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doc: add power test

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King Kévin 2023-12-04 11:52:54 +01:00
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CHANGELOG.md
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@ -11,6 +11,40 @@ changes:
- add one I/O to port (allowing 3-line protocols like SPI or I2S)
- change input capacitors (for manufacturability)
tests:
I tested the power supply to see if it capable of delivering 5A.
It was, but only for a couple of seconds.
It could provide 4A, but only for a 1-2 minutes.
Then the temperature protection would kick in.
There was no voltage drop, but stable 5V.
Putting a tiny aluminium heat sink would make it last a bit more.
What surprised me was that the SS510 diode D2 would get as warm as the TPS45460 voltage regulator, according to the infrared camera.
I changed the configuration for the TPS45460 to switch it from economic to efficient, hoping it would get less hot:
- inductor L1 from 6.8 uH to 2x6.8=13.6uH
- CLK resistor R18 from 200k to 470k to change switching frequency from 484 kHz to ~200 kHz
- AEC output capacitor was already large enough
It could now deliver 5A for one minute, before D2 SS510 died (short).
After changing the diode, it could deliver 4A for 5 minutes (without additional active/passive cooling), before the inductor desoldered from the board (the solder melted).
It could hold 3A for at least 30 minutes, stabilizing at around 140 degC.
There the IR camera confirmed that the diode was warmer than the regulator.
Conclusion: the regulator could be used with an average 3A output, with 4-5A peaks.
To continuously provide more than 3A I need to change the switching diode to a 50WQ10FN.
This has a much larger package (DPAK vs SMA) to better dissipate heat.
It has also a lower voltages drop (770mV vs 880mV), using less power.
But it is also much more expensive ($ 0.26 vs 0.05).
I would still strongly recommend to also put a heat sink on it, and if possible with forced air flow.
But this makes it more complicated to use, and not the intended usage of the board.
This also explains why commercial 60V to 5V 5A modules have such a large heat sink.
The board cannot be advertised as 5A capable anymore because it won't be able to hold it.
Because of that, I will downgrade it to 3A.
This way it can't damage itself.
I will probably change the TPS45460 to a LMR16030.
It has a 3A over-current protection, is simpler to use (fewer external components), and cheaper ($ 1.3 vs 0.7).
I will still use the lower frequency higher efficiency configuration.
v2
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