Other Parts Discussed in Thread: TMS320F28026
Our design combination is TMS320F28026 + DRV8301 to control a brushless motor
DRV8301 provide over current protection, it indicated in datasheet about OCP behavior and OCP limit calculation. I use our design parameter to calculate the result as below
OCP = 0.73/14(mOhm) = 52.14A.
that's mean the maximum current flow through each phase will be limited if current over 52.14A right? When DRV8301 detect current higher than 52.14A will send a pull low signal to nOCTW right?
I measure motor current as below picture around 6A OCP is triggered. Then I provide larger resistance to force motor drive more current, maximum current around 18A and it seems like this current limit touch a ceiling. thus there are some questions I would like to know
1. Why OCP is triggered at 6A, but the maximum current limit can reach 18A? OCP more like a "warning" and don't do anything to limit the current.
2. 18A still much smaller than the design value (52.14A), is there any limitation for DRV8301 to prevent large current flow?
3. Do TMS320F28026 have maximum output PWM duty cycle? I notice when current reach 18A, the PWM duty cycle from TMS320F28026 will reach 90%, is that reasonable?