Re: HCT4051 leakage


"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit dans le
message de news:d47so1h0tsdv3lr2jub84772s11n32aa9i@xxxxxxxxxx
> Hi,
>
> Has anybody measured typical leakage currents for an HCT4051 analog
> mux? I'm wondering about both ESD diode leakage (ie, to rails) and
> leakage through open switches. I'm running 0 and +5V rails.
>
> Indications are that everybody's 0.1 uA max spec is wildly
> pessimistic, but I was wondering if anybody knows more, before I have
> to drag my *** into the lab and make actual measurements. It's a lot
> easier to sit here and type and eat bon-bons.
>
> We're scanning eight RTDs. A +2.5 volt reference goes through a
> precision 270 ohm resistor and gets mux'd to a selected RTD. The
> voltage drop across the RTD gets differentially mux'd, too. A 24-bit
> delta-sigma ADC digitizes the voltage drop across the 270, then the
> voltage across the RTD, and does the math. We're getting errors in the
> tens of PPM, tolerable, but we're curious where they're coming from.
> The sensitivity analysis math here is a nuisance.
>
>

I did measure an old CD4053 about two years ago (sorry did not have 74HC).
It had +/-5V supplies and was arranged for 0V common mode at both switch
ends.
IIRC the leakages were about 1pA at room temperature.

One thing that surpised me was that, while static leakages were that low,
dynamic leakages (100kHz switching) were not negligeable at all.

Quizz: how do you pump fraction of a uA through the resistors with the
switch wired as below?

4053
.------------.
| | ___
| |--|___|- GND
___ | o---/| 50K
GND -|___|--|---o--__ |
50K | o--- | ___
| \|--|___|- GND
'------------' 50K


--
Thanks,
Fred.


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