GM6603-ATA3T 데이터 시트보기 (PDF) - Gamma Microelectronics Inc.

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GM6603-ATA3T

3.0A LOW DROPOUT PRECISION LINEAR REGULATORS

Gamma Microelectronics Inc. 

Output Voltage Sensing

GM6603 series is three terminal regulator, so they can-

not provide true remote load sensing. Load regulation

is limited by the resistance of the conductors connect-

ing the regulator to the load. For best results, GM6603

should be connected as shown in Figure 2.

VIN

VIN

VOUT

GM6603-3.3

GND

Conductor

Parasitic

RC Resistance

RLOAD

(a) Fixed Version

VIN

VIN

VOUT

GM6603-A

ADJ

(b) Adjustable Version

Conductor

Parasitic

RC Resistance

R1

RLOAD

R2

(a),(b)

FIGURE 2 Conductor Parasitic Resistance Effects are

Minimized by this Grounding Scheme For Fixed

and Adjustable Output Regulators

Calculating Power Dissipation and Heat

Sink Requirements

GM6603 series precision linear regulators include ther-

mal shutdown and current limit circuitry to protect the

devices. However, high power regulators normally oper-

ate at high junction temperatures so it is important to

calculate the power dissipation and junction tempera-

tures accurately to be sure that you use and adequate

heat sink. The case is connected to VOUT on GM6603

so electrical isolation may be required for some appli-

cations. Thermal compound should always be used

with high current regulators like the GM6603.

The thermal characteristics of an IC depend on four

factors:

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)

These relationship of these four factors is expressed

by equation (1):

TJ = TA + PD X RQJA

Maximum ambient temperature and power dissipa-

tion are determined by the design while the maxi-

mum 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

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 ther-

mal resistance. Like series electrical resistances,

these resistances 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

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 cur-

rent regulator such as GM6603, the majority of the

heat is generated in the power transistor section.

7

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