External Memory Interface Handbook Volume 2: Design Guidelines

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ID 683385
Date 5/08/2017
Public
Document Table of Contents

9.13.2.2. Slew Rate Setup, Hold, and Derating Calculation

Slew rate is calculated based on the nominal slew rate for setup and hold times. The total tIS (setup time) and tIH (hold time) required is calculated by adding the Micron data sheet tIS (base) and tIH (base) values to the delta tIS and delta tIH derating values, respectively.

For more information about slew rate calculation, setup, hold, and derating values, download the data sheet specifications from the following vendor websites:

  • Micron (www.micron.com)For example, refer to Command and Address Setup, Hold, and Derating section in the Micron DDR3 data sheet.
  • JEDEC (www.jedec.org)For example, refer to the DDR2 SDRAM Standard data sheet.

The following section describes the timing derating algorithms and shows you where to obtain the setup, hold, and derating values in the Micron data sheet.

The slew rate derating process uses the following timing derating algorithms, which is similar to the JEDEC specification:

tDS = tDS(base) + deltatDS + (VIHAC -VREF)/(DQ slew rate)

tDH = tDH(base) + delta tDH + (VIHDC -VREF)/(DQ slew rate)

tIS =tIS (base) + delta tIS + (VIHAC -VREF)/(Address/Command slew rate)

tIH= tIH(base) + delta tIH + (VIHDC -VREF)/(Address/Command slew rate)

where:

  • The setup and hold values for tDS(base), tDH(base), tIS(base), and tIH(base) are obtained from the Micron data sheet. The following figure shows an example of the values from the Micron data sheet.
    Figure 96. Setup and Hold Values from Micron Data sheet


  • The JEDEC defined logic trip points for DDR3 SDRAM memory standard are as follow:
    • VIHAC = VREF + 0.175 V
    • VIHDC = VREF + 0.1 V
    • VILAC = VREF - 0.175 V
    • VILDC = VREF - 0.1 V
  • The derating values for delta tIS, tIH, tDH, and tDS are obtained from the Micron data sheet.

    The following figure shows an image of the derating values from the Micron data sheet.

    Figure 97. Derating Values from Micron Data sheet


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