This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS769: TPS76950 Oscillates

Part Number: TPS769
Other Parts Discussed in Thread: TPS767,

Hi all I am using TPS76950 Fixed 5V regulator in my system which has following powerparameters

Input Voltage: 6V

Output voltage: 5V

Peak current consumption: 70mA

Constant current current consumption: 3mA

I have made the regulator circuit in the following way

and post wiring the output oscillates and the waveform look like this:

I have a 1uF decoupling on the input and a 0.1uF, 1uF &  100uF electrolytic on the output.

The part which is very funny is that each board had different behavior.

Urgent help will be appereciated.

Let me know if more information is needed from my end

Regards

Ashutosh Amin

  • I guess the schematic and waveform images which were inline were removed while posting...I am attaching them here

    Schematic:

    Waveforms:

  • Hi Ashutosh,

    The TPS767 needs a minimum of 50mOhm of ESR to be stable:

    the 0.1uF capacitor (C3) in parallel with C4 might have an ESR on the or of 4-5mOhm which may be the issue. Can you try removing this and see if there is a change?

    We have a newer device the TPS746 which is much less sensitive to output ESR.

    I hope this helps.

  • Dear John,

    Thanks for the prompt reply, I removed the 1uf and 0.1 uF and it worsens the problem so I added a 220uF electrolytic (as it was available at hand) and the output oscillations situation changed to the following. But still the DC voltage is showing on 2.3v

    Regards

    Ashutosh Amin

  • Hi Ashutosh,

    Did the problem worsen if you just removed C3 and not C4?

    The TPS767 datasheet recommends a minimum of 10uF even thought the stability plots show 4.7uF out Cout. Is there any chance you have other low ESR capacitors on the output (elsewhere in the schematic)?

    Regards,

  • Dear John,

    Removing C3 and keeping just C4 generates following waveform

    My schematic has many capacitors and mostly all are low ESR.

    I am attaching the schematic and layout PDF for you to refer.

    1323.Pick_to_light_HC11.pdf

  • Dear John,

    Removing C3 and keeping just C4 generates following waveform

    My schematic has many capacitors and mostly all are low ESR.

    I am attaching the schematic and layout PDF for you to refer.

    4810.Pick_to_light_HC11.pdf

  • Hi Ashutosh,

    The TPS769 requires a minimum ESR and capacitance of 4.7uF to be stable. Your schematic also has C5, C6, C,7, and C8 which are not helping. 

    I think you might be better off if you can switch the TPS769 out for the TPS7A24. This is pin to pin and stable with 1uF of ceramic output capacitance.

    Let me know what you think.

    Regards,