DRV8350R: DRV8350RHRGZT/DRV8350HRTVT heating when turning motor at low RPM

Hi Avihay,

Thank you for posting your question in the MD forum!

I have some questions and comments:

1. You mention that this device is a DRV8350HR device, but I don't see the buck converter pins or hardware on the schematic. Is it possible that you are using the DRV8350H device (without the buck), or is the buck just not shown in the schematic?
2. What is the part number for the MOSFETs you are using? It is possible that the IDRIVE is too high, but that depends on the MOSFET you are using.
3. What are the voltage ratings for the CPH-CPL, VCP-VDRAIN, VGLS-GND, and DVDD-GND capacitors?
4. What is the voltage supplied to the VM/VDRAIN pins (VBUS)?
5. For the IDRIVE, MODE, and VDS pins you have an option in the schematic to pull them up to 5V2 using a resistor, however the datasheet recommends pulling them to the DVDD pin of the device. Is there a reason you chose to not pull them to DVDD?

Regards,

Anthony Lodi

Hi Anthony,

thanks for your response,

im using both DRV8350RH & DRV8350H

Im using this FET BSC070N10LS5ATMA1 by infenion,

VM\VDRAIN is at 42 Volts, the rest i need to check again but nothing that is not compatibe to the datasheet,

I pulled it up to 5V2 because it is my Digital VDD for this circuit, is it Ok ? 

Thanks,

Avihay

3. Voltage rating- vcp: 25V ,cph-cpl: 100V, vgls:25V ,DVDD: 25V

 Hi Avihay,

Thank you for the additional information!

• I checked out the datasheet for your MOSFET and the Qgd is around 6nC. with the current IDRIVE setting the turn on time for the MOSFETs would be around 9nS. 9nS is really fast and could result in damage to the MOSFETs and/or DRV. Even the lowest IDRIVE setting (50mA/100mA) would result in about a 120nS rise time, which is still probably too fast. I would recommend using the lowest IDRIVE setting and adding a 10 ohm gate resistor to help slow down the IDRIVE even more. Most customers consider a 200nS rise time a fast rise time, and depending on the design of the layout 200nS may still be too fast for the system to handle. If you can provide a plot showing the gate to source voltage rise time of the MOSFET after you make the suggested changes that would be helpful so we can see if we need to further adjust the gate resistor value.

• Is 5V2 a 5 Volt supply? if so I don't see a problem with pulling it up to 5V2 if you would rather do that instead of the DVDD pin

Regards,

Anthony Lodi

Hi Anthony,

i dont understand how the idrive is causing the heating problem if it happens when changing enable to be active , in this stage there is no PWM to the motor and no current is passing through the FET's

5V2 is my 5V controlled voltage, to be precise its 4.96V and DVDD is not really equal to it, is it possible that its causing internal current between 5V2 and DVDD that cause this heating problem? 

I have 40 ohm serial resistance on each gate.

Any Advise regarding this ?

thanks in advance

Hi Anthony,

i dont understand how the idrive is causing the heating problem if it happens when changing enable to be active , in this stage there is no PWM to the motor and no current is passing through the FET's

5V2 is my 5V controlled voltage, to be precise its 4.96V and DVDD is not really equal to it, is it possible that its causing internal current between 5V2 and DVDD that cause this heating problem? 

Hi Avihay,

I would need to check with the design team to analyze the effects of using 5V2 instead of DVDD, and whether or not that would result in any unwanted current. I would recommend tying the pull up resistors of the MODE, IDRIVE, and VDS to DVDD since this is what the datasheet recommends and there may be some unintended effects of tying them to 5V2.

Regards,

Anthony Lodi