I'm working on a DC-DC buck circuit. I have it working well, with ringing and overshoot on the switched node well controlled, stable output, good transient response, etc. My problem is temperature.
The converter IC is a 6A-rated part with internal high-side FET, driving a 13A-rated external low-side FET and 11A-rated inductor. Max design load current is 4.8A. Max design ambient temp is 50°C, but no testing has yet been done above 25°C.
Minimum board size is a major design goal.
All of the parts have -40 to +125°C temperature ratings, except for a few X5R and NP0 capacitors. All caps are MLCCs.
I'm seeing case surface temps ~70°C (measured with a thermocouple, confirmed with an IR gun) on the converter IC, FET and inductor.
I experimented with a heatsink on the back side of the board (exposed copper ground plane, connected to top side with numerous thermal vias), but it only brought temps down ~10°C. Hardly worth the expense in BoM cost and manufacturing complication.
For manufacturing, I plan to use a DFN package with slightly better thermal performance for the converter IC (proto uses an 8-SOIC/EP), and specify 2-oz copper (proto has 1-oz copper), but I don't expect huge improvements from these changes.
So, my questions are these:
- What are safe and sensible operating temperatures for the converter IC, FET and inductor?
- How much worse are the temps likely to get at the design 50°C ambient?
- Am I chasing the last degree of improvement for no good reason?
- Generally speaking, what sort of MTBF penalty is paid as temperature rises?
Thanks.
The converter IC is a 6A-rated part with internal high-side FET, driving a 13A-rated external low-side FET and 11A-rated inductor. Max design load current is 4.8A. Max design ambient temp is 50°C, but no testing has yet been done above 25°C.
Minimum board size is a major design goal.
All of the parts have -40 to +125°C temperature ratings, except for a few X5R and NP0 capacitors. All caps are MLCCs.
I'm seeing case surface temps ~70°C (measured with a thermocouple, confirmed with an IR gun) on the converter IC, FET and inductor.
I experimented with a heatsink on the back side of the board (exposed copper ground plane, connected to top side with numerous thermal vias), but it only brought temps down ~10°C. Hardly worth the expense in BoM cost and manufacturing complication.
For manufacturing, I plan to use a DFN package with slightly better thermal performance for the converter IC (proto uses an 8-SOIC/EP), and specify 2-oz copper (proto has 1-oz copper), but I don't expect huge improvements from these changes.
So, my questions are these:
- What are safe and sensible operating temperatures for the converter IC, FET and inductor?
- How much worse are the temps likely to get at the design 50°C ambient?
- Am I chasing the last degree of improvement for no good reason?
- Generally speaking, what sort of MTBF penalty is paid as temperature rises?
Thanks.
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