Hello,
I want to use that IC for smoke dedector art number: RE46C180S16F
I've seen guard pins on IC, but Ionization chamber has 3 pins.
Could you explain function of "guard" pins and how can I connect?

 

It's a Screen guard for the Ionisation chamber to prevent false triggering.


Datasheet link...
http://ww1.microchip.com/downloads/...Vaw26eXMQOaVfU_8O9wIWDGHx&cshid=1560780855732

 

Notice that the guard traces run on both sides of the Detect trace, and connect nowhere else.This kind of arrangement protect the high impedance Detect input from leakage currents from other parts of the circuit board.

 

It's a Screen guard for the Ionisation chamber to prevent false triggering.


Datasheet link...
http://ww1.microchip.com/downloads/...Vaw26eXMQOaVfU_8O9wIWDGHx&cshid=1560780855732

Hello,
I could not download the datasheet.
I've found a datasheet, It says "An active guard is provided on both pins adjacent to the detect input. The voltage at these pins will be within 100 mV of the input signal."
I understand function but I don't understand connection.
Where sould I connect these pins?

 

These Guard pins are on the Pcb, to prevent false triggering, you don't need to connect them to anything, they just appear as tracks on the circuit board to the Smoke Chamber.


Datasheet link.

https://www.google.com/url?sa=t&sou...Vaw3K3eaui9Gs-C_A4Qdu2B3Q&cshid=1560782126075

 

Thanks for reply,
I've opened the smoke dedector box and looked at pcb:
Pin number 16 and 14 are connected and pcb trace creates a circle connection.
Isn't that what you're talking about?

 

Yes that is a Test Point,,.

 

Guard pins and traces on a circuit board are to prevent surface leakage currents from causing problems. The intention is that they are held at the same voltage as the line that they are guarding, so that no current will flow to the protected trace. The problem is that the surface of the PC board becomes slightly conductive due to contamination from stuff in the air, and dust. And in this case the circuit being guarded can be influenced by nearby voltages if those guard traces are not used.