UCC21541: I want a viable alternative to UCC21541 which isn't BO

Hey Don,

Thank you for your answer! As I tried to order them, you can see these are "fake" stock which is a common problem you guys are having right now because of the shortage. Plus, even if I could buy them, I can only buy a maximum of 5 of them. I need to produce 100 PCBs which would have 4 on every board. Is it possible to propose to me something else and confirm with your stock people that it works? 

Thank you for your time!

Hi, Sebastien,

That's odd. I tried entering an order, and I could buy 50 as the max limit. But, I am a TI employee (obviously) so maybe it's different for me for some reason.

Can you call our customer support center at 1-800-842-2737 and ask them for help? E2E is intended for technical support of our ICs.

Best regards,

Don

Hey Don,

Thank you for the fast answer! I will but believe me, it is a common error from your end, I've already had many discussions with your colleagues. Is it possible to offer me more than 1 alternative, please? 

Hey Don,

I was lucky enough to buy UCC21521DW from Mouser and they do have it in stock! Can you please confirm to me if it is a good alternative to UCC21541? Pïnout and physical dimension seems to be the same but I am wondering if I need to modify some electronics around that part since our design was configured for UCC21541. I've attached a picture of this part in my schematic. 

Thank you so much for your time!

Hi, Sebastien,

You're response made me chuckle! As you know (are painfully aware!) things are crazy in the semiconductor market right now. I'm glad you were able to find some parts!

Let me have my colleague confirm there is nothing special you need to do in order to change from UCC21541 to UCC21521.

BTW, I looked at your webpage, and your products are very cool! I am glad you are using our parts!

Best regards,

Don

Thank you very much Don! And yeah haha I've been trying to supply this part and/or an alternative for the last 4 weeks so this why I was excited. 

Hey Olivia, 

Thank you for your response! So basically, the only difference, besides that UCC21521 seems to be just "better" than UCC21541, is that the logic of the 5th pin is reversed? So basically, if I just modify the software we implemented to the opposite of what it was, everything should work smoothly? 

Hi Sébastien, 

Correct. I don't see any causes for concern with swapping in this new device. If you do run into any issues, please do follow up!

Best,

Olivia Brandel

Awesome thank you!

Hey Olivia,

I hope you are doing great! 

We received our new PCBs with the UCC21521 installed on them and it seems to have a problem. As discussed, the only difference I see compared to UCC21541 is about pin #5 which has a reversed logic. Therefore, we inverted the logic in our firmware but it still doesn't work properly. 

Could you please help me figure out if we missed any information regarding UCC21521 compared to UCC21541?

Thank you!

Hi, Sebastien,

I take it you're providing PWM input, and not seeing anything on the output?

Best regards,

Don

Hi Sébastien,

Sorry to hear that the switch did not go smoothly. One specification difference that could be having an impact is the power-up delay.

UCC21521 has a longer power-up delay than UCC21541. All isolated drivers in bootstrap configurations have a high-side pulse delay when Vboot starts below the UVLO threshold. Long start-up delay can sometimes lead to missed high-side pulses.

To account for this, we recommend using a bootstrap pre-bias routine to keep the bootstrap charged. This typically requires 3-10 low-side pulses before reaching normal operation. See this FAQ for an additional explanation and a visual.

Please let us know if this helps the issue! Otherwise, we can investigate further.

Best,

Olivia Brandel

That's great to hear. Thanks for the update, Sébastien! If there's nothing else we can assist with, please mark this thread as "resolved".  Thank you!