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SMG100VBR22RM5X11LL_Datasheet PDF

来源:LM317 Electronics Components编辑:Zetex时间:2021-06-15 14:47:14

Moreover, more-complex embedded systems can benefit from the existence of multiple processors that can execute the tasks in parallel. By using a soft-core processor and accompanying tools, it’s an easy matter to create a multiprocessor-based system-on-chip. The only restriction to the number of processors that you can add is the availability of FPGA resources.

To sense the presence of a finger, a capacitive sensing system must first know the sensor capacitance in the absence of a finger (see Figure 2a ), also known as the parasitic capacitance (Cp ). When a finger approaches or touches the sensor (see Figure 2b ), the sensor capacitance will change, resulting in another capacitance called the finger capacitance (Cf ) in parallel to the Cp . In the presence of a finger, the total sensor capacitance (Cx ) is given by Equation 1 :

Cx = Cp +_ Cf – Equation 1

SMG100VBR22RM5X11LL_Datasheet PDF

Figure 2(a): Sensor capacitance in the absence of finger

 

SMG100VBR22RM5X11LL_Datasheet PDF

Figure 2(b): Sensor capacitance in the presence of finger

To be able to analyze the sensor capacitance using a microcontroller, the sensor capacitance (Cx ) needs to be converted into a digital value. Figure 3 shows the block diagram of one of the capacitive sensing preprocessing circuit. (Note: There are several methods for measuring sensor capacitance.)

SMG100VBR22RM5X11LL_Datasheet PDF

Figure 3: Pre-processing circuit for capacitance measurement

Second, the ferrite bead must have high impedance at the switching frequency and harmonics of the DC/DC converter, in order to block the switching noise and switching spurs. Most of the available ferrite beads have their impedance specified at 100 MHz, while the switching frequencies of modern DC/DC converters typically are between 500 kHz and 6 MHz.

In our example, the ADS4149 evaluation module (EVM) uses a switching regulator with a switching frequency of 2.25 MHz. In this instance, we are using the TPS62590 for our switching regulator. Since DC/DC regulators have a square-wave output, the higher-order harmonics need to be considered as well. An electromagnetic interference (EMI) filter from Murata (NFM31PC276B0J3) was found to give a high impedance in that frequency range along with very low DC resistance .

Figure 1 compares the insertion loss of a traditional ferrite bead (68Ω at 100 MHz) against the Murata EMI filter. Power-supply circuits are very low impedance while the insertion loss is measured in a 50Ω environment. Hence, the insertion-loss magnitude of the power-supply filter may be slightly different, although the resonant frequencies won’t change.

Figure 2: Insertion loss comparison of different power-supply filter configurations  overlaid with the switching frequency and harmonics of the DC/DC converter. (Click on image to enlarge)

 The other components of the power-supply filter are the bypass caps. The values of the capacitors should be chosen so that their resonant frequencies, which create a low-impedance path to ground, are close to the switching frequency. This is so that switching noise passing through the bead is shorted to ground.

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