SI8920BC-ISR IC

SI8920BC-ISR Description

An analog amplifier with galvanic isolation is denoted by the model number Si8920. When a sensor needs to be segregated from the control system, such as when measuring the voltage across a current shunt resistor, the low-voltage differential input is the best alternative. The output is an analog differential signal with an increase of either 8.1 or 16.2 decibels. Control systems can respond quickly to fault occurrences or shifts in load because the Si8920 has an extraordinarily low signal latency. Because of the low offset and gain drift, the accuracy is consistent across the operating temperature range. Because of its very high common-mode transient immunity, the Si8920 can deliver precise measurements even in high-power switching, which is found in motor drive systems and inverters. This is the case because of its use of CMOS technology.

The Si8920 isolated amplifier uses Skyworks’ exclusive isolation technology to achieve maximum levels of signal purity. By UL1577, it has the capability of withstanding voltages of up to 5.0 kVrms. Compared to earlier isolation technology forms, this one boasts superior performance, a reduction in temperature and age-related change, improved part-to-part matching, and increased lives. An option is available for select part numbers of an automotive grade. At each stage of the manufacturing process, these items are produced using flows specific to the automotive industry. This ensures that the final products meet the stringent requirements of automotive applications, including high levels of robustness and low defectivity.

Industrial Applications

• Inverters for renewable and traditional sources of energy use.
• Control and drives for ac, dc, and brushless motors.
• Motor speed regulation in household appliances with variable speed control.
• UPS and isolated switch mode power sources.

Safety Regulatory Approvals

• UL 1577 recognized
• Up to 5000 Vrms for 1 minute
• CSA component notice 5A approval
• IEC 60950-1 (reinforced insulation)
• VDE certification conformity
• VDE0884 Part 10 (basic/reinforced insulation)
• CQC certification approval

Automotive Applications

• Onboard chargers
• Charging pedestals

System Overview

The input of the Si8920 is intended to receive the differential signals of low voltage. This is the perfect thing to use for connecting to low-resistance current shunt measurement resistors. Full-scale input for both the Si8920A and Si8920B is between 100 and 200 mV; the Si8920A has a 100 mV capacity. The 1.6 V internal gain controls the maximum output level in both cases. For the analog signal to be sent past the semiconductor-based isolation barrier, the Si8920 modifies it in a novel way. A pulse-width modulated digital signal is created from the input signal after it is first transformed. Additional modulation with a high-frequency carrier is applied to the call to send it across the isolation barrier. After passing through the isolation barrier, the signal undergoes demodulation, and the carrier component is removed. The analog signal is then faithfully reproduced by using the PWM signal that was produced as a result. The signal bandwidth and precision offered by this system are unparalleled.

Current Sense Application

An isolation barrier separates the high-voltage domain from the low-voltage domain. The Si8920 is utilized in the driver circuit below to amplify the voltage detected across the sense resistor, RSENSE, and transfer an analog signal to the low-voltage domain. Isolation is essential because the voltage of RSENSE in relation to the earth will oscillate between 0 volts and the high voltage rail connected to the drain of Q1.

In this application, the load may take the form of a motor winding or another type of inductive winding. This circuit would need to be repeated three times to accommodate a three-phase motor driving application, once for each phase. RSENSE ought to have a low resistor value, so there is less wasted power. On the other hand, a resistance that is much too low will cause the signal-to-noise ratio of the measurement to be lower. Si8920 has two different full-scale input options for maximizing the value of RSENSE. These alternatives are 100 mV (Si8920A) and 200 mV (Si8920B). Because trace resistance will introduce inaccuracy into the measurement, the AIP and AIN connections to the RSENSE resistor must be made as close as humanly possible to each end of the RSENSE resistor.

The differential input to the Si8920 requires that the traces on the PCB that lead back to the input pins be laid out in parallel. This guarantees that any large noise transients on the high-voltage side are linked equally to the AIP and AIN pins and that the Si8920 will reject them as common-mode signals. This ensures that any large noise transients on the high-voltage side are dismissed.

The Si8920 has an amplifier with a bandwidth of about 950 kHz approximately. In the event that more input filtering is required, an RC low-pass filter can be connected between RSENSE and the input pins. This filter can be considered a low-pass filter. R1 and R2 have values of 20, and C1 is equal to 10 nF.

Q1 gate driver has a 24 V floating supply. Each side of the Si8920 needs a power supply because its input and output are galvanically isolated. From this floating supply, the Q3, R3, C3, and D1 components create a regulator circuit that supplies power to the input side of the Si8920. At the base of Q3, the voltage that is established by D1 is 5.6 volts. R3 has been chosen to supply D1 with a Zener current of 10 mA. Q3’s emitter sends 5 V to VDDA via filtering at C3’s base. The symbol C2 denotes the bypass capacitor for the supply, and its proper placement is at the VDDA pin, with its return trace connected to the GNDA connection at the RSENSE terminal.

The local bypass capacitor for the B-side of the Si8920, designated as C4, should be positioned so that it is adjacent to the VDDB supply pin, and its return should be placed near GNDB. The output signal at AOP and AON is differential, and it has a standard mode voltage of 1.1 V and a nominal gain of either 8.1 (Si8920B) or 16.2 (Si8920A). A differential input ADC is used to take readings from the outputs. An anti-aliasing filter may be necessary for the ADC, depending on the sample rate at which it operates. It is possible to construct a clear anti-aliasing filter by using the passive components R4, C6, and R5. Q3’s emitter sends 5 volts to VDDA via filtering at C3’s base.

Conclusion

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