HIP5600
A thermal network that describes the heat flow from the inte-
grated circuit to the ambient air is shown in Figure 6. The
basic relation for thermal resistance from the IC surface, his-
torically called “junction”, to ambient (θ
JA
) is given in Equa-
tion 5. The thermal resistance of the heat sink (θ
SA
) to
maintain a desired junction temperature is calculated using
Equation 6.
PD
T
J
= JUNCTION
Example,
Given: V
IN
= 400V
DC
θ
JC
= 4.8
o
C/W
T
A
= +50
o
C
V
REF
= 1.18V
≡
I
V
OUT
= 15V
T
TS
= +127
ο
C
RF1 = 1.1k
I
LOAD
= 15mA
I
ADJ
= 80µA
P = 6.2W = (V
IN
- V
OUT
)(I
IN
)
I
θ
JC
T
C
= CASE
T
S
= HEAT SINK
IN
ADJ
+ ------------------ +
I
-
V REF
RF1
LOAD
θ
CS
θ
SA
HEAT SINK
Find:
Proper heat sink to keep the junction temperature
of the HIP5600 from exceeding T
TS
(+127
o
C).
Solution:
Use Equation 6,
T
A
= AMBIENT AIR
T TS
–
T A
θ
SA
= --------------------------- –
θ
JC
-
P
(EQ. 7)
(EQ. 8)
FIGURE 6.
TJ
–
TA
- --------
θ
JA
= ---------------------
°
C
P
W
Where:
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
∴
θ
SA
+
θ
Where:
CS
≈
θ
°
C
127
°
C
–
50
°
C
θ
SA
= ------------------------------------------ –
4.8
°
C
=
7.62
--------
-
6.2
W
(EQ. 5)
and
T J
=
T TS
SA
T TS
–
T A
= --------------------------- –
θ
-
P
The selection of a heat sink with
θ
SA
less than +7.62
o
C/W
would ensure that the junction temperature would not
exceed the thermal shut down temperature (T
TS
) of +127
o
C.
A Thermalloy P/N7023 at 6.2W power dissipation would
meet this requirement with a
θ
SA
of +5.7
o
C/W.
Operation Without A Heatsink
The package has a
θ
JA
of +60
o
C/W. This allows 0.7W
power dissipation at +85
o
C in still air. Mounting the HIP5600
to a printed circuit board (see Figure 39 through Figure 41)
decreases the thermal impedance sufficiently to allow about
1.6W of power dissipation at +85
o
C in still air.
Thermal Transient Operation
For applications such as start-up, the HIP5600 in the TO-220
package can operate at several watts
-without a heat sink-
for a period of time before going into thermal shutdown.
JC
(EQ. 6)
θ
JA
= (Junction to Ambient Thermal Resistance) The sum of
the thermal resistances of the heat flow path.
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
T
J
=
(Junction Temperature) The desired maximum junc-
tion temperature of the part. T
J
= T
TS
T
TS
=
(Thermal Shutdown Temperature) The maximum
junction temperature that is set by the thermal pro-
tection circuitry of the HIP5600
(min = +127
o
C, typ = +134
o
C and max = +142
o
C).
θ
JC
= (Junction to Case Thermal Resistance) Describes the
thermal resistance from the IC surface to its case.
θ
JC
=
4.8
o
C/W
θ
CS
= (Case to Mounting Surface Thermal Resistance) The
resistance of the mounting interface between the
transistor case and the heat sink.
For example, mica washer.
θ
SA
= (Mounting Surface to Ambient Thermal Resistance)
The resistance of the heat sink to the ambient air.
Varies with air flow.
T
A
= Ambient Temperature
P = The power dissipated by the HIP5600 in watts.
P = (V
IN
- V
OUT
)(I
OUT
)
Worst case
θ
SA
is calculated using the minimum T
TS
of
+127
o
C in Equation 6.
P
D
= I
IN
(V
IN
- V
OUT
)
T
J
= JUNCTION
0.6θ
JC
DIE/PACKAGE INTERFACE
0.4θ
JC
T
S
= HEAT SINK
OR CASE
θ
SA
T
A
= AMBIENT AIR
CS + 0.5C
P
0.5C
P
C
D
FIGURE 7. THERMAL CAPACITANCE MODEL OF HIP5600
Figure 7 shows the thermal capacitances of the TO-220
package, the integrated circuit and the heat sink, if used.
When power is initially applied, the mass of the package
absorbs heat which limits the rate of temperature rise of the
6
HARRIS [ HARRIS CORPORATION ]
