Question regarding Auto-Restart conditions of LNK3202

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Dear Sirs or Madams,

Please let me have one question regarding the Auto-Restart conditoins of LNK3202.
The question is as follows;
When the input voltage on D pin of LNK3202 behaves as follows, does Auto-Restart, which accompanies off-time, occur on LNK3202?
1) The voltage starts descending very slowly(please see below NOTE) from beyond 50V, which is the minimum operational voltage shown on the datasheet.
-> 2) The voltage decreases to below 50V but is still much higher than 0V, e.g. it reaches to 30V or so.
-> 3) The voltage starts rising and finally exceeds 50V.
NOTE : Here, "slowly" means that it takes more than some seconds for the input voltage on D pin to descend from beyond 50V to below 50V(30V or so).

Through the above question, I want to know whether there is some waiting time before LNK3202 starts switching after above 1)-3) have occurred.

Best regards,

Hi,

Do you have waveforms of this phenomenon which I could refer to?

From the datasheet, the auto-restart occurs for fault conditions including output short, open-loop and output overload. In the scenario where the line voltage falls from 50V to 30V (I'm assuming Vrms,AC), depending on the time of the line transient, the value of the bulk capacitor, and lastly the output loading condition, AR may occur if the the power requested exceeds what the input can provide.

I hope this helps.

Regards,

Dear PI-Kobe san,

I appreciate your response.
I add my comments to your comments and request below.

>Do you have waveforms of this phenomenon which I could refer to?
Please see the attached document.
On this document, some explanations on the waveform and also
the reason why I asked this question are shown.

>In the scenario where the line voltage falls from 50V to 30V (I'm assuming Vrms,AC),
The power inputted to LNK3204D D pin(yellow line) is DC, which is generated
by rectifying the input AC power and boosting it after the rectification.
And, please understand that the above mentioned "30V" is just an example and
the voltage shown on the attached document is not necessarily same with "30V".

As mentioned on the attached document,
I want to know whether the delay, which is observed on the waveform, is caused by
Auto-Restart of LNK3204D or not.
So, I'm pleased if you let me know your thoughts on this point.

Best regards,
Shinsuke Tanaka

TitleSize
Waveform.png457.41 KB

Hi,

I've taken a look at the waveforms you sent me. Based on what you've elaborated, please tell me if you agree with these observations:

1. the power supply is in AR mode for the first part of the waveform (which can be observed) because of the line transient at the AC side (50V to lower).
2. The delay could be one of two things, (1.) is that the re-start happens during the t-ar,off = 1.5 second period where the IC is still sampling whether there is a fault condition, hence a delay, or (2.) the input voltage may not be enough to power the board, hence, a delay, due to the charging of the bulk capacitor before it is able to meet regulated output voltage at the required loading condition.

I hope this helps.

Regards,

Dear PI-Kobe san,

I appreciate your rapid response.

>please tell me if you agree with these observations:
Before respond to your request, please let me confirm the details of your opinions
"1. the power supply is..." and "2-(1.)".
For details, please see the attached document.
Are my understandings on your opinions "1. the power supply is..." and "2-(1.)" correct?
If they are correct, I agree with these opinions.

>(2.) the input voltage may not be enough to power the board, hence, a delay,
>due to the charging of the bulk capacitor before it is able to meet regulated output voltage
>at the required loading condition.
But on the other hand, regarding your opinion "2-(2.)" I think it is less likely that
the AC power inputted to our board is insufficient.
The reason is that at normal powering up of the AC power, which means
AC power is inputted under the condition that
the power inputted to LNK3204D D pin(yellow line) is totally fixed to 0V,
such delay is not observed at all.

Best regards,
Shinsuke Tanaka

Hi,

If you used the cursor and measured the time from last retry sequence to the actual start-up time and found it to be 1.5 seconds, then I guess that explains the delay. The IC detected a fault and waited for the tAR,off = 1.5s to finish before retrying and eventually be able to start-up.

Regards,

Dear PI-Kobe san,

I appreciate your rapid response.

>If you used the cursor and measured the time from last retry sequence to
>the actual start-up time and found it to be 1.5 seconds, then I guess that explains the delay.
I understand that my understandings on your opinions regarding whether
LNK3204D Auto-Retry occurs are correct.
So, I think I can conclude that the delay is caused by LNK3204D Auto-Retry.

And, I'm sorry to bother you repeatedly, but would you please let me have
one simple question?
Q.
I understand that LNK3204D detects fault conditions and executes Auto-Retry.
And, regarding the types of fault conditions which cause Auto-Retry,
LNK3204D datasheet "Description" chapter mentions as follows;
input and output overvoltage faults,
device over-temperature faults,
lost regulation,
and power supply output overload
or short-circuit faults
Which fault is detected by LNK3204D on this case?
I guess that only "lost regulation" can apply to this case,
but "lost regulation" is ambiguous and it is difficult for me to understand
what the "lost regulation" actually means.

Hopefully, this would be the final question on this topic.

Best regards,
Shinsuke Tanaka

Hi,

To help you, here are some of the common causes for AR(may be found in the LNK-TN2 datasheet):
1. If current in BP pin exceeds I_bpsd for 2 to 3 cycles (can be used for OVP with additional circuitry)
2. If FB pin is not pulled high (if power supply does not reach regulation after 50ms)
3. Output short circuit fault
4. Open-loop condition (FB pin may be shorted to GND, hence an open-loop condition)
5. if the load current/output power exceeds the maximum recommended output power for the device (output overload condition)

I hope this helps in your debugging.

Regards,

Dear PI-Kobe san,

I appreciate your explanation.

>2. If FB pin is not pulled high (if power supply does not reach regulation after 50ms)
Among the fault conditions you showed, I conclude that the above 2. applies to this case.
We use LNK3204D on "High-Side Buck – Optocoupler Feedback" mode on our board.
And, I conclude as follows;
When the voltage on LNK3204D D pin descends, the voltage finally becomes lower than
the zener voltage of the zener diode implemented on output side of LNK3204D.
As a result, the Optocoupler stops lighting and FB pin is never pulled up.
And, after 50ms, LNK3204D detects fault condition.
Actually, on our waveform, the 5V power(green line) keeps 5V for 50ms and then becomes 0V
repeatedly, so from this point above conclusion is inconsistent with our waveform.

I think my question has been resolved, so this topic should be closed.

I appreciate your rapid responses and detailed explanations so much.

Best regards,
Shinsuke Tanaka

Hi,

You're welcome!. If you have any more inquiries, I'm sure you could find something in the datasheet that could help you later on.

Regards,

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