Output currentlimiting using External current control pin in TOP256YN

Hi...
I am trying to design a smps with maximum rating of 12V 3A rating using TOP256YN. Also, I want to add current limit feature using a resistor so that I could select resistor values depending on my current limit threshold (Output current limit can be 250mA to maximum 3A).

There is an external current control pin in TOP256YN, which will control primary current (mos-fet drain current).

What I have done, I used resistors with random values and monitored the secondary output, at what load (Wattage) the top-switch triggering it's overload protection. During this process different resistors values provided different results. I can control output current using this resistor.

My question is, Is it ok to use resistors at the external current control pin to limit the output current?

If yes then how to calculate this resistor value depending on my desired output current? In the datasheet it is saying that using this I can use the device from 30% to 100% current limiting factor, (The maximum current allowed is 2.76A at primary side) How can I calculate primary current depending on my output current? So that I could calculate my resistor value?


If no, then what is the best way to follow?

Please Help.

Thanks A lot.

Primary side current limit will limit only peak current. For accurate limiting of output side, use a current shunt at the output and use a comparator to drive an opto-coupler for remote on/off. Refer to the figure 37 and 39 of the data sheet.

Hi...

In the figure 37 an 39 it is showing the 'M' pin, but I don't have M pin in TOP256YN.

Refer to figure 24, there is a external current limit (X) pin, which can do the job.

papaisou11 said:

Hi...

In the figure 37 an 39 it is showing the 'M' pin, but I don't have M pin in TOP256YN.

Click to expand...

pin M and V have same function

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sac1991 said:

Refer to figure 24, there is a external current limit (X) pin, which can do the job.

Click to expand...

it is not for current limit, use to remotely on and off the regulator