MCP1824 datasheet(21/34 Pages) MICROCHIP

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DS22070A-page 21

MCP1824/MCP1824S

5.0

APPLICATION CIRCUITS/

ISSUES

5.1

Typical Application

The MCP1824/MCP1824S 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 MCP1824/

MCP1824S 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 MCP1824/

MCP1824S 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 MCP1824/

MCP1824S 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 MCP1824/

MCP1824S is 120 µA. Operating at a maximum VIN of

3.465V results in a power dissipation of 0.12 milli-Watts

for a 2.5V output. 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 MCP1824/MCP1824S is

+125°C. To estimate the internal junction temperature

of the MCP1824/MCP1824S, 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 SOT-223-5

package is estimated at 62° C/W.

EQUATION 5-3:

Package Type

SOT-223-5

Input Voltage Range

3.3V ± 5%

VIN maximum

3.465V

VIN minimum

3.135V

VDROPOUT (max)

0.350V

VOUT (typical)

2.5V

IOUT

300 mA maximum

PDISS (typical)

0.240W

Temperature Rise

14.88°C

10 µF

VOUT = 2.5V @ 300 mA

10 k

PWRGD

SHDN

GND

4.7 µF

Off

MCP1824-2.5

3 4 5

3.3V

VIN

LDO

IN 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

IGND

()

IN MAX

()

VIN

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)

JMAX

()

TOTAL

AMAX

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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