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switching the VSS line of an IC

Discussion in 'General Electronics Discussion' started by Rajinder, Feb 15, 2018.

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  1. Rajinder

    Rajinder

    437
    7
    Jan 30, 2016
    Dear all,
    I have a IC which I need to switch off when not in use as it draws a current of 100uA in standby. I think the best way of doing this would be to disconnect the 0V line via a switch i.e. transistor or FET. I have one pin of my PIC I/O line which I could do this with.
    I am looking at a NPN to control the FET (which will be in series with the 0V line). The FET needs to have a low RDS on.

    Can anyone help with the circuit or advise? I have a problem understanding the maths behind doing this too.

    Thanks in advance,
    Raj
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,350
    2,255
    Nov 17, 2011
    You better switch the positive supply to ensure a good Vss connection at all times. When you switch Vss, there will be a considerable resistance in series with Vss in the on state which is detrimental for most IC's operation.
    You also need to be careful about input and output connections to the IC. ICs have input protection diodes to Vss and to Vcc. When you turn off the supply voltage, these diodes can become conductive and supply the IC with power throughthe internal Vcc and Vss connections. As this is not a normal mode of operation, the IC can in the worst case consume even more power than in idle mode.
     
  3. WHONOES

    WHONOES

    940
    239
    May 20, 2017
    Try looking for an IC that will switch into ultra low power mode. They generally have a pin just for that purpose. Never used one.
     
  4. Alec_t

    Alec_t

    2,890
    775
    Jul 7, 2015
    What IC is it?
     
  5. WHONOES

    WHONOES

    940
    239
    May 20, 2017
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