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GM6605-A

5.0A PRECISION LINEAR REGULATORS

Unspecified 

GM6605

Output Voltage Sensing

The GM6605 series are three terminal regulators, so

they cannot provide true remote load sensing. Load

regulation is limited by the resistance of the conductors

connecting the regulator to the load. For best results

the GM6605 should be connected as shown in Figure

2.

VIN

VIN

VOUT

GM6605-3.3

Conductor

Parasitic

RC

Resistance

GND

RLOAD

(a) Fixed Version

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)

These 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.

VIN

VIN

VOUT

GM6605-A

ADJ

(b) Adjustable Version

RC

R1

R2

Conductor

Parasitic

Resistance

RLOAD

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),(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

The GM6605 series precision linear regulators include

thermal shutdown and current limit circuitry to protect

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)

the devices. However, high power regulators normally

operate at high junction temperatures so it is important

to calculate the power dissipation and junction temper-

atures accurately to be sure that you use and adequate

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

heat sink. The case is connected to VOUT on the The value for RQJA is calculated using equation (3)

GM6605, so electrical isolation may be required for

some applications. Thermal compound should always

be used with high current regulators like the GM6605.

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 GM6605 the majority of the heat is

generated in the power transistor section.

6

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