Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Decoupling caps on logic boards

Status
Not open for further replies.

Aronjohnson

Banned
Joined
May 16, 2015
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
0
logic boards decoupling caps are either tantalum, electrolytic or ceramic. Can I replace all the ceramic decoupling caps and use tantalum or electrolytic caps on logic board that has either TTL or CMOS logic chips or will this cause problems?

Why would you want to use ceramic decoupling caps
 

dick_freebird

Advanced Member level 5
Joined
Mar 4, 2008
Messages
7,281
Helped
2,126
Reputation
4,257
Reaction score
1,983
Trophy points
1,393
Location
USA
Activity points
58,396
Tantalum and electrolytic caps have a high ESL (especially the
older radial lead through-hole types) which makes them ineffective
at returning the switching current spikes whence they came.
The low value small body ceramic caps can be had with much
higher SRFs, low ESL/ESR and have their part to play.

You may find modern surface mount tantalums with ESR/ESL
approaching ceramics if you are willing to dig and spend. You
need to look at the details, often not even on the datasheet
but maybe found in app notes or product family marketing
literature, to determine whether you have a decent cap.

Figure your desired / expected risetime equates to a quarter
cycle of some frequency, and you want the SRF of the cap to
be above this point (like, 1nS risetime is 1/4 of a 250MHz sine
and you'd like a cap that is not lossy, much, at that frequency.
Loss rolls on fast after SRF.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top