8

GM6605

5.0A LOW DROPOUT

PRECISION REGULATOR

(a) Fixed version

(b) Adjustable version

Conductor

Parasitic

Resistance

R

C

V

IN

V

OUT

GM6605-3.3

GND

Conductor

Parasitic

Resistance

R

C

V

IN

V

OUT

GM6605-A

ADJ

R1

R2

Output Voltage Sensing

GM6605 series is a three-terminal regulator, so it 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, GM6605 should be connected as shown 1n F1gure 2.

Calculating Power Dissipation and Heat Sink Requirements

GM6605 series include thermal shutdown and current limit circuitry to protect the devices. However, high

power regulators normally operate at high junction temperatures so it is important to calculate the power

dissipation and junction temperatures accurately to be sure to use an adequate heat sink. The case is

compound should always be used with high current regulators like GM6605.

The thermal characteristics of an IC depend on four factors:

1.

2.

3.

4.

Thermal Resistance Junction to amb1ent

The relationship of these four factors is expressed by equation (1):

Maximum ambient temperature and power dissipation are determ1ned 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 expressed by equation (2):

where:

A heat sink effect1vely 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 resistance. Like series electrical resistances, these resistance are summed to determine

the total thermal resistance between the junction and the air. This is expressed by equation (3):

where:

The value for

value for

regulator such as GM6605, the majority of the heat is generated in the power transistor sect1on.

this grounding scheme.