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Window Regulartor Switch Avoid Reducing Signal To Noise Ratio
- May 15, 2017 -

Window Regulartor Switch It is important to minimize the output ripple and transients of the switching regulator, especially when supplying power to a noise-sensitive device such as a high-resolution ADC, the output ripple will behave as a unique spike on the ADC output spectrum. To avoid reduced signal-to-noise ratio (SNR) and spurious-free dynamic range (SFDR) performance, Window Regulartor Switch switching regulators are typically replaced by a low dropout regulator (LDO), sacrificing the efficiency of the switching regulator in exchange for cleaner LDO outputs. Understanding these artifacts allows designers to successfully integrate switching regulators into more high-performance, noise-sensitive applications.

An effective method for measuring the output ripple and switching transients in a switching regulator is presented. The measurement of these parameters is very careful because the bad settings may cause the reading to be erroneous and the loop formed by the oscilloscope probe signal and the ground lead will cause parasitic inductance. This will increase the transient amplitude associated with the fast switching transients, and therefore must maintain shorter connections,Window Regulartor Switch efficient methods, and wide bandwidth performance. Here, the ADP2114 dual-channel 2 A / single-channel 4 A synchronous buck DC-DC converter is used to demonstrate how to measure the output ripple and switching noise. This buck regulator is highly efficient and has a switching frequency of up to 2 MHz.

Output ripple and switch transients

Window Regulartor Switch The output ripple and the switching transients depend on the topology of the regulator and the values and characteristics of the external components. The output ripple is the residual AC output voltage, which is closely related to the switching operation of the regulator. The fundamental frequency is the same as the switching frequency of the regulator. The switching transients are high frequency oscillations that occur during switching. Their amplitude is expressed at the maximum peak-to-peak voltage,Window Regulartor Switch which is difficult to measure accurately because it is highly correlated with the test setup.

Window Regulartor Switch The regulator's inductor and output capacitor are the main components that affect the output ripple. Smaller inductors will produce faster transient responses, but the cost is greater current ripple; and larger inductors will make current ripple smaller,Window Regulartor Switch the corresponding cost is the transient response is slower. A low effective series resistance (ESR) capacitor is used to minimize output ripple. The ceramic capacitor with the dielectric X5R or X7R is a good choice. Usually use large capacitors to reduce the output ripple, but the output capacitor size and number is to sacrifice costs and PCB area to come.

For power engineers, it is useful to consider the frequency domain when measuring unwanted output signals. It provides a better perspective to see which discrete frequencies the output ripple and its harmonics are located, and what different Power level. Figure 2 shows an example of a spectrum. This information can help engineers determine whether the selected switching regulator is suitable for its broadband RF or high-speed converter applications.

Window Regulartor SwitchTo perform frequency domain measurements, connect a 50Ω coaxial cable probe across the output capacitor. The signal passes through a DC blocking capacitor that terminates at the 50Ω termination resistor at the input of the spectrum analyzer. The DC blocking capacitor prevents DC current from passing through the spectrum analyzer to avoid DC load effects. 50Ω transmission environment can minimize high frequency reflection and standing wave.

The output capacitor is the main source of the output ripple,Window Regulartor Switch so the measurement point should be as close as possible. The loop from the signal tip to the ground should be as small as possible to minimize the additional inductance that may affect the measurement results. Figure 2 shows the output ripple and harmonics in the frequency domain. The ADP2114 produces a 4 mV p-p output ripple at the base frequency under specified operating conditions.