cs5203a-1 ON Semiconductor, cs5203a-1 Datasheet - Page 7

• Manufacturer Part Number: cs5203a-1
• Description: 3.0 A Adjustable, And Fixed 1.5 V, 3.3 V And 5.0 V Linear Regulators
• Manufacturer: ON Semiconductor

Calculating Power Dissipation and Heatsink
Requirements
shutdown and current limit circuitry to protect the device.
High power regulators such as these usually operate at high
junction temperatures so it is important to calculate the
power dissipation and junction temperatures accurately to
ensure that an adequate Heatsink is used.
isolation may be required for some applications. Thermal
compound should always be used with high current
regulators such as these.
following four factors:
1. Maximum Ambient Temperature T
2. Power dissipation P
3. Maximum junction temperature T
4. Thermal resistance junction to ambient R
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type.
P D(max) + { V IN(max) * V OUT(min) } I OUT(max) ) V IN(max) I Q
where:
application
The CS5203A series of linear regulators includes thermal
The case is connected to V
The thermal characteristics of an IC depend on the
These four are related by the equation
The maximum ambient temperature and the power
The maximum power dissipation for a regulator is:
V
V
I
I
OUT(max)
Q
IN(max)
OUT(min)
is the maximum quiescent current at I
is the maximum input voltage,
is the minimum output voltage,
is the maximum output current, for the
T J + T A ) P D
D
(Watts)
CS5203A−1, CS5203A−2, CS5203A−3, CS5203A−5
OUT
on the CS5203A, electrical
R qJA
J
A
( C)
( C)
OUT(max)
qJA
( C/W)
.
http://onsemi.com
(1)
(2)
7
package to improve the flow of heat away from the IC and
into the surrounding air.
outside environment has a thermal resistance. Like series
electrical resistances, these resistances are summed to
determine R
junction and the surrounding air.
1. Thermal Resistance of the junction−to−case, R
2. Thermal Resistance of the case to Heatsink, R
3. Thermal Resistance of the Heatsink to the ambient
result can be substituted in equation (1).
for a given package type based on an average die size. For
a high current regulator such as the CS5203A the majority
of the heat is generated in the power transistor section. The
value for R
depends on factors such as package type, Heatsink interface
(is an insulator and thermal grease used?), and the contact
area between the Heatsink and the package. Once these
calculations are complete, the maximum permissible value
of R
For further discussion on Heatsink selection, see application
note
AND8036/D, available through the Literature Distribution
Center or via our website at http://onsemi.com.
A Heatsink effectively increases the surface area of the
Each material in the heat flow path between the IC and the
These are connected by the equation:
The value for R
The value for R
qJA
( C/W)
( C/W)
air, R
“Thermal
can be calculated and the proper Heatsink selected.
qSA
R qJA + R qJC ) R qCS ) R qSA
qSA
qJA
( C/W)
depends on the Heatsink type, while R
, the total thermal resistance between the
qJA
qJC
Management,”
is calculated using equation (3) and the
is normally quoted as a single figure
document
qCS
number
qJC
qCS
(3)