LM5046EVM / leakage inductance

K.Yaita

Other Parts Discussed in Thread: LM5046EVAL

Hi Team,

My customer found LM5046EVM and wants to know how much "leakage inductance" of transformer is estimated for this design.
http://www.tij.co.jp/jp/lit/ug/snva470b/snva470b.pdf
He also wants to know the value of estimated Coss as a reference for his design.

Is there any information?

Best Regards,
Yaita / Japan disty

over 9 years ago

0 K.Yaita over 9 years ago

Guru 29720 points

Your support would be appreciated.

Best Regards,
Yaita

0 Wangxin Huang over 9 years ago in reply to K.Yaita

TI__Intellectual 1550 points

Yaita,

Received. We will get back to you soon.

Regards,

Wangxin

0 K.Yaita over 9 years ago in reply to Wangxin Huang

Guru 29720 points

Hi Wangxin-san,

Thank you for your support.
I will wait for your team's reply..

Best Regards,
Yaita

0 Wangxin Huang over 9 years ago in reply to K.Yaita

TI__Intellectual 1550 points

Yaita,

To answer your questions,

1. The FETs used on the primary side are TI NEXFETs. You can find the Coss and other parameters on the datasheet (www.ti.com.cn/.../csd17303q5.pdf)

2. The transformer used on this EVM is PA0876.003NL from pulse. I've looked up on our internal database and manufacturer's website but could not find the leakage inductance information. I would suggest you to contact the manufacturer (www.power.pulseelectronics.com/.../switch-mode).

Regards,
Wangxin

0 K.Yaita over 9 years ago in reply to Wangxin Huang

Guru 29720 points

Hi Wangxin-san,

Thank you for your support.
I would like to confirm just in case.
I believe FETs used on the primary side are IRFH5053TRPBF(International Rectifier).
http://www.infineon.com/dgdl/irfh5053pbf.pdf?fileId=5546d462533600a40153561ad6851ea2
Is my understanding correct?
>1. The FETs used on the primary side are TI NEXFETs. You can find the Coss and other parameters on the datasheet (www.ti.com.cn/.../csd17303q5.pdf)

Best Regards,
Yaita

0 Wangxin Huang over 9 years ago in reply to K.Yaita

TI__Intellectual 1550 points

Yaita,

I double checked it. You are right. Primary FETs are IRs and SRs are NEXFETs. Thanks for the correction.

Regards,
Wangxin

0 John Griffin1 over 9 years ago in reply to Wangxin Huang

TI__Mastermind 34465 points

PA0876.pdf

Attached is the transformer drawing.

The leakage inductance specified is 0.45uH max

0 K.Yaita over 9 years ago in reply to John Griffin1

Guru 29720 points

Hi John-san, Wangxin-san,

Thank you for your support.
I would like to ask additional question.
There is following equation in application note.
---------------------------------------------------
(page.3)
http://www.tij.co.jp/jp/lit/an/snva610/snva610.pdf

---------------------------------------------------

I believe Cparasitic above is "Coss(Q1) + Coss(Q2)".
Is my understanding correct?

Best Regards,
Yaita

0 John Griffin1 over 9 years ago in reply to K.Yaita

TI__Mastermind 34465 points

Yaita-san,
Cparasitic is loosely defined in the data sheet as the capacitance from the mid-point node to ground.
The value of Cparasitic sets the theoretical value of Tap according to the equation above but in practice the equation used is :
RD(1,2) = Tap,Tpa/3pF
This is equation 3 in the data sheet.

The parasitic capacitance includes the Coss and the capacitance from the MOSFET package to the nearby components (transformer, decoupling capacitors, pcb traces and everything else.) PCB layout plays an important part.
The definition of Coss is the capacitance of the drain to source with the gate shorted to the source. This is a parameter measured by the semiconductor manufacturer.
The "parasitic capacitance" is related to this but it is more determined by the power supply design.

In practice equation 3 is used to approximate a value for RD1,2 and the value is adjusted based on the switching waveforms seen on the oscilloscope.

Regards,
John Griffin

0 K.Yaita over 9 years ago in reply to John Griffin1

Guru 29720 points

Hi John-san,

I really appreciate for your advice, I could find the same equation in datasheet.
I understood.

Best Regards,
Yaita

0 K.Yaita over 9 years ago in reply to K.Yaita

Guru 29720 points

Hi John-san,

I aplogize for asking maniy times..I would like to ask the following.

1)
LM5046EVAL shows R15=R16=20kΩ.
http://www.ti.com/lit/ug/snva470b/snva470b.pdf

How are these value decided?
Are these value adjusted based on the switching waveforms seen on the oscilloscope with equation 3 in datasheet?
I would also like to know if these values are decided from equation 6 and equation 7(theoretical value including L_leakage and C_parasitic) in datasheet.

2)
If R15 and R16 are decided from equation 6 and equation 7, could you tell me C_parasitic value of LM5046EVAL?

My customer wants to know above as a reference for his design.
Your support would be appreciated.

Best Regards,
Yaita

0 K.Yaita over 9 years ago in reply to K.Yaita

Guru 29720 points

Your support would be appreciated, my customer wants to know as soon as possible.

Best Regards,
Yaita

0 John Griffin1 over 9 years ago in reply to K.Yaita

TI__Mastermind 34465 points

Hi Yaita-san,

You can use equation 7 in the data sheet to calculate the parasitic capacitance.

The commutation inductance is approx. zero.

The leakage inductance is known from the data sheet

The value of Tpa is best measured with an oscilloscope.

Regards,

John

0 John Griffin1 over 9 years ago in reply to John Griffin1

TI__Mastermind 34465 points

0 K.Yaita over 9 years ago in reply to John Griffin1

Guru 29720 points

H John-san,

Thank you for your reply.
Does TI have C_parasitic value of LM5046EVAL?
My customer think TI has the value as design value of LM5046EVM and wants to know it as a reference for his design.

Best Regards,
Yaita

0 John Griffin1 over 9 years ago in reply to K.Yaita

TI__Mastermind 34465 points

Yaita-san,
I do not have the value. It was not used in the EVM design

Regards,
John

0 K.Yaita over 9 years ago in reply to John Griffin1

Guru 29720 points

John-san,

Could you tell me background to select IRFH5053TRPBF for LM5046EVM design?
My customer strongly requires the information not only that you gave me until now but also how to design LM5046EVM..
http://www.tij.co.jp/jp/lit/ug/snva470b/snva470b.pdf

He wants to know it as a reference for his design.
If it is impossible to disclose the information, please let me know.

Best Regards,
Yaita

0 K.Yaita over 9 years ago in reply to K.Yaita

Guru 29720 points

May I have the following information?
>Could you tell me background to select IRFH5053TRPBF for LM5046EVM design?

Best Regards,
Yaita

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LM5046EVM / leakage inductance