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CD4051B-Q1: Device Behavior while Supply is Off

Shinichi Yokota
Genius 9715 points
Part Number: CD4051B-Q1

Hello,

  • What will the switch state of CD4051B-Q1 be when power is not supplied and the INH pin is pulled down Low? Will the COM pin connect with any channel? Or, will all the channels be disabled?
  • The absolute Max rating of "DC Input Voltage" is VDD + 0.5 V, but is it OK to apply a voltage of more than VDD + 0.5 V if the "DC Input Current" is limited below 10 mA by external register? I assume the situation when the power is not supplied while a voltage divided by a resistor divider is applied to a channel.

Best regards,
Shinichi Yokota

  • 0
    TI__Genius 9132 points

    Hi Shinichi,

    1. The CD4051B-Q1 does not support powered-off protection that maintains a high-impedance state on the I/O and digital logic pins when the switch’s supply is unpowered. The channels will be disabled only when "INH" is HIGH.

    When INH is pulled down Low and there is voltage on the switch I/O path, if the I/O voltage exceeds the supply voltage rail, it will forward-bias the internal electrostatic discharge (ESD) protection diode that exists between the I/O pins and VDD. When the internal ESD diode is forward-biased, the voltage on the I/O path can backpower the switch supply pin and damage components on the power rail. Additionally, the forward biased diode can provide a path to back-power the signal switch itself, unintentionally turning on the I/O path. This is specd in the datashheet in the absolute max limits. VDD +.5V   

    In order to avoid back-powering, please ensure there are no active I/Os when VDD is 0 and ramping up. This may damage the device with excess current.

    2.  The abx max spec refers to when you have a supply VDD and the voltage on the signal path is less than -0.5 V or greater than VDD +0.5V  the current needs to be limited to <10mA to prevent permanent damage to the IC.

    You can use internal ESD diode to clamp the voltage as long as you maintain the current limits. This is a concept many customers implement in their systems. Here is a good  link to show how to use the internal diode, or an external diode to clamp the voltage, or use a series resistor to limit the current.

    What is the voltage requirement for your application - if you are not using dual supply and have low voltage application, I would  also recommend using the TMUX1308-Q1 that has back-powering protection along with other features (1.8-V compatible control inputs, Break-before-make, Injection current control).

    Regards

    Saminah