Other Parts Discussed in Thread: DRV8434
Stepper motor specifications: 2-phase, 1.8 degrees, 4.9 V nominal, 0.7 A nominal, 7 ohm phase resistance, Phase inductance of 5 mh.
The customer intends to use 32 microsteps for control, and now has the following questions:
1. Is it necessary to have the 8834 work in indexer mode, if microstepping control is used? Can other modes implement microstepping?
2. Spec 8.4.2 defines the selection of microsteps, and I currently have the monolithic IO pins directly connected to M0 and M1, so what should the monolithic do with the high-impedance state of M0?
3. Full-Range Current I-TRIP from Specification 8.3.1, dose this I-TRIP numeric mean the output current? Is it needed to configure by the customer? For example, the customer can configure the output current to 1A or the maximum 1.5 A, is that right?
4. continued with question 3, if customer configured I-TRIP to 1.5A, is the current flowing through the winding resistance 1.5A when driving stepper motor?
5. And also continuing with question 3, the 8834 has overcurrent protection, and the spec says the threshold is 2 A, so what is the meaning of setting the I-TRIP?
6. continuing with question 3, the xVREF in the equation should be an analogue, and as stated, I-TRIP should be dynamically adjusted with an analogue input, so that's the case. In the 9.2.3 reference design, xVREF is directly connected to VREFO (fixed value of 2V), whether the I-TRIP cannot be changed if the sample resistance parameters are determined.
7. continuing with the question 6, if the customer wants I-TRIP to be variable, would you recommend using a single-chip DAC to drive xVREF directly? Or use the 4051 analogue switch to select different sample resistors? If choose the former, can one DAC output be multiplexed to both AVREF and BVREF inputs?
8. The 8834 has three decay modes, fast, slow, mixed, and these decay modes, what are the pros and cons when the stepper motor is in operation?
9. continuing with question 8, in Specification 8.3.2 Table 1, which 0% and 100% correspond to slow decay? Also reference the 51 kohm recommended in the design, which is the 50% decay mode, is this corresponding to the mixed decay mode?
10. When the stepper motor starts up, the current is large, and specification 10.1 recommends increasing the tolerance of the decoupling capacitance of the VM. However, once the tolerance is too large, there is an overshoot current when the system is powered up, which may pull down the VM bus voltage. The customer would like to know if there are any empirical or recommended values for the selection of capacitance values in general.
Could you please help resolve this case? Thanks a lot.