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MAX3221: Device not working on new batch of PCB's

David Adams29
Prodigy 20 points
Part Number: MAX3221

Hi,

We have been using the MAX3221 device on a design for a while and have had a few occasional failures, but on a recent batch of boards the failure seem more frequent so I would like some advice to help resolve the issue.

On production test we use the RS232 port to load the firmware to a MCU via a bootloader.  This is not working and it seem the MAX3221 device is not working.  I have checked the V+ and V- levels and these are at 3.3V (V+) and 0.1V (V-).  On a working device this is +6V (V+) and -5.5V (V-), it looks like the boost circuit is not working? 

The design does use the auto shutdown feature but there is a valid signal on Rin and the Invalid output is high. 

I have attached a screenshot of the schematic.

 

Thanks 

Dave Adams

  • 0
    TI__Guru 62920 points
    Hi David,

    I don't see any issues with your schematic. Can you please confirm that the failures follow the chip rather than the PCB by swapping ICs from failing and passing systems?

    Do you think we could see the waveforms (voltage versus time) for the V+ and V- rails? That may give us a better understanding of what is going wrong and causing the DC (average) voltages to measure so low.

    What percentage of boards are failing? You mentioned seeing previous failures as well - were they of the same type? (Do you have lot trace codes for the old versus the new devices? Or, could you report the top-side markings to us?)

    Are the failures present at first power-on, or are they induced sometime during operation of the boards? I am trying to understand if the most likely cause is a defective unit of some kind, some kind of damage during assembly (or during in-circuit testing), or if there are any application-related stresses that may be inducing the failures (e.g., hot plug conditions, short circuits, VCC variation, etc.).

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 20 points

    Max,

    Thanks for your response.  I found the issue shortly after submitting the post, I found that layout allowed for C25 and C26 to be fitted 90 degrees out of position, hence not connected to the IC.

    These had not changed since the previous version of the PCB, and as they fitted perfectly on the pads it wasn't obvious at all. 

    Once C25 and C26 were fitted correctly the board worked as expected.

    Regards

    Dave

  • 0 in reply to David Adams29
    TI__Guru 62920 points
    Dave,

    Thanks for the follow-up! I'm glad you were able to resolve this quickly.

    Regards,
    Max