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AR# 61125

7 Series - Additional details on the Overshoot/Undershoot specification tables

Description

Why do the Tables for Overshoot and Undershoot appear to contradict the Recommended Operating Condition of VCCO + 0.20V or below GND - 0.20V.

Solution

The difference between the values is due to the difference between the Recommended Operating Conditions and the Absolute Maximum Ratings.

Absolute Maximum Ratings are stress ratings only, and functional operation of the device at these or any other conditions beyond those listed under Operating Conditions is not implied . The Absolute Maximum VIN of Vcco+0.55V or Absolute Minimum VIN of -0.5V is for the DC signal, so that is the 100% UI. If you overshoot for less time the overshoot limit is higher.

Unlike other Absolute Maximum Ratings, Overshoot and undershoot (with the values specified in the data sheet) will not affect the device reliability over the device lifetime, however data sheet specifications like the delay from IOB pad through the input buffer known as Tiopi might be affected. Tiopi is dependent on the rise and fall times.

In the first scenario the rise and fall times are not affected because the starting point of the falling edge is within the recommended operating conditions. The second scenario will cause the fall time for the I/O to be pushed out because it started above the recommended operating conditions. To understand the amount of push-out or pull-in due to this effect, use the IBIS or HSPICE model to simulate.



 


Another question that has been asked is about the NOTE for the HP bank that states "For UI lasting less than 20 us" which only applies to certain values in the table.

If the duration of the overshoot between Vcco+0.6V and Vcco+0.65V is less than 10us, then the time between Vcco+0.65 and Vcco+0.7 has to be less than 10us.


For example looking at Table 4: VIN Maximum Allowed AC Voltage Overshoot and Undershoot for PS I/O and PL HR I/O Banks of (DS187) Z-7010, Z-7015, and Z-7020 Data sheet the values are mapped into the diagram below to help explain the duration requirements of the table.


Note: In XCN14014 (v1.0) it is stated that the undershoot threshold for inputs is changing from GND - 0.30V to GND - 0.20V.

It was initially incorrectly documented and should have always been -0.2V.


AR# 61125
Date 04/07/2017
Status Active
Type General Article
Devices
  • Artix-7
  • Kintex-7
  • Virtex-7
  • Zynq-7000