What size heatsink is required for 3.3V quarterbrick at 20A, 48V input, 70C ambient, and 200LFM of airflow?

Using SynQor's PQ48033QGA25 data sheet figure 3, at 48V input, and with a 20A load, the power dissipated by the SynQor's 3.3V quarterbrick converter is about 8.5 Watts. The allowable temperature rise is simply the maximum baseplate temperature minus the worst case ambient temperature. So in this example, 100C - 70C = 30C allowable rise.

The thermal impedance of the heatsink required is simply the allowable temperature rise, divided by the power dissipated. In our example this is 30C/8.5Watts, giving a maximum thermal impedance requirement for our heatsink of 3.53C/W at 200LFM. Using any standard heatsink catalog you can now select a heatsink.

A good choice would be Intricast's (www.intricast.com) HS1361XM01 heatsink, which is 0.5" tall and has a thermal impedance of 2.60 C/W at 200LFM. More.

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