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TPS73433-Q1: Noise voltage under the specific condition

NAOKI CHIYODA
Prodigy 40 points
Part Number: TPS73433-Q1
Other Parts Discussed in Thread: TPS7A20, TPS7A13

Let us confirm the specification of output noise voltage under Vin=3.8V, Vout=3.3V, Iout=250mA.

As capacitances, CNR=0.01uF, Cin=1uF, and Cout=20uF will be used.

From the datasheet, can't see the data under similar conditions.

  • 0
    TI__Mastermind 42475 points

    Hi Chiyoda,

    Your use case condition is nearly approximated by the EC spec for noise. The main differences are the output capacitor and the output current, but 20uF is not enough to affect the 10Hz ~ 100kHz noise level, and the load current has a small effect on it as well. So, you can use the top line item (i.e. with CNR = 10nF) to a good approximation for the 10Hz ~ 100kHz noise level. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Hi Nick

    Thank you for your reply and comment on this.

    I understood that your recommendation is using the value of 36.3μVRMS (=11 x Vout ).

    Let me confirm the effect of Iout.

    In this case, the value is based on Iout=1mA from the datasheet.

    Is it O.K to remove the influence by Iout (1mA vs 250mA)?

    I understand it will affect the noise level largely...

  • 0 in reply to NAOKI CHIYODA
    TI__Mastermind 42475 points

    Hi Chiyoda,

    Sorry for the delayed response. I didn't see your comment come in.

    The loading condition changes the noise level only slightly normally. What is much more influential for noise is the output voltage setting because for most architectures the reference noise is gained up by the feedback divider, but the noise spec for this device includes the scaling for VOUT so that is covered as well. 

    Here are a couple examples to show the effect of loading on noise.

    TPS7A20:

    TPS7A13:

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 40 points

    Hi Nick

    Thanks for your feedback.

    O.K now we will see the value of 11xVout=36.3μVrms as a reference value.

    BTW, is it O.K to consider the same way for TPS78433?
    If yes, we consider 30μVrms as the typical value which was improved from TPS73433.

    Sorry for additional question in this case but we are planning to replace TPS78433 with TPS73433.

  • 0 in reply to NAOKI CHIYODA
    TI__Mastermind 42475 points

    Hi Chiyoda,

    For TPS78433 the noise spec in the EC table is the minimum since the output voltage for this spec is the minimum (1.2V), so the noise would be gained up to 3.3V by approximately 3.3/1.2 = 2.75 for an approximate total integrated noise of 2.75*30uVrms = 82.5uVrms for 10Hz ~ 100kHz. So, the noise would be much higher for TPS78433. 

    Regards,

    Nick

  • +1 in reply to Nick Butts
    Prodigy 40 points

    Hi Nick

    Thanks for your clarification.
    Now it's all clear.

    BRs.
    N. Chiyoda