# What is the purpose of inserting resistors (diodes?) directly on the path of the VCC and GND lines powering a PCB?

I am trying to learn electronics by looking at simple circuits and see how engineers get the job done.

Looking at a PCB featuring only one Texas Instruments ADS1115 ADC, I see that:

1. They bridge VCC and GND with a capacitor as close as possible to the power lines arriving at the PCB. I guess it's 100µF (shown in the picture).
2. They do the same on the VCC and GND as close as possible to the chip (not shown in the picture).
3. They have pull-up 10K resistors on the SDA, SCL and ADDRESS lines. I guess it's because they wish those to be high when not driven (not shown in the picture).

However, I do not understand why they have two parts (black 0805) inserted in the VCC and GND lines arriving on the board (shown at the top of the picture). Are these resistors ? What would their purpose be ? The board can be powered from 1.8 to 5 V.

Maybe they are only diodes? In that case, the polarity should be marked. And there would be a voltage drop across.

I am also puzzled, because these parts are across the VCC as well as the GND. In my mind, there is never any part splitting the GND line.

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These are MMZ2012Y152B ferrite filters and your 3rd guess about I2C pullups is correct.

The schema including components names is on the manufacturer Github.

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your 3rd guess is correct Is that referring to what the OP said about SDA, SCL lines? –  alexan_e Jan 4 at 14:50
Yes, a great link about it is : Effects of Varying I2C Pull-Up Resistors. –  user35082 Jan 4 at 14:52
The thing is that pulling these lines high isn't really a matter of the designers wish but rather a requirement for I2C lines. Your link was mis-formated but I'm sure you meant this one –  alexan_e Jan 4 at 14:59
Thank you for your reply. That's it, indeed. Here is the link we all try to post : dsscircuits.com/index.php/articles/… –  PeterG Feb 22 at 21:03

I think they may be inductors - a series inductor and a parallel capacitor across the target chip's power and ground line offer greater power supply rejection (in a lot of cases) compared to just a capacitor and no series component. Care has to be taken though; the series L and parallel capacitor can form a resonant tuned circuit and exaggerate certain frequencies of noise coming from the digital supplies.

Given that this is an TI chip, there may be a kit you can buy from them that uses this part - try looking up the details of the kit to see if you can track down whether these parts are inductors or not.

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