TMS320F28386S: Current Control Ramp Generation

Vishal D

Hello, I am working on a project where I want to do current control using CMPSS and EMPW module. In the system I am switching IGBT's in Synchronous buck converter mode at switching frequency of 10KHz.

For Slope compensation if I select max reference as 1000 and ramp dec value as 1, the ramp will come down to zero in just 1000 sys clocks (controller is operating at 200MHz). This is very small portion of the 10KHz(just 5%). frequency. So if I start the ramp when PWM Timer Counter is equal to zero it will cover only 5% duty cycle.

So wanted to know if my understanding about ramp slope is correct if the switching frequency is around 10KHz. If it is correct then can you please suggest how the ramp decrement rate can be reduced below 1 count per system clock or any alternative where this challenge can be mitigated.

Thanks,

Vishal

over 3 years ago

0 Hadi Moradisizkoohi over 3 years ago

TI__Expert 7100 points

Hi Vishal,

The reference 12-bit DAC uses the most significant 12 bits of the RAMPSTS countdown register as its input. The low 4 bits of the RAMPSTS countdown register effectively act as a prescale for the falling ramp rate configurable with RAMPDECVALA.

Regards,

Hadi

0 Vishal D over 3 years ago in reply to Hadi Moradisizkoohi

Prodigy 80 points

Hello Hadi, Thanks for clarifying, it will help me to address the lower ramp rate. I tried but unable to find out a driverlib function which can write to RAMPSTS countdown register., can you please help me with the function ?

0 Vishal D over 3 years ago in reply to Vishal D

Prodigy 80 points

Hello Hadi, Please ignore above query. As I can see the RAMPSTS is read only register and its value is updated using RAMPMAXREFS register upon PWM SYNC event.

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TMS320F28386S: Current Control Ramp Generation