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TPS7A7300: Output voltage ripple value

Part Number: TPS7A7300
Other Parts Discussed in Thread: TPS7A84A, TPS7A83A

Hi Team,

My customer is using TPS7A7300 for their application. And they would like to get specification of output voltage ripple < 3mV. As I know, this is simple to LDO.

But customer's test result is about 4.18mV in second image. The main low frequency noise is from power supply(first image) ,but I see the PSRR in datasheet, the noise should be eliminated. (third image is the 3.3V input for TPS7A7300)  and another high frequency causes the output ripple higher than 3mV.

1. Could you brief explain that how does the noise generate? 

2. How to eliminate it, both low and high frequency noise.

If noise isn't related to our device, but related their probe or measurement, please help explain it.

3. Could we use TPS7A84A to get higher performance?(<3mV) I saw the datasheet, they are P2P, is both of them pin compatible?

Thank you for your support.

  • Hi All,

    I suspect the noise is generated from probe, so I will tell the customer to short their probe V+ and V-.

    If there is noise showing in waveform. Do we clarify the noise is generated from probe, isn't LDO, right?

    Could you provide a better method to measure the LDO output ripple, thanks.

    Roy

  • Hi Roy,

    The underlying ripple you are seeing on the scope plot looks like it could be the 60Hz line frequency. Do you see this ripple when the probe is not connected to the TPS7A7300?

    To answer your questions:

    1. Could you brief explain that how does the noise generate?  * Low-frequency noise is very hard to filter. the PSRR of the LDO usually takes care of this. However, if this noise is coupled into the ground plane, there is no means to filter the noise. The PSRR of an LDO is a measure of how the LDO can filter the input ripple. The noise specification of an LDO is how little noise it produces att the output.

    2. How to eliminate it, both low and high-frequency noise. *For low-frequency noise, find an LDO with very good PSRR across the spectrum. For high-frequency noise, look at the noise specification of the LDO. 

    If noise isn't related to our device, but related their probe or measurement, please help explain it. *Need more details on the test setup they are using. 

    3. Could we use TPS7A84A to get higher performance?(<3mV) I saw the datasheet, they are P2P, is both of them pin compatible?  *The TPS7A83A is a much better device. However, if mentioned above if the line noise is somehow coupling into the ground plane of the PCB, they might see a similar issue (likely a little better as the TPS7A83A has better PSRR and lower noise).

     

    The TPS7A83A appears to be pin-compatible but the key layout difference is that they have a different reference. Meaning the TPS7A73 uses a 0.5V reference and the TPS7A83A uses a 0.8V reference. If using Any-Out, the pins add to this reference. So the PCB layout would have to change, If using a resistor divider, then the output voltage divider would need to be adjusted to set VOUT

     

    I hope this helps.

  • Hi John,

    Thank you for your reply. I think low frequency noise is coupled into ground. But customer concern the high frequency noise, do you have any idea to find the noise source? 

    Roy

  • Hi Roy,

    It is hard to guess at the noise source not knowing the system or test setup.  We do have a short video on PSRR as well as another as to how to measure noise and PSRR.

    Do either of these help?

  • Hi John,

    Thank you for your reply. I also would like to verify some points.

    If noise is generated from system power, LDO could filter the noise due to PSRR is high enough. (right?)

    So If they measure the output voltage which occur noise in it. So there is some probable factor cause the noise and I will suggest customer to modified the factor. (probe, GND noise......)  Do you have idea that I could send feedback to customer.

    Regards,

    Roy

  • Hi Roy,

    Without knowing more details it is hard to say, but in general, you are correct in that high PSRR will filter out the input noise.

    If the system noise is coupling onto their ground plane, then it is very difficult to filter the noise. Here is a short video on best practices for measuring noise.

    I hope this helps.

    Regards,