TC1266 查看數據表（PDF） - Microchip Technology

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TC1266

200mA PCI LDO

Microchip Technology 

4.0 THERMAL CONSIDERATIONS

4.1 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.

4.2 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 4-1:

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 4-2) is a function of the maximum ambient

temperature (TAMAX), the maximum allowable die

temperature (TJMAX) and the thermal resistance from

junction-to-air (θJA).

EQUATION 4-2:

PDMAX = (TJMAX – TAMAX)

θJA

Where all terms are previously defined.

TC1266

Equation 4-1 can be used in conjunction with

Equation 4-2 to ensure regulator thermal operation is

within limits. For example:

Given:

VINMAX = 5V ± 5%

VOUTMIN = 3.217V

ILOADMAX = 200mA

TJMAX = 125°C

TAMAX = 70°C

θJA

= 130°C/W (SOIC)

Find: 1. Actual power dissipation

2. Maximum allowable dissipation

Actual power dissipation:

PD ≈ (VINMAX – VOUTMIN)ILOADMAX

= (5.25V - 3.217V) 200mA

= 407mW

Maximum allowable power dissipation:

PDMAX = (TJMAX – TAMAX)

θJA

= (125 – 70)

130

= 423mW

In this example, the TC1266 dissipates a maximum of

407mW; below the allowable limit of 423mW.

© 2002 Microchip Technology Inc.

DS21377B-page 5

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