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TLV1117 with low ESR ceramic capacitor

Ryuji
Guru 20090 points
Other Parts Discussed in Thread: TLV1117

Hello,

Our customer using TLV1117 with low ESR ceramic capacitor.
They understood that TLV1117 can't use with ceramic capacitor.
However , they use TLV1117 since early times with their responsibility and there is no problem until recent times.

Now, the output oscillation of TLV1117 was occured and they would like to know the difference between non oscillation device and oscillation device.

Could you please let me know the parameter that it is thought that I affect the stability of TLV1117?

I understood that TLV1117 is operated with 0.2~10ohm ESR.
However there is the device which is oscillated with low ESR and non oscillated with low ESR.
I would like to know this difference for explanation to the customer.

Best Regards,
Ryuji Asaka 

  • 0
    TI__Guru**** 164746 points
    Ryuji-san,

    The minor variation in the bode plot of the TLV1117 can be the difference.
    Likely the bandwidth is different.
  • 0 in reply to Ron Michallick
    Guru 20090 points

    Hello Ron san,

    Thank you for the reply and sorry for my late response.
    Please see the attached file as the oscillation wave form of TLV1117-33.
    I measured output voltage of two TLV1117-33s which were mounted to TLV1117LVEVM.

    TLV1117-33 waveform.pdf

    As a result, oscillation freaquency is difference between two samples.
    I think that this reason is the difference of error amp bandwidth.

    Can I estimate the band width characteristics from this waveform?
    I would like to explain this difference cause to the customer.

    Best Regards,
    Ryuji Asaka

  • 0 in reply to Ryuji
    TI__Guru**** 164746 points
    Ryuji-san,

    The rise time of the saw-tooth wave will be related to the bandwidth, but there are other factors.
    The fall time of the saw-tooth is set mostly by the output capacitor discharge rate.
    V/s=i/C; falling slew rate in volts per second is output current load divided by output capacitance.
    If the waveform was sinusoidal then it would be an indication of bandwidth.

    For the device that has no oscillation in application, try a load transient using the application circuit.
    The response will likely ring a few cycles. This will tell the bandwidth which can be used to pick a appropriate ESR to add.