we are currently having some issues with the DRV8303 Chip by TI. It would be great if you could help us out fixing this problems.
We are using the Chip to drive a BLDC Motor which moves a large mass (A sliding door). Therefor we got 35V supply voltage and generating a peak current per phase of around 7.5A in the acceleration phase of the door. We also of course monitoring the supplyvoltage because of the voltage peaks which are generated while breaking. To prevent the destruction of the components we are shorting out the supplyvoltage over a 10 Ohm Power Resistor when the voltage reaches 42V and deactivate the short when the voltage is back down to around 36V. This is done over a comparator with hysteresis.
Now we are experiencing a phenomenon which we can`t explain. Every time this voltage limiter is activated (Voltage climbs to 42V) the PWM signals for the High-Side MOS-FETs are getting disturbed. In normal operation the Voltage of the PWM for the High-Side MOS-FETs is slightly higher then the supplyvoltage to get the High-Side N-MOS to conduct. In our case the PWM Signal rises up to the supplyvoltage and then breaks down again to zero volt. This is repeated several times until finally the PWM Signal overcomes the supplyvoltage and the N-MOS begins to conduct.
For better explanation please take a look at the following Screenshot of the Oscilloscope (Yellow trace is the Gate of the High-Side N-Mos, Blue trace is the Source of the High-Side N-MOS, Pink is the supplyvoltage):
I could send some Screenshots of the Schematic via mail. Just let me know.
Thanks in advance!
ciao
Hanno
