Dear all,
Many datasheet of hi speed, hi BW op-amp recommended to use a 10uF tantalum SMD cap and combined with 100nF polyester cap.
I'm planning to design my pre amp by op-amp, of course. So, how to choose right type for this application, a lot of tantalum SMD type in market. Some BOM list i have just say 10uF/35V tantalum SMD, not any info about type.
In other hand, can i use a poly propylene cap MKP to replacement that combination? We all know MKP cap have ESR characteristic lower than the polyester cap.
I would to use Vishay or Kemet brand.
Thanks for help me,
Regard,
Many datasheet of hi speed, hi BW op-amp recommended to use a 10uF tantalum SMD cap and combined with 100nF polyester cap.
I'm planning to design my pre amp by op-amp, of course. So, how to choose right type for this application, a lot of tantalum SMD type in market. Some BOM list i have just say 10uF/35V tantalum SMD, not any info about type.
In other hand, can i use a poly propylene cap MKP to replacement that combination? We all know MKP cap have ESR characteristic lower than the polyester cap.
I would to use Vishay or Kemet brand.
Thanks for help me,
Regard,
I would choose a 10uF with moderate ESR to damp ringing. If you use a tantalum 10uF type,
be sure to use an adequate voltage rating margin, as they fail when it is marginal.
An X7R ceramic cap is preferable to polyester for the 0.1uF. For a very wideband circuit,
0.01uF is preferable to 0.1uF. Be sure to use a solid, top layer ground plane for the best decoupling.
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Better to route all the signals on the top layer especially if all the devices are SMD and have a ground copper pour on the bottom layer, you are more likely to get a solid pour this way.
Thanks all for input,
So, I have more choice for decoupling cap. Ceramic caps seem great, lower cost than Tantalum.
Kemet also recommended in their paper kind of caps are X7R & NPO.
Regard,
So, I have more choice for decoupling cap. Ceramic caps seem great, lower cost than Tantalum.
Kemet also recommended in their paper kind of caps are X7R & NPO.
Regard,
The decoupling strategy will depend on your goals and the circuit bandwidth. X7R caps work well enough, though they can be a little non-linear. This is not an issue with audio circuits in most cases. NP0 are good but once you cross about 10nF they start becoming a little pricey. For DIY, this is usually not an issue because of the low volume, but almost all commercial products use X7R for opamp decoupling.
With Tantalum capacitors you'd better have some sort of polarity protection. They don't like reverse voltage at all, so if your implementation involves cabling between boards, a couple diodes would help.
10uF tantalum indicates large output currents, if you're dealing with a standard output cable load down to 1K||200pF (for example) around 2.2uF should be sufficient. If you have many opamps it is better to distribute these caps across them rather than using one at power entry alone and depending on the small ceramic per opamp. The AD797 datasheet has a nice illustration that would also help in PCB design.
For even smaller loads (such as a few opamps in active filters interacting with each other) 1uF is usually sufficient. As a general rule of thumb you can downsize the needed capacitance by 2 to 5 times when going from Electrolytic to Tantalum. Generally the smaller the cap the lower the load current it can adequately deal with, but the better the HF performance. So you have to take a call depending on circuit goals and measured performance.
And finally, the routing of signal, power and grounds will have much more impact on performance than the capacitor type. Look up AN-202 on Analog's site, it's quite informative. Good engineering will always trump 'better' parts.
With Tantalum capacitors you'd better have some sort of polarity protection. They don't like reverse voltage at all, so if your implementation involves cabling between boards, a couple diodes would help.
10uF tantalum indicates large output currents, if you're dealing with a standard output cable load down to 1K||200pF (for example) around 2.2uF should be sufficient. If you have many opamps it is better to distribute these caps across them rather than using one at power entry alone and depending on the small ceramic per opamp. The AD797 datasheet has a nice illustration that would also help in PCB design.
For even smaller loads (such as a few opamps in active filters interacting with each other) 1uF is usually sufficient. As a general rule of thumb you can downsize the needed capacitance by 2 to 5 times when going from Electrolytic to Tantalum. Generally the smaller the cap the lower the load current it can adequately deal with, but the better the HF performance. So you have to take a call depending on circuit goals and measured performance.
And finally, the routing of signal, power and grounds will have much more impact on performance than the capacitor type. Look up AN-202 on Analog's site, it's quite informative. Good engineering will always trump 'better' parts.
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