Hello, I am facing some problems ralated to the AVDD.
Everything works just fine with no load, but when trying to run a motor, using PWM mode 1 (with a 10.2 khz pwm), a nFault was reported by the dedicated nFault pin, and then the SPI 0x3 register show "AVDD undervoltage fault". It happened so quickly as the motor rotor was stucked, i.e., plugged but not running for some reason. Maybe the overcurrent might have been reached high values. Everything but the chip DRV8305N is ok (I know that because it happened before 4 or 5 times before..so it's just replace the DRV8305N chip for a new one). Now the chip responds to the SPI, but it does not let me down the AVDD flag, as if the AVDD block was damaged through the current sense amp.
These are the only SPI data transfered to the chip before code starts running: 0b0101000000111111 and 0b0011101100010110
In case it is a lack of protection of pins SN and SP,
1- How to protect efficiently these pins? The 1nF capacitor in parallel to the shunt resistor is not so efficient.
2- Is it ok to add a resistor in SN pin to limit the current through the amp? If yes, which values you recommend?
3- On the datasheet, page 45 (http://www.ti.com/lit/ds/symlink/drv8305.pdf?ts=1588552055324), it is shown the SP connected to GND and the SN to the shunt resistor. Is that right? (I am assuming it is a mistake, based on the name of these pins: The "positive" S connected to the GND and the "negative" S to the higher potential, related to GND)
4- Is it effective and recommended to place a pair of zener diodes from each SN pin to the GND to prevent them to go bellow -2v and 5v? That would work to avoid these problems I am facing?