LVC14A

(x6)

MCU

(MSP43x)

Push Butt on

GND

1Y

1A

SN54LVC14A, SN74LVC14A

SCAS285AA – MARCH 1993 – REVISED JUNE 2015

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10 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

10.1 Application Information

Physically interactive interface elements like push buttons or rotary knobs offer simple and easy ways to interact

with an electronic system. Many of these physical interface elements often have issues with bouncing, or where

the physical conductive contact can connect and disconnect multiple times during a button push or release. This

bouncing can cause one or more faulty transient signals to be passed during this transitional period. These faulty

signals can be observed in many common applications: for example, a television remote with bouncing error can

adjust the TV channel multiple times despite the button being pushed only once. In order to mitigate these faulty

signals, we can use a Schmitt-trigger, or a device with hysteresis, to remove these faulty signals. Hysteresis

allows a device to "remember" its history, and in this case, the LVC14A uses this memory to debounce the

physical element's signal, or filter the faulty transient signals and pass only the valid signal each time the element

is used. In this example, we show a push button signal passed through an LVC14A that is debounced and

inverted to the MCU for push detection.

10.2 Typical Application

The signal effects of the debounce circuit can be seen when comparing Figure 5 and Figure 6. In Figure 5, the

input is a very poor quality signal due to the error in the physical push button. If the MCU attempts to sample this

input to detect a push, there is high probability that multiple push events will be falsely detected. Once the

debounce circuit has been implemented, the input is cleaned up, and the MCU can perform push detection

without any error, as seen in Figure 6.

Figure 4. Debouncer Application Diagram

10.2.1 Design Requirements

The SN74LVC14A device uses CMOS technology and has balanced output drive. Take care to avoid bus

contention because it can drive currents that would exceed maximum limits.

The SN74LVC14A allows for performing logical Boolean functions with hysteresis using digital signals. All input

12

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