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SN74HCS266

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SCLS780 – JUNE 2020

Product Folder Links: SN74HCS266

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8 Detailed Description

8.1 Overview

This device contains four independent 2-input XNOR gates with open-drain outputs and Schmitt-trigger inputs.

Each gate performs the Boolean function Y = A

⊕ B in positive logic.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 CMOS Open-Drain Outputs

output is not actively pulling the line low, it will go into a high impedance state. This allows the device to be used

for a wide variety of applications, including up-translation and down-translation, as the output voltage can be

determined by an external pull-up resistor.

The current drive capability of this device creates 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 for the power output of the device to

be limited to avoid thermal runaway and damage due to over-current. The electrical and thermal limits defined

the in the Absolute Maximum Ratingsmust be followed at all times.

The SN74HCS266 can drive a load with a total capacitance less than or equal to the maximum load listed in the

Switching Characteristics connected to a high-impedance CMOS input while still meeting all of the datasheet

specifications. Larger capacitive loads can be applied, however it is not recommended to exceed the provided

load value. If larger capacitive loads are required, it is recommended to add a series resistor between the output

and the capacitor to limit output current to the values given in the Absolute Maximum Ratings.

8.3.2 CMOS Schmitt-Trigger Inputs

Standard CMOS inputs are high impedance and are typically modeled as a resistor from the input to ground 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).

which makes this device extremely tolerant to slow or noisy inputs. While the inputs can be driven much slower

than standard CMOS inputs, it is still recommended to properly terminate unused inputs. Driving the inputs slowly

will also increase dynamic current consumption of the device. For additional information regarding Schmitt-trigger

inputs, please see Understanding Schmitt Triggers.