UCC256403: datasheet question

Feeney Xiao

Intellectual 2680 points

Part Number: UCC256403

Hi expert

my customer had two question about UCC256403

1. there isn't show the max voltage of pin5(FB), pin7(VCR), what voltage can these pin support?

2. is this HB in picture is right? we think it may be HS？

6 months ago

0 JCHK 6 months ago

TI__Mastermind 44620 points

HI Feeney,

The abs max for the FB and VCR pins should be less than 5.5V, but I can double-check with the design team.

As for the above, HV and HB are correct as both of these voltages with respect to the IC GND. The HO and HS pins float above the HB rail so these pins see HB as their virtual GND.

i hope this answers your question

0 Feeney Xiao 6 months ago in reply to JCHK

TI__Intellectual 2680 points

Hi JCHK

thank you, after you check with design team, please tell me.

0 JCHK 6 months ago in reply to Feeney Xiao

TI__Mastermind 44620 points

Hi Feeney,

I am checking now. Hopefully will have a response today.

0 JCHK 6 months ago in reply to JCHK

TI__Mastermind 44620 points

HI Feeny,

I confirmed that the abs max rating for the FB and VCR pins is 7V.

Regards,

John

0 Feeney Xiao 6 months ago in reply to JCHK

TI__Intellectual 2680 points

Hi JCHK

thank you. more questions:

1. while pin8 BW connect to GND by 0ohm, what's the suitable BMTL/BMTH

2.the pin6 crush current is high when power on, sometimes it's may cause OCP. do you have any advice to avoid this risk, from bom, parameter and other side..

3. while there isn't load, we don't want the device enter the burst mode, how to do it.

0 Manikanta Pallantla 6 months ago in reply to Feeney Xiao

TI__Genius 13245 points

Hi Freeney,

Please see my responses below:

Feeney Xiao said:
while pin8 BW connect to GND by 0ohm, what's the suitable BMTL/BMTH

I am not sure whether I understand your question correctly.

For OCP1 to be activated, the ISNS pin voltage needs to be more than OCP1 threshold for 4 consecutive cycles.

3. You can use the option 7 for burst disable.

Regards

Manikanta P

0 Feeney Xiao 6 months ago in reply to Manikanta Pallantla

TI__Intellectual 2680 points

Hi Manikanta

thank you

we have another question: while pin8 BW is 2.42k-3.04k, it's burst disable. but if we set 2.7k, the output voltage is vary from 23V to 26V, it doesn't work normal. this is the schematic which customer used, do you have any advice, how can it work at burst disable mode normally

UCC256403A.pdf

0 Manikanta Pallantla 6 months ago in reply to Feeney Xiao

TI__Genius 13245 points

Hi Feeney,

To operate in the normal mode, The resonant tank needs to be designed such that during no load , the operating frequency is not too high. Also, you need to make sure FBReplica is more than BMTL threshold.

Regards

Manikanta P

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UCC256403: datasheet question