MCP1804_13 datasheet(21/36 Pages) MICROCHIP

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DS20002200D-page 21

MCP1804

6.0

APPLICATION CIRCUITS AND

ISSUES

6.1

Typical Application

The MCP1804 is most commonly used as a voltage

regulator. Its low quiescent current and wide input

voltage make it ideal for Li-Ion and 12V battery-

powered applications.

FIGURE 6-1:

Typical Application Circuit.

6.1.1

APPLICATION INPUT CONDITIONS

6.2

Power Calculations

6.2.1

POWER DISSIPATION

The internal power dissipation of the MCP1804 is a

function of input voltage, output voltage and output

current. The power dissipation resulting from the

quiescent current draw is so low it is insignificant

(50.0 µA x VIN). The following equation can be used to

calculate the internal power dissipation of the LDO.

EQUATION 6-1:

The maximum continuous operating temperature

specified for the MCP1804 is +85°C. To estimate the

internal junction temperature of the MCP1804, the total

internal power dissipation is multiplied by the thermal

resistance from junction to ambient (R

JA). The thermal

resistance from junction to ambient for the SOT-23 pin

package is estimated at 256°C/W.

EQUATION 6-2:

The maximum power dissipation capability for a

package can be calculated given the junction-

to-ambient thermal resistance and the maximum

ambient temperature for the application. The following

equation can be used to determine the package

maximum internal power dissipation.

EQUATION 6-3:

EQUATION 6-4:

EQUATION 6-5:

Package Type

= SOT-23

Input Voltage Range

= 3.8V to 4.2V

VIN maximum

= 4.6V

VOUT typical

= 1.8V

IOUT

= 50 mA maximum

GND

VOUT

VIN

CIN

1µF

COUT

1µF Ceramic

VOUT

VIN

4.2V

1.8V

IOUT

50 mA

Ceramic

SHDN

PLDO

VIN MAX



VOUT MIN



–

 I

OUT



Where:

PLDO = Internal power dissipation of the LDO

Pass device

VIN(MAX) = Maximum input voltage

VOUT(MIN) = Minimum output voltage of the LDO

TJMAX



PTOTAL RJA



TAMAX



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

PDMAX



TJMAX



TAMAX



–





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

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

TJRISE



PDMAX







Where:

TJ(RISE) = Rise in the device’s junction

temperature over the ambient

temperature

PD(MAX) = Maximum power dissipation of the

device

JA = Thermal resistance from junction to

ambient

TJRISE



Where:

TJ = Junction Temperature

TJ(RISE) = Rise in the device’s junction

temperature over the ambient

temperature

TA = Ambient temperature

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