UCC28950: Questions Regarding SLUA560D and SLUSDB2B Design and Calculations

Conor

Part Number: UCC28950

Tool/software:

Hi Mike,

I am proceeding with a design based on the application note SLUA560D: "UCC28950 600W Phase Shifted Full Bridge Design Review/Application Report (Rev. D)", and I have encountered several questions where the formulas and calculation results appear to be inconsistent. These include topics that have been discussed in related threads to date, but I would appreciate clarification on the following points:

Q1. Regarding Formula (11) in SLUA560D
Shouldn't the denominator of Formula (11) be "/2" instead of "/4"?
According to Formula (31) in the datasheet SLUSDB2B, the denominator is "/2", which would give a result of 50A. Could you confirm which is correct?

Q2. Regarding Formula (61)
Based on Formula (61), VdsQE should be 39V, but in the diagram you previously provided, it is shown as 19.5V.
Could you explain how 19.5V was calculated?

Q3. Regarding Coss_qe_avg in the diagram
In the diagram mentioned in Q2, Coss_qe_avg is shown as 2262.07 pF.
I believe this value may have been calculated using Formula (64) where the numerator and denominator are reversed incorrectly.
Could you kindly verify this calculation?

Q4. Regarding PBUDGET calculation error
When I perform an automatic calculation using the parameters provided in the application note, PBUDGET becomes negative, and an error occurs.
Therefore, I suspect that there may be a mistake either in the application note itself or in the provided Excel design tool.
Could you please check this issue in detail?

Q5. Regarding SYNC Pin Handling (SLUSDB2B Datasheet)
In the datasheet SLUSDB2B, there are two different recommendations regarding how to handle Pin 16 (SYNC) when the synchronization function is not used:

In Section 6.3.15 (Synchronization SYNC):

"If the synchronization feature is not used, then the SYNC pin may be left floating, but connecting the SYNC pin to GND through a 10kΩ resistor will reduce noise pickup and switching frequency jitter."

In Section 7.4.1 (Layout Guidelines):

"For the SYNC pin: this pin is essentially a digital I/O port. If it is unused, then it may be left open circuit or tied to ground through a 1kΩ resistor."

Could you clarify whether either 1kΩ or 10kΩ to GND is acceptable?

Best regards,

Conor

7 months ago

0 Mike O' 7 months ago

TI__Guru* 86286 points

Hello,

Your inquiry has been received and will be answered in the order that it has been received.

Regards,

0 Mike O' 7 months ago in reply to Mike O'

TI__Guru* 86286 points

Hello,

Connor, I feel that we have answered these questions for you in the past. Could you double check past threads to see if these questions have already been answered for you?

If the excel tool gives you a negative value for the power budget that means your efficiency goal cannot be met with the components selected. So, you will have to select other components to meet your efficiency goals.

Regards,

0 Conor 7 months ago in reply to Mike O'

Guru 12365 points

Hi Mike,

I have checked all past UCC28950 posts.

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1440408/ucc28950-error-in-calculation-results-from-excel-design-tool

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1436436/ucc28950-calculation-inconsistency-with-application-note-slua560d-3

You have already checked Q4 and answered that "the efficiency target cannot be achieved with the selected components." I apologize for this duplicate post.

I also do not seem to have received any answers to items other than Q4, so could you please answer them again? In particular, Q1 and 3 seem to be typos in the documentation, so I think we can check them immediately.

Thanks,

Conor

0 Mike O' 7 months ago in reply to Conor

TI__Guru* 86286 points

Hello,

I am sure you asked these on the e2e before. No worries. I will look into them for you.

I will answer them one at a time.

Q1. Regarding Formula (11) in SLUA560D
Shouldn't the denominator of Formula (11) be "/2" instead of "/4"?

Formula 11 in the application note SLUA560D is correct.

According to Formula (31) in the datasheet SLUSDB2B, the denominator is "/2", which would give a result of 50A. Could you confirm which is correct?

Equation 31 in the data sheet is not correct.

Regards,

0 Mike O' 7 months ago in reply to Mike O'

TI__Guru* 86286 points

Hello,

From question 2 I can see are using an old excel tool. This was correct some time ago. Please down load the latest tool. https://www.ti.com/tool/download/SLUC222

I will look into your other questions when time permits.

Regards,

0 Conor 7 months ago in reply to Mike O'

Guru 12365 points

Hi Mike,

Thank you for your reply, I understand. I am also looking forward to your answers to the two questions in Q3.5.

Thanks,

Conor

0 Mike O' 7 months ago in reply to Conor

TI__Guru* 86286 points

Hello,

Q3 I reviewed equations 64 and you are correct. I will let the documentation team now so it can be corrected in the next revision.

Q5 I have seen this pin terminated with 10 k and 1 K and both have worked.. The lower impeadence will supress noise easier but the will dissipate more power.

Regards,

Power management

Power management forum

UCC28950: Questions Regarding SLUA560D and SLUSDB2B Design and Calculations