DRV8316: DRV8316 Schematic Questions

Hi Daniel,

Thank you for your questions! 

1. To disable the buck you can write a 1 to the BUCK_DIS bit in the Control_6 register. This will disable the operation of the buck. You still will need to have the external components on the buck output, so I would suggest using the resistor/capacitor combination since that would result in the smallest components/cost.

2. 3x PWM is beneficial to use for sinusoidal commutation since for sinusoidal commutation all three phases are always active (never HiZ), so the INLx pins can all be tied to AVDD and thus the number of GPIOs used can be reduced. 3x PWM mode can also be used in a similar way with FOC control, but our FOC code is designed for 6xPWM applications, so it would be necessary to modify the code to use 3xPWM mode. here is a related post that goes into more detail on the differences between different PWM modes.

3. DRVOFF is simply a control that allows you to turn off all the gates of the FETs. If you don't need this function you can tie the pin to GND. Keep in mind this pin gives you the flexibility if you want to manually shut down the gates of the FETs such as when a particular fault occurs, since not all faults result in the gates shutting down (depending on the fault)

4. The DRV8316 can operate using 2 modes, either using the current limiting mode or sense amplification mode. The voltage at the VREF/ILIM pin determines which mode is used. To use the SOx outputs of the DRV8316, the voltage at the VREF/ILIM pin must be between 2.8V and AVDD. In this mode, the output of the SOx pins have an offset of VREF/2 to allow for negative and positive current readings.

To use the current limiting mode, the voltage at the VREF/ILIM pin must be between AVDD/2 and AVDD/2 - 0.4V. since AVDD is a 3.3V LDO, the range of operation is 1.65V to 1.25V. The voltage at the VREF/ILIM pin should be selected to result in the internal comparator to trigger at the desired current limit. When the current through the coils reaches the level that results in Vmeas equaling the voltage at the VREF/ILIM pin, the comparator will send a signal to the driver to turn off the high side MOSFET to prevent more current being applied to the motor. Once the current falls below the threshold then the driver resumes switching the high side MOSFET on the next PWM edge. 

Since you are using FOC you will want to operate it in the VREF mode since you will need to use the sense amplifier outputs as feed back for the FOC algorithm. Therefore in this mode you cannot use the current limiting mode of operation for this device.

5. The SDO pin can be configured either as a push pull pin or as an open drain pin. This is set by configuring the SDO_MODE bit in the CONTROL_2 register. If you configure it as an open drain pin, then a pullup resistor will need to be used on the SDO pin (our EVM uses a 5.1k pullup)

6. For your particular design you should be able to use a single ground instead of a split ground, especially since you won't be using the buck. Having a single ground will help with thermal dissipation. 

Let me know if you have any further questions,

Anthony 

Hi Daniel,

1. For the resistor/cap combination I would recommend using the recommended 22R and 22uF combination since the default setting in the register is for the buck to be enabled, so every time you power up the device the buck will start up until the BUCK_DIS bit is written a 1, at which time the buck will be disabled.

2. 3x PWM mode should work as you described as long as the outputs of the code corresponds correctly for a 3x PWM application.

7. For the low pass filter, using a 330 ohm resistor and 22pF capacitor is a good place to start. This will result in a cutoff frequency in the 20MHz range. If there is still too much noise then you can try using a filter with a lower cutoff frequency. Just keep in mind that if the cutoff frequency is too low than the response time of the SOx to changes in the current can be longer, which could eventually result in inaccurate sampling by the ADC.

Glad to hear that the release of the DRV8316 resulted in a more cost effective solution for your application!

Regards,

Anthony