GM6603
3.0A LOW DROPOUT
PRECISION REGULATOR
Output Voltage Sensing
GM6603 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, GM6603 should be connected as shown 1n F1gure 2.
Conductor
Parasitic
R
C
Resistance
R
LOAD
V
IN
V
OUT
V
IN
V
OUT
Conductor
Parasitic
R
C
Resistance
R
LOAD
GM6603-3.3
GND
GM6603-A
ADJ
R1
R2
(a) Fixed version
(b) Adjustable version
Figure 1.
Conductor Parasitic Resistance Effects are Minimized by
this Grounding Scheme.
Calculating Power Dissipation and Heat Sink Requirements
GM6603 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
connected to V
OUT
on GM6603, so electrical isolation may be required for some applicat1ons. Thermal
compound should always be used with high current regulators like GM6603.
The thermal characteristics of an IC depend on four factors:
1.
2.
3.
4.
Maximum Ambient Temperature T
A
(°C)
Power Dissipation P
D
(Watts)
Maximum Junction Temperature T
J
(°C)
Thermal Resistance Junction to amb1ent
θ
JA
The relationship of these four factors is expressed by equation (1):
T
J
= T
A
+ P
D
x
θ
JA
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):
P
D(MAX)
= (V
IN(MAX)
– V
OUT(MIN)
) x I
OUT(MIN)
+ V
IN(MIN)
x I
Q
where:
V
IN(MAX)
is the maximum input voltage,
V
OUT(MIN)
is the minimum output voltage,
I
OUT(MAX)
is the maximum output current
I
Q
is the max1mum quiescent current at I
OUT(MAX)
.
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
θ
JA
,
the total thermal resistance between the junction and the air. This is expressed by equation (3):
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
where:
θ
JC
is the thermal resistance of Junction to Case,
θ
CS
is the thermal resistance of Case to Heat Sink,
θ
SA
is the thermal resistance of Heat Sink to Ambient air.
The value for
θ
JA
is calculated using equation (3) and the result can be substituted in equation (1). The
value for
θ
CS
is 3.5°C/W for a given package typed based
on an average d1ie size. For a high current
regulator such as GM6603, the majority of the heat is generated in the power transistor sect1on.
7
GM6603
V1.00
GAMMA [ GAMMA MICROELECTRONICS INC. ]
