dissipated within the MCP1727 is the

sum of the power dissipated in the LDO pass device

and the P(IGND) term. Because of the CMOS

construction, the typical IGND for the MCP1727 is

120 µA. Operating at a maximum of 3.465V results in a

power dissipation of 0.49 milli-Watts. For most

applications, this is small compared to the LDO pass

device power dissipation and can be neglected.

The

maximum

continuous

operating

junction

temperature specified for the MCP1727 is +125°C. To

estimate the internal junction temperature of the

MCP1727, the total internal power dissipation is

multiplied by the thermal resistance from junction to

ambient (R

θJA) of the device. The thermal resistance

from junction to ambient for the 3x3 DFN package is

estimated at 41° C/W.

EQUATION 5-3:

Package Type = 3x3DFN8

Input Voltage Range = 3.3V ± 5%

VIN maximum = 3.465V

VIN minimum = 3.135V

VDROPOUT (max) = 0.525V

VOUT (typical) = 2.5V

IOUT = 1.5A maximum

PDISS (typical) = 1.2W

Temperature Rise = 49.2°C

VIN

SHDN

GND PWRGD

CDELAY

Sense

VOUT

10 µF

VOUT = 2.5V @ 1.5A

10 µF

VIN = 3.3V

Off

VIN

1000 pF

MCP1727-2.5

10k

PWRGD

PLDO

VIN MAX)

()

VOUT MIN

()

–

() I

OUT MAX

)

()

Where:

PLDO = LDO Pass device internal

power dissipation

VIN(MAX) = Maximum input voltage

VOUT(MIN) = LDO minimum output voltage

PIGND

()

VIN MAX

()

IVIN

Where:

PI(GND = Power dissipation due to the

quiescent current of the LDO

VIN(MAX) = Maximum input voltage

IVIN = Current flowing in the VIN pin

with no LDO output current

(LDO quiescent current)

TJMAX

()

PTOTAL RθJA

TAMAX

TJ(MAX) = Maximum continuous junction

temperature

PTOTAL = Total device power dissipation

θJA = Thermal resistance from junction to

ambient

TAMAX = Maximum ambient temperature

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