Dear all,
I have some riddle with the system utilising DRV8899. I am using it to drive small stepper motor, and as a part of CubeSat subsystem, we were performing some TVAC testing. Motor driver works good in room temperature, and during actuation with some load it consumes 800 mA Irms. For hot case scenario (around 60 deg C), Irms goes up to around 1-1.1A. For cold case, around -5 deg C, Irms drops to around 550-600 mA and we lose a lot of torque - mechanism is stuck.
As far I know, Irms is affected by environment temperature (Rds ON of the j bridge), and with some calculation, it looks that change in Irms is reasonable. Is this Irms drop and drop in torque caused only by mosfet temperature or is there anything else? We tried to just hold the torque and warm up the switches but it didn't solved the issue. I am thinking about adding small heater on top of the chip to warm it up before operation (if needed). Would it be typical practice, or I am missing something? The goal is to be able to operate when environment temperature is around -40 deg C.
For the hot case, around 60 deg when Irms rise above 1 A, we get undervoltage error. In real situation, in LEO environment we won't get to this temperature inside satellite, also heatsing is quite sufficient so we shouldn't get that high in nominal operation (also I am switching with new iteration to DRV8889 which has bigger package and heatsink. Problem here is the undervoltage - we have to supply the motor driver with 5V line, and undervoltage starts to act around 4.5V. Also, this problem is strongly affected with longer cables (which is reasonable). My question here is, if the bus voltage is low, and we operate in nominal range, just keepiong bulk capacitance high, would solve the issue? Or utilising higher voltage is unevitable? In the new iteration i changed ceramic bulk capacitance to polymer tantalum but I still need to test it.
I will be glad for any suggestions!
Best regards,
Slawomir