UCC28950: open loop could use cycle-by-cycle current limit?

Paul Lai

Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951-Q1,

In open loop condition, compensation pin injects about 5V, so will get the IC’s full duty, in this case, can we still use ‘’cycle by cycle current limit’’ this function?

over 7 years ago

0 Colin Gillmor over 7 years ago

TI__Mastermind 25570 points

Hello Paul

Yes you can. Even if the controller is operated closed loop - when the CS pin reaches the cycle-by-cycle current limit point the output voltage will drop and the comp pin will saturate high - exactly as it is doing in your open loop test setup.

Certainly use the UCC28950 for initial testing, if you intend that your application will have UCC28950 running at DMAX all the time and the cycle-by-cyle current limit is for protection then I would suggest you consider using the UCC28951-Q1 instead. The two devices are almost identical except that the UCC28951-Q1 works better at Dmax in current limit. http://www.ti.com/lit/an/slua853/slua853.pdf

Regards

Colin

0 Paul Lai over 7 years ago in reply to Colin Gillmor

Prodigy 30 points

What is the difference between UCC28950 and UCC28951-Q1 when running at DMAX and cycle-by-cycle?

Let's UCC28950 use in VCM, the cycle-by-cycle protection will be trigger when the CS pin reaches 2V?

0 Colin Gillmor over 7 years ago in reply to Paul Lai

TI__Mastermind 25570 points

Hello Paul

The UCC28951-Q1 eliminates the behaviour described in the earlier post at http://e2e.ti.com/support/power_management/isolated_controllers/f/188/t/292928

You are correct, if you use the UCC28950 in VCM then the cycle-by-cycle protection will trigger once the CS pin reaches 2V irrespective of the operating duty cycle.

Regards

Colin

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UCC28950: open loop could use cycle-by-cycle current limit?