CS5205-1GDP3 データシートの表示（PDF） - ON Semiconductor
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CS5205-1GDP3 Datasheet PDF : 9 Pages
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CS5205−1, CS5205−3, CS5205−5
Calculating Power Dissipation and Heat Sink
Requirements
The CS5205−x series of linear regulators includes thermal
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 heat sink is used.
The case is connected to VOUT on the CS5205−x,
electrical isolation may be required for some applications.
Thermal compound should always be used with high current
regulators such as these.
The thermal characteristics of an IC depend on the
following 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 four are related by the equation
TJ + TA ) PD RQJA
(1)
The maximum ambient temperature and the power
dissipation are determined by the design while the
maximum junction temperature and the thermal resistance
depend on the manufacturer and the package type.
The maximum power dissipation for a regulator is:
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, for the
application
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 and
into the surrounding air.
Each material in the heat flow path between the IC and the
outside environment has a thermal resistance. Like series
electrical resistances, these resistances are summed to
determine RqJA, the total thermal resistance between the
junction and the surrounding air.
1. Thermal Resistance of the junction to case, RqJC
(°C/W)
2. Thermal Resistance of the case to Heat Sink, RqCS
(°C/W)
3. Thermal Resistance of the Heat Sink to the ambient
air, RqSA (°C/W)
These are connected by the equation:
RQJA + RQJC ) RQCS ) RQSA
(3)
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 current regulator
such as the CS5205−x the majority of the heat is generated
in the power transistor section. The value for RqSA depends
on the heat sink type, while RqCS depends on factors such as
package type, heat sink interface (is an insulator and thermal
grease used?), and the contact area between the heat sink and
the package. Once these calculations are complete, the
maximum permissible value of RqJA can be calculated and
the proper heat sink selected. For further discussion on heat
sink selection, see application note “Thermal
Management,” document number AND8036/D, available
through the Literature Distribution Center or via our website
at http://onsemi.com.
ORDERING INFORMATION
Orderable Part Number
Type
Package
Shipping†
CS5205−1GT3
CS5205−1GDP3
CS5205−1GDPR3
5.0 A, Adj. Output
5.0 A, Adj. Output
5.0 A, Adj. Output
TO−220−3, STRAIGHT
D2PAK−3
D2PAK−3
50 Units / Rail
50 Units / Rail
750 / Tape & Reel
CS5205−3GT3
CS5205−3GDP3
CS5205−3GDPR3
5.0 A, 3.3 V Output
5.0 A, 3.3 V Output
5.0 A, 3.3 V Output
TO−220−3, STRAIGHT
D2PAK−3
D2PAK−3
50 Units / Rail
50 Units / Rail
750 / Tape & Reel
CS5205−5GT3
5.0 A, 5.0 V Output
TO−220−3, STRAIGHT
50 Units / Rail
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
http://onsemi.com
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