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UCC21750-Q1: Measuring accuracy for sensing 1000Vdc

Naveen Kumar reddy Nelavoy
Intellectual 500 points
Part Number: UCC21750-Q1
Other Parts Discussed in Thread: UCC21750

Hi all,

Wanted to use AIN in UCC21750 for measuring Vdc = 1000V, but i have some doubts regarding duty variation over temperature. In datasheet it is mentioned that duty may vary 15% Vin = 4.5V , in SLUA988 it is shown that  absolue error with Ain is 5% accuracy and after calibration we can achieve +/-1%. Is the duty error a constant or it varies with temperature. If it is constant then we may calibrate it at single point of T=25 deg

  • 0
    TI__Expert 4875 points

    Hello Naveen,

    The datasheet range at each VAIN voltage reflects the variation over both process and temperature. The APWM error over process and temperature is lower when AIN voltage is less than 2.5V. The SLUA988 shows the AIN voltage is conditioned such that it also falls within this voltage range, resulting in good performance. The duty error does vary slightly over temperature, but not significantly. The duty cycle for a given voltage will be highest at the highest temperature. A single point calibration at room temperature will be important to account for process variation and with a low VAIN range you will see small error over temperature.  

    Regards,

    Audrey

  • 0 in reply to Audrey Dearien7
    Intellectual 500 points

    Hello Audrey,

    If we design for AIN voltage less than 2.5V, then as per datasheet error in duty is +/-3%. With single point calibration if i can calibrate for process error, what would be the remaining error in % over temperature. I could not find this anywhere in datasheet, but it is stated that we achieve +/-1% with calibration. So can we consider that 1% is due to temperature. 

  • 0 in reply to Naveen Kumar reddy Nelavoy
    TI__Expert 4875 points

    Hello Naveen,

    As you pointed out, the total variation given in the datasheet covers process and temperature since we do not separate out temperature vs process in our production tests. This range is guaranteed, where the APWM accuracy will be within +/-3% at 2.5V. When you calibrate out the process variation, it will be smaller. I cannot guarantee the temperature variation, as we do not test this over thousands of units and is not specified in the production test. However, based on some bench test data of 30 units with AIN at 2.5V I can say that we have observed the variation due to temperature was less than +/-1%. As I mentioned, it can be lower with VAIN less than 2.5V. This is not guaranteed as it is not specified in the datasheet and not tested across all production units, but based on this I can say that your assumption is probably accurate.

    Regards,

    Audrey