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Advantages of STOP function in low-noise data acquisition applications

Electromagnetic noise refers to any kind of excess electromagnetic energy that is strong enough to distort the signal. Therefore, when designing high-performance data acquisition applications or any system with particularly sensitive signal paths, the noise problem must be overcome.

Electromagnetic noise refers to any kind of excess electromagnetic energy that is strong enough to distort the signal. Therefore, when designing high-performance data acquisition applications or any system with particularly sensitive signal paths, the noise problem must be overcome.

In terms of power supply, due to its basic working principle, a high-efficiency DC/DC converter may become an important noise source. They not only generate low-frequency ripple at the switching frequency of the converter, but also high-frequency noise caused by the rapid switching of voltage and current in the converter power stage.

Examples of noise reduction techniques used in conjunction with switching regulators include additional filtering passive components, such as snubber circuits, ferrite beads, and feedthrough capacitors, or the inclusion of linear power supplies in the power path, such as low dropout regulators . Although these solutions work well in most applications, they may have trade-offs in terms of efficiency, solution size, and the cost of the total power supply solution, especially in areas such as patient monitors, smart meters, and smart In applications that are always on, such as sensors and IoT systems.

Many applications will definitely benefit from a noise-free environment during data acquisition and/or radio frequency (RF) communication events. However, power supply designers need to consider whether the trade-offs between efficiency (in other words, battery life), board space, and component cost make sense for their design. When proving that there may be a problem, modern DC/DC converters do provide features that help reduce the impact of design trade-offs. An example is the TPS62840 DC/DC converter, which is an ultra-low (60nA) quiescent current, high-efficiency, 750mA step-down regulator designed to maximize battery life in always-on applications and can be used to Start the application.

The STOP input pin of TPS62840 (see Figure 1) immediately (after the current switching cycle) and temporarily stops the switching of the voltage regulator. During this time, the charge stored in the output capacitor powers the application; the regulator will never generate ripple or switching noise. In this case, the application can perform distortion-free, accurate data acquisition and RF communication procedures.

Advantages of STOP function in low-noise data acquisition applications
Figure 1: Typical application circuit showing the STOP input pin

Of course, when the system is running, it is important to restart the device before the output voltage of the device reaches the critical level of the system. Once a logic low level is applied to the STOP pin, the voltage regulator will immediately resume switching operation without any start-up and/or soft-start delay. Figure 2 illustrates the STOP characteristic used to operate a DC/DC converter with pulse frequency modulation (PFM) (Figure 2a) or forced pulse width modulation (PWM) (Figure 2b).

Advantages of STOP function in low-noise data acquisition applications

Figure 2: In PFM operation (a), VIN = 3.6 V, VOUT = 1.8 V and IOUT = 10 mA and forced PWM operation (b), use TPS62840STOP mode operation (the blue is the input signal of the STOP pin, the magenta is the output voltage, and the green is the Inductor current). Measurement value includes COUT= 10 µF.

The time required for noise-free measurement/RF communication event in STOP mode depends on the set output voltage VOUT,SET, Output capacitance value COUT, The required output current IOUTAnd the voltage tolerance of the application. In the example in Figure 2 (VIN = 3.6 V, VOUT,SET = 1.8 V, IOUT = 10 mA, COUT = 10 µF), a voltage drop of approximately 50 mV is reached after time t = 38 µs. If the constant output current IOUTTo discharge the output capacitor COUT, you can use Equation 1 to estimate the output voltage behavior V in STOP modeOUT(T) as a function of time t:

VOUT

When designing a power architecture for always-on applications with strong noise control requirements, make sure to check the STOP function of the TPS62840. In combination with other features, such as 80% light-load efficiency at output currents as low as IOUT = 1μA, or the possibility to choose between 16 predefined output voltages by connecting a single resistor to the VSET pin , TPS62840 can help maximize the battery life of the system while minimizing the number of additional components required.

The Links:   LB064V02-TD01 NL8060BC2630G