The basics: How to layout a PCB for an op amp

RE: The basics: How to layout a PCB for an op amp

Johny Kim — Sat, 21 Aug 2021 10:38:34 GMT

Noted on this - It is extremely important to place decoupling capacitors as close to the supply pins as possible. Having dry wall contractor long traces between the decoupling capacitor and the supply pin adds inductance on the supply pin, which can degrade performance. I wasn't aware of this info, thank you for sharing.

RE: The basics: How to layout a PCB for an op amp

Nightwish_flf — Tue, 28 Feb 2017 07:07:40 GMT

Hello Timothy Claycomb, thank you for your reply

RE: The basics: How to layout a PCB for an op amp

Tim Claycomb — Mon, 27 Feb 2017 16:33:45 GMT

Hello Nightwish_flf,

Thank you for your interest in my blog. I have provided answers to your questions below.

1. Yes, you can place the via on the pad of the C1, C2, R1 and R3. However, I have been told that in some cases when assembling the PCBs having a via on the pad of a component can cause issues. Therefore, I avoid any via on the pad of a component when possible.

2. The reason VCC gets routed under Vin is because in a real application the input to the amplifier (Vin) would likely come from a sensor or the output of another amplifier. In that case it would be very difficult or impossible to route VCC around Vin. Therefore, to show what might occur in a realistic application, I routed the power supply under Vin. Also, in an end product there is a good chance that a company would choose to use manufacture a 4 layer (or more) board in which case there would be a solid power plane for VCC and -VCC which would eliminate the trace routing under Vin.

Again thank you for your interest in my blog,

Tim Claycomb

RE: The basics: How to layout a PCB for an op amp

Nightwish_flf — Mon, 27 Feb 2017 08:48:30 GMT

I have some questions :

1. the via maybe need to be placed just under the pads of the components C1,C2,R1,R3, to reduce the loop inductance

2.is the VCC- routed in the top plane better? In the final layout, the power line is routed under the signal loop, each other coupling, maybe just route it around the VIN

Hope for your reply. Thank you!

RE: The basics: How to layout a PCB for an op amp

Soufiane Bendaoud — Fri, 18 Mar 2016 17:06:00 GMT

Great article Tim. Speaking of ground pins, here's some of the history behind it...

e2e.ti.com/.../where-did-the-ground-pin-go

RE: The basics: How to layout a PCB for an op amp

Tim Claycomb — Tue, 19 Jan 2016 14:35:23 GMT

Hello Georgy and Farrokh,

Thank you for your comments.

Georgy,

These are very good points you have mentioned. There are always things to consider when laying out a PCB.

Farrokh,

Are you referring to the ground connection to the via connecting to component C2? If so, the bottom ground plane connection is simply being covered up by the top ground plane. If I were to delete or hide the top ground plane, you would be able to see the connection to the via on the bottom ground plane.

Thank you again for the comments,

- Tim Claycomb

RE: The basics: How to layout a PCB for an op amp

Farrokh Eshragi Azar — Mon, 18 Jan 2016 18:00:35 GMT

Good stuff but the picture shown as "final" doesn't appear to be complete. It is given that the ground plane should be connected to the ground pin on the bottom side, but the picture does not show this.

RE: The basics: How to layout a PCB for an op amp

Georgy — Mon, 18 Jan 2016 09:05:34 GMT

I think no satisfaction.

1 negative sourse line will going around left via "Uin", so ground plane will not ruptured.

2 make traces VCC as wide as possible? There not are...

3 groundplane will not be placed ander Vin line, it decrease parasitic capacitance.

4 you will read Figure 65. Operational Amplifier Board Layout for Noninverting Configuration DATASHEET from.