MCT8316Z: Issues about the MCT8316Z data sheet

Hi Cherry,

Please find my answers below:

1. On page 21 of the data sheet, is there a difference between PWM mode 6 and PWM mode 7 in the table PWM_MODE Configuration (continued) when using?

There is no difference between Mode 6 and 7 - both configures Synchronous Modulation and enables ASR and AAR. 

2. On page 21 of the data sheet, does the INHx and INLx pin mentioned in Note refer to the internal pins of the chip? These pins are not in the QFN package pins of the chip.

You are correct, this got copied over from the DRV8316 datasheet accidentally. I would recommend to set DRVOFF = 1 before switching the Mode setting. We can fix this in the RTM version of the datasheet. 

3.Both asynchronous and synchronous debug modes have the Align process, why it isn't  the rotor pre-bit processing? The MCT8316Z supports the trapezoidal waveform control algorithm for Hall sensors. For BLDC square wave control with position sensor support, is pre-set processing also required?

Can you please elaborate what you mean by "rotor pre-bit processing" and "BLDC square wave control"? The MCT8316Z has Hall comparators that can accept digital or analog Hall inputs and will commutate the motor to the next state based on the 1x PWM commutation table in the datasheet. All you need to commutate the motor is Hall sensor feedback to HPx if using digital inputs or HPx/HNx if using analog inputs. The device will detect the BEMF crossings automatically and determine whether Hall_A,  Hall_B, and Hall_C are true depending on the mode setting.

In the DRV8306 datasheet, these signals look like this. I don't think this is shown in the MCT8316Z datasheet. So for Align, the internal Hall_A, Hall_B, and Hall_C must be true to align the motor. 

4. As mentioned on page 26 of the data sheet, Buck Inductor Mode can support a maximum load current of 200 mA or 50 mA with different inductance values selected, and Buck Resistor mode is used to support load current of less than 40 mA.

However, in the block diagram on page 18, page 19 of the data sheet, there is a description, "Replace Inductor (LBK) with Resistor (RBK) for larger external load or to reduce power dissipation,"

Does the description here conflict with the description on page 26? Why replace the inductance with a resistor when it is overloaded?

Using an external resistor (i.e. 22ohms) will dissipate the power of the buck load current through the resistor externally. This will lower device power losses and reduce temperature in the device. If an inductor is used (i.e. 22uH or 47uH), this will generate buck switching losses in the device. Keep in mind though that Resistor Mode is only for loads of less than 40mA because using a resistor will lower the efficiency.

5.On page 44 of the data sheet,  why is the phase current negative for a small inductor?

An inductor resists change in current. According to V = L (di/dt), smaller inductance yields larger change in current. When using asynchronous rectification as shown on pg. 44, current gets pulled from GND to the motor output through the LS FET, yielding negative current. AAR will turn off the MOSFET automatically so that negative torque does not occur. 

6. Is the data check bit in the SDI Input Data Word Format set with the instruction code when the controller sends an instruction to the MCT8316? How is this check bit used and what is the verification mechanism?

The device generates the parity bit from the address and data bits. If there is an even # of "1"s, PARITY = 0. If there is an odd # of "1"s, PARITY = 1. You can cross reference the parity bit with a parity checking function in software to verify SPI writes. 

7. When will the Advance Angle feature be used?

Advance angle is used to align the phase current with the phase voltage. If a large inductance motor is used, then it can create lag between phase current and phase voltage, which will lag the Hall sensor feedback into the MCT8316Z. The advance angle corrects this delay in hall sensor feedback to align the phase current and voltages. Please see this tuning guide for correcting lead angle adjustment. https://www.ti.com/lit/pdf/slaa561

Starting at 0 degrees is a good default setting. 

Thanks,
Aaron