UCC256303: Capacitor at VBLK pin

Kazuki Itoh

Genius 10820 points

Part Number: UCC256303
Other Parts Discussed in Thread: UCC256403

Hello team,

Could you please let me know about the capacitor at VBLK pin?

My customer observed periodic pulse waveform at VBLK pin when the capacitor at VBLK pin is removed.

Please find internal link here for the schematic and waveforms.

What is the purpose for the capacitor at BLK pin? Is this just for noise filtering?
Could you let me know the possible cause of the periodic pulse waveform?
Is the periodic waveform likely to be caused by the BLK pin cap removal?
Why the controller doesn't stop while the VBLK exceeds VBLKOVRise?
Why the controller doesn't restart while the VBLK goes below VBLKOVFall?

My customer is asking because it is similar to the waveform that customer observed when start-up failed (seldom happens).

Regards,

Itoh

over 4 years ago

0 Benjamin Lough over 4 years ago

TI__Mastermind 27145 points

Hi Itoh-san,

1. The capacitor on BLK is just for noise filtering.

2. From the shape, it looks like switching noise is coupling into the BLK pin.

3. Yes, by removing the capacitor, the switching noise is not getting filtered out.

4 and 5. The BLK waveform is moving too quickly. It does not stay above BLKOVRise or below BLKOVFall for enough time for the internal BLK comparators to trip.

I would also like to mention we have a newer version of this controller called UCC256403. It contains several feature improvements.

Best Regards,

Ben Lough

0 Kazuki Itoh over 4 years ago in reply to Benjamin Lough

TI__Genius 10820 points

Hello Ben-san,

Thank you so much for your prompt support.

How much time does it need to trip the internal BLK comparator?

Regards,

Itoh

0 Benjamin Lough over 4 years ago in reply to Kazuki Itoh

TI__Mastermind 27145 points

Hi Itoh-san,

I would need to check with the IC designer for the exact number but I believe it is on the order of several 10s of ns to 100s of ns.

Best Regards,

Ben Lough

0 Kazuki Itoh over 4 years ago in reply to Benjamin Lough

TI__Genius 10820 points

Hello Ben-san,

Could you please check the exact number of the comparator trip time with the designer?

My customer hopes to know the detailed value.

Regards,

Itoh

0 Benjamin Lough over 4 years ago in reply to Kazuki Itoh

TI__Mastermind 27145 points

Hi Itoh-san,

I have asked the design team for this number. I will update once I hear back.

Best Regards,

Ben Lough

0 Benjamin Lough over 4 years ago in reply to Benjamin Lough

TI__Mastermind 27145 points

Hi Itoh-san,

The delay time is 50us.

Best Regards,

Ben Lough

0 Kazuki Itoh over 4 years ago in reply to Benjamin Lough

TI__Genius 10820 points

Hello Ben-san,

Is the 50us minimum or typical value?

My customer would like to check the minimum value.

Regards,

Itoh

0 Benjamin Lough over 4 years ago in reply to Kazuki Itoh

TI__Mastermind 27145 points

Hi Itoh-san,

It is typical value but there is not much varability to the delay time.

Best Regards,

Ben Lough

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UCC256303: Capacitor at VBLK pin