I want to drive it by 3~5 KHz PWM freq. based on its spec. (Up to 10KHz as mentioned in its Datasheet). but when apply upper 1KHz PWM freq.(at low duty cycle 10%) to this chip, it get hot as if shutdown.(by the way i also install a heatsink).
I attached the driver schematic.
We connect INA to +5V and INB to GND (for CW direction) and PWM pin to PWM output of a microcontroller, also connect +5V pin to five regulated voltage to enable VNH.
We have tested the driver in 6 below frequencies:
245, 488, 978, 1.96K, 3.9K, 7.8K Hz. Our observation is as follows:
1) Power dissipation (VNH Chip temperature) depends on two parameters:
-- PWM frequency: by increasing the frequency of PWM signal from 245Hz to 7.8KHz, power dissipation increased (increasing switching dissipation).
-- Duty cycle of PWM signal (Motor Speed): in each frequency when we decrease duty cycle of PWM, the power dissipation (VNH Chip temperature) increased significantly. The effect of this parameter is very high but we don’t have any reasonable cause for that.
2) In 7.8KHz PWM freq. and low duty cycle (10%) the chip temperature increased terribly in a way that the soldering of VNH pad is melt so that we pick it up from PCB!!! and after that we solder it again and VNH doesn't damage!!!
Finally, we decide to drive VNH in 245Hz freq. (despite of its mentioned frequency capability in its datasheet- up to 10KHz) because in other freq. at the low duty cycles (below 10%) the VNH temperature isn’t reasonable.
As you know 245Hz PWM freq. isn’t a good freq. for driving motor because of mechanical resonations and producing annoying sounds. Our experimental work shows that the minimum best freq. is up to 20KHz, so what could we do to solve our problem?
Thanks a lot.