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TPS736: TPS736

Part Number: TPS736

Hi,

  Can you share the test procedure/testsetup for validating the Reverse leakage current, internal reference and  output noise voltage of an LDO in bench testing.

Regards

Anuraj NK

  • Hi Anuraj NK,

    To test the reverse leakage current on TPS736 the part must be disabled then force a voltage higher than Vin on the ouput and measure the current from the output supply.

    To test the output noise voltage of an LDO you will want to look at this application note www.ti.com/.../slyy076.pdf. It details how to AC couple the output and then gain it up to put into a spectrum analyzer. Once you have the spectrum analyzer measurement you can do some quick math (Riemann sum) to get the total output voltage noise. If you do not have a spectrum analyzer available to you, you can build a gain amplifier with a bandwidth of 10Hz-100kHz and then measure the RMS output voltage of that amplifier on an oscilloscope. That will give you a quick ballpark measurement, but it will not show the frequency components like the spectrum analyzer will.

    Hope this helps.

    Best Regards,

    Mark
  • Thanks Mark for your quick replay.Now I can prepare the test procedure for  reverse leakage current and Noise testing with reference to your above mail.Can you tell me the procedure for validating the internal reference voltage for adjustable LDO, which you missed to address in the previous mail.

  • Hi Anuraj NK,

    The easiest way to validate the internal reference will be to look at the output of the LDO. If you were using the fixed output you would be able to put a high impedance meter (<10G ohm) on the NR pin and validate what the reference voltage is. However, with the adjustable regulator the easiest way is to put it in unity gain and just measure the output voltage as you use different loads, startup waveforms, etc.

    If you measure the output noise of the LDO in this configuration you should be able to get a good idea of what the noise level of the internal reference is as well. As you increase the output voltage of the ldo the refrence noise will scale linearly as there is no way to filter that out.

    Best Regards,
    Mark
  • Hi Mark,

      I understood the method for fixed regulator. I am confused with your answer for adjustable regulator. I am not interested to check the value of internal feedback when the output is stable. My requirement is to validate the FB pin voltage range (as mentioned in datasheet) to make the output stable. It is for IC validation purpose.

    Regards

    Anuraj NK

       

  • Hi Anuraj NK,

    Would you be able to give some more detail about what you are trying to test?

    Are you talking about the line listed in the electrical characteristics table? If so the easiest way to test this will be to put the LDO is unity gain and measure the output voltage of the LDO using the test conditions listed in the datasheet.

    The LDO uses an amplifier to assist in regulating the output voltage. One input terminal to the amplifier is the internal reference to the LDO the other is the FB node, when the LDO is regulating the output voltage the two nodes should be equal to each other. When the LDO is regulating the output voltage the FB voltage should be equal to the reference voltage. If the LDO is in dropout the FB voltage will be less than the reference voltage. And if the output is greater than the target voltage the pass FET will be off and and FB voltage will be greater than the reference voltage.

    Best Regards,

    Mark

  • Hi Mark,

       Yes, I am trying to validate the  line listed in the electrical characteristics table.

    Configuring the LDO to unity gain is using the transformer by inject an AC signal into the feedback path between points "A" and "B" as shown below or any other procedure is available. Please let me know.

    Regards

    Anuraj NK

  • Hi Anuraj NK,

    This configuration is what you would use to test the loop response of the LDO where you are injecting a small signal into the FB node to measure the gain and phase margin of the LDOs error amplifier.

    To configure it in unity gain all you would have to do is connect the FB node to the output of the LDO.

    Regards,
    Mark
  • Hi Mark, 

    Connect the LDO as per below config. Measure the output voltage and verify that the output is with in the range of internal feedback reference mentioned in the electric characteristics of datasheet ( Between 1.198V - 1.210V)  Is that you mean for validating internal voltage refernce.Please confirm.

    Regards

    Anuraj NK

  • Hi Anuraj NK,

    Yes that is what i mean by connecting it in unity gain to test the internal reference. Let me know if there is anything else I can do to help you.

    Regards,
    Mark
  • Thanks Mark for your support