STK404-050S View Datasheet(PDF) - SANYO -> Panasonic
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STK404-050S Datasheet PDF : 5 Pages
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STK404-090S
Thermal Design Example
If we define Pd, the total power dissipation on the board when this hybrid IC is in operation, the heat sink thermal
resistance, θc-a, is determined as follows:
Condition 1: The hybrid IC substrate temperature Tc must not exceed 125°C.
Pd × θc-a + Ta < 125°C ... (1)
Ta: Guaranteed ambient temperature for the end product.
Condition 2: The junction temperature of each transistor must not exceed 150°C.
Pd × θc-a + Pd/N × θj-c + Ta < 150°C ... (2)
N: Number of power transistors
θj-c: Thermal resistance per power transistor
We take the power dissipation in the power transistors to be Pd evenly distributed across those N power transistors.
If we solve for θc-a in equations (1) and (2), we get the following inequalities:
θc-a < (125 – Ta)/Pd ... (3)
θc-a < (150 – Ta)/Pd – θj-c/N ... (4)
Values that satisfy both these inequalities at the same time are the required heat sink thermal resistance values.
Example:
For actual music signals, it is usual to use a Pd of 1/8 of POmax, which is the power estimated for continuous signals in
this manner. (Note that depending on the particular safety standard used, a value somewhat different from the value of
1/8 used here may be used.)
When VCC = ±32V and RL = 6Ω, we get the following expression for the total power dissipation on the board, Pd:
Pd = 23W (when 1/8 POmax is 6.3W) ... (5)
The number, N, of power transistors in the hybrid IC’s audio amplifier block is 2. Since the thermal resistance, θj-c, per
transistor is 2.2°C/W, the required heat sink thermal resistance, θc-a, for a guaranteed ambient temperature of 50°C will
be as follows:
From inequality (3): θc-a < (125 – 50)/23=3.26 ... (6)
From inequality (4): θc-a < (150 – 50)/23 – 2.2/2=3.24 ... (7)
Therefore, the thermal resistance that satisfies both these expressions (6,7) at the same time is 3.24°C/W.
Note that this thermal design example assumes the use of a constant-voltage power supply, and is only provided as an
example for reference purposes. Thermal designs must be tested in an actual end product.
No.7728-4/5
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