LM3478: Webench simulation

Hi Tom,

Thank you for reaching out. You have a tiny output power of 80mW. You mentioned that Vout decreases as load increases. What is the Vout when Iout=1mA and 2mA?

Also, some waveforms would be very helpful.

Best Regards,

Feng Ji

Hello Feng

Thank you for your cooperation.
I am a colleague of the questioner.
I contact you on behalf of the inquirer.

1. We sent the simulation results to Mr. TOM.
　Currently, "design cannot be created" is shown on the PC display.
　Is this result appropriate?
　If appropriate, what is the cause of the inability to simulate?
　And what can we do to achieve the desired results?
　

2. The schematic we sent to TOM is the result of our simulation last week. (Today it is "design cannot be created")
　Is this schematic appropriate?
　In this circuit, the output voltage drops when the output current is increased.
　What is the cause of this?
　Please let me take the solution.


3. Iout and Vout results are shown below.

Iout=0.58mA：Vout=40.17V
Iout=1.47mA：Vout=40.16V
Iout=1.79mA：Vout=36.40V
Iout=2.14mA：Vout=35.10V


4. What part is the waveform you need?

Best Regards,
KAMIMURA Yasuhiro

Hi KAMIMURA,

1. Are you using webench power designer?
2. I have not seen the schematic. One possible reason is the peak current limit that caused output voltage drop?
3. The Vout changed a lot.
4. Vgs and Vds waveforms of the MOSFET are most helpful.

Best Regards,

Feng Ji

Hi Feng,

The attached is the result of simulation at WEBENCH.
The output power is 5.5 W and is much larger than 80 mW.
5V and 2A circuit diagrams are also shown on the first page of the data sheet.

Is our condition (parameter) outside the simulation guarantee range?
Then, please teach how the circuit design should be carried out.

Beat Regards,
Tom Liu

Hi Tom,

I am confused. I could not see any file attached.

What is you output power? 5.5W or 80mW?

Best Regards,

Feng Ji

Hi Feng

Sorry, I forgot the attached.

The output power of the attached if 5.5W.

Beat Regards,
Tom Liu

Hi Tom,

From your first post:

The design parameters are as follows.
Vin = 5V
Vout = 40V
Iout = 0 ~ 2mA
Fs = 500 ~ 600kHz (changeable)

From your last post:

Vin = 5-6V
Vout = 5V
Iout = 1A

I suppose these are two different applications. Which is the application you want to discuss in this thread?

Best Regards,

Feng Ji

Hi Feng,

I think we encountered some problems in our communication.

Please allow me ask again.

The design parameters are as follows.
Vin = 5V
Vout = 40V
Iout = 0 ~ 2mA
Fs = 500 ~ 600kHz (changeable)

The result of the simulation shows "design cannot be created" by changing the parameters a little.
Also, when the circuit is actually manufactured and evaluated, Vout = 40V when Iout = 0mA (load circuit open), but Vout decreases as the load current increases.

This is out original question.

And then you said "You have a tiny output power of 80mW" in your reply.

I misunderstood than the simulation has a 80mW output power limit so it is shown "design cannot be created".

However I just confirmed your response again and I found you didn't mean that.

Therefore could you clear the following confusion first？

Why WEBENCH shows "design cannot be created"?

Beat Regards,
Tom Liu

Hi Tom,

You should always ask one question in one thread.

I just tried with the following conditions in WEBENCH, as it shows some designs.Can you try again?

Vin = 5V
Vout = 40V
Iout = 0 ~ 2mA

Best Regards,

Feng Ji

Hi Feng,

We use LM3478(boost) to simulate and the screenshot is as below:

Beat Regards,
Tom Liu

Hi Tom,

Thank you for using E2E forums, we will look into this issue and get back to you as soon as possible. Please allow us some time so that we can look into this.

BR,

Haroon

Hi Haroon,

I'm sorry to bother you.

Is there any update for this case?

Beat Regards,
Tom Liu

Hi Tom,

It would take some time to know why there is a error.

For now, you can use webench LM3478 with the following condition:

Vin = 5V
Vout = 40V
Iout = 5mA

Best Regards,

Feng Ji

Hi Feng,

I am sorry to bother you again.

Since my customer is waiting for response of this problem, it will be very helpful if I can know your estimate schedule.

Beat Regards,
Tom Liu

Hi Tom Liu,

We are looking into this query with high priority. We will get back to you soon.

Thanks & Regards,
Praveen

Hi Shaheen,

Sorry for my late response.

Could you inform us after the next WEBENCH release?

Thank you!

Hi Shaheen,

I tried and still have the error as below:

Beat Regards,
Tom Liu