A 1980s filter chip that uses switched capacitors | Hacker News Reader

A 1980s filter chip that uses switched capacitors

righto.com

36 pointspwg10 comments

This is an interesting part because it seems to fit a niche, yet TI doesn't support it much. One forum post said the support team for the part moved on. Another said the next gen part is EOL and there's nothing to replace it. It's one of those parts they have that you can tell they really don't want to have. At least linear tech (now ADI) has some equivalent one? The LTC1060. Unlike some others where TI is literally the only one, like the TUSB1310/A.

Author here for your filter questions...

Good article!

You have to publish a book!

As a noob to chip design, I've always wondered; why can't chip packages integrate filter caps at the outputs directly? Instead of having boards put a ton of them on the PCB as close to the chip connections as possible?

Is it a matter of current handling? Or repairability (easier to replace one external smoked cap than a whole IC...)?

(I know the filtering here is a little different in purpose, but it just made me wonder).

On-chip decoupling capacitors do get used [1]. The main problem is that they take up a lot of valuable die space for not much capacitance.

[1] https://doi.org/10.1109/SBCCI.2003.1232837

Some can (see modern CPUs which have a huge chunk of them integrated into the package). It's likely to be quite expensive for most packaging processes and realistically for a lot of them there isn't really enough space. (on older style DIP packages there might be enough space for some of the modern smaller caps but the caps available at the time would not fit).

With on-die capacitance you can't realistically get enough capacitance for decoupling in the right frequency range (though it is still relevant: in practice decoupling is a case of multiple overlapping filters, from the response of the regulator itself, to any bulk capacitance, to local decoupling capacitors on the PCB, to the plane capacitance of the PCB itself, to the capacitance of the power distribution inside the IC. Each of these stages has a lower inductance but also a correspondingly lower capacitance and so deals with a higher-frequency part of the load).

WWW.JCY - early webpage obv

Hah, I just went thru this identification problem with another Harris IC. They use their 'H' logo like it's part of the chip name.

In my case I was trying to find a 'D1-15531-9' when the actual part number is 'HD1-15531-9'

Someone in their marketing thought they were being cool back then, but it's just confusing.

Thanks, that explains the part number. I never would have guessed that the logo was included.

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