GM1117-1.5 Просмотр технического описания (PDF) - Gamma Microelectronics Inc.

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GM1117-1.5

1.0A LOW DROPOUT PRECISION LINEAR REGULATORS

Gamma Microelectronics Inc. 

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MICROELECTRONICS

Power Management

GM1117

1.0A LOW DROPOUT PRECISION LINEAR REGULATORS

The thermal characteristics of an IC depend four fac-

tors:

1. Maximum Ambient Temperature TA (°C)

2. Power Dissipation PD (Watts)

3. Maximum Junction Temperature TJ (°C)

4. Thermal Resistance Junction to ambient RQJA

(°C/W)

The relationship of these four factors is expressed by

equation (1):

TJ = TA + PD X RQJA ........(1)

Maximum ambient temperature and power dissipa-

tion are determined by the design while the maximum

junction temperature and thermal resistance depend

on the manufacturer and the package type.

The maximum power dissipation for a regulator is ex-

pressed by equation (2):

PD(max) = { VIN(max)- VOUT(min) } IOUT(max) + VIN(max)IQ ........(2)

where:

VIN(max) is the maximum input voltage,

VOUT(min) is the minimum output voltage,

IOUT(max) is the maximum output current

IQ is the maximum quiescent current at IOUT(max).

A heat sink effectively increases the surface area of

the package to improve the flow of heat away from

the IC into the air. Each material in the heat flow path

between the IC and the environment has a thermal re-

sistance. Like series electrical resistances, these re-

, sistance are summed to determine RQJA the total

thermal resistance between the junction and the air.

This is expressed by equation (3):

RQJA = RQJC + RQCS+ RQSA ........(3)

Where all of the following are in °C/W:

RQJC is thermal resistance of junction to case,

RQCS is thermal resistance of case to heat sink,

RQSA is thermal resistance of heat sink to ambient air

The value for RQJA is calculated using equation (3)

and the result can be substituted in equation (1). The

value for RQJC is 3.5°C/W for a given package type

based on an average die size. For a high current reg-

ulator such as the GM1117 the majority of the heat is

generated in the power transistor section.

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