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LNK3202 maximum power in MDCM/CCM mode

Posted by: Nomien on

Dear PI
In the datasheet of the LNK3202D we see that for MDCM mode the maximum output current is 63mA. This is what is specified in the application note as 0.5x Ilimit,min = 0.5x 126mA
But for the maximum output current in CCM mode I would expect like mentioned in the application note 0.8x Ilimit,min = 100.8mA. But the datasheet mentions 80mA?
Can this be explained?

Comments

Submitted by PI-Chloe on 05/13/2020

Hi KarelVanHaver,

Thanks for having your time to inquire and look to Power Integration products.
The 80% Ilimit min of the application notes is based on the whole series.

The 80mA output current specification is the maximum current that can be loaded from 85Vac to 265Vac.

Operating at 100mA at 85Vac could result to Output Overload (Auto Restart).

As per datasheet page 5:
"To provide overload protection if no cycles are skipped during a 50 ms period, LinkSwitch-TN2 will enter auto-restart, limiting the average output power to approximately 3% of the maximum overload power."

At 85Vac and above 80mA, the energy stored at the inductor is low due to the input voltage. The IC will continuously pulse to regulate the output. This will cause the output to shutdown as stated in the above clause in the datasheet.

I hope this can help you.

Thanks

Regards

PI-CHLOE

Submitted by Nomien on 05/14/2020

Can we calculate somehow for a minium input voltage of 207VAC instead of 80VAC what the increase is towards the 80mA? Because this 80mA maybe also is based on the minimum inductance required for this device?

Can I learn something from the di/dt calculation?

Submitted by Nomien on 05/14/2020

In my application I only have a short peak current during 50ms of around max 100mA which happens with a very low duty cycle. I measured the FB pin and still see enough blanking time during this 50ms interval on the FB pin. So correct I can conclude there is no problem because auto-restart will only be triggered when I would have no blanking intervals during this 50ms pulse? See picture

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Submitted by PI-Chloe on 05/17/2020

Hi Nomien

For 207vac, there will be no issue in operating at 100mA since the Ilimit for high line increases (as per datasheet). Higher input voltage and higher Ilimt will not require the controller to continuously pulse for 50msec.

If your 100mA loading is less than 50msec, risk of Auto restart will not be seen.
For the waveform, Please advise what is CH1 and CH2.

Thanks

Regards

PI-Chloe

Submitted by Nomien on 05/18/2020

Thanks PI-Chloe
CH1 is measured on the FB pin of the LNK3202 towards system GND, so not towards SOURCE which is GND reference of FP. I also could have measured SOURCE pin of course but FB pin was easier in my setup :-)

CH2 is just trigger signal to find the 50ms slot. The fact that it fluctuates can be ignored and is due to how i made it :-)

So, thanks again for the input