MCP1799 datasheet(14/25 Pages) MICROCHIP

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DS20006248A-page 14

MCP1799

5.0

APPLICATION INFORMATION

5.1

Typical Application

The MCP1799 is used for applications that require

high input voltage and are prone to high transient

voltages 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 MCP1799 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 MCP1799 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 MCP1799 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 MCP1799 is

typical 50 µA at full load. Operating at a maximum VIN

of 45V results in a power dissipation of 2.25 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 MCP1799 is +150°C. To

estimate the internal junction temperature of the

MCP1799, the total internal power dissipation is

multiplied by the thermal resistance from junction-to-

ambient (R

JA) of the device. For example, the thermal

resistance from junction-to-ambient for the 3-Lead

SOT-223 package is estimated at 70°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.

VIN

VOUT

GND

MCP1799

COUT

1 µF

VDC

CIN

1 µF

0V DC

VBAT = 4.5V to 45V

µController

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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