TC1262 datasheet(4/20 Pages) MICROCHIP

4 / 20 page

TC1262

DS20001373D-page 4

 2002-2023 Microchip Technology Inc. and its subsidiaries

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:

The

maximum

allowable

power

dissipation

(Equation 4-2) is a function of the maximum ambient

temperature (TAMAX), the maximum allowable die

temperature (TJ

MAX) and the thermal resistance from

junction-to-air (



JA).

EQUATION 4-2:

Table 4-1 and Table 4-2 show various values of

JA for

the TC1262 packages.

TABLE 4-1:

THERMAL RESISTANCE

GUIDELINES FOR TC1262 IN

SOT-223 PACKAGE

*Tab of device attached to topside copper

TABLE 4-2:

THERMAL RESISTANCE

GUIDELINES FOR TC1262 IN

3-PIN DDPAK/TO-220

PACKAGE

*Tab of device attached to topside copper

Equation 4-1 can be used in conjunction with

Equation 4-2 to ensure regulator thermal operation is

within limits. For example:

Given:

VINMAX

= 3.3V ± 10%

VOUTMIN = 2.7V ± 0.5%

ILOADMAX = 275 mA

TJMAX

= 125°C

TAMAX

= 95°C

JA

= 59°C/W (SOT-223)

Find: 1. Actual power dissipation

2. Maximum allowable dissipation

Actual power dissipation:

PD  (VINMAX –VOUTMIN)ILOADMAX

= [(3.3 x 1.1) – (2.7 x .995)]275 x 10–3

= 260 mW

Maximum allowable power dissipation:

In this example, the TC1262 dissipates a maximum of

260 mW; below the allowable limit of 508 mW. In a

similar manner, Equation 4-1 and Equation 4-2 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 508 mW into Equation 4-1, 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

45°C/W

1000 sq mm 2500 sq mm 2500 sq mm

45°C/W

225 sq mm

2500 sq mm 2500 sq mm

53°C/W

100 sq mm

2500 sq mm 2500 sq mm

59°C/W

1000 sq mm 1000 sq mm 1000 sq mm

52°C/W

1000 sq mm

0 sq mm

1000 sq mm

55°C/W

Where:

= Worst case actual power dissipation

VINMAX

= Maximum voltage on VIN

VOUTMIN = Minimum output voltage

ILOADMAX = Maximum output (load) current

VINMAX VOUTMIN

–

 I

LOADMAX





PDMAX

TJMAX TAMAX

–





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

Where all terms are previously defined.

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

125sqmm

2500sqmm 2500 sq mm

35°C/W

PDMAX

TJMAX TAMAX

–





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

125 95

–



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

508mW

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