UCC2897A: 求助 TI技术人员，UCC2897A的应用资料SLUA535中第25页的第54式中，有疑问。

谢谢

Hello Dushimutong

My TI translator app gives me the following translation and I'll answer as best I can - in red

Problem: In UCC2897A SLUA 535 of shop 9 on Page 12 of the application file(s)
The values given by Calculation formulas are not would be 285.568 does uF, is an error for an error or formula?

I think that the formula is correct, but the values of the parameters that go into it are not very clear. You need to know the gate charge of the MOSFETs you are driving and the switching frequency. You also need to know the capacitance at the VREF pin - I assumed 0.22uF. The equation is dominated by the charge needed to switch the MOSFET gates and by the soft start time. None of this is particularly clear in the app note - so my advice would be to use the equation as is and to see what sort of start-up time you can get with a 330uF capacitor. For example, if you set tss to 200ms, and Ic = 3mA and Qg = 30nC and Vhyst = 4.4V you will get a Cboot of  3007uF.

Issue 2: Does in UCC2897A SLUA 535 of the section on Page 17 of the application file(s) 23, is it less by the Iqf (RMS) ?

I'm not sure I understand your question but Equation 23 calculates only the switching loss of QF. the forward conduction losses in the Rds_on will add to this loss (calculated in equation 26) as will the conduction losses if the body diode conducts for some of the switching cycle, (calculated in equation 25)

Question 3: In UCC2897A SLUA 535 of page 54on Page 25 of the application file(s)
1: Qgc definition of what is?

I think you mean Equation 54 on Page 25 - Qgc is the gate charge of the MOSFET - this is usually given in the MOSFET datasheet. Equation 54 is calculating an effective capacitance from gate to drain. It has been extrapolated from the MOSFET datasheet. This effective capacitance is then used to estimate the switching losses in the main MOSFET (equation 55)

2: Qmain is main MOS tube DP of Si7846 is the total gate charge Qg? 

I'm sorry but I don't understand this question.

Question 4: In UCC2897A SLUA of the application file(s) 535, gain/frequency curves is MathCAD Calculation or Simulation of the idea of which software I can I use as a formula simulation diagram thank follow some difference between figure on the material.  TI never released a MathCAD file for this device but there is an internal file that you may find helpful - attached.
/cfs-file/__key/communityserver-discussions-components-files/196/2768.UCC2897A_5F00_Power-Stage-Design_5F00_Rev-0.xmcd

Please let me know if I can be of any further help.

Regards
Colin

Hello Dushimutong

I made a mistake in the calculation for Cboot - 'Cboot of 3007uF' should read 'Cboot of 300uF'.
Regards
Colin

Helo Colin

Thank you very much.

问题2中：公式23中，开关损耗的计算时，如果不引入电流，则公式得不到功率单位瓦特（W）。

问题3中：公式54中，如果Qgc代表MOS的栅极电荷，那Qmain代表什么呢。也就是说，我不知道引入什么数据来计算。

问题4中：这个SLUA535文件，中的Figure20,Figure21,Figure22,Figure23,Figure24,Figure25,Figure26,Figure27，是用什么软件仿真的?

Regards

dushimutong

Hello Colin
请问附件中提到的（Unitrode Power Supply Design Seminar SEM-1100）这个文件，原文你有没有，或者你是否知道在哪能下载。Thank you .

Regards
dushimutong

Hello Dushimutong

: formula of 23 in the calculation of switching losses, if does not introduce a current, the formula would lose Solutions power in watts (W) in question 2.

I'm sorry, Equation 23 is dimensionally incorrect - it calculates a Voltage (V) and you are correct - this needs to be multiplied by a Current (A) to give a Power (W). Assuming that the current is 33nC*250kHz then I calculate as follows  5V*16.5ns*250kHz*33nC*250kHz = 0.17mW    This is in line with my expectation that the switching losses on the low voltage output are very small - I think the 506mW in the app note is an overestimate.

Question 3: In equation 54 is calculated if MOS Qgc represents what about gate charge - the Qmain representative. That is, I'm not sure what data is introduced.
COSS_QMAIN_100V is taken from the MOSFET datasheet - it is the Coss value at a drain to source voltage of 100V. The COSS_QAUX_100V is the same parameter for the Aux MOSFET.

SLUA for question 4: This 535 files in Figure 20, Figure 21, Figure 22, Figure 23, Figure 24, Figure 25, Figure 26, Figure 27 that is to use what software emulation?   It's not possible to say -  the original graphs may have been generated in MathCAD or possibly in EXCEL. The Technical Writer would normally take these source files and re-format them into a standard TI format -

My TI translator isn't doing a very good job but I think you are asking about where you can download the Unitrode SEM-1100 paper -  This may be found at http://www.ti.com/ww/en/power-training/login.shtml?DCMP=psdslibrary&HQS=tlead-power-psdslibrary-apec2015-pwrhouse-20150312-lp-en   - along with all the other design seminar papers - It's organised along topic lines not by seminar number but if you put 'sem-1100' into the search field you may find the topic you need.

Please let me know if you need any further help.

Regards

Colin

Hello Colin
Thank you very much.
Question 3：In equation 54 ，if Qgc is Gate charge of the MOS . What the mean of the Qmain?

Regards
dushimutong

Hello Colin
Thank you very much.I have no doubt.
Do you have any other contact information? Such as e-mail.
Regards
dushimutong

Hello Dushimutong

Yes, I'm at colingillmor@ti.com Please note that we prefer to deal with queries on the e2e forum because the answer is publicly available so I would ask you to post your questions here.

The exception, of course, is if the question being asked or the information being requested from the customer is confidential - in that case we will move the discussion onto emails - otherwise, please continue to use e2e.

Regards
Colin

Hello Colin

Okay thank you.

Regards

dushimtuong

Hello Colin
Do you have Mathcad of LM5026.Thank you very much.
Regards
dushimutong

Hello Dushimutong

No - I'm sorry we don't have an Mathcad file for the LM5026.

You may find the information in the .pdf at www.ti.com/.../slua672.pdf  useful.

You probably have already found the SEM1000 material but the SEM1000 topics at https://www.ti.com/seclit/ml/slup108/slup108.pdf and https://www.ti.com/seclit/ml/slup112/slup112.pdf may be of help.

Regards

Colin

Hello Colin
Thank you very much.
I have found these files.
Thank you.
Regards
dushimutong

Hello Colin
I'm sorry to bother you again.
When I designed the active clamp with the UCC2897A chip, I did not understand the equation 49 in the application file SLUA535.
Question 1: How to determine whether the core has been reset, or which parameters can indicate that the core has been reset.
Question 2:How should I design the primary inductance, leakage inductance and clamp capacitance to ensure the resonant period and core reset time.
Question 3:Assuming that the time required for the core reset is t, then t should be less than (1-Dmax)*Ts.
This is my understanding, if my understanding is wrong, please correct me.

Regards
Neil