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LAUNCHXL2-570LC43: N2HET high output only 0.9V

Oxana Oosterlee
Prodigy 20 points
Part Number: LAUNCHXL2-570LC43

I am using a LAUNCHXL2-570LC43 to control solenoids using N2HET pins as output. The pins are each connected to the gate of a mosfet switching 24V solenoids with a flyback diode in parallel. This works properly most of the time, but sometimes a N2HET pin seems broken and stops outputting 3.3V when set high. As an example, we currently have a brand new launchpad with a N2HET2_8 pin outputting 0.9V when high (and near 0V when low, which is fine). This launchpad pin seemed 'broken' from the beginning, but with other launchpads sometimes a pin stopped working after some time. I find it very strange that a pin like that 'breaks'. Could this be  fixed in the software? Or is it in the hardware?

  • 0
    TI__Guru**** 196776 points
    Hello Oxana,

    Is this N2HET pin used as GPIO? Is there any code running in N2HET RAM? Is the internal pull enabled? Is there an external pull-up or pull-down?
    Which pin is used for N2HE2[8], K16 or V2?
  • 0 in reply to QJ Wang
    Prodigy 20 points
    Yes, the N2HET pin is used as GPIO. There is no code running in the RAM. The internal pulldown is enabled and there is also an external pull-down. The pin used for H2HET2 is K16.
  • 0 in reply to Oxana Oosterlee
    TI__Guru**** 196776 points
    Hello Oxana,

    Can you monitor the voltage level of K16 and V2? The issue may be caused by latch up. When the solenoid relay is witching on and off, it may create voltage spikes which may cause the MCU pin's latchup. The latchup will not disappear until your reset the device.

    Adding a small capacitor to NHET pin is helpful. I think you have a big diode and small cap in parallel with the solenoid.