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TPS65130: Low load currents with forced PWM mode (for low noise) and high efficiency?

Olaf Albert
Intellectual 320 points
Other Parts Discussed in Thread: TPS65130

Hi there,

I have an acoustic application that draws low currents but is susceptible to the pulse burst repetition frequency (about 50kHz) of the converter. That is why I would like to use the forced PWM mode (PSP = PSN = low). Is there an aid to calculate new coil and perhaps control loop compensation components for a given Iout (at Vout +15V and -15V)? Or am I on the wrong track?

Webench designer does not seem to offer this mode for calculations.

Acutally the current at the primary Vin = 5 V rises about 50mA for the forced PWM mode. Changing the coils to 12µH alone did not help to get rid of the bursting in power saving mode nor did not change much in respect to the rising primary current.

Thank you for your help!

Best regards,

Olaf

  • 0
    TI__Guru 58225 points

    Hello Olaf,

    If you change from PFM to PWM mode by setting the PSx pins low, the input current needs to increase because now the converters are switching permanently. This causes power dissipation in the system which automatically increases the input current. So having an increased input current in PWM mode is expected.

    The power save mode entry or exit is just slightly dependent on the used inductor. We recommend 3.3uH to 6.8uH. Increasing the inductor values is possible, but as mentioned will not reduce the bursting a lot, if your system is in the load range, the IC bursts.

    Maybe it is possible in your system to turn on PWM only when the audio is on?

    Best regards,

    Brigitte

  • 0 in reply to Brigitte
    Intellectual 320 points

    Hello Brigitte,

    Thank you for your answer! PFM? The data sheet says (p. 1)  there is only PWM mode: with and without pulse skipping.

    Our industrial acoustic sensor is always listening. So audio will be always on...

    Okay, if the current range can not be lowered by increasing the inductors: is there a more suitable IC that can produce +15 and -15V with about 10mA ... 50mA with low noise (= without pulse skipping) and small PCB footprint? Perhaps there is something in the production queue that will come soon and is not online?

    Best regards,

    Olaf

  • 0 in reply to Olaf Albert
    TI__Guru 58225 points

    Hello Olaf,

    TPS65130 is the best fit we can promote for +/-15V. If you keep the IC in PWM mode, pulse skipping should not happen in the above load range. Do you still observer pulse skipping at the lowest load?

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 320 points
    Hello Brigitte,

    It took me some days to figure out some more values. Sorry for that!
    I_V15P < 30mA, I_V15N < 35 mA.
    With 16µH for the negative voltage converter I can get rid off the bursting there. But for the positive voltage converter even 100µH are not sufficient - the converter is still bursting. Now I have to think about what to do next. Changing the converter?

    Thank you for your answers!

    Best regards,

    Olaf
  • 0 in reply to Olaf Albert
    TI__Guru 58225 points

    Hello Olaf,

    Please check the stability for the negative converter with the bigger inductor.

    For the positive converter, I wonder if you find some other loads in your system that might need 15V to increase the output current on TPS65130.

    Another possibility would be a reduced input voltage. Maybe you have 3.3V available?

    And yes, there might be another part, but at least I cannot propose you one from the portfolio that I support because I do not have another one that supports +/-15V.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Intellectual 320 points

    Hello Brigitte,

    Thank you again for your answer! I will check it and I still have an idea how to change the circuitry but this will take some more days to test.

    I think we can stop here this thread. Not all answers has to be positive - and perhaps the TPS65130 is just not the right means for the task.

    All the best,

    Olaf