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UCC21710-Q1: The accuracy of UCC21710 isolated signal sensing function

Part Number: UCC21710-Q1

Hi Expert,

I have a few questions about UCC21710-Q1.

In the isolated analog signal sensing chapter. It's said that "There is an internal 200uA current source internally with 3% accuracy through temperature, which can forward bias the thermal diodes or create a voltage drop on the temperature sensing resistors". While in the example of figure 19, "the duty cycle output has the accuracy of ±3% throughout temperature without calibration. ".

The duty cycle's accuracy is the same with the internal 200uA current source. Is the duty cycle output's ±3% accuracy just caused by the inaccuracy of the internal 200uA current source?

With one time calibration, the accuracy of the duty cycle can be improved to ±1%. Could you tell the method how you do the one time calibration?

  • Hello,

    The internal current source has +/-3% variation, which is about +/-6uA. Depending on the type of temperature sensor (NTC, PTC, thermal diode), the voltage will be affected differently.

    The duty cycle accuracy is solely based on the conversion from voltage at AIN to Duty at APWM, and not the current source. For example, if the input voltage is 2.5V at AIN, then the APWM at maximum positive error could be 53% (as opposed to 50%).

    The meaning of the one-time calibration means to measure AIN/APWM under your operating conditions to determine the shift in Duty Cycle based on process variation and operating range. Then this offset can be applied to increase the accuracy of the measurement. 

    I hope this answered your question!

    Regards,

    Audrey