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TPS62242-Q1: Calculating output voltage ripple in PFM mode

adevries
Intellectual 945 points
Part Number: TPS62242-Q1

Hello,

I am interested in using the  TPS62242-Q1 to power an IC that needs 1.2V +/-5% input. I am trying to determine if the voltage ripple on the output of the  TPS62242-Q1 will violate that. Equation 5 in the datasheet tells how to calculate voltage ripple:

Following that equation, I calculated a ripple of 5.185mV when Vout = 1.2V, Vin = 4V, L = 2.2uH, F = 2.25MHz, Cout = 10uF, and ESR = 0.025 ohms.

However, it is my understanding that this equation is only applicable when the device is operating in PWM mode. Since it looks like the ripple in PFM mode will be worse, I'm interested in calculating that as well. The datasheet talks about a PFM comparator threshold and an on-time that it turns the switch on for, but does not mention any specific time. Can someone offer some guidance on how I can predict the maximum voltage ripple in this use case?

Thanks!

  • 0
    TI__Genius 14270 points
    Hi Adevries,

    The output ripple in PFM mode depends on output cap and inductor. There is no specific equation to calculate the output ripple as frequency varies in PFM mode. The example of output ripple behavior is shown in figure 12 in a datasheet.

    Best regards,
    Tanvee