TPS23753A： VC電流のばらつき

Hello Michael san

Thank you for your quick reply.

I have summarized the problems, so please give me some advice.

Attach the file.Summar of Issue _25-Aug-2021.xlsx

Hello, 

Can you send me a full schematic?

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Thank you for your support.

I send the schematic data.(our schematic and reference schematic)

Circuit.zip

Hello Ohkawa san, 

Thank you for providing schematic. I focus on the circuit on VC. 

I am curious, does the design damage if there is a large current on VC? Additionally, something interesting is that this does not happen on every board. Could that be different Betas for different BJT's? Can you test this?

To me, it makes sense as we decrease the zener diode voltage it decreased voltage on the base of the NPN resistor so the current flow is less. I just wonder if now there is not enough current for VC or too low of a voltage? What is the voltage on VC with the lower zener diode? I reviewed other buck designs, and if there is a circuit like this, the zener is 11V-12V. 

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

こんにちはマイケルさん

ご支援いただきありがとうございます。

> VCに大電流が流れると、設計が損傷しますか？ 

->はい、実際に壊れています。Q1が過負荷になったので壊れたと思います。

>それは異なるBJTの異なるベータである可能性がありますか？

->申し訳ありませんが、意味がわかりません ので、改めてご説明ください。

>下部ツェナーダイオードを使用したVCの電圧はいくつですか？

->ツェナー電圧が9.4vの場合、Vc電圧は7.5vです。

ツェナー電圧が9.8vの場合、Vc電圧は7.9vです。

この現象の発生率は4％です。

Please tell me if you have any concerns.

Regards.

Hello Michael san

>does the design damage if there is a large current on VC?

->Yes, actually broken. I think  overloads Q1.

>Could that be different Betas for different BJT's?

->Sorry I can't understand meaning. Please explain again.

 >What is the voltage on VC with the lower zener diode?

->When the zener voltage is 9.4v, the Vc voltage is 7.5v.

When the zener voltage is 9.8v, the Vc voltage is 7.9v.

This is a 4% incidence.

Please tell me if you have any concerns.

Regards.

Hello,

Okay thank you for the information. 

Do you notice if the issue follows the BJT, if you try moving a BJT to a different board?

Hello Michael san

Already tried.

Result, the phenomenon does not move.

Example:

When PWB=A & BJT(Q1)=A, Vc is 5mA

When PWB=B & BJT(Q1)=B, Vc is 40mA

PWB=A & BJT(Q1)=B -> Vc is 5mA

PWB=B & BJT(Q1)=A -> Vc is 40mA

Hello, 

Thank you for confirming, must not be the BJT then. I will check with the original designer on this phenomenon. For now, will the 10V diode work?

I think an issue with lower voltage diode could be that VC voltage is not above 9V UVLO rising threshold. 

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

I can not arrange 10.0V but I can 10.2V, so I try 10.2V but do not work.  In this time, the Vc voltage is 8.3v.

Is the IC the cause of this phenomenon?

Regards.

Hello,

Oh okay understood. No I do not think it is the IC, but there is a minimum VC threshold we must meet at ~9V. 

I talked with circuit designer and these are his suggestions for debug:

1. suggest customer remove the circuit  and use a external power supply bias VC inserted a diode between VC and external power supply. If converter can power up normally and runs well, we can narrow down the issue to this “LDO” circuit. If not, there is other issue exist.
2. Decreasing the R1 to 10k-40k seeing what happens.

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Thank you for your supports.

I try the suggested debug 1 & 2 this weekend. Please wait a few days. And I will report results.

Regards.

Hello, 

Thank you, let us know the results. 

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

I tried 1 & 2 debug. 

Please refer to attached excel file(Sheet1).

Regards.

Summar of Issue _03-Sep-2021.xlsx

Hello, 

Thank you for the reply. I am OOO today, but I can review these materials on 9/7. Thank you!

Hello, 

So i see we tried the experiment with an external supply, and that did not change the VCC current. However, are we observing any damage with this circuit?

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

I check this PWB circuit. Please wait a few days.

Regards.

Hello, 

Thank you, let us know if device is damaging. 

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Sorry too late my reply.

I checked circuit, but there was no damage.

And I tried, please refer to Sheet2 of attached file.

What do you think of this phenomenon?

And I would like to know following, please let me know.

-Maximum current rating of Vc.

Regards.

Summar of Issue _13-Sep-2021.xlsx

Hello Michael san

I made a mistake in the description.

I replaced U1(IC), not Q1.

Attach the modified file.

Summar of Issue _13-Sep-2021-2.xlsx

Regards.

Hello, 

I do find that very interesting that the different IC's have different currents. I wonder if we need to submit a request for quality control? I will contact that team and get their opinion. 

However, if the design is not damaging, but works with 12V zener, do we still want to pursue issue?

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Thank you for your supports.

I would like to hear from the quality team, but is it costly?

I think the Vc current of 46mA (for example No.22) is a large current.

From the results, I think this phenomenon is caused by the IC(U1).

The first thing I want to solve is to know the tolerance of Vc current(Maximum rating).

(How about specifications?)

 Is the Vc current 20mA OK?

 Is the Vc current 30mA OK?

 Is the Vc current 46mA OK?

Next,

If 46mA(example) is abnormal, I want to know if the IC is damaged.

If normal, I will consider changing Q1.

Regards.

Hello, 

So i do not think that the IC is damaged and probably will not be. But we expect that the BJT is damaging from thermal/high current. 

I talked with quality and they will not look at the issue since there is no damage to our part. I will check with another power expert for his opinion on this matter. 

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Thank you for your big supports.

I will wait your(another power expert) comments.

Regards.

hello, 

i am in discussion, and we wanted to know, does the IC experience any heating if there is a large VC current?

Additionally, is VC connected to anything else? Is it driving any optocuplers?

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

Thank you for your supports.

>does the IC experience any heating if there is a large VC current?

->Yes, the higher the current, the higher the heat of the IC.

>is VC connected to anything else?

->No, It is as the circuit diagram I sent before.

Regards.

Hello, 

Okay thank you very much. And another question, does VC stay regulated? when the IC is hot, is the VC voltage stable?

Hello Michael san

Thank you for your supports.

>when the IC is hot, is the VC voltage stable?

->Yes, voltage is stable.

Regards.

Thank you for your answer, let me circle back with the team. Thank you

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hello Michael san

 I would like to know the tolerance of Vc current(Maximum rating).

Because redesign the Q1 or D1 and other device.

Regards.

Hello Michael san

Thank you for your strong supports.

I understand and will tell the factory this information.

Regards