| ??? 12/31/05 17:38 Modified: 12/31/05 17:46 Read: times |
#106294 - Is because... Responding to: ???'s previous message |
Vignesh said:
is the Tantalum for filtering, apart from 100nF for decoupling? In another thread we learnt something about decoupling caps: Better is not better... 100nF decoupling caps in combination with longer and narrow supply traces can result in some resonances: The ripple at certain Vcc pins is higher than needed. One way to reduce this ripple is to connect a tantal in parallel to 100nF. Then, the resonances are eliminated. An example: The formula for a LRC series resonance circuit to avoid resonance is R > SQRT (2 x L / C) Now let's have a board with 5cm long supply traces between the chips and using 100nF caps. Then, R must greater than about SQRT (2 x 50nH / 100nF) = 1 Ohm, remembering that 5cm copper track gives about 50nH inductance. As the 100nF cap shows an equivalent series resistance of about 0.1 Ohm, there's a danger of generating of resonances. If, on the other hand, a tantal of 10µF is paralleled, then the formula yields a minimum R of about 0.1 Ohm. Equivalent series resistance of 10µF tantal is about 0.3 Ohm, and Voilà, no resonances! Also, using a tantal at micro is always a good idea, especially when relevant capacitive loads need to be driven at the ports. Kai |
| Topic | Author | Date |
| Second layer of PCBs | 01/01/70 00:00 | |
| hmmm | 01/01/70 00:00 | |
| Another idea... | 01/01/70 00:00 | |
| A very good idea! | 01/01/70 00:00 | |
| A clarification | 01/01/70 00:00 | |
| This way? | 01/01/70 00:00 | |
| No problem | 01/01/70 00:00 | |
| better... | 01/01/70 00:00 | |
| That's the solution | 01/01/70 00:00 | |
| Farady Cage ? | 01/01/70 00:00 | |
| Oops! | 01/01/70 00:00 | |
| Single double-sided PCB ! | 01/01/70 00:00 | |
| Depends | 01/01/70 00:00 | |
| Layer | 01/01/70 00:00 | |
| wow 12 replys in 1 hour !// | 01/01/70 00:00 | |
| Yeah! | 01/01/70 00:00 | |
| Close and solid ground plane | 01/01/70 00:00 | |
| Thank you! | 01/01/70 00:00 | |
| Some pics | 01/01/70 00:00 | |
| Your Supply tracks are too thin | 01/01/70 00:00 | |
| Thickness | 01/01/70 00:00 | |
| Decoupling caps? | 01/01/70 00:00 | |
| Top or botttom | 01/01/70 00:00 | |
| Draw it | 01/01/70 00:00 | |
| Ink != Etch resist | 01/01/70 00:00 | |
| Indeed | 01/01/70 00:00 | |
| Time consuming | 01/01/70 00:00 | |
| Special ink | 01/01/70 00:00 | |
| I would... | 01/01/70 00:00 | |
| is it for? | 01/01/70 00:00 | |
| Is because... | 01/01/70 00:00 | |
| Cant get anything better! | 01/01/70 00:00 | |
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| Great! | 01/01/70 00:00 | |
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| Another doubt | 01/01/70 00:00 | |
| Remedies | 01/01/70 00:00 | |
| My idea | 01/01/70 00:00 | |
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| Try SMD | 01/01/70 00:00 | |
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| SMD | 01/01/70 00:00 | |
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| Interesting link | 01/01/70 00:00 | |
| Kai, you are right | 01/01/70 00:00 | |
Highly interesting article! | 01/01/70 00:00 | |
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| For your views.. | 01/01/70 00:00 | |
| Without schematic... | 01/01/70 00:00 | |
| Schematic | 01/01/70 00:00 |