For various reasons, it may be necessary to filter at the input or output of the current sense amplifier (CSA). Today, we will focus on using NCS21xR and NCS199AxR current sense amplifiers to implement filter circuits when using really small shunt resistors (below 1 mΩ). Shunt resistors below 1 mΩ have parallel inductance, which can cause spike transient events on the current sense line, thereby overloading the CSA front end. Let's talk about the main considerations for filtering out these specific spike transient events. In some applications, the measured current may have inherent noise. In the presence of noisy signals, filtering after the output of the current-sense amplifier is usually simpler, especially when the amplifier output is connected to a high-impedance circuit. The amplifier output node provides the greatest degree of freedom when selecting components for the filter, and it is very simple to implement, although it may require subsequent buffering. When the shunt resistance value decreases, the parallel inductance has a significant effect on the frequency response. In the case of less than 1 mΩ, the parallel inductance produces a zero in the transfer function, which usually results in a corner frequency at a low frequency of 100 kHz. This inductance increases the amplitude of high-frequency spike transient events on the current sense line, thereby overloading the front end of any parallel current sense integrated circuit (IC). This problem must be solved by filtering at the input of the amplifier. Please note that regardless of the manufacturer's claims, all current sensing ICs are susceptible to this problem. Even if the peak frequency is higher than the rated bandwidth of the device, it is necessary to filter at the input of the device to solve this problem. Other applications, such as DC-DC converters and power supply applications may also require filtering at the input of the current sense amplifier. Figure 1 shows the proposed input filtering schematic. Figure 1. The input filter compensates the parallel inductance of the shunt resistor less than 1 mΩ, and high-frequency noise in any application Input filtering is complicated because the increased resistance of the filter resistance and the related resistance mismatch between them will adversely affect gain, common mode rejection ratio (CMRR), and VOS. Part of the effect on VOS is also due to the input bias current. Therefore, the input resistance value should be limited to less than 10 Ω. At least, the capacitor is selected to accurately match the time constant of the shunt resistor and its inductance; or, the capacitor is selected to provide a pole below this point. Make the input filter time constant equal to or greater than the parallel resistance and its inductance time constant: This is simplified to determine the CFILT value of each RFILT based on the use of 10 Ω resistors: If the main purpose is to filter out high-frequency noise, the capacitor should be increased to provide the required filtering value. For example, a filter frequency of 100 kHz requires an 80 nF capacitor. The capacitor can have a low rated voltage, but it should have good high frequency characteristics. The required capacitor value can be calculated by the following formula: Transient suppression In applications where the transient common-mode voltage is greater than 30 volts (V), a transient suppression circuit is required. For details on how to design a transient suppression circuit, see the basic connection application note in the NCS21xR data sheet. Filtering is not always necessary, a battery-powered DC circuit with minimal dynamic current will be an example. Large, complex systems may have high-speed changes in power supply current or voltage (such as servers, computers), and often require filtering to provide clean signals for current control, measurement, and analysis. For more information about ON Semiconductor's current sense amplifiers, please visit our website: • NCS21xR ▫NCS210R, NCV210R, NCS211R, NCV211R, NCS213R, NCV213R, NCS214R, NCV214R • NCS199AxR ▫NCS199A1R, NCS199A2R, NCS199A3R Etching cutting die is mainly used in the die-cutting industry to cut product labels. Generally applied to trademarks, printing and packaging, various paper art, fabric creation, home beautification, office decoration, double-sided adhesive, single-sided adhesive, stickers and more. Hard Mould Cutting Die,Diverse Patterns Mould, High Hardness 65 Mn Steel,Die cuts SHAOXING HUALI ELECTRONICS CO., LTD. , https://www.cnsxhuali.com
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