Logic Design for Array-Based Circuits

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White

 

Power Considerations

Last Edit July 22, 2001


Step 7: Compute the Worst-Case Overhead Current

Multiply both the IEE and ICC overhead currents by the worst-case current multiplier for the overhead current (WCCM3) to obtain the worst-case overhead currents

    IoverheadCCwc = WCCM3 * IoverheadCC
    IoverheadEEwc = WCCM3 * IoverheadEE

Step 8: Sum the ICC and IEE Currents

Sum the internal macro, interface macro, and overhead worst-case currents, keeping ICC and IEE separate to find the total IEE and ICC worst-case currents

    ICCwc = SUM IinternalCCwc + IinterfaceCCwc + IoverheadCCwc
    IEEwc = SUM IinternalEEwc + IinterfaceEEwc + IoverheadEEwc

Step 9: Multiply by the Worst-Case Voltage

The worst-case voltage is dependent on whether the circuit is commercial or military and the specified allowed power supply variations. The array data sheet carries this information. The typical variation is shown below. For commercial circuits, with a -5.2V or a +5V supply, the voltage variation is usually 5%. For commercial circuits using VEE = -4.5V, the variation is 7%

For military circuits, the voltage variation is usually 10%. Note: The worst-case voltage for the -4.5V supply as listed on the Q20000 data sheet, where -4.5V supply varies 7%. The worst-case voltage is taken as -4.8V for military or commercial circuits

Table 7-14 Example Worst-Case Voltages

Nominal Commercial MILITARY
+5.0V +5.25V +5.5V
-5.2V -5.46V -5.72V
-4.5V -4.8V -4.8V

Multiply the worst-case DC current by the appropriate worst-case voltage:

    PEEDC = IEEwc * VEEwc
    PCCDC = ICCwc * VCCwc

This product is the worst-case DC power due to the macros on the array.

Copyright @ 2001, 2002 Donnamaie E. White, White Enterprises
For problems or questions on these pages, contact dew@Donnamaie.com