Calculating the power dissipation of a CMOS logic IC

Power dissipation should be calculated from both of the following:

- Static supply current
- Dynamic supply current

Power can be obtained by multiplying current by the voltage applied to an IC.

**Static power dissipation: P _{S}_{
}**While CMOS logic is in a static state (i.e., while its input voltage remains almost unchanged), little current flows in it except tiny leakage current that flows across the internal reverse-biased pn junction (known as static supply current, I

P

I

**Dynamic power dissipation: P _{L}+P_{PD}**

Dynamic power dissipation is dynamic supply current multiplied by the voltage applied to the p-channel or n-channel MOSFET.

For the sake of simplicity, the following calculation assumes that this voltage is equal to V

**Dynamic power dissipation due to load capacitance (C _{L}): P_{L
}**P

The amount of charge (Q

Q

Let the output signal frequency be f

I

P

P

**Dynamic power dissipation due to internal equivalent capacitance (C _{PD}): P_{PD
}**CMOS logic ICs have various parasitic capacitances as shown by the right-hand figure. These capacitances are equivalently expressed as C

P

Note, however, that P

P

_{TTL}) can be obtained as the sum of static power dissipation (P_{S}) and dynamic power dissipation (P_{L} + P_{PD}):

P_{TTL}＝ P_{S} + P_{L} + P_{PD}

Handling of Unused Input Pins

Input Rise and Fall Time Specifications

Multiple Outputs from a General-Purpose CMOS Logic IC Come Into Conflict (Short-Circuiting)

Connecting a Load Capacitance to a CMOS Output Pin

Level Shifting Using an Input-Tolerant Function

Example of Application of the Power-Down Protection Function (Partial Power-Down)

Input-Tolerant and Output Power-Down Protection Functions Available with Each Series

Types of Noise to be Noted

Countermeasures for Reducing Switching Noise

Countermeasures for Signal Reflection

Countermeasures for Crosstalk

Countermeasures for Hazards

Countermeasures for Metastability

Countermeasures for Latch-Up

Countermeasures for ESD Protection

**Application Notes****FAQ**

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