TC1014 datasheet(13/22 Pages) MICROCHIP

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DS21335E-page 13

TC1014/TC1015/TC1185

5.0

THERMAL CONSIDERATIONS

5.1

Thermal Shutdown

Integrated thermal protection circuitry shuts the

regulator off when 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

output 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 (

θJA). The 5-pin SOT-23 package has a

θJA of approximately 220°C/Watt.

EQUATION 5-2:

Equation 5-1 can be used in conjunction with

Equation 5-2 to ensure regulator thermal operation is

within limits. For example:

Given:

Find:

Actual power dissipation

Maximum allowable dissipation

Actual power dissipation:

PD ≈ (VINMAX – VOUTMIN)ILOADMAX

= [(3.0 x 1.1) – (2.7 x .975)]40 x 10–3

= 26.7 mW

Maximum allowable power dissipation:

In this example, the TC1014 dissipates a maximum of

26.7 mW below the allowable limit of 318 mW. In a

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

used to calculate maximum current and/or input

voltage limits.

5.3

Layout Considerations

The primary path of heat conduction out of the package

is via the package leads. Therefore, layouts having a

ground plane, wide traces at the pads, and wide power

supply bus lines combine to lower

θJA and therefore

increase the maximum allowable power dissipation

limit.

VINMAX VOUTMIN

–

()I

LOADMAX

≈

Where:

PD = Worst-case actual power

dissipation

VINMAX = Maximum voltage on VIN

VOUTMIN = Minimum regulator output voltage

ILOADMAX = Maximum output (load) current

Where all terms are previously defined.

PDMAX

TJMAX TAMAX

–

()

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

VINMAX =3.0V +10%

VOUTMIN = 2.7V – 2.5%

ILOADMAX =40 mA

TJMAX =125°C

TAMAX =55°C

PDMAX

TJMAX TAMAX

–

()

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

125 55

–

()

220

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

318 mW

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