UCC28950: UCC28950 in slave configuration

Karthika

Part Number: UCC28950
Other Parts Discussed in Thread: UCC27714

I am using this part in Slave mode. I have given clock pulse in synchronous pin and got the PWM out from outpin A. But i see the PWM out from the out pin is varying like pulse width modulation.

My intend is to create a fixed duty cycle pulses from out A,B,C,D of UCC28950. Please provide your inputs.

I have attached here the waveform

over 3 years ago

0 Harish Ramakrishnan5 over 3 years ago

TI__Mastermind 24375 points

Hi Greeshma,

This has been assigned to a product expert, please allow one or two business days for a response.

Regards,

Harish

0 Mike O' over 3 years ago

TI__Guru* 86286 points

Hello,

The Out A and Out B pulses should not be varying in duty cycle. If you have the device setup in slave mode you should be able to synchronize it with a 50% duty cycle pulse.

This pulse should be synchronizing the UCC28950 output A. It looks like you are using simulation module that is having issues synchronizing. You might want to increase the sample points and sample resolution in your model to see if you can get the device to synchronize.

The following link will bring you to an application note that discusses in detail how to synchronize the UCC28950 in detail.

https://www.ti.com/lit/pdf/slua609

Regards,

0 Karthika over 3 years ago in reply to Mike O'

Prodigy 100 points

I have attached the here the screenshot of model for your reference. This is based on your application note u have sent.. Can u let me know, what is causing pulse width modulation like waveform and what do for the 50% fixed duty cycle

Clock gen circuit,

PWM controller

0 Mike O' over 3 years ago in reply to Karthika

TI__Guru* 86286 points

Hello,

Your circuit seems to be setup correctly.

For proper synchronization, your sync frequency needs to be faster than the programed frequency.

We recommend that the sync frequency be set at least 20% faster the programed frequency.

The master clock is set at 2*fswA = 217 kHz. Your sync frequency should be 217kHz*1.2 = 260 kHz.

I think that your sync frequency may not be fast enough to properly sync the device. Try syncing it to a faster freqeuncy.

Regards,

0 Karthika over 3 years ago in reply to Mike O'

Prodigy 100 points

Thanks for your comment.

I could synchronize and able to get fixed duty cycle. But i see the pulses generated are 30%ON and 70% OFF . Do you have any inputs for 50% ON and 50%OFF Pulses.

0 Mike O' over 3 years ago in reply to Karthika

TI__Guru* 86286 points

Hello,

Looking at your schematic I see that you are trying to force a voltage at COMP. You might want to try a few things to see if it may help you to get yoru model to sync.

1. Setup the voltage amplifier as a voltage follower by tying comp to EAN. Put a voltage divider on EAP from the reference.

2. Populate DELAB, DELCD, DELEF and TMIN. You use typical values for the data sheet.

3. If that does not work most likely there is most likely something wrong with the software model. If this is the case I would suggest getting some UCC28950 and testing them in an open loop circuit and/or ordering and evaluation module (EVM) to evaluate and modify. The following link will bring you to the UCC28950 evaluation modules User's guide. https://www.ti.com/lit/pdf/sluub02 This EVM can be ordered on line.

Regards,

0 Karthika over 3 years ago in reply to Mike O'

Prodigy 100 points

Thanks Mike for the support.

0 Mike O' over 3 years ago in reply to Karthika

TI__Guru* 86286 points

Hello,

I was glad that I could help.

Regards,

0 Karthika over 3 years ago in reply to Mike O'

Prodigy 100 points

Hello,

I have few more queries in addition. As per your suggestions mentioned above im planning to procure some UCC28950 for my projects.

1.I see the lead time of the UCC28950 is very high around 62 weeks with digikey and Mouser. Is there any stock available from TI directly say some samples of 5-10 qts?

2. I see the evaluation kit you suggested has two board, one power stage and other daughter board with UCC28950 controller. Is it possible to get daughter board(highlighted) alone so that i can get 5 qtys of daughter board,