Philips Semiconductors
Preliminary specification
Full bridge vertical deflection output circuit
in LVDMOS
TDA8357J
Heatsink calculation
The required heatsink thermal resistance is given by:
The value of the heatsink can be calculated in a standard
way with a method based on average temperatures.
The required thermal resistance of the heatsink is
determined by the maximum die temperature of 150 °C.
In general we recommend to design for an average die
temperature not exceeding 130 °C.
Tj – T
Rth(h – a)
=
amb – (R th(j – c) + Rth(c – h)
)
-----------------------
Ptot
When we use the values given we find:
110 – 40
Rth(h – a)
=
– (5 + 2) = 16 K/W
----------------------
3.0
The heatsink temperature will be:
Th = Tamb + (Rth(h-a) × Ptot) = 40 + (3 × 16) = 90 °C
EXAMPLE
Measured or given values: Ptot = 3 W; Tamb = 40 °C;
Tj = 110 °C; Rth(j-c) = 5 K/W; Rth(c-h) = 2 K/W.
1999 Nov 10
11
NXP [ NXP ]
