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Logic Design for Array-Based Circuits

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White

 

Power Considerations

Last Edit July 22, 2001


Computing DC Power Dissipation

To compute the worst-case DC power for a non-CMOS circuit, perform the following steps. There will be some variation in the complexity of the steps between vendors, depending on the method used to specify current or power dissipation for individual macros.

Steps To Compute Maximum Worst-Case DC Power

The following example methodology assumes that typical current is specified. It applies to any power-supply configuration

  • Sum all individual interface macro currents and multiply by the interface macro worst-case current multiplier. Keep IEE and ICC separate

  • Sum all individual internal macro currents and multiply by the internal macro worst-case current multiplier. Keep IEE and ICC separate. Skip this step for the BiCMOS arrays

  • Find the IEE and ICC overhead currents and multiply them by the worst-case overhead current multiplier. Keep IEE and ICC separate

  • Add all IEE currents together

  • Add all ICC currents together

  • Find the worst-case VCC and VEE voltages

  • Multiply IEE * VEE

  • Multiply ICC * VCC

  • Compute ECL static power dissipation:
    1.3 * termination current * number of outputs.
    Adjust the equation when the standard assumptions are not met

  • Add all items together. This is the worst-case maximum DC power dissipated by the circuit if it is bipolar. It is the interface macro worst-case maximum DC power if the circuit is for the BiCMOS arrays

Reduction for single-supply circuits

There is an obvious reduction in the complexity of the steps if the circuit uses only one power supply. Under this condition, IEE becomes ICC when a +5V reference circuit is being analyzed. There is no ICC in a -5.2V or -4.5V single-supply circuit

Table 7-11 Currents Present By I/O Mode

Power Supply Technology Compute IEE Compute ICC
SINGLE, +5V 100% TTL - X
SINGLE, +5V 100% ECL - X
SINGLE, +5V ECL/TTL - X
SINGLE, -5.2V 100% ECL X -
SINGLE, -4.5V 100% ECL X -
DUAL, +5V -5.2V 100% ECL X -
DUAL, +5V -5.2V ECL/TTL X X
DUAL, +5V -4.5V 100% ECL X -
DUAL, +5V -4.5V ECL/TTL X X

The unusual dual-supply 100% ECL circuits (DECL) shown in Table 7-11 are required for minimum cell 25 ohm terminations (see the AMCC Q20000 Series Darlingtons)

 

 

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




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