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Hello. When working with all TI devices, it's important to reference the TI product data sheet which can be found on the product page. The product page can be found on ti.com. For additional troubleshooting information, please refer to ti.com/troubleshooting. When debugging potential output errors from an ADC, it can be a difficult task. In today's demonstration, we're going to cover an op amp specification known as output swing. Measuring this specification can help you identify the root cause of the ADC anomaly.

Before we begin, let's cover some additional training collateral that TI has on ti.com. Some of the prerequisites that are important to reference are, TI-Precision Lab courses such as Output and Input Limitations. In addition, TI provides free simulation software known as TINA-TI. This software can be downloaded for free on ti.com/tina-ti.

Now that we've covered op amp prerequisites, let's talk about op amp test loops. The op amp test we'll be covering is the false summing junction. The majority of DC data sheet parameters can be measured utilizing the false summing junction circuit shown on the screen. The majority of DC parameters can be measured with just the use of four resistors in the circuit. Some of the op amp specifications to call out for this demonstration are VOS, which is defined as the differential input voltage required to force the output to mid supply, and output swing. Output swing can be measured by forcing the output voltage near the positive or negative supply by applying a voltage to the VOC pin denoted in the schematic in the slide.

Now that we've covered op amp test loops, let's get into more detail about this specification called output swing. The first and a very important thing to mention before discussing output swing in detail is that output swing is not the same as offset voltage of an amplifier. The offset voltage of an amplifier is strictly defined in our data sheets when Vout and the common mode voltage are equal to mid supply. When we discuss output swing, we can describe it as how close the output voltage of the op amp can reach the positive or negative supply voltage.

For example, this is when Vout is not equal to mid supply. Thus, we are outside of where VOS is defined in the TI product data sheet. Let's show what output swing looks like from a visual perspective using an animated graph. In this graph, we see the x-axis is Vout and the y-axis being the supply voltage. Between the middle region of the graph, we see that this is a linear region. This is where the output voltage tracks in a linear progression.

As we move outside of this output region, we see that the output voltage tends to saturate towards a value known as VOL or the output swing. This is some distance away from the negative supply but not reaching the negative supply voltage. So before testing output swing, it's important to review the TI product data sheet for the test conditions. Reviewing the data sheet excerpt below, we can see that the output swing specification has different values for each different load specified in the data sheet.

Now that we've covered output swing in detail, let's go ahead and get into the demonstration. For this demonstration, we're going to be using the conditions shown on the slide deck. For this demonstration, we're going to measure the output swing from the positive rail as defined by the TI product data sheet. Before ending the demonstration, we will measure the output voltage of the amplifier. For this demonstration, we'll make use of three pieces of equipment-- two power supplies for the DC voltages. The power supply on the top will be used to supply the input voltage to force the output to 12 volts. And we'll use the digital multimeter to measure the output voltage of the amplifier.

We've recreated the false summing junction circuit utilizing a universal prototyping board, otherwise known as a universal breadboard. Now, let's begin the demonstration by providing plus or minus 12 volts to our operational amplifier using the bottom power supply. It's important to mention that we're using a 10 kiloohm load resistor as defined by the TI product data sheet. The digital multimeter is measuring the output swing voltage on the white wire shown here. The digital multimeter is reading 11.904 volts, which is 95 millivolts from the positive supply rail of the operational amplifier.

Now that I've shown you this technique on how to measure output swing of an operational amplifier, it's important to apply this technique when troubleshooting ADC output errors in your application. For additional troubleshooting tip information, please refer to ti.com/troubleshooting. Thank you for watching.

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