TC1070 Ver la hoja de datos (PDF) - TelCom Semiconductor Inc => Microchip

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TC1070

50mA ADJUSTABLE CMOS LDO WITH SHUTDOWN

TelCom Semiconductor Inc => Microchip 

100mA ADJUSTABLE CMOS

LDO WITH SHUTDOWN

Equation 2 can be used in conjunction with Equation 3

to ensure regulator thermal operation is within limits. For

example:

Given:

VINMAX = 3.0V ±10%

VOUTMIN = 2.7V ±0.5V

ILOAD = 98mA

TAMAX = 55°C

Find: 1. Actual power dissipation

2. Maximum allowable dissipation

Actual power dissipation:

PD ≈ (VINMAX – VOUTMIN)ILOADMAX

= [(3.0 x 1.1) – (2.7 x .995)]40 x 10–3

= 60mW

Maximum allowable power dissipation:

PDMAX = (TJMAX – TAMAX)

θJA

= (125 – 55)

220

= 318mW

In this example, the TC1071 dissipates a maximum of

only 60mW; far below the allowable limit of 318mW. In a

similar manner, Equation 1 and Equation 2 can be used to

calculate maximum current and/or input voltage limits. For

example, the maximum allowable VIN is found by substitut-

ing the maximum allowable power dissipation of 318mW

into Equation 1, from which VINMAX = 5.9V.

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.

PRELIMINARY INFORMATION

TC1071

TC1071-01 6/13/97

5

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