STA540 datasheet(13/23 Pages) STMICROELECTRONICS

13 / 23 page

STA540

Thermal information

13/23

Thermal information

In order to avoid the intervention of the thermal protection, placed at Tj =150° C for thermal

muting and Tj=160° C for thermal shutdown, it is important to calculate the heatsink thermal

resistance, Rth_HS, correctly.

The parameters that influence the calculation are:

maximum dissipated power for the device (Pdmax)

maximum thermal resistance junction to case (Rth_j-case)

maximum ambient temperature Tamb_max

There is also an additional term that depends on the Iq (quiescent current).

5.1

Heatsink specification examples

5.1.1

Rth_HS calculation for 4 single-ended channels

Given VS = 14.4 V, RL = 4 Ω x 4 channels, Rth_j-case = 1.8° C/W, Tamb_max = 50° C and

Pout = 4 x 7 W then

the maximum power dissipated in the device is:

and the required thermal resistance of the heatsink is:

5.1.2

Rth_HS calculation for 2 single-ended channels plus 1 BTL channel

Given VS = 14.4 V, RL = 2x 2 Ω (SE) + 1x 4 Ω (BTL), Pout = 2 x 12 W + 1 x 26 W then

the maximum power dissipated in the device is:

and the required thermal resistance of the heatsink is:

dmax

NChannel

-------------------

42.62

10.5W

⋅

th_HS

150

amb_max

–

dmax

------------------------------------------ R

th_j-case

150

–

10.5

---------------------- 1.8

7.7

°C/W

–

dmax

-------------------

------------------

25.25

10.5

21W

⋅

th_HS

150

amb_max

–

dmax

------------------------------------------ R

th_j-case

150

–

---------------------- 1.8

°C/W

–

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