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SE5230 Datasheet(PDF) 10 Page - ON Semiconductor |
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SE5230 Datasheet(HTML) 10 Page - ON Semiconductor |
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10 / 18 page  NE5230, SA5230, SE5230 http://onsemi.com 10 REMOTE TRANSDUCER WITH CURRENT TRANSMISSION There are many ways to transmit information along two wires, but current transmission is the most beneficial when the sensing of remote signals is the aim. It is further enhanced in the form of 4.0 to 20 mA information which is used in many control−type systems. This method of transmission provides immunity from line voltage drops, large load resistance variations, and voltage noise pickup. The zero reference of 4mA not only can show if there is a break in the line when no current is flowing, but also can power the transducer at the remote location. Usually the transducer itself is not equipped to provide for the current transmission. The unique features of the NE5230 can provide high output current capability coupled with low power consumption. It can be remotely connected to the transducer to create a current loop with minimal external components. The circuits for this are shown in Figures 6 and 7. Here, the part is configured as a voltage−to−current, or transconductance amplifier. This is a novel circuit that takes advantage of the NE5230’s large open−loop gain. In AC applications, the load current will decrease as the open−loop gain rolls off in magnitude. The low offset voltage and current sinking capabilities of the NE5230 must also be considered in this application. The NE5230 circuit shown in Figure 6 is a pseudo transistor configuration. The inverting input is equivalent to the “base,” the point where VEE and the non−inverting input meet is the “emitter,” and the connection after the output diode meets the VCC pin is the collector. The output diode is essential to keep the output from saturating in this configuration. From here it can be seen that the base and emitter form a voltage−follower and the voltage present at RC must equal the input voltage present at the inverting input. Also, the emitter and collector form a current−follower and the current flowing through RC is equivalent to the current through RL and the amplifier. This sets up the current loop. Therefore, the following equation can be formulated for the working current transmission line. The load current is: IL + VIN RC (eq. 2) and proportional to the input voltage for a set RC. Also, the current is constant no matter what load resistance is used while within the operating bandwidth range of the op amp. When the NE5230’s supply voltage falls past a certain point, the current cannot remain constant. This is the “voltage compliance” and is very good for this application because of the near rail output voltage. The equation that determines the voltage compliance as well as the largest possible load resistor for the NE5230 is as follows: RLmax + Vremote supply * VCC min * VIN max IL (eq. 3) Where VCC min is the worst−case power supply voltage (approximately 1.8 V) that will still keep the part operational. As an example, when using a 15 V remote power supply, a current sensing resistor of 1.0 W, and an input voltage (VIN) of 20 mV, the output current (IL) is 20 mA. Furthermore, a load resistance of zero to approximately 650 W can be inserted in the loop without any change in current when the bias current−control pin is tied to the negative supply pin. The voltage drop across the load and line resistance will not affect the NE5230 because it will operate down to 1.8 V. With a 15 V remote supply, the voltage available at the amplifier is still enough to power it with the maximum 20 mA output into the 650 W load. Figure 6. The NE5230 as a Remote Transducer Transconductance Amp with 4.0 − 20 mA Current Transmission Output Capability T R A N S D U C E R V REMOTE POWER SUPPLY NE5230 VCC VEE VIN IOUT 3 2 4 5 6 7 + − RC RL + − NOTES: 1. IOUT = VIN/RC 2. RL MAX ≈ VREMOTE * 1.8V * VINMAX IOUT For RC = 1.0 W IOUT 4mA VIN 4mV 20mA 20mV Figure 7. The Same Type of Circuit as Figure 6, but for Sourcing Current to the Load VCC NE5230 3 2 4 5 6 7 + − VEE + IOUT + − VIN RC RL VCC + − |
Similar Part No. - SE5230 |
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Similar Description - SE5230 |
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