MCP1810 datasheet(21/32 Pages) MICROCHIP

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DS20005623A-page 21

MCP1810

5.0

APPLICATION CIRCUITS AND

ISSUES

5.1

Typical Application

The MCP1810 is used for applications that require

ultra-low quiescent current draw.

FIGURE 5-1:

Typical Application Circuit.

5.2

Power Calculations

5.2.1

POWER DISSIPATION

The internal power dissipation within the MCP1810 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 MCP1810 as a

result of quiescent or ground current. The power

dissipation as a result of the ground current can be

calculated by applying Equation 5-2:

EQUATION 5-2:

The total power dissipated within the MCP1810 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 MCP1810 is

maximum 290 µA at full load. Operating at a maximum

VIN of 5.5V results in a power dissipation of 1.6 mW.

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 MCP1810 is +85°C. To

estimate the internal junction temperature of the

MCP1810, the total internal power dissipation is

multiplied

the

thermal

resistance

from

junction-to-ambient (R

JA) of the device. The thermal

resistance from junction to ambient for the 2x2 VDFN

8-Lead package is estimated at 73.1°C/W.

EQUATION 5-3:

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.

Equation 5-4 can be used to determine the package

maximum internal power dissipation.

EQUATION 5-4:

VIN

VOUT

GND

MCP1810

CIN

COUT

SHDN

ESR

LDO

IN MAX



OUT MIN



–

 I

OUT MAX





Where:

PLDO = Internal power dissipation of the

LDO pass device

VIN(MAX) = Maximum input voltage

VOUT(MIN) = LDO minimum output voltage

IOUT(MAX) = Maximum output current

IGND



IN MAX



GN D



Where:

PI(GND) = Power dissipation due to the

quiescent current of the LDO

VIN(MAX) = Maximum input voltage

IGND = Current flowing into the GND pin

JMAX



TOTAL





AMAX



Where:

TJ(MAX) = Maximum continuous junction

temperature

PTOTAL = Total power dissipation of the device

JA = Thermal resistance from junction to

ambient

TA(MAX) = Maximum ambient temperature

DMAX



JMAX



AMA X



–





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

Where:

PD(MAX) = Maximum power dissipation of the

device

TJ(MAX) = Maximum continuous junction

temperature

TA(MAX) = Maximum ambient temperature

JA = Thermal resistance from

junction to ambient

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