On 2020-05-06 23:00, bitrex wrote:
On 5/6/2020 2:27 PM, John Larkin wrote:
We have people working at home, but some wretched soul has to come in
to work and support them. Me.
I finally got the last assembled PCB for my 3-phase alternator
simulator, the control board.
I powered up the first board and the 3.3 volt supply wouldn't come up.
It was millivolts. This drove me crazy. I checked everything five
times and finally replaced the TPS54302 chip. That didn't help, as
replacing chips tends to not help.
Finally I noticed tiny pulses on the 3.3 volt rail, so the switcher
was at least trying a little.
I connected a big bench supply to 3.3 and ramped up the current limit.
Got 0.5 amps at 0.2 volts. Hard short. The little switcher was trying
occasionally, giving up for a long time, and hardly making any
So I thermal imaged it and the ARM chip was hot. It's rotated 90
degrees. I'm waiting for it to be replaced.
The chip appears to have molded indexes in three corners. The little
one is pin 1.
I thought the TPS switcher might have been backwards too, since it's
basically impossible to see the pin 1 indication.
Maxim "solved" that problem by making this i2c isolator
rotation-symmetrical and then they just don't put a dot indicator on
They don't tell you that explicitly though AFAIK, they like you to
puzzle over why there isn't one and then figure out how clever they
are on your own.
Lots of small signal dual MOSFETs are like that, e.g.:
I put a lot of N-channel and P-channel like that in several designs. I
had to explain more than three times to production that there was no pin
1 marking because it worked the same when reversed.