SN74HCS09
SCLS779A – JUNE 2020 – REVISED OCTOBER 2020
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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 ΔVT(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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