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AR# 65036

UltraScale FPGAs - Will driving the I/Os of an unpowered bank cause damage to the part?


Will driving the I/Os of an unpowered bank cause damage to the part?

How much current can the clamp diodes sink?


When driving an I/O in an unpowered I/O bank, there are two aspects of the device specifications that must be considered:

  1. Ensure the input current specification, Iin, from the data sheet is not violated.
    Unpowered pins still have clamp diodes present that will be forward biased when a pin voltage is applied.
    The IBIS model includes an IV curve for these diodes and can be used to determine clamping current.
  2. Voltage applied to pins in an unpowered bank can reverse power the bank in some circumstances.
    The overall system needs to be able to handle this situation.

For Example:

Clamp/ESD diode threshold will range from 0.43 to 0.64V. The worst case of 0.43V is at Tj = 100deg C. An unpowered part will remain close to ambient temperature.

For a C grade device, with Tj = 85 degrees C, assume diode drop = 0.53V. Then, Vcco could be reverse powered by Vin up to the Maximum Vcco- Diode drop at Tj = 85 degrees C (that is, 3.465V - 053V = 2.935 V).

At 85 degrees C, this condition could affect long-term reliability of the device if the power distribution system of the PCB does not sink enough current.

AR# 65036
Date 07/04/2016
Status Active
Type General Article
  • Kintex UltraScale
  • Virtex UltraScale
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