UCC256302: IPolarity detection threshold by ISNS pin

user6304160

Part Number: UCC256302
Other Parts Discussed in Thread: UCC256402

Hi Team,

There is a description on the data sheet, "If there is no slew detected, IPolarity signal is used. The next gate will be turned on at the next IPolarity flip event."

What is the threshold for detecting IPolarity flip events?

Please see waveform below;

-CH2 LowSideINV_Vds

-CH3 LowSideINV_Vgs

-CH4 ISNS Pin

I thought that the detection of IPolarity flip event was the zero cross of ISNS, but it seems that it is actually detected at the threshold value deviated from 0V.

It also looks like the threshold changes depending on the timing.

Q1.What is the threshold for detecting IPolarity flip events?

Q2.Please tell me the factors that change the threshold. If it is determined by RVCC or internal AVDD etc, please tell me the fluctuation characteristics for them.

Q3.Are there any requirements for accurate IPolarity flip event detection? For example, dV / dt and connected impedance.

Best regards

over 2 years ago

0 Manikanta Pallantla over 2 years ago

TI__Genius 13245 points

Hi,

Could you show VCR signal too along with the three signals you shared (I mean LO,HS,ISNS,VCR signals). I will reply to your questions once you share that waveform.

Regards

Manikanta P

0 user6304160 over 2 years ago in reply to Manikanta Pallantla

Prodigy 140 points

Hi Team,

I additionally confirmed the waveform of the VCR terminal. However, it is a waveform of HO, not LO.

Please see waveform below;

-CH1 VCR Pin

-CH2 LowSideINV_Vds

-CH3 HighSideINV_Vgs

-CH4 ISNS Pin

Best regards

0 Adam E2E over 2 years ago in reply to user6304160

TI__Intellectual 2430 points

the threshold is ideally 0mV ,so it is only the hysteresis that makes the comparator threshold. Ex, with nominal 30.7mV, the rising edge can be +15.3mV and falling edge -15.3mV.

you can refer the datasheet 6.3.14 section for the ZCS protection.

you can refer the app note to migrate to UCC256402.

https://www.ti.com/lit/pdf/slua966

0 user6304160 over 2 years ago in reply to Adam E2E

Prodigy 140 points

Hi Adam

I am aware that there is hysteresis in the threshold.

Actually, the maximum hysteresis is 44.7 mV, but it is detected at 180 mV or -130 mV.

Furthermore, it seems that the threshold value changes depending on the timing.

Please tell me the reason why the threshold is fluctuating.

You said that the threshold is ideally 0 mV, but is there a condition that is not 0 mV?

Best regards.

0 Adam E2E over 2 years ago in reply to user6304160

TI__Intellectual 2430 points

it should be trigger by noise., you can fine tune the Isns RC filter.

0 user6304160 over 2 years ago in reply to Adam E2E

Prodigy 140 points

Hi Adam

Are there any requirements for accurate IPolarity flip event detection?

Ex, is it impossible to detect if the voltage change of ISNS is too steep or too slow?

0 Adam E2E over 2 years ago in reply to user6304160

TI__Intellectual 2430 points

Hi,

we didn't define the Ipolarity detection slew rate on the datasheet.

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UCC256302: IPolarity detection threshold by ISNS pin