STK400-060 Sanyo Semiconductor Corporation, STK400-060 Datasheet - Page 4

• Manufacturer Part Number: STK400-060
• Description: af Power Amplifier (35W+35W+35W)
• Manufacturer: Sanyo Semiconductor Corporation

Heatsink Design Considerations
The heatsink thermal resistance, c-a, required to cover
the hybrid IC’s total power dissipation, Pd, is determined
as follows:
Condition 1: Hybrid IC’s substrate temperature not to
exceed 125 C.
where Ta is the guaranteed maximum ambient tempera-
ture.
Condition 2: Power transistor junction temperature, Tj, not
to exceed 150 C.
where N is the number of power transistors and j-c is the
thermal resistance per power transistor. Note that the
power dissipated per transistor is the total, Pd, divided
evenly among the N power transistors.
Expressions (1) and (2) can be rewritten making c-a the
subject.
The heatsink required must have a thermal resistance that
simultaneously satisfies both expressions.
The heatsink thermal resistance can be determined from
(1) and (2) once the following parameters have been
defined.
• Supply voltage
• Load resistance
• Guaranteed maximum ambient temperature
Pd
Pd
c-a < (125 Ta)/Pd ............................................. (1)
c-a < (150 Ta)/Pd
c-a + Ta < 125 C ........................................ (1)
c-a + Pd/N
Output power per channel, P
j-c + Ta < 150 C ................. (2)
j-c/N .............................. (2)
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: V
: R
: Ta
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STK400-060
The total device power dissipation when hybrid IC’s V
= 28V and R
a maximum of 81W, as is in Pd-P
When estimating the power dissipation for an actual audio
signal input, the rule of thumb is to select Pd correspond-
ing to 1/10 P
sine wave input. For example,
The hybrid IC has 6 power transistors, and the thermal
resistance per transistor, j-c, is 1.8 C/W. If the guaran-
teed maximum ambient temperature, Ta, is 50 C, then the
required heatsink thermal resistance, c-a, is:
From expression (1) : c-a < (125 50)/49.2
From expression (2) : c-a < (150 50)/49.2 1.8/6
Therefore, to satisfy both expressions, the required heat-
sink must have a thermal resistance less than 1.52 C/W.
Similarly, when hybrid IC’s V
From expression (1) : c-a < (125 50)/58
From expression (2) : c-a < (150 50)/58 1.8/6
Therefore, to satisfy both expressions, the required heat-
sink must have a thermal resistance less than 1.29 C/W.
This heatsink design example is based on a constant-volt-
age supply, and should be verified within your specific set
environment.
Pd = 49.2W (for 1/10 P
Pd = 58W (for 1/10 P
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Output power per channel, P
max (within safe limits) for a continuous
= 6 , for a continuous sine wave signal, is
O
O
max = 3.5W)
< 1.52
< 1.73
< 1.29
< 1.42
max = 3.5W)
CC
= 23V and R
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graph.
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No. 5704—4/6
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= 3 :
CC