Ceramic and Tantelum SMD suggestions?

[@dmin]

Hello,

Your website has been a great guide in the past for can style capacitors but, I'm finding that the same companies don't offer much in the SMD realm...

I'm doing an academic thesis/research project that uses a Bluetooth and a RS232 Transceiver in a battery powered device. As part of my college degree I have to work with a company and do a project that will help them.

The transceiver needs 4 .1 uf capacitors. Then for general power filtering I need some ceramic .1uf and 2.2uf capacitors. When sourcing parts I keep ending up with Multicomp, AVX, and TDK. I'm hoping for the case size to be 1206 as well since I think that's the smallest I can solder with out buying a hot air rework thing. Being able to buy 1 unit at a time is also influencing my decision. I don't want to buy 1000 if I only need 12. The end device will be subjected to lots of interference such as poorly shielded 440v industrial machines as well as the Bluetooth antenna. I have a CS background but found my self in EE project for my co-op thesis. Cost is kind of important as well. I'm kind of poor and submitting reimbursement forms takes forever.

If someone knows of a brand or feed back on the brands listed that would be nice. As, well as some guidance to understanding interference requirements.

One last question, the micro controller I am using uses 3.3v logic but case sizes of 1206 are all 50v or 100v. Will this cause any issues?

Thanks in advanced.

[mariushm]

Re: Ceramic and Tantelum SMD suggestions?

multicomp is farnell/newark's brand of capacitors, not an actual manufacturer. It's several brands from several sources under a brand, multicomp.

Not saying they're bad, just be aware the datasheets are usually basic, and uality may vary.

I think you would have very little problems soldering 0805, they're still big enough imho.
Also you can still buy radial leaded capacitors, ceramic, but they're more expensive than smd capacitors.

If you go smd route, you want to get capacitors labeled with temperature coefficient X7R, X5R or COG ... ignore everything else, as their capacitance will vary a lot (too much) on voltage and frequency going through the capacitor.

Voltage... the capacitance of ceramic capacitors decreases as the voltage gets close to their rating, so you actually want to use ceramic capacitors rated for a larger voltage. 25-50v will be fine imho.

Quantity, don't buy 1 at a time, if you can buy 10-25 pcs of what you need, you get discount. At digikey, the surface mount ceramic capacitors are about 0.1 dollars each at 1 pcs, but 0.03 dollars at 100pcs so for 3$ you get 100 capacitors.
Radial (through hole) ceramic capacitors are a bit more expensive at 0.22 dollars each at 1pcs, 0.08 at 100 pcs.

Use digikey.com, newark.com , mouser.com etc

see http://en.wikipedia.org/wiki/EIA_Class_2_dielectric

and http://www.kemet.com/kemet/web/homepage/kfbk3.nsf/vaFeedbackFAQ/0F05C4C1F74A2D2485256F170052CD15/$file/2008-11%20Update%20-%20Ceramic%20versus%20Tantalum.pdf for some details about ceramic caps.

as for more protection against interferences, try to use ferrite beads on the transmission traces

http://www.digikey.com/product-searc...-chips/3408555

I wouldn't know exactly which is more suitable, but being low speed serial transmission, 9600 baud something, i doubt it really matters, something with low dcr resistance would probably work.

and if you're really paranoid maybe some optical isolators near the microcontroller's serial port pins to prevent surges from getting into the controller if traces act as antennas, but i really doubt it would be necessary.

If you power the microcontroller directly, it's really not recommended, I suggest using a low drop regulator which will also smooth out the voltage and protect it somewhat.

i don't recommend tantalum capacitors, lots of manufacturers don't use them because they have potential to blow up with nice flames if you push too much voltage or reverse the voltage into them. 0.1 and 2.2uF are both values you can easily find in ceramic capacitors

[@dmin]

Re: Ceramic and Tantelum SMD suggestions?

Thank you very much for this info!

i don't recommend tantalum capacitors, lots of manufacturers don't use them because they have potential to blow up with nice flames if you push too much voltage or reverse the voltage into them. 0.1 and 2.2uF are both values you can easily find in ceramic capacitors

I guess I just don't know enough. The reason I was going to use tantalum capacitors is, on page 9 https://cdn.badcaps-static.com/pdfs/...df1cfea3ec.pdf the diagram shows polarity on the capacitors. I was under the impression that ceramics were non-electrolytic and didn't have polarity. From what I remember non of the data sheets I looked at showed polarity.

[LLLlllou]

Re: Ceramic and Tantelum SMD suggestions?

Thank you very much for this info!



I guess I just don't know enough. The reason I was going to use tantalum capacitors is, on page 9 https://cdn.badcaps-static.com/pdfs/...df1cfea3ec.pdf the diagram shows polarity on the capacitors. I was under the impression that ceramics were non-electrolytic and didn't have polarity. From what I remember non of the data sheets I looked at showed polarity.

"NOTES: A. Resistor values shown are nominal.
B. NC − No internal connection
C. Nonpolarized ceramic capacitors are acceptable. If polarized tantalum or electrolytic capacitors are used, they should be
connected as shown"

[mariushm]

Re: Ceramic and Tantelum SMD suggestions?

I forgot.

I'm not sure what you're using the max3233e for, but if it's just to connect to the device using serial port, you might wanna look into ft230xs

http://uk.farnell.com/ftdi/ft230xs/i...?ref=lookahead

You just give it the data and it shows up as a virtual com port in windows when you connect it to the usb.
And the connection is pretty simple, here for example is used in a portable power supply:

https://cdn.badcaps-static.com/pdfs/...04e356f402.pdf

It looks complicated in that design, because it's meant to be isolated, so optical isolators are used on the tx and rx lines, but you don't have to use those, the chip is tolerant up to 5.5v on those lines.

This is the whole section you'd care about:



And the added benefit is that the chip is only 2$, maybe even less.

[@dmin]

Re: Ceramic and Tantelum SMD suggestions?

"NOTES: A. Resistor values shown are nominal.
B. NC − No internal connection
C. Nonpolarized ceramic capacitors are acceptable. If polarized tantalum or electrolytic capacitors are used, they should be
connected as shown"

Ugh, I feel like an idiot, not sure why I missed that...

I forgot.

I'm not sure what you're using the max3233e for, but if it's just to connect to the device using serial port, you might wanna look into ft230xs

http://uk.farnell.com/ftdi/ft230xs/i...?ref=lookahead

You just give it the data and it shows up as a virtual com port in windows when you connect it to the usb.
And the connection is pretty simple, here for example is used in a portable power supply:

https://cdn.badcaps-static.com/pdfs/...04e356f402.pdf

It looks complicated in that design, because it's meant to be isolated, so optical isolators are used on the tx and rx lines, but you don't have to use those, the chip is tolerant up to 5.5v on those lines.

This is the whole section you'd care about:

-sniped image

And the added benefit is that the chip is only 2$, maybe even less.

the reason I'm using a max232 is that with it having 2 drivers I can have TX, RX, and DTR|RTS.
The cable to the device I need data from uses DTR and RTS for powering it's photocell and LED (for communication).



Over engineered in my opinion.

I might use that chip in another project at home... Thanks!

[PeteS in CA]

Re: Ceramic and Tantelum SMD suggestions?

Large form factor SMT monolythic ceramic capacitors are evil. Seriously, they crack easily if flexed, and soldering them evenly is imperative. Cracked SMT MLCCs tend to be shorts, and can damage or destroy your PCBs.

When it comes to temperature and voltage coefficients, use only NPO/CGO, X7R or X8R if possible. If you use the latter two types, the rated voltage of the part must be at least 5X the voltage in the circuit. Z5U and Y5V parts have horrible temperature and voltage coefficients. In a really warm environment with a circuit voltage close to the rated voltage a 1uF cap could be .1uF to .15uF! While X7R and X8R have decent temperature coefficients, used at a voltage close to their rated voltage their actual capacities can be 15% - 20% lower than what the parts are when measured with a meter.

MLCCs have some wonderful characteristics, but you have to use them carefully and choose what you use carefully. I see MLCCs as a necessary evil.

[@dmin]

Re: Ceramic and Tantelum SMD suggestions?

Thanks for warnings/tips!

I'm going to order some 603's and 805's as well as going to pick up a used hot air reflow station.

Any recommended Brands?
I think I'm going to use the more expensive Panasonic's on the voltage regulators as those will probably take more abuse.