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RAMCHECK Application Note

Testing Legacy EDO/FPM DRAM Devices at 5V or 3.3V

--Created 9-22-10

Legacy EDO/FPM DRAM devices were introduced initially at 5V operation and later lower voltage 3.3V version came to the market.

When the RAMCHECK / RAMCHECK LX unit is set at the Auto/Default mode, the test program uses a proprietary heuristics algorithm that attempts to determine the operational voltage, 5V or 3.3V. It should be noted that some legacy DRAM devices that are designed for 5V may still work at 3.3V, and vice versa, due to the fact that the CMOS process is inherently tolerant for 3.3V/5V. Therefore, by merely testing at 5V or 3.3V one cannot determine for sure if the device is made for 5V or 3.3V. Please note that most of the "5V" test phases are actually conducted at 4.5V to 4.6V, in view of the safe operation range of the 3.3V devices. In particular, BASIC TEST runs at 4.5V-4.6V if the device is set to 5V.

Our algorithm to automatically detect the voltage is based on the well known phenomenon that access times decrease at lower voltages. For example, a 5V device will tests at slower speed at 3.3V compared the "normal" voltage of 5V. On the other hand, a 3.3V device may have smaller degradation of speed compared to testing at 5V. Therefore, our heuristic algorithm tests a small section of the memory device under test (DUT) at both 3.3V and 5V and compares the measured access times. It determines if the speed degradation between the two test voltages (5V and 3.3V) is above an arbitrary threshold. DUTs that score above the threshold are flagged as 5V, the rest are flagged as 3.3V.

It is very clear that this voltage detection algorithm cannot be very accurate. In fact, all modern memory devices encode the operational voltage within the SPD, so that the controller may select the proper voltage. The legacy EDO/FPM devices do not have such a built in identification. We therefore cannot guarantee that the RAMCHECK/RAMCHECK LX will auto select the correct voltage for every FPM/EDO you test.

To achieve consistent results, you must determine from the published data sheet of the DUT whether it is 5V or 3.3V and verify that the RAMCHECK/LX identifies the voltage correctly. We recommend that if you have questionable test results testing any FPM/EDO device, make sure that you monitor the voltage level at which the device is run.

If you do not have the data sheet for your tested devices, we recommend that you manually set the test at 3.3V as described below.

When testing legacy devices, we strongly recommend that you manually adjust the test voltage when dealing with legacy EDO/FPM devices through the "Setup" option.

Please make sure at the end of Basic Test that an automatic detection of 5V is correct before continuing with Extensive Test and Auto-Loop. This is particularly important when testing individual chips, where the auto voltage detection is generally less accurate.

Manual 5V or 3.3V Setup

To set up the tester to 5V or 3.3V, access Setup from Standby mode by pressing F2. Follow the Parameters menu to reach the Voltage menu where you set the desired voltage. You can also change the voltage during the test using the "Change-On-The-Fly" feature, by simply pressing F2 during Basic Test and select the Voltage menu.

If you have additional questions, please contact our technical support department at (281) 879-6226 M-F 9:00-5:00 Central Time, or send your E-mail to support@innoventions.com, or fax your message to (281) 879-6415. Please remember to include your phone and e-mail.

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