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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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HCPL-7860 Fiches technique(PDF) 17 Page - AVAGO TECHNOLOGIES LIMITED |
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HCPL-7860 Fiches technique(HTML) 17 Page - AVAGO TECHNOLOGIES LIMITED |
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17 / 18 page  17 Shunt Connections The recommended method for connecting the isolated modulator to the shunt resistor is shown in Figure 17. VIN+ (pin 2 of the HPCL-7860/HCPL-786J) is connected to the positive terminal of the shunt resistor, while VIN- (pin 3) is shorted to GND1 with the power-supply return path func- tioning as the sense line to the negative terminal of the current shunt. This allows a single pair of wires or PC board traces to connect the isolated modulator circuit to the shunt resistor. By referencing the input circuit to the nega- tive side of the sense resistor, any load current induced noise transients on the shunt are seen as a common-mode signal and will not interfere with the current-sense signal. This is important because the large load currents flowing through the motor drive, along with the parasitic induc- tances inherent in the wiring of the circuit, can generate both noise spikes and offsets that are relatively large com- pared to the small voltages that are being measured across the current shunt. If the same power supply is used both for the gate drive cir- cuit and for the current sensing circuit, it is very important that the connection from GND1 of the isolated modulator to the sense resistor be the only return path for supply cur- rent to the gate drive power supply in order to eliminate potential ground loop problems. The only direct connec- tion between the isolated modulator circuit and the gate drive circuit should be the positive power supply line. In some applications, however, supply currents flowing through the power-supply return path may cause offset or noise problems. In this case, better performance may be obtained by connecting VIN+ and VIN- directly across the shunt resistor with two conductors, and connecting GND1 to the shunt resistor with a third conductor for the power-supply return path, as shown in Figure 19. When connected this way, both input pins should be bypassed. To minimize electromagnetic interference of the sense sig- nal, all of the conductors (whether two or three are used) connecting the isolated modulator to the sense resistor should be either twisted pair wire or closely spaced traces on a PC board. The 39 : resistor in series with the input lead (R2) forms a lowpass anti-aliasing filter with the 0.01 PF input bypass capacitor (C2) with a 400 kHz bandwidth. The resistor per- forms another important function as well; it dampens any ringing which might be present in the circuit formed by the shunt, the input bypass capacitor, and the inductance of wires or traces connecting the two. Undamped ringing of the input circuit near the input sampling frequency can alias into the baseband producing what might appear to be noise at the output of the device. Figure 19. Schematic for Three Conductor Shunt Connection. + - MOTOR HV- HV+ RSENSE FLOATING POSITIVE SUPPLY GATE DRIVE CIRCUIT VDD1 VIN+ VIN- GND1 VDD2 MCLK MDAT GND2 HCPL-7860/ HCPL-786J C1 0.1 μF C2a 0.01 μF R2a 39 Ω R1 D1 5.1 V C2b 0.01 μF R2b 39 Ω |
Numéro de pièce similaire - HCPL-7860 |
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Description similaire - HCPL-7860 |
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