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TLVM13630: Output capacitance for 1V output voltage

Julia Jonsson
Prodigy 10 points
Part Number: TLVM13630
Other Parts Discussed in Thread: TLV62090

Hi TI,

I need a 5V input - 1V output buck converter, and I am considering to use TLVM13630. Why is the recommended output capacitance so large? It is written 300uF in the datasheet for Vout 1V.

The load current in my design is maximum 500mA. Is it possible to reduce the output capacitance? If yes, what would you recommend? In my current design, there is no room for several capacitors in parallel...

Thank you for your attention!

  • 0
    TI__Mastermind 30430 points

    Hi Julia, this converter is more tuned for lower output capacitance for 5V and 3.3V output. With the internal compensation, a 1V reference with no capability for phase boost with an external feed forward network,  a higher output capacity is required to achieve the required crossover frequency.

    If your design only requires 5V max input and 500mA max load current, then, TLVM13630 may not be the best device choice.

    You could consider a lower input voltage device and/or lower current device and you will be able to reduce the BOM count.

    Please use the parametric search on ti.com if you would like to look an alternative options.

  • 0
    Prodigy 10 points

    Hi Marshall,

    Thank you for your fast answer.

    For the sake of simplicity, I would like to use the same buck converter IC to generate  3.3V, 1.8V and 1V. 

    In an previous version of this circuit, we used the IC TLV62090, but it didn't widthstand the background radiation in the application environment.

    We made radiation tests with TLVM13630 evaluation board and it works fine with lower output capacitance.

    What would the risks be to use lower capacitance? Would the Vout regulation be unstable? 

    Best regards, 

    Julia

  • 0 in reply to Julia Jonsson
    TI__Mastermind 30430 points

    Hi Julia,

    You are welcome.

    I understand.

    If you were to use less output capacitance than recommended you can have an unstable design.

    To examine the loop response with varying output capacitances you can preform load transients with the EVM to verify you have a damped response, or examine it in Webench designer.

  • 0 in reply to Marshall_Beck
    TI__Guru 53082 points

    Julia,

    You can also use the quickstart calculator to check the loop gain characteristic:

    TLVM136x0 Buck Module Quickstart Calculator - revA.xlsm

    Note that the VOUT-to-FB feedback gain increases at lower Vout. In this case with Vout = 1V, the feedback gain is effectively unity (i.e. there is no attenuation from the feedback resistor network). Thus, higher Cout is needed to reduce the gain and maintain a reasonable loop crossover frequency (10-15% of Fsw).

    Regards,

    Tim