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Reg: Developing high side switch for 20uA continuous current.

Prakash S
Prodigy 150 points

Dear All,

I have a sensor which can give a signal in terms of 0 - 17 V with the maximum current of 20 uA. Actually I don't have an issue in developing the signal conditioner circuits.

My system consist of three main components (sensor, signal conditioning, Energy management circuit (EMC)).

When I am connecting my EMC circuit to the senor, the signal will completely dip to 0 V. Because the EMC has very low impedance. Actually I need a switch type of circuit connected in series fashion (sensor - switch - EMC). In this case I can use the configuration of High side MOSFET, but problem is I need high side MOSFET driver mechanism and etc. 

My requirement is some switch circuit rated for 100 uA circuit  can be controlled by high (3.0) low (0) logic. When logic is high, switch should in open circuit and vice versa. 

Actually my requirement may appear very wired, but I am struggling very badly to solve this issue. 

 Thank you,

  • 0
    TI__Mastermind 26383 points

    Hey S.P

    My understanding is that you have a 17V signal with a current of 20uA. Now what happens next is where you lost me a little bit.But i'm understanding that you need a enable Low device who's logic level are Vih = 3V and is a 1:1 switch to connect and disconnect the signal.
    If these are the criteria you're looking for, then unfortunately we won't have a device that matches all of those perfectly.

    But we do have some that are close.
    Are these differential signals or just single wire?

    We do have devices such as the CD4066B that can handle up to 20V when using a single sided supply but the Vih (voltage required for high state) unfortunately exceeds your needs. 

    Your best bet may be something like the MUX36D04 or MUX36S08 (depending if differential or not). Both these meet most the requirements, Can handle 17V, 20uA, Vih level is 2V, Vil is 0.8V. But unfortunately the logic is reverse what you're looking for ("When logic is high switch should be in open circuit'. You'll have extra paths but you'll just need to switch to an unused grounded channel to disconnect the device instead.

    Let me know if i've understood this properly. If not, maybe a diagram or figure would help better!

    Rami Mooti

  • 0 in reply to Rami Mooti1
    Prodigy 150 points

    Dear rami mooti,

    Are these differential signals or just single wire?

    (single wire)

    Actually, I have attached the image. There you can find Q1 in the schematic, it need a driver circuit to drive it. Since my current is 20 uA, every thing are passed through it due to leakage current of Q1. I actually looking for mechanical MEMS switch can be open an close as per my requirement.

    Thank you,

  • 0 in reply to Prakash S
    TI__Mastermind 26383 points

    Hey S.P,

    TI unfortunately doesn't have mechanical MEMS that I know of. I may be mistaken and it's worth taking a look.
    As I mentioned above there are switches that will hit certain requirements and will miss on others. If you decide to go with electrical switching though let me know and perhaps we can look into some power switches that may meet all your requirements? 

    Thanks,
    Rami