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MSP430F133 intermittently won't start and then does not reset

stephen connell
Prodigy 40 points
Other Parts Discussed in Thread: TPS3839, MSP430F133, MSP-TS430PM64

I have an MSP430F133 on a multi-layer board with a GND plane. I'm using the TPS3839 brownout reset component and have verified that it holds reset for 200mS after the 3.3V supply is valid. Occasionally, the Device does not start and when it doesn't start, if I force the reset pin active (to GND) it does not reset. The device is not warm so I don't think it's latched up. If I unplug the AC power cord to the AC/DC power supply, I have to wait about 10 seconds for the 3.3V supply to drop to almost GND before the MSP430 will recover for the next power up. The 8MHz clock looks fine. For what reasons will the MSP430 not react to a reset? Any ideas? thank you in advance.  

  • 0
    TI__Guru**** 202266 points
    It appears that the MSP430F133 hardware may be in violation of the PUC/POR conditions stated in the device datasheet. VCC rise time must be greater than +1 V/ms and likewise the fall time should be greater than -1 V/ms. Failure to do so could keep the device in a POR state which can only be corrected by driving the VCC voltage below 200 mV. Please follow the passive component recommendations for device pins, including 10 uF + 100 nF capacitors to GND on all VCC lines and a 47 kOhm pull-up resistor and 2.2 pF pull-down capacitor on the RST line. You can use the MSP-TS430PM64 schematic as a reference, included in the MSP430 Hardware Tools User's Guide (SLAU278): www.ti.com/.../slau278y.pdf

    Regards,
    Ryan
  • 0
    Prodigy 40 points
    Thank you Ryan, taking VCC below 200mV fixes our problem. The problem was that the when the unit is powered down by removing the AC power, the AC/DC 15V power supply that drives the 3.3V regulator for the MSP430F133 decays very slowly and hangs around 1V for a long time. The 3.3V can take up to a couple of minutes to drop below 200mV. When the unit is re-powered it exhibits the problem. By adding a load resistor to the 15V it drops to 0V in less than a second, the micro-controller then starts up fine.

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