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There is a certain system (PCB) which is built around an ARM microcontroller. In order to test the system, I used a DAQ by National Instruments which is able to simulate various conditions (both analog and digital) that enable me to fully test the device.

So here is the problem - One of the central tests is to measure the leakage current of the board when the MCU sleeps. Normally this works fine and the readings are in the tens of microamps. When the NI DAQ pins are connected this figure goes up much higher, to a point that the test makes no sense at all. Disconnecting all the pins physically solves the problem, however this is not something I can do as the tests should be fully automatic.

I was thinking about using some form of bi-directional tri-state buffers in order to disconnect digital pins (they function as I/Os) when testing leakage and use mechanical relays for analog pins. This is in order to reduce the number of required relays.

Any other way out of this? I think I'll be able to tolerate a leakage of 1 to 2uA. System runs on 3.3V.

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Mechanical relays are not really necessary for any of your pins.

Virtually any CMOS SPST should be able to stay way below 1 µA off-leakage. They do present a little more parasitics than relays but are much more reliable/long-lived on the upside.

They come with various on-resistance ratings between about 1 Ohm and 1 kOhm, where the more resistant ones have capacitance on the order of pF, whereas the lower-resistance ones are near ~nF.

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  • \$\begingroup\$ TS12A4515D which is an old part with 'high' ON of 10 to 20 Ohms (OK in my use case) has between 1 to 10 nA leakage when OFF. I can live with that. \$\endgroup\$
    – user733606
    Sep 28 at 10:43
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A relay is the completely wrong component. Reasons to pick relays is when you need to switch high currents and/or high voltages and/or galvanic isolation and/or easy maintenance.

Some of the down-sides with relays are: very slow, relatively expensive, reverse EMF upon activation, signal bouncing, limited life time, relatively high Rds(on), may "weld".

For delicate low current analog signals you use an analog switch, which is a certain kind of IC. They are explicitly designed to change the signal as little as possible, and to switch fast with as little disruption as possible.

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