Datasheet NCV5230 (ON Semiconductor) - 10

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NCV5230
What this means is that several instruments, such as a chart ground to convert the current back to voltage. Again, the recorder, a meter, or a controller, as well as a long cable, can current sensing resistor will set up the transconductance and be connected in series on the loop and still obtain accurate the part will receive power from the line. readings if the total resistance does not exceed 650 W. Furthermore, any variation of resistance in this range will
TEMPERATURE TRANSDUCER
not change the output current. A variation on the previous circuit makes use of the supply Any voltage output type transducer can be used, but one current control pin. The voltage present at this pin is that does not need external DC voltage or current excitation proportional to absolute temperature (PTAT) because it is to limit the maximum possible load resistance is preferable. produced by the amplifier bias current through an internal Even this problem can be surmounted if the supply power resistor divider in a PTAT cell. If the control pin is connected needed by the transducer is compatible with the NCV5230. to the input pin, the NCV5230 itself can be used as a The power goes up the line to the transducer and amplifier temperature transducer. If the center tap of a resistive pot is while the transducer signal is sent back via the current output connected to the control pin with one side to ground and the of the NCV5230 transconductance configuration. other to the inverting input, the voltage can be changed to The voltage range on the input can be changed for give different temperature versus output current conditions transducers that produce a large output by simply increasing (Figure 8). For additional control, the output current is still the current sense resistor to get the corresponding 4.0 to proportional to the input voltage differential divided by the 20 mA output current. If a very long line is used which current sense resistor. causes high line resistance, a current repeater could be When using the NCV5230 as a temperature transducer, inserted into the line. The same configuration of Figure 7 can the thermal considerations in the previous section must be be used with exception of a resistor across the input and line kept in mind. VCC IOUT 3 7 REMOTE + + V POWER − SUPPLY 6 NCV5230 2 5 − VEE 4 10W RL 200 RC NOTES: 1. IOUT = VIN/RC V 2. R REMOTE * 1.8V * VINMAX L MAX ≈ I For RC = 1W OUT IOUT VIN 4mA 4mV 20mA 20mV
Figure 8. NCV5230 remote temperature transducer utilizing 4.0 − 20 mA current transmission. This application shows the use of the accessibility of the PTAT cell in the device to make the part, itself, a transducer. www.onsemi.com 10