MPC50x analog mux for audio?

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PRR

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> MPC507: 8-channel differential

These are second-source for a very old Harris Gates part.

The series has been available for about 20 years, so it is probably not going to vanish soon.

These used to cost a heck of a lot more than $8, though I do recall them falling past $25 quite a few years ago.

Voltage handling is very good.

ON-resistance is very high. You need to consider this in all phases of design. The last time I considered them, the ON-resistance promised more noise than I could accept in a microphone preamp. It is not a big issue in line-level work. However the resistance variation with voltage, while small, is not clearly specified. You typicially need a LARGE swamping impedance to mask Ron variations and get low THD numbers.

In fact Ron for this heavily-protected part looks higher than I remember on the Harris parts.

Note this TI tip:

"Keep loading impedance as high as possible. This minimizes the resistive loading effects of the source resistance and multiplexer ON resistance. As a guideline, load impedance of 10^8Ω or greater will keep resistive loading errors to 0.002% or less for 1000Ω source impedances. A 10^6Ω load impedance will increase source loading error to 0.2% or more."

They want you to use 100MegΩ load! The error they are discussing isn't what we call distortion: THD will be lower than static DC error. But clearly you want at least 1 Meg.

Ah, TI has good Ron curves. Not very precise: drawn flat/level from -10V to +4.6V, but you can eyeball significant error above +5V. This may not be too important at line-level, and you may not need a super-high load impedance.
 

PRR

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Joined 2003
Paid Member
PRR said:
ON-resistance is very high. You need to consider this in all phases of design. The last time I considered them, the ON-resistance promised more noise than I could accept in a microphone preamp. It is not a big issue in line-level work. However the resistance variation with voltage, while small, is not clearly specified. You typicially need a LARGE swamping impedance to mask Ron variations and get low THD numbers.


Does this mean that you can't use them to source a power amp ?

Power amps have input impedance more or less around 50k

Having a 1k input source is still a problem ?
 
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