MCP1792 datasheet(16/32 Pages) MICROCHIP

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DS20006229C-page 16

MCP1792/3

5.0

APPLICATION INFORMATION

5.1

Typical Application

The MCP1792/3 is used for applications that require

high input voltage and are prone to high transient volt-

ages on the input.

FIGURE 5-1:

Typical Application Circuit using a High-Voltage Battery Pack.

5.2

Power Calculations

5.2.1

POWER DISSIPATION

The internal power dissipation within the MCP1792/3 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 MCP1792/3 as a

result of quiescent or ground current. The power

dissipation as a result of ground current can be

calculated by applying Equation 5-2:

EQUATION 5-2:

The total power dissipated within the MCP1792/3 is the

sum of the power dissipated in the LDO pass device

and the PI(GND) term. Because of the CMOS

construction, the typical IGND for the MCP1792/3 is

typical 100 µA at full load. Operating at a maximum VIN

of 55V results in a power dissipation of 5.5 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 MCP1792/3 is +150°C. To

estimate the internal junction temperature of the

MCP1792/3, the total internal power dissipation is

multiplied

the

thermal

resistance

from

junction-to-ambient (

JA) of the device. For example,

the thermal resistance from junction-to-ambient for the

5-Lead SOT223 package is estimated at 75°C/W.

EQUATION 5-3:

The maximum power dissipation capability for a pack-

age can be calculated given the junction-to-ambient

thermal resistance and the maximum ambient tem-

perature for the application. Equation 5-4 can be used

to determine the package maximum internal power

dissipation.

PLDO

VIN MAX



VOUT 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

PIGND



VIN MAX



IGND



Where:

PI(GND) = Power dissipation due to the ground

current of the LDO

VIN(MAX) = Maximum input voltage

IGND = Current flowing into the GND pin

TJMAX



PLDO JA



TAMAX



Where:

TJ(MAX) = Maximum continuous junction

temperature

PLDO = Total power dissipation of the device

JA = Thermal resistance from 

junction-to-ambient

TA(MAX) = Maximum ambient temperature

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