Hello Cole,
Thanks for the quick and detailed answer.
I found out that I cannot enter Dots in the text boxes at the DRV10987 GUI program, but I can enter Commas. It seems that I have kind of a German number format. Moreover, when I enter 0,65 into the textbox 'Phase Resistance', the value is rounded to '1'. If I insert 0,25, the value is shown as '0'. A Labview Runtime Engine issue?
When I enter 0,65 for Phase Resistance and 35,7 as Kt and save the motor configuration. The values in the .csv file for the config registers are:
CONFIG1 Register at address 0,90 is 0x003d. RMShift is 0b011. RMValue is 0b1101. 0b1101 << 0b011 is 0b1101000 = 0x64 = 100
CONFIG2 Register at address 0x91 is 0x2a49. KtShift is 0b010. KtValue is 0b1010. 0x1010 << 0b010 is 0b101000 = 0x24 = 36
I don't know about the number representaion.
EDIT: I found the lookup table in the datasheet.
- The bit fields in CONFIG2 correspond to Kt = 36.8 mV/Hz
- The bit fields in CONFIG1 correspond to RM = 1.0088 Ohm
For Kt, I did the measurement: f = 3.91 Hz, Upp = 270 mV. I get 34.5 mV/Hz. That's what I calculated from the datasheet: 1/(Drehzahlkonstante 1682 rpm/V) = 35.7 mv/Hz.
When I enter 34,5 at the Kt textbox (ignoring the fact that the number in the textbox shows '1'), now the system is able to get into closed-loop operation after unchecking 'CLoopDis'. The motor is able to spin at very low speeds up to ca. 30,000. Above ca. 24,000, I get a Fault Code 'BEMF abnormal', but it still spins. This Fault Code persists at any speed then. Above 30,000 it suddenly stops, and Fault code 0 and 2 show up (no text in the Fault Code box).
Regarding the L/R constant: We have to use this motor because of customer's specification, unfortunately. Are there other BLDC motor drivers available from TI that have lower limit for L/R?
Best regards
Alois