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TPS65219: TPS6521902　Buck2　1.8V

YOSHINORI KODAMA
Prodigy 50 points
Part Number: TPS65219


Tool/software:

Hi Team,


Buck2 of TPS6521902 does not output 1.8V.

It must be resolved immediately, and I am in a lot of trouble.
Please help me.


Phenomenon

[1] Supply 5V to PVIN.
[2] GPO2 becomes High.
[3] 3.3V is output.
[4] Approximately 0.7V is output from Buck2. (Originally 1.8V)
[5] GPO2 goes Low after about 20ms.
Buck2 voltage drops.
3.3V voltage drops.
Steps [2] to [5] are repeated.

Is there anything wrong with the circuit diagram?

Similar phenomena

e2e.ti.com/.../5518765

Regards,

  • 0
    Prodigy 50 points

    Hi Team,

    I have confirmed the following today. Do you have any idea what might be causing this issue?

    MODE/RESET = High (PU to VSYS)
    MODE/STBY = High (PU to VSYS)
    VSEL = Low (PD to GND)
    All loads on Buck1, Buck2, and Buck3 have been removed.
    FB has been connected with a short cable.

    The phenomenon has changed.
    Buck2 has changed from 0.7V to 1.8V. But, after outputting 1.8V for 1ms, the output drops. It repeats outputting 1.8V for 1ms and then the output drops (this repeats infinitely).

    nINT (3.3V PU) goes Low.
    nINT goes Low at the same time Buck2’s output starts to drop.

    Changing MODE/STBY to Low (PD to GND) does not change the phenomenon.

    Changing Buck2’s capacitor to 10u, 32u (10u+22u), 54u (10u+22u x2), or 79u (10u+22u+47u) does not change the phenomenon.

    When Buck2 has a load, VLDO1 and VLDO3 remain at 0V. When Buck2 has no load, VLDO1 and VLDO3 alternate between 1.8V and 0V.

    regards,

  • +1
    Prodigy 50 points

    Hi Team,

    The issue of Buck2 cycling between 1.8V and OFF has been resolved.

    It seems the inductor was the cause.

    I suspected a voltage drop because of the large ripple after the inductor attached to Buck2 and the fact that nINT was asserted.

    I considered that the LC filter was insufficient because the frequency characteristics of the inductor were not adequate.

    Since I didn’t have an inductor that could maintain inductance at high frequencies on hand, I substituted it with a ferrite bead, which reduced the ripple and maintained the ON state.

    The issue of Buck2 dropping to 0.7V remains unresolved. We would greatly appreciate your assistance.

    Regards,

  • +1
    Prodigy 50 points

    Resolved.

    The 3.3V line was backfeeding into Buck2.
    Immediately after 3.3V generation, Buck2 becomes 0.7V.
    This was detected as Residual Voltage, and it did not generate 1.8V.
    I was able to resolve the issue by looking through various tickets.

    Thank you, everyone.