UCC2897A: Line Undervoltage Protection

Sam Ting

Part Number: UCC2897A

Hi sirs,

Our customer is concerned about the output voltage rebound when the line undervoltage protection is triggered. What is the reason for this output voltage bounce? Is this the expected behavior? Thank you!

Please find the waveform of normal operation below, the output voltage will not rebound if the input voltage returns to normal level after Vss < 3.6V. The operation resumes through a soft start after Vss > 2.5V.

However, during line under-voltage protection, if the input voltage returns to normal before Vss reaches 3.6V, the output voltage will return to the normal output level and wait for Vss to discharge below 3.6V, then the device enters the line undervoltage protection mode again.

Best regards,

Sam Ting

over 7 years ago

0 John Griffin1 over 7 years ago

TI__Mastermind 34465 points

Hello Sam,
The ic will stop switching when
(1) VDD reaches UVLO or
(2) VSS less than 2.5v or
(3) FB less than 2.5V.
I don't understand the reason that Vin drops and recovers to its original level but the soft start continues even though Vin should be above the under voltage level .

Can you get waveforms of VDD , UVLO, VSS and Vo and that may help with analysis.
Thanks
John

0 Sam Ting over 7 years ago in reply to John Griffin1

TI__Expert 3610 points

Hi John,

The waveforms were added for analysis. Thanks for your support!

Case 1:

Ch1: VDD, Ch2: VSS, Ch3: UVLO and Ch4: Vo

Case 2:

Ch1: VDD, Ch2: VSS, Ch3: UVLO and Ch4: Vo

Best regards,

Sam Ting

0 John Griffin1 over 7 years ago in reply to Sam Ting

TI__Mastermind 34465 points

Hi Sam,
I have asked one of my TI colleagues who has lots of experience with this part to review this issue
and he will reply in next few days
Regards
John

0 John Griffin1 over 7 years ago in reply to John Griffin1

TI__Mastermind 34465 points

Hi Sam,
It has been 4 weeks and I was not able to get any further information on this issue so I will close this thread.
If you have further questions then please open a new posting
Regards
John

0 Sam Ting over 7 years ago in reply to John Griffin1

TI__Expert 3610 points

Hi John,

The issue was closed. We think there are 3 intervals, DMAX Limit => UVLO Triggered => Disable Delay (Soft Stop). Thanks for your support!

Best regards,

Sam Ting

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UCC2897A: Line Undervoltage Protection