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Original question:

LM2901AV-Q1: Vcc=0 conditions

LM2901AV-Q1: LM339LV-Q1: inputs active while unpowered

Alex L
Prodigy 180 points

Part Number: LM2901AV-Q1
Other Parts Discussed in Thread: LM339LV, LM339LV-Q1, LM2901AV, LM2901, LM339, LM393LV

Tool/software:

Dear staff

How would the LM339LV(-Q1) react when it is unpowered (supply voltage=0)
and inputs are tied to a non-ground positive source, 0V < V+ < +6V and/or 0V < V- < +6V (following the abs. max.) for an extended amount of time ?

How would the LM339LV(-Q1) react when it is unpowered (supply voltage=0)
and inputs are tied to a non-ground negative source, -1V < V+ < 0V and/or -1V < V- < 0V with a R > 1K resistor for an extended amount of time ?
This case would also be consistent with the abs. max. ratings, since current draw is less than 1mA.

Regarding powered LM339LV(-Q1), i.e. 1.8V <= supply voltage < +6V,
how would it react when inputs are tied to a non-ground negative source, -1V < V+ < 0V and/or -1V < V- < 0V with a R > 1K resistor for an extended amount of time ?
This case would be consistent with the abs. max. ratings, too, since current draw is less than 1mA.

Best regards

  • 0
    Guru 320330 points

    For positive voltages, no current flows.
    For negative voltages, a limited current flows out of GND.
    In both cases, you are below the absolute maximum ratings, so the device will not be damaged.

    Negative voltages when powered are outside the recommended operating conditions, so correct operation is not guaranteed.

  • 0
    TI__Guru 64586 points

    Hello Alex,

    Please see section 6.4.3 of the datasheet. This is all answered there.

    The inputs are what we call "failsafe", where you can apply a voltage to the inputs when the power is off (or pulled above supply) and the inputs will remain high-impedance and will not be damaged (obviously, the output is dead).

    You may apply a voltage continuously to the inputs without damage, even with the power off. The inputs are specifically designed for this condition.

    As Clemens mentioned - NO negative voltages are good. ESD diodes are not sized for continuous current dissipation so the less current the better. If negative voltages are expected during normal operation, we would recommend adding an external Shottky clamping diode to keep the currents off the ESD diodes in addition to the series resistor. I would keep the current to 1mA or less - as low as you can. The lower the current, the lower the Vf of the diode.

    As mentioned in 6.4.3.2 - whenever both inputs are out of input range, positive or negative, the output is *indeterminate*. This is pretty typical of R-R input devices with a complicated input sage.

  • 0 in reply to Paul Grohe
    Prodigy 180 points

    Thank you very much.

    In reference to chapter 6.4.3.2 of LM339LV-Q1 datasheet, what do you refer as the 'specified input voltage range'? (abs. max.?)

    And moreover, provided inputs are 'fail-safe', i.e. high impedance up to 6V also when power is OFF,
    is the output high impedance, too, when device is not powered, no matter what voltage is on the inputs?

    Finally,
    are LM2901AV(-Q1) inputs 'fail-safe' in the same meaning ?
    (i.e. -from what I understand- when device is unpowered, inputs are high impedance within abs. max. limits,
    with output being high impedance no matter what voltage is on the inputs)

    Many thanks in advance and best regards.

  • +1 in reply to Alex L
    TI__Guru 64586 points

    Hi Alex,

    Abs Max numbers are not guaranteed. Do not design to Abs Max.

    The "specified input range" is the "Input Voltage Range" shown in the Electrical Characteristic table.

    See the "Input Voltage Range" of the electrical table:

    This is the range where proper operation is guaranteed to datasheet limits. Both inputs must remain within this range for specified operation. The "one input out" behavior described in 6.4.3.2 is not considered proper operation and may not meet the datasheet limits during that time.

    For this device, the input range is between GND and V+, or between the rails. Proper operation may not occur if the applied voltage to either input exceeds the rails (either positive or negative).

    So if you have a single 5V supply, the "specified input range" is 0 to 5V.

    As this device is an Open Collector output, the output can be taken up to 6V, even with the power off. So the output will also be "high impedance" when the power is off.

    The inputs are designed to be high impedance (<1nA) at all times from 0V up to 6V (Abs Max), even when the supply is off. This allows direct measuring of load sensitive sources, such as a battery (< 6V), when the power is off.

    The LM2901 is considered the first "fail safe" device. The difference is that the LM2901 is a bipolar device that has a defined bias current (~5nA) flowing OUT of the input pins. When the input range is exceeded, the input stage gets cut off (Vcc-1V) and the current drops to the pA's all the way up to 36V.

    This is all explained in section 6.4 the LM339 family appnote:

    Application Design Guidelines for LM339, LM393, TL331 Family Comparators

    Also see section 2.3 of the Comparator Input Types appnote:

    Comparator Input Types

    The important to remember is that the LM2901 is a 36V bipolar device and the LM393LV is a 5V CMOS device - so there is a difference in the bias currents (and operating voltage!). The LM339LV is designed to be a low voltage (<5V) drop-in replacement for the LM2901/LM339 family.