AD8170 not working as expected on a SMD layout?

[pavjayt]

I have a circuit that uses AD8170 to switch between two signals when the select signal is either 0 or 5V. The output when the select is 0V is fine, but I can't see the output that I am feeding into IN1 when the select signal is 5V.

I checked on a scope at IN0 and IN1 and select pins and they are fine, but none at the output when select is 5V, but output is fine when select is 0V which is equivalent to IN0.

The exact same circuit works fine using normal DIP and through hole components.

Any ideas/suggestions?

thanks

 

[kubeek]

Maybe bad soldering? What is feeding the select pin? What is that thing on the bottom connected to pins 2 and 3 of the ad8170?

 

[pavjayt]

Maybe bad soldering? What is feeding the select pin? What is that thing on the bottom connected to pins 2 and 3 of the ad8170?

Not sure what you are pointing under pin2&3. Pin 2 is connected to GND and Pin 3 is connected to -5V and the components to their left are capacitors.

Pin1(select) is fed by a square wave of 0-5V.

 

[kubeek]

I meant that there is some hidden component under C77, but now that I look at it it probably is another decoupling cap.
Why don´t you show the whole schematic and board? Lots of people here use eagle. Showing the ground plane on the pcb wouldn´t hurt too.

So, can you check that the input singal is really going into those input pins as well as the control pin?

 

[pavjayt]

I meant that there is some hidden component under C77, but now that I look at it it probably is another decoupling cap.
Why don´t you show the whole schematic and board? Lots of people here use eagle. Showing the ground plane on the pcb wouldn´t hurt too.

So, can you check that the input singal is really going into those input pins as well as the control pin?

Well, I checked all the pins on the IC and everything is fine except the output.

The one I am talking about is the AD8170 that's on the top of the board.

 

[kubeek]

I don´t see why it should not work. Have you checked the noise etc. on the supply rails? Did you chcek the IC signal right at the point where the pin leaves the package? Is only one IC acting up or all four of them?

 

[pavjayt]

---Removed as I started another thread on this different topic---

 

[pavjayt]

LM556 tuning

-Message removed for the same reason above-