Electronics > Projects, Designs, and Technical Stuff
Programmable Electronic Load, 0-5A
MasterT:
L2 1m - never put inductor in the grounding path.
JeanLeMotan:
--- Quote from: MasterT on February 25, 2019, 04:52:54 am ---L2 1m - never put inductor in the grounding path.
--- End quote ---
I copied this from an Adafruit breakout board, I imagined it helps with filtering but maybe I copied it wrong.
Not that you mention it it does ring a bell and I've heard/read a lot this phrase "low-inductance path to ground" - so adding an inductance in the ground path seems like the wrong thing to do. But why?
In the VCC path it's ok because if blocks high frequency noise from reaching the circuit, but in the ground path it would prevent high frequency noise from ... exiting the circuit?
MasterT:
Any inductance or resistance in the ground path prevents interferencing AC/ RF noise to leave an IC/ crystal of Si. And this AC/ RF disturbance is gonna to intermodulate in-between with: DC signal at input pins, DC power supply, one couple/ pair of inputs to another and digital bus to analog inputs. I see you put a cap across Vdd and Vss, but there are many ways for interference to find a path inside ADC, including but not limited to capacitive coupling or direct RF injection, and data bus is certainly the most obvious.
JeanLeMotan:
--- Quote from: MasterT on February 26, 2019, 07:46:15 pm ---Any inductance or resistance in the ground path prevents interferencing AC/ RF noise to leave an IC/ crystal of Si. And this AC/ RF disturbance is gonna to intermodulate in-between with: DC signal at input pins, DC power supply, one couple/ pair of inputs to another and digital bus to analog inputs. I see you put a cap across Vdd and Vss, but there are many ways for interference to find a path inside ADC, including but not limited to capacitive coupling or direct RF injection, and data bus is certainly the most obvious.
--- End quote ---
That makes perfect sense. Thanks a lot!
I removed the ground inductor from the schematic and pcb.
aiq25:
--- Quote from: JeanLeMotan on February 26, 2019, 05:58:33 pm ---I copied this from an Adafruit breakout board, I imagined it helps with filtering but maybe I copied it wrong.
Not that you mention it it does ring a bell and I've heard/read a lot this phrase "low-inductance path to ground" - so adding an inductance in the ground path seems like the wrong thing to do. But why?
In the VCC path it's ok because if blocks high frequency noise from reaching the circuit, but in the ground path it would prevent high frequency noise from ... exiting the circuit?
--- End quote ---
It's interesting Adafruit added it but the supply for the IC does not have it since it's directly connected to VDD and GND, not to the "filtered" pins (i.e. after the inductor). Also not sure if 1uF is needed for your circuit, depends on what the power supply rail looks like though and your layout but I would assume you would be fine with 1uF. I have always put 0.1uF for all IC's and add then in parallel with 1uF when needed. I'm curious, what does your power supply circuit look like? I might have missed it but I don't the schematic for it.
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