NCP1086 ON, NCP1086 Datasheet - Page 8

• Manufacturer Part Number: NCP1086
• Description: 1.5 A Adjustable and 3.3 V Fixed Output Linear Regulator
• Manufacturer: ON

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.
where:
V
V
I
I
package to improve the flow of heat away from the IC and
into the surrounding air.
P D(max) + { V IN(max) * V OUT(min) } I OUT(max) ) V IN(max) I Q
OUT(max)
Q
IN(max)
OUT(min)
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:
A heatsink effectively increases the surface area of the
is the maximum quiescent current at I
is the maximum input voltage,
is the maximum output current, for the application
is the minimum output voltage,
T J + T A ) P D
D
(W)
OUT
, and electrical isolation
R QJA
J
A
( C)
OUT(max)
( C)
qJA
.
( C/W)
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(eq. 1)
(eq. 2)
NCP1086
8
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.
regulator such as the NCP1086 the majority of the heat is
generated in the power transistor section. The value for
R
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 via our website at www.onsemi.com.
qSA
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
( C/W)
( C/W)
air, R
qJA
depends on the heatsink type, while R
“Thermal
can be calculated and the proper heatsink selected.
qSA
R QJA + R QJC ) R QCS ) R QSA
qJA
( C/W)
, the total thermal resistance between the
qJA
qJC
Management,”
is calculated using Equation 3 and the
is 3.5 C/W. For a high current
document
qCS
depends on
qJC
qCS
number
(eq. 3)