TSU111: The Most Precise Nano-Power Op Amp from ST, 25 Years on a Single Battery!

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The TSU111 is ST’s most precise nano-power operational amplifier (op amp) by a wide margin, which enables the creation of longer-lasting and better-performing devices. The smart revolution, characterized by a myriad of sensors measuring everything and everyone, has brought on a fantastic paradox: this increasingly digital world is highly analog! Many components tasked with tracking their environment use an analog micro-electro-mechanical system. One of the challenges inherent to such components is that their low amplitude signal needs amplification. As a result, engineers use an operational amplifier before the analog signal reaches the digital components. However, this process can consume a lot of power, and introduce serious imprecision, which defeats the purpose of low power sensors. Hence, we start to understand why the outstanding specifications of the TSU111 took the market by storm to completely change what we thought possible.

TSU111: New Performance Record for Nano-Power Op Amps

The symbol for operational amplifiers

With a current consumption of only 900 nA at 25 ºC, the TSU111 inherits ST’s mastery in power management to be one of the lowest consumption op amps in the company’s portfolio. In fact, only the TSU101 requires less energy since it only draws 580 nA. However, whereas the latter has an offset voltage of 3 mV, the TSU111 has a maximum input offset voltage (Vio) of only 150 µV, making it vastly more precise while still remaining under 1 µA.

In a perfect world, the analog signal captured by a sensor would be perfectly amplified by an op amp with infinite gain. In this theoretical scenario, applying an input voltage of 0 V to the op amp results in an output voltage of 0 V. Unfortunately, the laws of physics that govern real life are a lot more problematic, and as the signal passes through the amplifier, noise and mismatches between the components inside the device lead to the introduction of errors and imprecision. If we use our previous example, applying an input voltage of 0 V to a real op amp will result in a negative or positive output voltage, depending on the device. In other words, the bigger the difference between the input and output voltages, the more imprecise is the op amp.

To better quantify that precision, we use the input offset voltage, or the voltage applied to the input terminals so the op amp can output 0 V. Hence, the TSU111’s offset voltage of only 150 µV, compared to the TSU101’s 3 mV, is an enormous difference that completely changes the precision that was originally possible with previous generation nano-power op amps.

Impressive Application Versatility

The TSU111 op amp is perfect for CO detectors (click to enlarge)

Despite making the TSU111 much more precise than the TSU101, ST was able to keep an identical supply voltage range of 1.5 V to 5.5 V. Such a low voltage, coupled with a sub-micro amp input current, means the TSU111 could operate on a 220 mAh CR2032 coin type battery for more than 25 years! Hence, adding multiple op amps like these would have a trivial impact on the circuit’s consumption, which makes the TSU111 a perfect fit for applications that must rely on a single battery for a very long time, like CO, O2, and H2S detectors found in homes and industrial settings.

The TSU111 also inherits the rail-to-rail design of the TSU101, meaning that the rail powering the circuitry can also power the op amp, greatly simplifying designs, while increasing the output’s dynamic range to ensure it can reach the negative and positive voltage of the power supply. This is particularly important because a rail-to-rail structure is indispensable in small applications.

Finally, the TSU111 has a typical gain-bandwidth product of 11.5 kHz, which is particularly high if we compare it to the 8 kHz of the TSU101. In a nutshell, it can help determine the maximum gain obtainable from the op amp at a particular frequency, which explains why the TSU111 is great for photovoltaic applications. Harvesting the current of a photodiode often demands a current-to-voltage converter, and given its high bandwidth and low current bias, the op amp can vastly improve the design’s efficiency by optimizing this particular conversion.

To know more about the different operational amplifiers available, please visit ST’s Op Amp section on its website.