UCC28056EVM-296: combination problem with use of UCC256302 DC88V input

Hiroshi Doi35

Expert 2845 points

Part Number: UCC28056EVM-296
Other Parts Discussed in Thread: UCC28056,

Hi Ben-san,

Here is new problem for your supported DC88V input.

I think it is required more change for EVM.

I will wait for your come back.

Input current waveform problem is written in the attached PDF.

UCC28056&UCC256302 problem more.pdf

over 5 years ago

0 Sonal Singh over 5 years ago

TI__Expert 6080 points

Hello Doi-san,

The dip in the line current might be cause due to the impedance divider at the ZCD/CS divider. Please plot the ZCD/CS and te drain voltage for the original and new value of R5. Also, please share the schematic to know what is R5.
May I ask what drove this change of the current sense resistor?(I assume R5 is current sense).

Regards,
Sonal

0 Hiroshi Doi35 over 5 years ago in reply to Sonal Singh

Expert 2845 points

Hi Sonal-san,

Are you looking at UCC28056EVM-296 Cct.?

R5 is connected to MOSFET Drain and Anode of boost diode.

Do you have another choice of change parts, to get good result at DC88V input?

DC88V is equal to AC62V. It's very tough for UCC28056EVM-296.

I want more concrete advice like " Rxxx change to yyyohms"

0 Hiroshi Doi35 over 5 years ago in reply to Hiroshi Doi35

Expert 2845 points

Hi Sonal-san,

My customer' try is corresponding to this,

Nov 2, 2018 5:12 AM

In reply to Hiroshi Doi:

Hi Doi-san,

Changing the divider ratio of the resistor chain between the MOSFET drain and the ZCD/CS pin will adjust the start threshold.

Best Regards,
Ben Lough

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26225 points

Hi Doi-san,

you likely need to adjust C10 or C11 to account for the change in the resistor string. Check the voltage at the ZCD/CS pin and compare the ZCD/CS pin waveform to the mosfet drain voltage divided by the resistor divider ratio formed by R5, R6, R7 and R8. For reference, take a look at the ZCD/CS pin waveforms shown on page 36 of the UCC28056 datasheet:www.ti.com/.../ucc28056.pdf. For reference, take a look at the text in datasheet right after equation 64. This section talks about why the capacitance can affect the ZCD/CS waveform.

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Hi Ben-san,

They do not have differential probes. They can not see because there is no 100: 1 probe.

So they can not see the pin.

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26225 points

Hi Doi-san,

Do you have a single ended probe rated to 400V or so? This would also be ok to use.

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Hi Ben-san,
They have 100:1 prove but it's 20pF over.
No way for look at ZCD/CS pin waveform.
( of course I have differential probe but it is not for rent )

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26225 points

Hi Doi-san,

Would they be able to use the 100:1 probe to measure the drain to source voltage and a low capacitance probe to look at the ZCD/CS pin?

Best Regards,
Ben Lough

0 Hiroshi Doi35 over 5 years ago in reply to Benjamin Lough

Expert 2845 points

Hi Ben-san,

They have 100:1 probe but unfortunately their cheep 100:1 probe is over 20pF.

So they cannot look at ZCD/CS pin.

0 Benjamin Lough over 5 years ago in reply to Hiroshi Doi35

TI__Mastermind 26225 points

Hi Doi-san,

Let's try calculation. Have your customer set up their ZCD/CS divider for the appropriate brown-in point. Based on this resistor divider ratio, the ratio of the capacitance divider should be the same. Use equation 56 in the UCC28056 datasheet to recalculate the bottom capacitor for the ZCD/CS pin.

Best Regards,
Ben Lough

Power management

Power management forum

UCC28056EVM-296: combination problem with use of UCC256302 DC88V input