Gates, Packaging, and Boards: Properties and Modeling

Abstract

This chapter talks about how packaging and circuit boards affect logic gates (actually, logic inputs and outputs) and reviews concepts like noise margin, drive strength, and source resistance. It also discusses heat and temperature and the different options that exist for modeling boards and circuits.

Homework

• 1. Consider an output from a chip that is driving a circuit with 50 pF of capacitance. The output switches between 0 and 3.3 V and toggles at an average frequency of 625 MHz:

  • (a) How much power does it dissipate?

  • (b) Where is the power dissipated – in the chip, the wiring, or the circuit that the chip is driving?

  • (c) What three things could be done to reduce power dissipation?

• 2. Consider a 78 M05 voltage regulator design:

  • The regulator goes into thermal shutdown at a junction temperature of 125 °C or above.

  • 1 Amp output current.

  • The regulator takes in voltage at 9VDC and outputs 5VDC. So the power that it dissipates is calculated by multiplying the current by 4 V (the voltage drop).

  • Heat sink design has a thermal coefficient of 45 °C/W. (The junction temperature is 45 °C/W above the ambient temperature.)

    • (a) At what ambient temperature does the 78 M05 go into thermal shutdown?

    • (b) Consider the same design, except that now it operates at a maximum ambient of 80 °C. At what current does it go into thermal shutdown?

• 3. Consider a capacitor has a capacitance of 10 μF, a resistance of 0.2 Ω, and an inductance of 0.3 nH:

  • (a) Calculate the self-resonant frequency. (See formula 3.7.)

  • (b) Construct a SPICE simulation and compare results.

• 4. A datasheet lists the self-resonant frequency for a 25 μF capacitor as 5.2 MHz. What is the ESL of the capacitor?