UCC21710-Q1: Over current detection in UCC217x gate drive chips with kelvin pin and shunt resistor

Hi,

This is an interesting question. Let me look into it and get back to you. 

Best,

Nancy

Hi,

If the FET you are using has a senseFET connection, you can use the UCC21732,  the UCC21710, or the UCC21737 with 2-3 RC components to do the overcurrent detection. Otherwise, you will need the additional circuitry. 

Best,

Nancy

Nancy

We are not using Sense FET's were using SiC FETS in the TO-247 package.

It is getting to the point that in higher power SiC Mosfets, they only come in 4 pin packages and I'm surprised TI is not coming up with gate drive chips that allow over current detection on them.  Am I looking for the wrong solution and this should not be done at the gate drive level?

Maybe this should be done at the MCU level?  I've noticed that the newer MCU chips like the C2000 F2806xhave built in circuitry for cycle by cycle detection, but I was hoping to keep this at the gate driver level because right now our MCU is offboard and I was concerned with having long leads bringing back the shunt differential voltage to the MCU being a challenge.

Also we are operating 4 full bridges on a single board so all of the extra circuitry for the voltage mirror or isolating the shunt signal to bring it back to the MCU will add a lot of complexity, board space and failure points.

Is there someone at TI who can educate us on this or do you have a good app note for us to catch up on this subject.

Dave

Hi Dave,

Thanks for your interest with UCC217xx devices for your application.

The following article talks about how to use 4 pin Kelvin sense pin to use for OC detection. But it involves additional circuitry as explained in the message.

Please let us know if it helps to plan for your system.

Thanks

Sasi

Sasikala

I did look over that circuit in the link you provided.  The idea of a current mirror is interesting and if it was just a pair of transistors and two resistors to adjust the inverse voltage gain it leads to interesting possibilities to operate with a lower loss shunt at higher powers, and still generate the 0.7 Volts signal needed to trip the overcurrent pin.

But, it appears that each instance where we use this, we will have to supply an independent isolated power supply putting out 5V.  We cannot use the isolated power supply that the gate driver as its referenced to the Kelvin pin, does this sound accurate?

Is there a good reason TI doesn't just come out with a version of this gate drive chip that references the overcurrent pin to a negative 0.7 volts so that 4 kelvin pin transistors can be used easily.

I am intrigued by the ability to adjust the gain the voltage inverter circuit, but we don't have the resources to develop this system and will just continue to use an external current sensor with a 'fast' OC detection system, but these still wait up to 5 cycles before shutting down at our 85kHz switching frequency.

I was hoping TI was coming up with something for this as the UCC21710 and UCC2173x series gate drivers seem to be leading the field with over current shutdown for the 3 pin and 4 pin devises with the sensefet feature.

Thanks for following up :-)

Dave

Hello Dave,

Sasikala is out of the office at the moment, she or someone on the team should respond to your questions within the next business day.

Regards,

Hi Dave,

Thanks for sharing your feedback. Most of the customers are interested in DESAT circuitry instead of OC. As resistor shut method has additional power loss, it’s not preferred. So we have the app note about how to enable the 4 pin TO-274 to be connected with additional circuitry.

Hope it helps.

Thanks

Sasi

Also the EVM shows how to generate 5V supply from the VDD isoalted bias, as shown below. Hope it helps.