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THS4520 Input Characteristics and Protection When Powered Off?

Bill Bordy
Prodigy 30 points
Other Parts Discussed in Thread: THS4520


I wish to use the THS4520 differential amplifier to receive a differential signal pair from another card via a differential cable. I am concerned about a situation where the THS4520 is powered off, VS+ and VS- at ground, but a signal is applied to the differential inputs. I have examined the specification document and the TI WEB site and the only information I can find of use is the absolute maximum ratings specifications Vi and Vid. Vi states the limit as +-Vs and Vid as 4V. However, neither of these take into the current limiting of the input resistors, Rg. I realize the bias input current is very low when the device has power applied, but I do not know what the input characteristics are when the device is not powered. How can I assure the THS4520 is not damaged if I have a signal applied to the input Rg resistors and the THS4520 is not powered up?

  • 0
    TI__Expert 4115 points

    Bill Bordy,

    The THS4520 has built in ESD protection. In the case where power in not on and the supplies are at ground, an input sigal will turn on the ESD protection devices at about a diode drop (0.7V to 1V). The characteristic of the signal determines whether or not it will damage the device. ESD type discharges are listed in the absolute maximum table. These are fast events that only last for short time duration. Of more concern is long duration DC currents. A sustained DC current into the devices (or any device) will cause migration of the metal used in the traces on the die. Due to this, long term DC current should be limited to < 10mA. If the signal is AC or short term, a higher amount is tolerated, but should still be limited if possible.

    To calculate the current, subtract 1V from the signal and divide by the value of RG.