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AD8205YRZ-R7 Fiches technique(PDF) 11 Page - Analog Devices |
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AD8205YRZ-R7 Fiches technique(HTML) 11 Page - Analog Devices |
11 / 12 page Data Sheet AD8205 Rev. | Page 11 of 12 APPLICATIONS INFORMATION A typical application for the AD8205 is high-side measurement of a current through a solenoid for PWM control of the solenoid opening. Typical applications include hydraulic transmission control and diesel injection control. Two typical circuit configurations are used for this type of application. HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE SWITCH In this case, the PWM control switch is ground referenced. An inductive load (solenoid) is tied to a power supply. A resistive shunt is placed between the switch and the load (see Figure 19). An advantage of placing the shunt on the high side is that the entire current, including the re-circulation current, can be measured since the shunt remains in the loop when the switch is off. In addition, diagnostics can be enhanced because shorts to ground can be detected with the shunt on the high side. In this circuit configuration, when the switch is closed, the common-mode voltage moves down to near the negative rail. When the switch is opened, the voltage reversal across the inductive load causes the common-mode voltage to be held one diode drop above the battery by the clamp diode. +IN VREF1 +VS OUT –IN GND VREF2 NC INDUCTIVE LOAD AD8205 CLAMP DIODE 42V BATTERY SHUNT SWITCH NC = NO CONNECT 5V Figure 19. Low-Side Switch HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE SWITCH This configuration minimizes the possibility of unexpected solenoid activation and excessive corrosion (see Figure 20). In this case, both the switch and the shunt are on the high side. When the switch is off, this removes the battery from the load, which prevents damage from potential shorts to ground, while still allowing the recirculating current to be measured and providing for diagnostics. Removing the power supply from the load for the majority of the time minimizes the corrosive effects that could be caused by the differential voltage between the load and ground. When using a high-side switch, the battery voltage is connected to the load when the switch is closed, causing the common- mode voltage to increase to the battery voltage. In this case, when the switch is opened, the voltage reversal across the inductive load causes the common-mode voltage to be held one diode drop below ground by the clamp diode. +IN VREF1 +VS OUT –IN GND VREF2 NC INDUCTIVE LOAD AD8205 CLAMP DIODE 42V BATTERY SHUNT SWITCH NC = NO CONNECT 5V Figure 20. High-Side Switch Another typical application for the AD8205 is as part of the control loop in H-bridge motor control. In this case, the AD8205 is placed in the middle of the H-bridge (see Figure 21) so that it can accurately measure current in both directions by using the shunt available at the motor. This is a better solution than a ground referenced op amp because ground is not typically a stable reference voltage in this type of application. This instability in the ground reference causes the measurements that could be made with a simple ground referenced op amp to be inaccurate. The AD8205 measures current in both directions as the H-bridge switches and the motor changes direction. The output of the AD8205 is configured in an external reference bidirectional mode, see the Output Offset Adjustment section. +IN VREF1 +VS OUT –IN GND VREF2 NC AD8205 SHUNT 5V 2.5V 5V CONTROLLER NC = NO CONNECT MOTOR Figure 21. Motor Control Application D |
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Description similaire - AD8205YRZ-R7 |
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