What are timing characteristics?
Watch this video to learn how switch timing characteristics are measured and where to find them in the datasheet.
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Hello. And welcome to the Multiplexer Series on Basics of Multiplexers and Signal Switches. This video series explains the basics of analog signal switches offered by Texas Instruments. In this video, we will have a short discussion on timing characteristics of switches and multiplexers such as turn-on time, turn-off time, break-before-make delay, and transition time. The goal of this video is to understand the timing characteristics of switches and where to find these characteristics in the data sheet.
Let's start with t-on. This characteristic may also be called t-switch or t-enable in different data sheets. T-on is the time required for the switch path to be charged to the on state. For this example switch, the t-on time for VIOA and B are measured from the time the select line reaches the logic low or high threshold to the time VIOA or B reaches 90% of its expected high-state voltage.
Similarly, t-off is the time required for the switch path to be charged to the off state. T-off is measured from the time the select line reaches the logic low or high threshold to the time the VIO reaches 10% of its high-state voltage. These timing characteristics determine how fast you can switch to different inputs, which is important for applications which need to cycle through inputs quickly, such as sample and hold applications and protection systems.
Break-before-make delay is a safety feature that prevents two inputs from connecting when the device is switching. The output first breaks from the on-state switch before making the connection with the next on-state switch. The time delay between the break and the make is known as Break-Before-Make delay, or TBBM. In this circuit, TBBM is measured from the time VIO drops to 90% of its on-state value until the time that it rises again to 90% of its on-state value. Without brake-before-make, you could see unwanted glitches in your output.
Transition time, t-transition or sometimes t-tran, is defined as the time taken by the output of the device to rise or fall 10% after the select signal has risen or fallen past the logic threshold. The 10% transition measurement is utilized to provide the timing of the device. System level timing can then account for the time constant added from the load resistance and load capacitance.
Please note that most devices are measured at the 10% and 90% points. But some devices may have been measured to the 50% point. These timing characteristics can often be found in the electrical characteristics section or a timing requirements section of the data sheet.
These characteristics are specified under certain test conditions as listed in the data sheet. These conditions may include load resistance and capacitance as well as differing supply voltage and signal voltage. Some data sheets may even include figures showing the measurement set up for each timing characteristic, located in the parameter measurement information section or detailed description section of a data sheet. In addition, the typical characteristics section of the data sheet may show curves of certain timing characteristics as a function of supply voltage or temperature.
Thank you for watching the timing characteristics video of the TI Precision Labs Multiplexers Basic Series. To find more multiplexers and signal switches, technical resources, and search products, visit TI.com.
This video is part of a series
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Precision labs series: Understanding switches and multiplexer's features and parameters
video-playlist (15 videos)