6.3 Feature Description

6.3.1 Balanced CMOS Push-Pull Outputs

This device includes balanced CMOS push-pull outputs. The term balanced indicates that the device can sink

and source similar currents. The drive capability of this device may create fast edges into light loads, so routing

and load conditions should be considered to prevent ringing. Additionally, the outputs of this device are capable

of driving larger currents than the device can sustain without being damaged. It is important to limit the output

power of the device to avoid damage due to overcurrent. The electrical and thermal limits defined in the Absolute

Maximum Ratings must be followed at all times.

Unused push-pull CMOS outputs must be left disconnected.

6.3.2 Standard CMOS Inputs

This device includes standard CMOS inputs. Standard CMOS inputs are high impedance and are typically

modeled as a resistor in parallel with the input capacitance given in the Electrical Characteristics. The worst

case resistance is calculated with the maximum input voltage, given in the Absolute Maximum Ratings, and the

maximum input leakage current, given in the Electrical Characteristics, using Ohm's law (R = V ÷ I).

Standard CMOS inputs require that input signals transition between valid logic states quickly, as defined

by the input transition time or rate in the Recommended Operating Conditions table. Failing to meet this

specification will result in excessive power consumption and could cause oscillations. More details can be found

in Implications of Slow or Floating CMOS Inputs.

Do not leave standard CMOS inputs floating at any time during operation. Unused inputs must be terminated at

VCC or GND. If a system will not be actively driving an input at all times, then a pull-up or pull-down resistor can

be added to provide a valid input voltage during these times. The resistor value will depend on multiple factors; a

10kΩ resistor, however, is recommended and will typically meet all requirements.

6.3.3 Clamp Diode Structure

As shown in Figure 6-2, the inputs and outputs to this device have both positive and negative clamping diodes.

CAUTION

Voltages beyond the values specified in the Absolute Maximum Ratings table can cause damage

to the device. The input and output voltage ratings may be exceeded if the input and output clamp-

current ratings are observed.

GND

Logic

Input

Output

VCC

Device

-IIK

+IIK

+IOK

-IOK

Figure 6-2. Electrical Placement of Clamping Diodes for Each Input and Output

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CD74AC151

SCHS333B – MARCH 2003 – REVISED MAY 2025

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