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AMC7834: Sudden reset?

Kai Parow-Souchon
Prodigy 40 points
Part Number: AMC7834

Hi,

I have a custom PCB with an AMC7834 and a MSP430 microcontroller, which works fine for RF MMIC biasing in the lab. It is powered using a LDO from a +12V supply.

This PCB however was recently integrated in an instrument, and is behaving very oddly in this specific situation. It appears that the AMC7834 is suddenly resetting after several minutes of operation without (known) external cause for reset. the MSP430 is monitoring the general status, clamp, and alarm registers as well as the power state register. It only happens in the instrument, the same configuration of a lab power supply is working fine.

Without raising any alarm, it goes into low power mode, powers down PA_ON and engages the clamps. The sleep pins are disabled, reset driven high by the MSP430 (in addition to a 10k pullup). Monitoring of the 5V rail and input rail does not show any obvious dips, and should be picked up by the AMC monitoring as well.

It appears to be some kind of EMI issue, unless there's something I missed?

Is there any other way that would lead to a reset of the AMC?

Cheers,

Kai

  • 0
    TI__Guru 54043 points

    Hi Kai,

    Do you have a capacitive load on the DAC outputs? Your lab instrument might be current limiting the supply.  If you have a capacitive load on the output you could be causing the DACs to momentarily reach the short circuit limit.  This might momentarily collapse the supply enough to trigger a reset.  You could monitor the LDO output to see if you can catch this behavior, or increase the current limit to see if you can avoid the collapse to begin with.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 40 points

    Hi Paul,

    Thanks for the quick reply.

    The bipolar dacs have a capacitive load with the mmics gate and bypass caps. The unipolar dacs are driving the drains with a current buffer. 

    At the time of reset the unit is in steady state, with no change happening - there shouldn't be any load changes, but the source seems to come from external.

    It appears switching to the external 15v rail (rather than 12v) fixes the issue, so it appears there is some pollution on the 12v.

    The msp430 is powered from the same supply, and again, no alarms are observed from either msp430 or the amc.

    Cheers

    Kai

  • 0 in reply to Kai Parow-Souchon
    TI__Guru 54043 points

    Hi Kai,

    I think you need to you monitor the supply current to see if there a sudden collapse? Could the LDO be going into thermal shutdown?

    Thanks,

    Paul