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confusion about the current limit resistor on pinx of top261

Posted by: aneeshn.etrx on

Hi,
As per the design in PIexpert software the resistor on pin x is R8 current limit. the design has potentiometer where is the third pin connected. two pins are shown third is not connected.plz advise

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Submitted by PI-Quark on 02/23/2021

Hi aneeshn.etrx,

Thank you for your interest in PI Expert Online.
The resistor connected in Pin X (R8) is actually a FIXED RESISTOR, not a potentiometer. The arrow just signifies that the reference designator and its associated resistor value is pointing to that particular resistor component symbol, since the reference designator is quite distant to the symbol it represents.

I hope this makes things clear to you. Let me know if you have any concerns and clarifications regarding this.

Submitted by aneeshn.etrx on 02/25/2021

Hi,
thanks for your reply, why the R8 resistor is not connected to the source or why the gate is not connected to source . The design works only if i connect the gate,x pin to source orelse the ic blows off

Submitted by PI-Quark on 02/25/2021

Hi aneeshn.etrx,

The G pin is not the "gate" - instead it's the signal ground. In order to improve noise-immunity on large TOPSwitch-HX Y package parts, the F pin has been removed (TOP259-261YN are fixed at 66 kHz switching frequency) and replaced with a SIGNAL GROUND (G) pin. This pin acts as a low noise path for the C pin capacitor and the X pin resistor. It is only required for the TOP259-261YN package parts.

Submitted by aneeshn.etrx on 02/26/2021

Hi,
I have tried the attached circuit exactly but the output is only 200mV. I am not confident to apply ac voltage so i applied a dc 125v it doesnt work . whats the issue ?as i said works only if source connected to g pin. i.e if all source ,pin G, pin x resistor are connected to capcitor gnd only then we get output. The Pi expert generated sch has cap gnd and G pin unconnected

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Submitted by aneeshn.etrx on 03/01/2021

when my question is in english why the answer is in russian..

Submitted by PI-Quark on 03/01/2021

Hi aneeshn.etrx,

I sincerely apologize on the messages earlier as they were spam messages. We deleted it already.
With regards to your concern, TOP261YN supposedly have the signal ground (G) pin to be NOT CONNECTED to the source (S) pin, as shown in the schematic in PI Expert. This is also evident on TopSwitch-HX application note (AN43, Page 20) and TopSwitch-HX family datasheet (Page 2).
We are currently investigating your problem and I will get back to you as soon as we find a possible resolution to your design issue.

Submitted by aneeshn.etrx on 03/02/2021

Hi,

yes the datasheet says signal ground (G) pin to be NOT CONNECTED to the source (S) pin but it does not work all materials are connected as per design only difference is that instead of LTV817 i am using pc817 and VR1 i have removed as it gets hot and short circuited but rest all gives me proper 24V dc output and 6 amp current on both ac and dc after 6A it cuts off the supply as short circuit.. Perfect as per req (not tested full load on 230v, tested on 130v dc as safety).. My design is ready and awaiting production let me know what should i do ???

Submitted by aneeshn.etrx on 03/02/2021

reminder

Submitted by PI-Kenobi on 03/02/2021

Hi aneeshn.etrx,
Please send an email to piexpert@power.com with your problem so that a local FAE in your area can provide you timely support.
Thanks.