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UCC21750: Questions about the UVLO, RST/EN , AIN

Hongmei Wan
Intellectual 720 points
Part Number: UCC21750

Hi,

1. datasheet page 20: -3V threshold voltage of VEE UVLO, with 400mV hysteresis. Does this mean VEE have to be lower than -3V?  

I am at circuit design stage. First I used the power supply which can provide 20V and -5V, which is good for this driver. Then I found out the max. Vgs of our Infineon SiC MOSFET is 20V so I have to use 15V for VDD and the corresponding VEE is -3V. I come back to check this driver and found out UVLO VEE of this driver is -3V.  We already bought this drivers and Infineon devices and had to use it.  If VEE must be lower than -3V, I have to find another power supply.

2. datasheet page 3: RST/EN serves two purposes. Can I use this at the same time for this two purposes or only can choose one?

a. Enable or shutdown the driver, no driving outputs. 

b. Reset the fault signaled on FLT pin.

so when it is active low, the FLT signal is clear and driver is disabled? I am confused.

3. datasheet page 24: An internal current source IAIN in AIN pin is implemented in the device to bias an external thermal diode or temperature sensing resistor. 

please see below. RTH is integrated in SiC MOSFET module in gray block and there are two terminals called NTC.

a. The voltage across the RTH = IAIN *RTH =200uA*5000k=1V if RTH=5kohms. Is this right?  If it is right, then RTH requires 2.5kohms to 22.5khoms to meet AIN voltage of 0.5V to 4.5V.  Or my schematic is in wrong connection?

b. What is relationship between AIN and APWM? How to monitor the temperature using these pins?

datasheet only provides three special cases  at VAIN=0.5V, 2.5V, 4.5V. I can use one case to set the max temperature but can not monitor the temperature.

Thanks,

Hongmei Wan

  • 0
    TI__Expert 4875 points

    Hi Hongmei,

    Thank you for your questions. Please see my responses below:

    1. VEE UVLO is NOT implemented in this device. That sentence will be removed from the final datasheet with the full release of this device.

    2. The nRST/EN pin serves BOTH purposes at the same time. In normal operation, the pin should be pulled HIGH through a 10kohm resistor in order to enable the driver (it has an internal pulldown resistor if it is left floating which disables the driver). In the case of a fault, you would then pull down the nRST/EN for >800ns in order to reset the fault. 

    3. Your connection is correct. The voltage at AIN is dependent on RTH*IAN. APWM is a duty cycle output with a frequency of 400kHz.

    The relationship from 0.5 V to 4.5 V is given on page 9 of the datasheet and the relationship between AIN voltage and APWM duty cycle is linear. In other words, the equation could be written as, APWM_Duty = -20*V_AIN+100 where V_AIN is the voltage at AIN and APWM_Duty is the output at APWM in %.

    Regards,

    Audrey

  • 0 in reply to Audrey Dearien7
    Intellectual 720 points

    Thank you very much, Audrey.