TC1263_13 datasheet(8/18 Pages) MICROCHIP

8 / 18 page

TC1263

DS21374D-page 8

 2002-2012 Microchip Technology Inc.

5.0

THERMAL CONSIDERATIONS

5.1

Thermal Shutdown

Integrated thermal protection circuitry shuts the

regulator off when the die temperature exceeds 160°C.

The regulator remains off until the die temperature

drops to approximately 150°C.

5.2

Power Dissipation

The amount of power the regulator dissipates is

primarily a function of input and output voltage and out-

put current. The following equation is used to calculate

worst-case actual power dissipation:

EQUATION 5-1:

The

maximum

allowable

power

dissipation

(Equation 5-2) is a function of the maximum ambient

temperature (TAMAX), the maximum allowable die

temperature (TJMAX) and the thermal resistance from

junction-to-air (



JA).

EQUATION 5-2:

Table 5-1 and Table 5-2 show various values of



JA for

the TC1263 package types.

TABLE 5-1:

THERMAL RESISTANCE

GUIDELINES FOR TC1263 IN

8-PIN SOIC PACKAGE

TABLE 5-2:

THERMAL RESISTANCE

GUIDELINES FOR TC1263 IN

5-PIN DDPAK/TO-220

PACKAGE

Equation 5-1

can

used

conjunction

with

Equation 5-2 to ensure regulator thermal operation is

within limits. For example:

Find:

Actual power dissipation

Maximum allowable dissipation

Actual power dissipation:

Maximum allowable power dissipation:

In this example, the TC1263 dissipates a maximum of

260 mW below the allowable limit of 500 mW. In a

similar manner, Equation 5-1 and Equation 5-2 can be

used to calculate maximum current and/or input

voltage limits. For example, the maximum allowable

VIN is found by substituting the maximum allowable

power dissipation of 500 mW into Equation 5-1, from

which VINMAX = 4.6V.

Copper

Area

(Topside)*

Copper

Area

(Backside)

Board

Area

Thermal

Resistance



JA)

2500 sq mm

2500 sq mm 2500 sq mm

60°C/W

1000 sq mm

2500 sq mm 2500 sq mm

60°C/W

225 sq mm

2500 sq mm 2500 sq mm

68°C/W

100 sq mm

2500 sq mm 2500 sq mm

74°C/W

* Pin 2 is ground. Device is mounted on top-side.

Where:

VINMAX

VOUTMIN

ILOADMAX

PD = Worst-case actual power dissipation

= Minimum regulator output voltage

= Maximum output (load) current

= Maximum voltage on VIN

IN MAX

OUTMIN

–

I

LOA DMAX

Where:

VINMAX

VOUTMIN

ILOADMAX

PD = Worst-case actual power dissipation

= Minimum regulator output voltage

= Maximum output (load) current

= Maximum voltage on VIN

DMAX

JMAX

AMAX

–



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

Copper

Area

(Topside)*

Copper

Area

(Backside)

Board

Area

Thermal

Resistance



JA)

2500 sq mm

2500 sq mm 2500 sq mm

25°C/W

1000 sq mm

2500 sq mm 2500 sq mm

27°C/W

125 sq mm

2500 sq mm 2500 sq mm

35°C/W

* Tab of device attached to top-side copper

Given:

VINMAX

=3.3V ± 10%

VOUTMIN

=2.7V ± 0.5%

ILOADMAX

=275 mA

TJMAX

=125°C

TAMAX

=95°C



60° C/W (SOIC)

INMAX

OUTMIN

–

I

LOADMAX



3.3

1.1





2.7

.995





–

275

–



260 mW

DMAX

JMAX

AMAX

–



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

DMAX

125

–



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

DMAX

500 mW

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