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UCC5870-Q1: UCC5870-Q1 - gate voltage monitoring

Part Number: UCC5870-Q1

Dear TI experts,

we are currently evaluating a UCC5870-Q1 gate driver IC in combination with SiC MOSFET.
Our goal is to monitor the voltage of the gate of the mosfet as close as possible to the real device due to safety reasons.
During evaluation the following questions come up:

1.) Please confirm, that Vgth Monitor can only be run in Config Mode and not in Active Mode. Thus Vgth measuring can’t be done with active load.

2.) Document slyp764 from TI website shows a gate voltage monitoring circuit on page 29 which senses the gate voltage of the power switch after the external gate resistors directly at the power switch.
Unfortunately we can’t find any description of this voltage monitoring inside the datasheet SLUSD86C. Figure 7-31 only shows a circuit with voltage sensed before the gate resistors.
Can you please provide some additional information?
For example: Which pin is used for gate voltage monitoring? Which software configuration has to be used? Which role does Vbst plays?

3.) Is the functionality behind SM24 and SM25 from SLUA883 (03/2020) identical to figure 7-31 from datasheet?
Maybe the connections in SLUA883 are false connected?

Thank you in advance & Kind regards

Andreas Storbeck

  • Hi Andreas,

    Thank you for reaching out to E2E!

    The gate threshold monitoring feature is intended to be used as an early failure detection mechanism. Over the lifetime of a power switch (SiC, IGBT, etc..) the stress of normal operation will overtime deteriorate the switch. Deterioration of the switch can cause for there to be a delta on the threshold voltage over time. Taking the gate threshold measurement and looking at the delta over time can enable customers to keep track of the switch health. This measurement is only meant to be taken once per system operation, or however often customer see fit.

    To answer your questions:

    1. VGTH measurement can only be done in configuration 2 mode, NOT in active mode. This measurement is not meant to be taken with an active load. During system power up before normal operation the threshold at which the switch turns on and begins to conduct is measured. This gate threshold is meant to be measured over time to use the delta of the threshold voltage to predict power switch health.
    2. The gate threshold monitoring feature is described in section 7.3.5.14 VGTH Monitor of the datasheet. When the command CONTROL2[VGTH_MEAS] bit is toggled to enable the measurement an internal FET from the DESAT pin to OUTH will turn on which will enable the DESAT current source to charge up the gate of the power switch(Figure 7-33). Once the power switch has charged up to the threshold voltage the power switch will begin conducting. Once conducting the DESAT current source will be re-routed through the external DESAT circuitry into the drain/collector of the power switch(Figure 7-34). At this point the voltage at the gate will remain at the power switch threshold voltage allowing the ADC to measure the gate voltage through the OUTH pin. This voltage will stored in the ADCDATA8 register for the MCU to read through SPI. After the measurement is taken the current source will stop bringing the gate LOW again and CONTROL2[VGTH_MEAS] will automatically toggle back to disabled. Whole measurement takes ~2.5ms.
    3. Gate threshold measurement and Gate voltage monitoring are two different features. Gate threshold is as described in my answer 2 above and section 7.3.5.14 VGTH Monitor of the datasheet. Gate voltage monitoring is described in section 7.3.5.13 Gate Voltage Monitoring and Status Feedback of the datasheet is meant to alert the MCU if the output state is not the intended state determined by the PWM input (IN+/IN-).

    I believe there is some confusion between 2 different features (gate threshold monitoring vs gate voltage monitoring). I hope the information above helped clarify both.

    If the intention is to measure the gate voltage during normal operation the best option would be to use one of the 6 ADC analog inputs (AIx pins). To read more about UCC5870-Q1 ADC functionality refer to section 7.3.3 Integrated ADC for Front-End Analog (FEA) Signal Processing in the datasheet.

    Let me know if there's any additional questions.

    Best regards,

    Andy Robles