Problem while generating Multiple PWM using eZDSP 2407A

Hello

I am assuming you have checked PWM output levels and frequency to make sure everything is working according to your code. If you are certain that PWM outputs are generated correctly then please check the driver portion of your inverter. Is this inverter designed in-house? You should get proper driver output to control your IGBT/MOSFETs. Basically you will need to go down the line checking one item at a time to identify the possible issue. There are various example codes and systems which can be downloaded from TI site as reference.

On a separate note , if this is a new design/project then please check out 280xx devices instead of 24xxx family - you will have the newer core and next generation peripherals with 28x family. Good luck.

Hi,

I have checked all the outputs. All the output are in accordance to my code. But, when I run the code and check connectivity between two PWM output ports there it shows a resistance of  less than 100ohm(almost like a short). Can you tell me what could be a possible reason for this??

Actually, I never measured connectivity between two PWM outputs ... do you need a specific output impedance for your IGBT/MOSFET driving circuit? May be TI folks will reply on output impedance of PWM channels. In the mean time, please describe your complete system and the specific issues your are facing for me to better answer your question.

Is it the output impedance of pwm driver that is important? I really don't know your board, but if you can measure signals with CRO, you measure with a very high impedance at the output. Means, there's just a small current out of pwm output. What's the impedance of your driver circuit? If you measure 0V at the output it may drive a short circuit.  I would try to connect a line driver between pwm output and driver input, so driving current is no problem.
Maybe it would be good if you post a schematic of your design.

I'm trying to implement Multiple PWM based control for3-phase induction motor. To drive the motor we have a IGBT based inverter. The inverter is compatible to ezDSP 2407A kit. There is no information given about the input imepedence in the inverter manual.  When I connect a single pair of PWM output  it works fine. But, when I try to connect all the PWM's to the inverter it shows that there is a short.

I had a quick look at the datasheet of LF2407. On page 62 are the maximum output currents for the different pin groups.
The total current consumption is important. If you just connect two pwm's to the inverter it works..  because current consumption is low.

To limit current you can also connect series resistors to the pwm signals.

here's the link to the datasheet:

http://focus.ti.com/lit/ds/symlink/tms320lf2407.pdf

thanks Eggi I will try it...

Eggy,

I tried what you have suggested, but no success. Though it is now showing high resistance but still there is problem when I connect it to the inverter.  

It is possible that this particular 2407 device is damaged but at the same time it is also possible that the inverter section has problems - are you sure your inverter driving section is working correctly? How are you driving your IGBTs? Are you using any gate driving IC? or have you designed your own gate driver? You can check your gating signals at the output of your gate driver - depending on your selected driver IC or driver design the output should be around +12/+15 volts (when PWM is high) and 0/-2 volts (when PWM is low). Also, check all the IGBTs of your inverter - any shorted/damaged IGBT/MOSFET may create short when pulsed. Also, check your deadband - insufficient deadband will create short when IGBT/MOSFETs are switched. Finally, if you are convinced that the problem is not in inverter then you may try another 2407 device or eZdsp board as your last resort to make sure the problem is not related to the device.

I am hoping one of the above items will help you to identify the problem. Good luck.

you just check whether IGBT on/off  when you are giving pulses,for that you need power CRO,normal CRO will not work(some grounding problem) if your code is proper and your pwm output is proper then it is not more challenging,you just check when you are giving pulse at the same time what is the status of IGBT if it is proper it should work. i m also working on ezdsp2407,you can contact me 919712389169