V2-1: Hot plugging blows main board (MOSFETs)
When plugging the board in a powered VME crate (something one should not
do anyway), the MOSFETs driving the transformers blow up and breaks the
Likely the 24V supply is already on and the circuitry to drive drives the MOSFETs conducting for a long time. As there is no current limitation they will blow.
- Check what happens during normal power-on (maybe a similar problem exists, but just shorter duration than during hot plugging)
- Check configuration time of Xilinx
- Check the full MOSFET drive circuit
- Seems Xilinx drives a SN64BCT25244 buffer with OE (IC4a, IC4b) that drives in turn MOSFET
- Check what drives this OE and what's the behavior during turn-on
- Note that during hot-plug 12V can be earlier or later than 5V and 3V3 rails!
- Check if problem can be solved by disabling 24V supply until the
Xilinx is configured
- The reset circuit TPS3808,
IC29, page 2 of
can maybe be held off until the Xilinx is configured
- either by adding a pull-down on MR_n (Xilinx configured to float outputs during configuration)
- or by using C230, the CT capacitor (time can be set up to 10s), a value higher than the mentioned 100nF should be used.
Not sure actually if this can work if only 12V is supplied
- It seems that in that case 24V is happily generated and that MOSFETs will be conducting.
- So maybe a more serious change is needed such as limiting the current by design (discharge a slowly charged capacitor, current limit by resistor?)
- The reset circuit TPS3808, IC29, page 2 of schematics can maybe be held off until the Xilinx is configured
- Test by powering board with only 12V, only 3V3, or 5V
Note: the comment "Capacitor CT not mounted: delay of 570ms" on page 2
of the schematic is wrong too.
According to the datasheet of the TPS3808 (fig.14) CT open results in only a 20ms delay.