9.2.1.1 Power Considerations

Ensure the desired supply voltage is within the range specified in the Recommended Operating Conditions. The

supply voltage sets the device's electrical characteristics as described in the Electrical Characteristics.

The ground must be capable of sinking current equal to the total current to be sunk by all outputs of the

SN74HCS09 plus the maximum supply current, ICC, listed in Electrical Characteristics. The logic device can only

sink as much current as is provided by the external pull-up resistor or other supply source. Be sure not to exceed

the maximum total current through GND listed in the Absolute Maximum Ratings.

Total power consumption can be calculated using the information provided in CMOS Power Consumption and C

pd Calculation.

Thermal increase can be calculated using the information provided in Thermal Characteristics of Standard Linear

and Logic (SLL) Packages and Devices.

CAUTION

The maximum junction temperature, T J(max) listed in the Absolute Maximum Ratings, is an

additional limitation to prevent damage to the device. Do not violate any values listed in the Absolute

Maximum Ratings. These limits are provided to prevent damage to the device.

9.2.1.2 Input Considerations

Input signals must cross Vt-(min) to be considered a logic LOW, and Vt+(max) to be considered a logic HIGH. Do

not exceed the maximum input voltage range found in the Absolute Maximum Ratings.

Unused inputs must be terminated to either V CC or ground. These can be directly terminated if the input is

completely unused, or they can be connected with a pull-up or pull-down resistor if the input is to be used

sometimes, but not always. A pull-up resistor is used for a default state of HIGH, and a pull-down resistor is used

for a default state of LOW. The resistor size is limited by drive current of the controller, leakage current into the

SN74HCS09, as specified in the Electrical Characteristics, and the desired input transition rate. A 10-kΩ resistor

value is often used due to these factors.

The SN74HCS09 has no input signal transition rate requirements because it has Schmitt-trigger inputs.

Another benefit to having Schmitt-trigger inputs is the ability to reject noise. Noise with a large enough amplitude

can still cause issues. To know how much noise is too much, please refer to the ΔV T(min) in the Electrical

Characteristics. This hysteresis value will provide the peak-to-peak limit.

Unlike what happens with standard CMOS inputs, Schmitt-trigger inputs can be held at any valid value without

causing huge increases in power consumption. The typical additional current caused by holding an input at a

value other than VCC or ground is plotted in the Typical Characteristics.

Refer to the Feature Description for additional information regarding the inputs for this device.

9.2.1.3 Output Considerations

The ground voltage is used to produce the output LOW voltage. Sinking current into the output will increase the

output voltage as specified by the VOL specification in the Electrical Characteristics.

Open-drain outputs can be directly connected together to produce a wired-AND. This is possible because the

outputs cannot source current, and thus can never be in bus-contention.

Unused outputs can be left floating. Do not connect outputs directly to VCC or ground.

Refer to Feature Description for additional information regarding the outputs for this device.

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SN74HCS09

SCLS779A – JUNE 2020 – REVISED OCTOBER 2020

Copyright © 2020 Texas Instruments Incorporated

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Product Folder Links: SN74HCS09