This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TRF7964A: Dropout voltage for Vdd_x (Digital supply regulator output)

Part Number: TRF7964A

If my Vin (pin2) is 3.3V, what is the maximum output voltage that can be achieved on the Vdd_x output (pin 32) with the appropriate register setting? 

Table 6-2 in the datasheet states the various register settings for various output voltage values of Vdd_x, specifically for the 3V system.  However, it has a register setting for a Vdd_x value of 3.4V.  However I don't believe that the internal regulators are buck-boost, so don't think one can achieve a 3.4V output with only a 3.3V input.

I would however like to know the maximum output Vdd_x voltage value that can be achieved with a 3.3V input.

Thanks!

Kind Regards

Paul Lotter

  • Hello Paul,

    You are correct it is not a Buck Boost, however the table does not assume a flat 3.3V input. We probably could do a bit better about clarifying this, but in any case, the maximum possible output voltage in your situation would be 3.3V.

    However, there typically is drop off voltage difference in the VDD_X output vs VIN, so you should expect to account for that. I want to say it's 200-250 mV, but I don't quite remember off the top of my head and can't take the measurement currently, I am going to ask a colleague of mine to see if he can get you those numbers tomorrow.
  • Hello Paul,

    because the datasheet is not very clear in this point, I did a measurement for the VDD_X output.
    The regulator is a low dropout type and so the output voltage with no load is nearly the VIN. Max current for the VDD_X, as specified in the datasheet, is 20mA.

    Assuming VIN = 3.3V; 3V setting; regulator setting 3.4V; this is the result.

    Load VDD_X
    ---------------------
    0mA 3.29V
    5mA 3.26V
    10mA 3.22V
    15mA 3.19V
    20mA 3.15V

    The max. dropout voltage is 150mV. Just a measurement at a single device but should give a good indication.

    Best regards,
    Helfried
  • Hi Ralph

    Thank you for you reply.  Much appreciated.

  • Hi Helfried,

    This is the exactly the information that I was looking for. Thank you!