[sdiy] bypass caps, subbing MLCC for Electrolytic

[Tony Rolando]

  Well in the case of this App Note (and others), all of the 10uF 
electrolytics are paired with a .1uF ceramic, which would have the lower 
ESR, so wouldn't that defeat the purpose of the higher ESR on the 10uF?

T

On 10/5/10 3:32 PM, Harry Bissell wrote:
> I have seen an app note for a switching power supply chip which
> said that electrolytics might be preferred because of their
> inherently higher ESR. too low of a value would make their
> chip unstable.  OTOH they did say you could arrange to have higher ESR by adding a series
> resistor or equivalent length of circuit trace (which might be bad for
> other reasons)
>
> I forget whether it as a Linear Tech part, or Maxim. I used the Linear Tech with the
> ceramic caps.
>
> Ceramic caps could be an advantage for board manufacture, there is no polarity to
> get wrong (and explode - tantalum :^)
>
> H^) harry
>
> ----- Original Message -----
> From: Tony Rolando<tony at makenoisemusic.com>
> To: Harry Bissell<harrybissell at wowway.com>
> Cc: David G. Dixon<dixon at interchange.ubc.ca>, synth-diy at dropmix.xs4all.nl
> Sent: Tue, 05 Oct 2010 14:24:34 -0400 (EDT)
> Subject: Re: [sdiy] bypass caps, subbing MLCC for Electrolytic
>
>    Thanx for the insights guys. David, it is the diameter. I could put a
> 1206 MLCC in the same spot.
>
> Harry, I was going to use either X7R or X5R, 1206 MLCC. The ap note for
> the IC (PCM1807 ADC) did specify Electrolytic, but did not say why... I
> suppose I am wondering what the electrolytic could offer that the MLCC
> could not. Perhaps as you noted the lower ESR could be "bug" in this
> case. I just prefer MLCC since they are longer life and not polarized.
>
> Texas Instruments had the following to say this morning when I ask this
> same question:
>
> "They (electrolytics) are used in relatively high-current and
> low-frequency electrical circuits, particularly in power supply filters,
> where they store charge needed to moderate output voltage and current
> fluctuations in rectifier output. They are also widely used as coupling
> capacitors in circuits where AC should be conducted but DC should not.
>
> So, they were particularly recommended for their ability to better block
> DC, and moderate output voltage. If you aren't worried too much about
> these characteristics, then it should be fine to use the ceramic versions."
>
>
> I've never heard anybody say electrolytic blocks DC better?
>
>
> Tony
>
>
>
> On 10/5/10 12:37 PM, Harry Bissell wrote:
>> The ceramic caps are just fine for bypassing, except in some
>> critical switching power supply designs that might specify to
>> USE ONLY electrolytic or USE ONLY MLCC (depends on whether the ESR
>> is a "bug" or a "feature"
>>
>> Ceramics are nice in that they take high SMT temperatures, and are
>> inherently non-polar.  Watch out for the dielectric... some like
>> Y5V (there is a cap in the circuit, its size is basically unknown and you don't care...)
>> are really crap (Z5U is not much better). I prefer X7R if they would
>> be small enough...
>>
>> H^) harry
>>
>>
>> ----- Original Message -----
>> From: David G. Dixon<dixon at interchange.ubc.ca>
>> To: 'Tony Rolando'<tony at makenoisemusic.com>, synth-diy at dropmix.xs4all.nl
>> Sent: Tue, 05 Oct 2010 12:26:34 -0400 (EDT)
>> Subject: Re: [sdiy] bypass caps, subbing MLCC for Electrolytic
>>
>>>     Hello, Has anybody ever had any problems subbing a MLCC type cap for
>>> an electrolytic in a bypass situation? Low ESR is not required. 16V 10uF
>>> Electrolytic was called, I'd like to use 16V 10uF MLCC in order to save
>>> space.
>> I use 10uF electrolytics in this application which are only about 0.2" in
>> diameter and about 0.5" high, and have 0.1" lead spacing.  Is it the
>> diameter or the height that you are worried about?
>>
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