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TPS65133: NEG 5v stuck at 0.6V

Stefan Knoll
Prodigy 20 points
Part Number: TPS65133
Other Parts Discussed in Thread: OPA4134, OPA2134,

Hi,

We have used the TPS 65133 in our design which providessplit rail power to 3x OPA4134 opamps and 1x OPA2134 audio amplifiers.

The TPS 65133 is capable of powering 3 of the 4 opamps (total of 60mA on the -5v rail with 3 opamps) but when the 4th opamp is connected, the +5V stays on but the -5V goes to 0.6V.

We haved used x7r capacitors and wire wound inductors with correct component values, however couldnt source the recommended components.

Any assistance would be appreciated.

Thank you

  • 0
    TI__Mastermind 18550 points

    Hello,

    Schematics/design is fairly simple for this device so I am sure yours is correct but please do send the schematics/BOM for a quick review.

    Also, does the device work if you start up with 3 op amps only and than add the fourth one after the converter has ramped up as opposed to starting up into 4 op-amps? If possible, can you please also capture waveforms of the input supply, negative output and negative switch node at the time of startup? Negative converter should easily support the load currents you mentioned so it is likely some board assembly or component specification issue.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Prodigy 20 points

    Hi Liaqat,

     Components used:

    4.7uH: LQH32CN4R7M33L - 650mA

    3x 10uF: GRM21BR71A106KA73L

    1x100nF: CL10B104JB8NNNC

    Some tests:

    • With 4 audio (OPAx134) opamps and the tps65133 removed, the opamps load on 2 bench supplys (for split rail)  is under -80mA on the -5V rail.
    • With opamps the TPS negative output is 0.66V.
    • With pure resistive load (34 Ohm), the -5 drops to -4.4V supplying 142mA (resistor directly connected to chip pin to rule out trace impedances).

    Shematic:

    Layout with 0.5mm trace width for power rails

    5v positive and negative with no load

    5V input LDO under load is OK

    Negative 5V under load at 0.66V which shouldnt be possible

    Any assistance would be appreciated.

    Thanks,

    Stefan

  • 0 in reply to Stefan Knoll
    TI__Mastermind 18550 points

    Hello Stefan,

    I got your e-mail also on this same subject but did not get a chance to review it yet because of being very busy with some other issues. I will review and respond to your e-mail directly by tomorrow.

    Kind Regards,

    Liaqat