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Х pin on TOP268KG breaks through

Posted by: Konstantin on

Hey.

We use the TOP268KG controller when developing a 5V 6A power supply. We are trying to limit the output current through pin X. When you try to change the resistor at pin X, the pin breaks through and rings to ground. What could cause this to happen? Afraid of the temperature or static current output?

评论

Submitted by PI-Sugomi on 12/21/2021

Hello Konstantin,

If I understand it correctly, you mean you are afraid that you might have damaged the X-pin while soldering? If that's the case it is unlikely that you can damage it by just the heat of your soldering iron with typical temperatures of 700F. But when soldering, it is advisable to remove any probes connected to your board and make sure that your soldering iron is properly grounded as this may induce stray voltages that may damage your device.

Is your power supply working before you try and replace the Xpin resistor? what value did you use before and after?

best regards,

Sugomi

Submitted by Konstantin on 12/21/2021

Hi Sugomi

We first soldered a 13.5K resistor, but that wasn't enough.

Then they soldered 27kOhm, but did not receive a response from the microcircuit.

Testing has shown that pin X is out of order.

The power supply is still working, but there is no current limitation.

All pins of the microcircuit were in good condition before soldering.

Submitted by PI-Sugomi on 12/22/2021

Hi Konstantin,

Changing the Xpin resistor is intended to change the primary drain to source peak current and not the output currents directly. Your output current will still be influenced by your input voltage (high or low line) and what switching frequency you are operating in.

Have you tried probing your TOP268KG's drain-to-source current? If you can probe your drain to source current before and after changing the Xpin resistor, you should be able to see the difference in peak currents.

Submitted by Konstantin on 12/22/2021

I realized that the drain current is limited by this resistor, as shown in Figure 37 in the datasheet. There is also a dependency Isec = K * Ipri. As I understand it, by limiting the peak drain current, we also limit the output current.

The F pin is set to a frequency of 132 kHz. According to the datasheet, the frequency can vary within 119-145 kHz.

I also think that I should choose a less powerful microcircuit.

Submitted by PI-Sugomi on 12/23/2021

Hello Konstantin,

 

That's correct. If you want a power limiting function that adjusts against line variation you can also try the configuration shown in Figure 19. And if you see that you still deliver high powers with a significant reduction in current limit then you can try using the next lower size of TOPSwitch.