DRV8701: negative overshoot

Hey Raymond,

What is your IDRIVE resistance?  It is possible the IDRIVE setting selected is not sufficient to turn on the external FET.

Can you provide circuit diagram and MOSFET part number? 

Regards,

Jacob

hi jacob

IDRVE resistance=200kΩ，NMOS  CRSM060N06L2，thanks

Hi Raymond,

Could you please provide the output current and voltage waveforms.

If you could please provide motor voltage and circuit diagram it would help to further analyze the issue. 

Best,

David

dear david

Channel 1(yellow) is GH2-to-ground, and channel 2(Green) is SH2-to-ground，thanks

Hey Raymond,

For IDRVE resistance=200kΩ your Source Current is 25mA and Sink Current is 50mA per Table 5. IDRIVE Pin Configuration Settings.

IDRIVE > (Qgd / RT) per the equation in 8.2.1.2.2 IDRIVE Configuration.  For your MOSFET, Qgd = 4.3nC, and rise time (RT) is shown as 72ns.  so IDRIVE > 4.3nC/72nS = 59.72 mA.  I think your existing drive current isn't strong enough to drive your FET.  

You need an IDRIVE current greater than 59mA, so I would pick the ">500 kΩ to GND, High-Z" option for 100mA source / 200mA sink option.  

Try removing your R_IDRIVE resistor as seen in the middle image of Table 6. IDRIVE Pin Resistor Settings

Regards,

Jacob

dear

it shows another waveform in 560k resistance，any advise？thanks in advance

Hi Raymond,

To get a better a better understanding, if possible, please provide the following specs:

- PWM frequency

- Bulk capacitance size

- Schematic, or wiring diagram

- Supply voltage

- Is this on the DRV8701EVM or a new design

Best,

David

dear

 Supply voltage=24v and PWM frequency=16.8khz attachment is sch， thanks

Hi Raymond,

After looking at the schematic, it appears that the diodes D21-D24 are not necessary and could be removed.

It does remain difficult to diagnose the issue with the schematic alone, so if possible could you please provide the layout. 

Another possible cause could be with the IDRIVE current. Try reducing the IDRIVE current by using a smaller IDRIVE resistance. Perhaps the MOSFETs are switching to fast. 

Best,

David

Hi david

Is htere any design risk about  negative overshoot of the gh2 foot exceeds the specification requirement of -0.3v, and the time is ns level？ and attachment is PCB,thanks

Hi Raymond,

We do not recommend devices to exceed absolute maximum ratings for any period of time. Devices that exceed absolute max ratings may cause permanent damage to the device and exposure to absolute max rating conditions may affect device reliability.

Best,

David