MCP1790-3002ESLASHEB datasheet(18/34 Pages) MICROCHIP

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MCP1790/MCP1791

DS22075A-page 18

5.0

APPLICATION CIRCUITS /

ISSUES

5.1

Typical Application

The MCP1790/MCP1791 is most commonly used as a

voltage regulator. It’s high voltage input capability and

thermal protection make it ideal for automotive and 24V

industrial applications.

FIGURE 5-1:

Typical Application.

5.1.1

APPLICATION INPUT CONDITIONS

5.2

Power Calculations

5.2.1

POWER DISSIPATION

The internal power dissipation of the MCP1790/

MCP1791 is a function of input voltage, output voltage

and output current. The power dissipation, as a result

of the quiescent current draw, is so low, it is insignifi-

cant (70.0 µA x VIN). The following equation can be

used to calculate the internal power dissipation of the

LDO.

EQUATION 5-1:

The

maximum

continuous

operating

junction

temperature specified for the MCP1790/MCP1791 is

+125°C. To estimate the internal junction temperature

of the MCP1790/MCP1791, 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-223-5 package is

estimated at 62°C/W.

EQUATION 5-2:

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 5-3:

EQUATION 5-4:

EQUATION 5-5:

Package Type = SOT-223-5

Input Voltage Range = 8V to 24V

VIN maximum = 24V

VOUT typical = 5.0V

IOUT =70 mA maximum

COUT

4.7 µF Ceramic

CIN

1µF

24 VDC

1N4002

Ceramic

PWRGD

VOUT

VIN

5V@70 mA

10 k

MCP1791

LDO

IN MAX

)

()

OUT MIN

()

–

() I

OUT MAX

)

()

PLDO = LDO Pass device internal power

dissipation

VIN(MAX) = Maximum input voltage

VOUT(MIN) = LDO minimum output voltage

JMAX

()

TOTAL

AMAX

TJ(MAX)

Maximum continuous junction

temperature.

PTOTAL

Total device power dissipation.

Thermal resistance from junction

to ambient.

TAMAX

Maximum ambient temperature.

DMAX

()

JMAX

()

AMAX

()

–

()

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

PD(MAX)

Maximum device power

dissipation.

TJ(MAX)

Maximum continuous junction

temperature.

TA(MAX)

Maximum ambient temperature.

Thermal resistance from junction

to ambient.

JRISE

()

DMAX

()

TJ(RISE) = Rise in device junction

temperature over the ambient

temperature.

PTOTAL = Maximum device power

dissipation.

Thermal resistance from

junction-to-ambient.

JRISE

()

TJ = Junction Temperature.

TJ(RISE) = Rise in device junction

temperature over the ambient

temperature.

TA = Ambient temperature.

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