• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 80 subscribers
  • Views 448 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Power network blows CPU

Reuel Haavrahami
Prodigy 130 points

Other Parts Discussed in Thread: MSP430F5529

Hi

I have a custom board which receives power from 3 sources: JTAG, USB (VUSB) and PSU. The USB  power line is fed to the VBUS pin of the CPU supplies the VUSB source. Each of these three sources are fed into BAT54C diodes to "select" the power source for the rest of the 3V circuit.

However, when I have JTAG and USB connected and add the PSU, the CPU gets fried somehow sometimes.

To note: I am working on a laptop that is unearthed, and after I blew the first board I also unearthed the external PSU that feeds my SMP PSU on the board. That worked for some time, but now a second board has blown as well and I don't know how to solve this issue.

The board has a MSP430F5529.

Perhaps someone knows how to help.

  • 0
    Guru 34873 points

    How you know that CPU is fried. It doesn't respond to BSL/JTAG entry sequence, respond with blown fuse, it is hot when you touch it with fingers? All 3 GND lines on custom board are connected together without any problems?

    On my MSP430F5xx USB boards, there is jumper between VUSB (output from internal reg)  pin and 3.3V supply lines. If external 3.3V source is used, I just remove jumper, and everything is working OK, with USB module supplied by VBUS if the device is connected over USB to PC.

  • 0 in reply to zrno soli
    Prodigy 130 points

    I know the CPU is fried because it gets REALY hot, the 3V3 line drops to 1V6 and the current shoots up. The CPU do not respond to BSL/TJAG.

    All works very good with the JTAG and USB connected, except for the CPU that keeps on resetting when I boot only from USB (This I will solve when later, probably a code bug). All seems to work fine from the PSU/SMP/LDO side too.  Only when I apply this last said PSU while the JTAG and USB are connected, the CPU gets blown sometimes.

  • 0
    Prodigy 130 points

    I may have found my problem. When using our external power supply, I can see large spikes when pressing the power button to on. These spikes seems to seep through the SMP circuit obtained from TI, creating spikes on 5V supply and also on the 3V3 derived from the 5V through an LDO!!

    When not using the power switch from the external PSU (rather leaving the external PSU on, and connecting power to the banana socket when needed) these spikes do not exist. Both SMP and LDO act as expected.

  • 0 in reply to Reuel Haavrahami
    Guru 227245 points

    So you should either replace your PSU to a better one or attach some suppressor diodes to its output.

    The P6KE6.8CA can short peaks of up to 100A/600W (steady state: 5.0W) while clamping the voltage down to 6.45..7.14V. The remaining peak should be swallowed by the 3.3V regulator easily.

    Reuel Haavrahami said:
    also on the 3V3 derived from the 5V through an LDO!!

    Usually, LDOs have a maximum input voltage. If it is exceeded, regulation is lost (best case) or the regulator is fried. Even the best LDO can only regulate input voltage peaks up to its maximum input voltage.

**Attention** This is a public forum