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INH signal High when IC is unpowered

Category: Datasheet/Specs
Product Number: MAX4051

Hello, 

In my application, MAX4051 is supplied with +5.5V & -4V. I am applying 3V3 on INH Pin when my IC is unpowered. Will it damage the IC MAX4051? Will the IC gets powered up through 3V3 on INH pin ?

  • Hello Krn,

    The part will not be damaged.

    Not sure how the IC gets powered via INH which is very unlikely. Regardless, the switch will be inhibited/off.

    Please share your schematics if possible.

    Regards,

    edo

  • Hello Edo,

    In my application, initially V+(+5V5) & V-(-4V0) supply is not available i.e. V+ & V- are 0V but +3V3 is available & +3V3 is applied on ADD pin like the schematic below.

    When V+ & V- is Zero & ADD pin voltage is 3V3, I am exceeding the absolute maximum voltage rating of the pin. I want to understand that will the part get damaged in this condition.

    Also, as per Internal Diode structure at each pin, it is likely that 3V3 from ADD pin can powerup V+ rail, thereby power up the IC.

    One solution to add series resistor of 10k to ADD pin powered from 3V3. Can you share if the slow-rise Input signal on ADD pin will cause any issue?

    Please share your comments.

    Regards

  • 0
    •  Analog Employees 
    in reply to Krn

    Hi Krn,

    Not sure where you got the AMR for the ADD pin and its value. The min Vih for ADD is 2.4 V with V+ at 5 V and this threshold will rise as far as 3.1 V if V+ rises (to 12 V). So 3V3 will not damage the ADD pin.

    The notion of ADD pin at 3V3 with no V+ available will power the V+ through the diodes appears baseless, the internal diode structures that you have shown are those on the analogue input signal; if input signal voltage is present and the switch is powered off, there is the possibility to power the switch with V+ not available. Is this your real question, since you have shifted your initial question from INH pin to ADD pin.

    Please, can you detail your project, the volume of this business? Thanks.

    Regards,

    edo

  • Hello edo,

    Thank you for the reply. My application is Industrial & volume is 1k EAU.

    In my application, there exist a time when +3V3 on INH & ADD pin exist while V+/V- is 0V. I missed to mention that my concern is with both INH & ADD pins.

    Regarding Absolute Max Rating & Internal Diode structure, I am referring to datasheet section (below) which states that "Signals at any terminal are clamped with internal diodes".

    In order to limit current to INH & ADD terminal, I intent to put series resistor but it has a drawback that it slows rise/fall time of ADD signals.

    Please can you just help me with the maximum allowed transition time (rise time/fall time) for ADD signal.

    Regards

  • 0
    •  Analog Employees 
    in reply to Krn

    Hi Krn,

    The terminals the datasheet refers to are the analogue pins (NO, COM).

    I do not think there is a max allowed value stated in the datasheet for rise/fall time for ADD signal. You are controlling the ADD with a +3V3, so when the Vih/Vil are passed the signal levels gets registered accordingly.

    You can measure the rise time either as 10 - 90 % or 20 - 80 % of +3V3 and the fall time as 90 - 10 % or 80 - 20 % without placing any series resistor between the driver and the switch. There is a capacitance on your board trace, as well as input capacitance on the ADD pin (these values are not known to me). I do not know why you want to place a 10K Ohm resistor on the ADD signal line.

    Rise time formular = RC, so if you assume the capacitance on the ADD trace line to be 20 pF and rise time is 3 ns, then your series resistance is 150 Ohms.

    Regards,

    edo