TC2186-2.6VCTTR View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

TC2186-2.6VCTTR

50 mA, 100 mA, and 150 mA CMOS LDOs with Shutdown and Error Output

Microchip Technology 

5.0 THERMAL CONSIDERATIONS

5.1 Thermal Shutdown

Integrated thermal protection circuitry shuts the

regulator off when the die temperature exceeds

approximately 160°C. The regulator remains off until

the die temperature cools to approximatley 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.

Equation 5-1 is used to calculate worst case power

dissipation:

EQUATION 5-1:

PD ≈ (VINMAX – VOUTMIN)ILOADMAX

Where:

PD

= Worst-case actual power dissipation

VINMAX = Maximum voltage on VIN

VOUTMIN = Minimum regulator output voltage

ILOADMAX = Maximum output (load) current

The maximum allowable power dissipation

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

temperature (TAMAX), the maximum allowable die

temperature (125 °C) and the thermal resistance from

junction-to-air (θJA). The 5-Pin SOT-23A package has

a θJA of approximately 220°C/Watt when mounted on a

typical two layer FR4 dielectric copper clad PC board.

EQUATION 5-2:

PDMAX

=

T----J--M-----A---X----–-----T---A----M----A---X-

θJA

Where all terms are previously defined.

TC2054/2055/2186

Equation 5-1 can be used in conjunction with

Equation 5-2 to ensure regulator thermal operation is

within limits. For example:

Given:

VINMAX

VOUTMIN

ILOADMAX

TAMAX

= 3.0V +10%

= 2.7V – 2.5%

= 40 mA

= +55°C

Find:

1. Actual power dissipation

2. Maximum allowable dissipation

Actual power dissipation:

PD = (VINMAX – VOUTMIN)ILOADMAX

= [(3.0 × 1.1) – (2.7 × 0.975)]40 × 10–3

= 26.7mW

Maximum allowable power dissipation:

PDMAX

=

T----J--M-----A---X----–-----T---A----M----A---X-

θJA

= 1---2---5-----–-----5--5--

220

= 318mW

In this example, the TC2054 dissipates a maximum of

only 26.7 mW; far 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.

© 2009 Microchip Technology Inc.

DS21663D-page 13

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