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Old 22nd August 2006, 07:22 AM   #1
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Default Bypassing

Hi guy's just a quick question.
Bypass caps for 13.8V into an oPA134....
Are SMT's the way to go or should I use a couple of different types?

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Old 22nd August 2006, 07:29 AM   #2
AndrewT is online now AndrewT  Scotland
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Hi,
smd should perform well at these voltages. They also allow the very short tracks that are necessary.

You will put them on the other side from the opamp, directly between the power pins?
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Old 22nd August 2006, 07:55 AM   #3
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Quote:
Originally posted by AndrewT
Hi,
smd should perform well at these voltages. They also allow the very short tracks that are necessary.

You will put them on the other side from the opamp, directly between the power pins?

Yup, that's what I was thinking of, solder one (10nf?) directly between the pins, but I wonder if I should bypass that with another tank cap, Low ESR FM or something?
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Old 22nd August 2006, 08:33 AM   #4
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Just use one cap, multiple ones - especially low ESR - can create resonant circuit.
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Old 22nd August 2006, 11:04 AM   #5
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Quote:
Originally posted by richie00boy
Just use one cap, multiple ones - especially low ESR - can create resonant circuit.
Thanks for that, do you think 10nf would be Ok or should I put something bigger in there?
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Old 22nd August 2006, 12:48 PM   #6
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The actual value should in an ideal world be determined with the actual board etc, but 100nF is a popular choice.
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Old 22nd August 2006, 12:58 PM   #7
AndrewT is online now AndrewT  Scotland
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Hi,
the manufacturer usually gives precise advice on bypassing in the datasheet, including occasional dual cap bypasses, grounded and direct between pins.
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Old 22nd August 2006, 05:03 PM   #8
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Quote:
Originally posted by AndrewT
Hi,
the manufacturer usually gives precise advice on bypassing in the datasheet, including occasional dual cap bypasses, grounded and direct between pins.
that's the thing....No real talk of bypassing just a schematic of the trim feature with 10uf to ground on + & - (not across the pins).
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Old 23rd August 2006, 07:24 AM   #9
AndrewT is online now AndrewT  Scotland
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Hi,
the manufacturer's data is usually reliable and often adequate.

An extra pin to pin bypass cap using a small fast ceramic may help attenuate glitches moving into the supply rails and may even be an improvement over doing without.
But, doing other than the recommendation will require a bit of luck and/or extensive testing.
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