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One more schematic clarification

electronicsLearner77

Jul 2, 2015
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Sorry that I have to post multiple threads on schematic clarifications. Now I am finding the schematic with 0 ohm resistor. What does that mean? Will it have any impact on the functionality? Was placed for some other purpose?
 

Martaine2005

May 12, 2015
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Many reasons for 0Ω resistors. Sometimes it’s just cheaper than a wire link.
Other times it might just be a weak link to protect the circuit up stream.


Martin


Martin
 

davenn

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Sometimes it’s just cheaper than a wire link.
used because it was cheaper than going to a multilayer circuit board.

cheaper isnt the reason
the body of the resistor, of whatever value is easier for a computer controlled component placement machine
picking up something with a body rather than a thin wire
 

Harald Kapp

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0 Ω resistors are commonly used when you have a connection that may be required sometimes, but not always. For example when you have one pcb with multiple assembly options. You can then use the 0 Ω resistor like a jumper or switch e.g. to turn on or off parts of the circuit. The advantage of using 0 Ω resistors is that these can be automatically placed by a machine.
Other option to achieve the same result are e.g. solder jumpers. A thin trace connects two 1/2 pads. When the connection is not required, the thin trace is cut open. Should the connection be required agina fter cutting, a solder blod can cross the gap. This includes manual labor and is prone to errors (e.g. track not completekly cut open). This method is therefore less preferable on an industrial scale - but works well for very small volume production or hobbyists.
 

PETERDECO

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That's one of the reasons we use them. We have a recordable sound effects circuit that has 2 possible modes, latch (push button on, push again off) and momentary (push button on, release off) by cutting off the 0Ω resistor.
 

Harald Kapp

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I don't understand this as well, what part is this, it looks like kind of switch.
It is possibly not a "component". This may be a placeholder for a layout symbol that allows placement of a resistor (R786) in either of 2 positions: 1-2 or 3-2. A 0 Ω resistor (aka jumper) would be used to supply either from +3V3 or from P3_3V to "pin" 2.

One could have used two resistor symbols and mark one of them as "not assembled". If for some reason the designer wanted to have the two locations in a defined arrangement on the pcb, he would have had
to add a layout directive so the layouter knows what to do. By using a dedicated symbol in the schematic (with a corresponding pattern in the layout) this can be avoided and correct placement is ensured.
 

electronicsLearner77

Jul 2, 2015
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Another clarification
upload_2022-7-28_8-31-10.png

The VDDIO, LDO3_3V3 are the pins of the VR5510 power management ic, https://www.nxp.com/docs/en/data-sheet/VR5510.pdf
My question is, I know that LDO3_3V3 is the power output from the VR5510 ic and VDDIO is the input power for the digital interfaces from the datasheet. But the picture gives a different impression that LDO3_3V3 is derived from VDDIO, what am I missing here? Is it a mistake in the representation of the picture?
 

Harald Kapp

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But the picture gives a different impression that LDO3_3V3 is derived from VDDIO,
Why does it give you that impression?
Consider the way the resistor (0 Ω) can be placed either in pos. 1-2 or 2-3. That makes VDDIO coming from either LDO3_3V3 or from VPRE_3V3.
 
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