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TPS562200: Output falls for 1.2ms due to line disturbance

Tim Dunn
Prodigy 100 points
Part Number: TPS562200
Other Parts Discussed in Thread: TPS54427

TPS562200 12.0V Input gets disrupted for 100us due to a new type of expandable subsystem powering up.  During this time the TPS562200 3.3V falls linearly to 1.875V over 300us, holds flat for another 300us, and then ramps linearly back to regulation over about 500us.

The 3.3V load is about 500mA and is not appreciably changing during this disturbance.

This circuit has been in production for 2 yeas without issues and this is a newly identified incompatibility.  Similar systems that employ the TPS54427 are riding through the same disturbance without issues.

Suggestions to diagnose and cure are appreciated.

  • 0
    Prodigy 100 points

    Working further with this finds that C28 and C84 as placed on the PWB could have been located closer to pins 1 and 3 of the TPS562200 at U12.  C84 is located near pins 4-6 of U12.  I found that increasing it to 10uF reduces the 3.3V disturbance due to line variation.  

  • 0
    TI__Expert 4795 points

    Hi Tim,

    We suggest to place C84 as close to Pin1, 3 as possible. Could you help capture PIN5 EN waveform for further analysis? By the way, are these kinds of disrupt haapeded in previous projects?

  • 0 in reply to Tim Dunn
    TI__Expert 4875 points

    Hi Tim,

    For this kind of input transient, we call line transient. The output voltage should recover back quickly by control loop response. It is abnormal to see this long recovery time. Please help to check with SW and EN waveform like Vincent proposed. We need to check more to know whether the device is shut down or not in the transient. Meanwhile, it is good to place more input cap value to filter this input transient. 

  • 0 in reply to Anthony Lang
    Prodigy 100 points

    Thanks for the comments.  Yes the EN pin is sagging down to 1V when the 12V rings for 100us down to 8V.  I will take steps now to correct this and I expect the TPS562200 will not drop its output when the EN stays high.

  • 0 in reply to Vincent Zhang(BSR)
    Prodigy 100 points

    The type of 12V load exhibiting this problem is new to our systems and this is why no testing previously identified the issue.