This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMH6401: Unpowered Maximum Input Power/Voltage

Genius 13859 points
Part Number: LMH6401

Hi Experts,

I have a customer who share an interesting topic about this RF amplifier.

The datasheet states the absolute maximum input voltage is VS- to VS+. This implies that the device may be damaged if any input signal is applied to the LMH6401 when it is not powered (VS- = 0V, VS+ = 0V) and if any current flows into the device when not powered. Is this true? Usually the limit is a diode drop from the supply voltages due to ESD diodes. If it's not true, then what are the actual absolute maximum input voltage limits? There application is approx +10dBm input power when the device is unpowered, which seems fine to me but technically exceeds absolute maximum ratings so I have to ask. I'm not sure how I would protect against this, is there a device with Ioff protection or something I can add in series?

Thank you for supporting.

Regards,

Archie

  • Hi Archie,

    I want to be sure I am understanding your question. Are you talking about a case where the device is in shutdown mode or a case where both of the supply rails are grounded?  If you were to place both the rails at 0V with an uninterrupted path to ground as you suggest and drive the inputs, it seems to me that one of the  ESD protection diodes (depending on the polarity of the input drive) would be at the mercy of the current limiting ability of the input impedance (100 Ohm + any series Rg). This would be very unusual to see in a typical application, because turning off power does not imply shorting the rail to ground, merely creating an open circuit (no current, no problem).

    Best,

    Sam

  • Hello Sam,

    Thanks for this reply. I received response from the client as follows:

    >>

    I'm talking about the case where the power supply is disabled and there is an RF input signal into a LMH6401 IC.
    When our power supply is disabled, we have a 510Ω resistor & QTY-9 LMH6401 ICs between VS+ and VS- (GND); so it's not a hard short like I implied.

    So if you know the maximum ESD diode current then we could figure what input voltage level would cause damage.
    Some datasheets give/imply maximum ESD diode current and minimum ESD diode drop in the abs ratings, but not this one.

    Also the LMH6401s won't be in power-down, so whatever back-current through the ESD diode will be trying to power the chips and it might increase when reaching above minimum supply voltage of 2.0V.

    <<

    Thank you for your support.

    Regards,

    Archie A.

  • Hi Archie,

    Thank you for clarifying. The max ESD diode current is 10mA.

    Best,
    Sam