4 ms·

I've been working with audio recently and found so many of the devices that convert 3.7V to 5V for example inject noise into the rail that make's it in the micr

by hcfman 2y ago

I've been working with audio recently and found so many of the devices that convert 3.7V to 5V for example inject noise into the rail that make's it in the microphone input source. The battery support from pisource does this terribly. But so do many battery sources. It's not just microphones that get affected, but also other sensitive sensors like accelerometers. I hope that other people making DC-DC convertors put some effort into making sure the supply is so clean so as to prevent this in future.

euroderf 2y ago
Isn't this like 95% fixable with a capacitor ? Aren't there cables with small embedded caps ?
- dragontamer 2y ago
  Oh hell no. I think a lot of people are overly cautious of DC-DC conversion in this topic, but you've gone full-tilt in the opposite direction and are severely underestimating the problems that occur. 1. Its not "power-conversion" that's hard per se, its EMC that's very hard and not taught very well at a bachelor's level. 2. DC-DC Voltage Converters usually handle the entirety of your board's power, meaning they are the highest power component. 3. High power and high-frequency is a difficult EMC problem. This means that a bad design will absolutely send your electrons / energy out and radiate out like an antenna. And if things on the same board pick it up, it will be called crosstalk. And if things off-board pick it up, its called electromagnetic interference which almost certainly leads to a compliance problem. --------------- 1. Hobbyists don't care about compliance. So bam. We are already dealing with the biggest problem by simply not caring about it. (Maybe you can care and go into deeper studies, but... if you're a beginner just don't care. Learn this very difficult stuff later). 2. Prevent crosstalk by following good board design rules: have a 4-layer board. Use Power+Signal / GND / GND / Power+Signal stackup. Use two vias (one for signal-1 to signal-4 traversals), and a 2nd via for GND2 to GND3 traversal of the return current). Thinking of both the forward current and a tightly bound reverse current is basically all you need to do to avoid difficult crosstalk problems on board. Done. Point#2 requires deeper studies than is typical in bachelor's level electrical engineering. But it truly isn't very difficult once you learn the theory. Tight ground-planes reduce crosstalk (and EMI problems), and furthermore thinking of the return-current explicitly prevents problems. Now you could have some truly difficult "ringing" from trace inductance and other such nasty problems... but that tends to occur beyond 100MHz. I'm thinking most beginners are going to be under 20MHz for most of their designs and thus never deal with those advanced "PDN" / Power Delivery Network problems. Though if you do go into PDNs, its obviously a tough subject with huge amounts of study and reading involved. But most of the problems truly are at very high frequencies and/or at EMI compliance. Beginner Hobbyists avoid the most difficult issues entirely by nature of beginner (aka: low-speed) and hobbyist (and therefore don't have to follow regulators). ---------- I'm not a professional. But my understanding is that top-level EEs who work on PDNs will simulate the circuit-board itself to figure out trace inductances / capacitances in the board itself. (Closer planes of ground/power will create more capacitance. Long traces tend to increase trace inductance, etc. etc.). And tight simulations are the only way to truly understand the PCB and how it interacts at high frequencies with high-power. But such methodologies are gross overkill for a 1MHz boost converter with a pre-made PCB Layout, and a list of capacitors + inductors already picked out for you. (ex: https://www.microchip.com/en-us/product/mcp1640 https://www.microchip.com/en-us/product/mcp1640) Seriously: Page 17 (https://ww1.microchip.com/downloads/aemDocuments/documents/APID/ProductDocuments/DataSheets/MCP1640-Family-Data-Sheet-DS20002234E.pdf https://ww1.microchip.com/downloads/aemDocuments/documents/A...) already gives you the PCB-layout you need for this, with recommended components. Don't overthink it, just copy the design from the document.
  - Max-q 2y ago
    We have a couple of challenges today. Hobbyists often go over 20MHz, because they put WiFi, BT or USB on their boards, giving EMC issues. Also, the speed of the modern ICs tend to be very high. If you have a 9600 Hz UART signal, that is not a 9600 Hz signal if it's a square wave with a modern IC with very short rise time on the pins. So a good old, slow serial line can with modern MCU emit noise up in the hundreds of MHz range. So your PCB layout tips are important, even on slow circuits these days.
    - dragontamer 2y ago
      Unless a beginner plans to sell a design on the public, there is no EMC (compliance) issue. Maybe EMI crosstalk. But WIFI and BT are supposed to eminate out like a radio and jump across boards. That's the point. --------- USB is a matched impedance differential pair. Are beginners really running high speed USB differential pairs down their circuits today? Because that's a really.... Erm.... strange.... definition of a beginner. IMO anyway.
      - archi42 2y ago
        Depends on your definition of beginner. It's trivial to put a nrf52 module (like [1]) in a PCB design and wire a USB socket to it; just make sure to route the data lines as a differential pair in kicad (add protection diodes if feeling fancy). And speak a little prayer that it actually works as intended. No need to understand what any of that means. Of course the notion of using such a module might be a step up from beginner for you, but IMHO it's more about the understanding. But I agree that there is no definite definition. Disclaimer: I'm a beginner by my definition. [1] example module: https://www.waveshare.com/core52840.htm https://www.waveshare.com/core52840.htm
  - Youden 2y ago
    > Use Power+Signal / GND / GND / Power+Signal stackup. I'm just a novice (maybe intermediate) so I'm wondering: the common 4-layer stackups available to hobbyists seem to be 1oz/0.5oz/0.5oz/1oz and I assume the outer layers have better thermal dissipation since they're only kept from the air by solder mask; so wouldn't it be better to put power/ground on the outer layers and keep signals in the middle? Also maybe I'm weird and this is pointless but I typically put a filled copper zone tied to ground on every single layer, unless I have a reason to put some other kind of zone in a particular area. Is it necessary to have a full, dedicated ground plane, rather than ground + signal or ground + power?
- magicalhippo 2y ago
  As the sibling comment mentions there are several aspects. You'll need proper input filtering which may require a non-trivial filter network. You'll also need proper output filtering, which does include slapping a lot of capacitors on there, but also careful selection of those capacitors both type and size. Parasitic inductance of larger packages can mean they can't filter high frequencies, and MLCC capacitors have a DC bias which means the effective capacitance is significantly reduced when they have a DC bias on them which they will have in a DC-DC converter. Then you need to take great care about component placement and board layout, to minimize the return path of the currents and such. You can skip all of that and get a board that functions as a DC-DC converter if you measure it with a multimeter, but actually be horrible. And you just can't fix bad layout by slapping more capacitors on there. And even with a not terrible layout, you can't fix it by using the wrong kind of capacitors. Like anything through-hole is just not gonna pass.
klysm 2y ago
Making a noise-free DC-DC converter is very difficult. Any buck/boost style converter is going to introduce ripple and switching noise into the system. This is inherently unavoidable, and it’s very sensitive to the layout of the board. Actively or passively filtering out all this broadband frequency content is far from trivial, and there is no general solution - only a large, high dimensional tradeoff space. You’re right that noise is a concern for any analog circuitry though, and if you want to, you can spend a lot of money on specialized DC/DC converter modules with integrated inductors that do their best to eliminate this noise.

by hcfman 2y ago

euroderf 2y ago

Isn't this like 95% fixable with a capacitor ? Aren't there cables with small embedded caps ?

dragontamer 2y ago
Oh hell no. I think a lot of people are overly cautious of DC-DC conversion in this topic, but you've gone full-tilt in the opposite direction and are severely underestimating the problems that occur. 1. Its not "power-conversion" that's hard per se, its EMC that's very hard and not taught very well at a bachelor's level. 2. DC-DC Voltage Converters usually handle the entirety of your board's power, meaning they are the highest power component. 3. High power and high-frequency is a difficult EMC problem. This means that a bad design will absolutely send your electrons / energy out and radiate out like an antenna. And if things on the same board pick it up, it will be called crosstalk. And if things off-board pick it up, its called electromagnetic interference which almost certainly leads to a compliance problem. --------------- 1. Hobbyists don't care about compliance. So bam. We are already dealing with the biggest problem by simply not caring about it. (Maybe you can care and go into deeper studies, but... if you're a beginner just don't care. Learn this very difficult stuff later). 2. Prevent crosstalk by following good board design rules: have a 4-layer board. Use Power+Signal / GND / GND / Power+Signal stackup. Use two vias (one for signal-1 to signal-4 traversals), and a 2nd via for GND2 to GND3 traversal of the return current). Thinking of both the forward current and a tightly bound reverse current is basically all you need to do to avoid difficult crosstalk problems on board. Done. Point#2 requires deeper studies than is typical in bachelor's level electrical engineering. But it truly isn't very difficult once you learn the theory. Tight ground-planes reduce crosstalk (and EMI problems), and furthermore thinking of the return-current explicitly prevents problems. Now you could have some truly difficult "ringing" from trace inductance and other such nasty problems... but that tends to occur beyond 100MHz. I'm thinking most beginners are going to be under 20MHz for most of their designs and thus never deal with those advanced "PDN" / Power Delivery Network problems. Though if you do go into PDNs, its obviously a tough subject with huge amounts of study and reading involved. But most of the problems truly are at very high frequencies and/or at EMI compliance. Beginner Hobbyists avoid the most difficult issues entirely by nature of beginner (aka: low-speed) and hobbyist (and therefore don't have to follow regulators). ---------- I'm not a professional. But my understanding is that top-level EEs who work on PDNs will simulate the circuit-board itself to figure out trace inductances / capacitances in the board itself. (Closer planes of ground/power will create more capacitance. Long traces tend to increase trace inductance, etc. etc.). And tight simulations are the only way to truly understand the PCB and how it interacts at high frequencies with high-power. But such methodologies are gross overkill for a 1MHz boost converter with a pre-made PCB Layout, and a list of capacitors + inductors already picked out for you. (ex: https://www.microchip.com/en-us/product/mcp1640 https://www.microchip.com/en-us/product/mcp1640) Seriously: Page 17 (https://ww1.microchip.com/downloads/aemDocuments/documents/APID/ProductDocuments/DataSheets/MCP1640-Family-Data-Sheet-DS20002234E.pdf https://ww1.microchip.com/downloads/aemDocuments/documents/A...) already gives you the PCB-layout you need for this, with recommended components. Don't overthink it, just copy the design from the document.
- Max-q 2y ago
  We have a couple of challenges today. Hobbyists often go over 20MHz, because they put WiFi, BT or USB on their boards, giving EMC issues. Also, the speed of the modern ICs tend to be very high. If you have a 9600 Hz UART signal, that is not a 9600 Hz signal if it's a square wave with a modern IC with very short rise time on the pins. So a good old, slow serial line can with modern MCU emit noise up in the hundreds of MHz range. So your PCB layout tips are important, even on slow circuits these days.
  - dragontamer 2y ago
    Unless a beginner plans to sell a design on the public, there is no EMC (compliance) issue. Maybe EMI crosstalk. But WIFI and BT are supposed to eminate out like a radio and jump across boards. That's the point. --------- USB is a matched impedance differential pair. Are beginners really running high speed USB differential pairs down their circuits today? Because that's a really.... Erm.... strange.... definition of a beginner. IMO anyway.
    - archi42 2y ago
      Depends on your definition of beginner. It's trivial to put a nrf52 module (like [1]) in a PCB design and wire a USB socket to it; just make sure to route the data lines as a differential pair in kicad (add protection diodes if feeling fancy). And speak a little prayer that it actually works as intended. No need to understand what any of that means. Of course the notion of using such a module might be a step up from beginner for you, but IMHO it's more about the understanding. But I agree that there is no definite definition. Disclaimer: I'm a beginner by my definition. [1] example module: https://www.waveshare.com/core52840.htm https://www.waveshare.com/core52840.htm
- Youden 2y ago
  > Use Power+Signal / GND / GND / Power+Signal stackup. I'm just a novice (maybe intermediate) so I'm wondering: the common 4-layer stackups available to hobbyists seem to be 1oz/0.5oz/0.5oz/1oz and I assume the outer layers have better thermal dissipation since they're only kept from the air by solder mask; so wouldn't it be better to put power/ground on the outer layers and keep signals in the middle? Also maybe I'm weird and this is pointless but I typically put a filled copper zone tied to ground on every single layer, unless I have a reason to put some other kind of zone in a particular area. Is it necessary to have a full, dedicated ground plane, rather than ground + signal or ground + power?
magicalhippo 2y ago
As the sibling comment mentions there are several aspects. You'll need proper input filtering which may require a non-trivial filter network. You'll also need proper output filtering, which does include slapping a lot of capacitors on there, but also careful selection of those capacitors both type and size. Parasitic inductance of larger packages can mean they can't filter high frequencies, and MLCC capacitors have a DC bias which means the effective capacitance is significantly reduced when they have a DC bias on them which they will have in a DC-DC converter. Then you need to take great care about component placement and board layout, to minimize the return path of the currents and such. You can skip all of that and get a board that functions as a DC-DC converter if you measure it with a multimeter, but actually be horrible. And you just can't fix bad layout by slapping more capacitors on there. And even with a not terrible layout, you can't fix it by using the wrong kind of capacitors. Like anything through-hole is just not gonna pass.

klysm 2y ago

Making a noise-free DC-DC converter is very difficult. Any buck/boost style converter is going to introduce ripple and switching noise into the system. This is inherently unavoidable, and it’s very sensitive to the layout of the board. Actively or passively filtering out all this broadband frequency content is far from trivial, and there is no general solution - only a large, high dimensional tradeoff space. You’re right that noise is a concern for any analog circuitry though, and if you want to, you can spend a lot of money on specialized DC/DC converter modules with integrated inductors that do their best to eliminate this noise.