XTR106: 4-20mA Current Transmitter with Bridge Excitation And ...

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REVERSE-VOLTAGE PROTECTIONThe XTR106’s low compliance rating (7.5V) permits theuse of various voltage protection methods without compromisingoperating range. Figure 6 shows a diode bridgecircuit which allows normal operation even when the voltageconnection lines are reversed. The bridge causes a twodiode drop (approximately 1.4V) loss in loop supply voltage.This results in a compliance voltage of approximately9V—satisfactory for most applications. A diode can beinserted in series with the loop supply voltage and the V+pin as shown in Figure 8 to protect against reverse outputconnection lines with only a 0.7V loss in loop supplyvoltage.OVER-VOLTAGE SURGE PROTECTIONRemote connections to current transmitters can sometimes besubjected to voltage surges. It is prudent to limit the maximumsurge voltage applied to the XTR106 to as low as practical.Various zener diode and surge clamping diodes are speciallydesigned for this purpose. Select a clamp diode with as low avoltage rating as possible for best protection. For example, a36V protection diode will assure proper transmitter operationat normal loop voltages, yet will provide an appropriate levelof protection against voltage surges. Characterization tests onthree production lots showed no damage to the XTR106 withloop supply voltages up to 65V.Most surge protection zener diodes have a diode characteristicin the forward direction that will conduct excessivecurrent, possibly damaging receiving-side circuitry if theloop connections are reversed. If a surge protection diode isused, a series diode or diode bridge should be used forprotection against reversed connections.RADIO FREQUENCY INTERFERENCEThe long wire lengths of current loops invite radio frequencyinterference. RF can be rectified by the sensitiveinput circuitry of the XTR106 causing errors. This generallyappears as an unstable output current that varies with theposition of loop supply or input wiring.If the bridge sensor is remotely located, the interference mayenter at the input terminals. For integrated transmitter assemblieswith short connection to the sensor, the interferencemore likely comes from the current loop connections.Bypass capacitors on the input reduce or eliminate this inputinterference. Connect these bypass capacitors to the I RETterminal as shown in Figure 6. Although the dc voltage atthe I RET terminal is not equal to 0V (at the loop supply, V PS )this circuit point can be considered the transmitter’s “ground.”The 0.01µF capacitor connected between V+ and I O mayhelp minimize output interference.V REF 5V REF 2.55V54V IN+R G1413V+10Maximum V PS must beless than minimumvoltage rating of zenerdiode.+ R B –R GXTR106Q 10.01µFD 1(1)1N4148DiodesBridgeSensor0.01µF0.01µF32R G–V INI RET6I OEB 9 87The diode bridge causesa 1.4V loss in loop supplyvoltage.R LV PSNOTE: (1) Zener Diode 36V: 1N4753A or MotorolaP6KE39A. Use lower voltage zener diodes with looppower supply voltages less than 30V for increasedprotection. See “Over-Voltage Surge Protection.”FIGURE 6. Reverse Voltage Operation and Over-Voltage Surge Protection.14www.ti.comXTR106SBOS092A
V REF 50.01µFSee ISO124 data sheetif isolation is needed.6kΩ4.8kΩ1MΩV REF 2.5IsothermalBlock20kΩOPA2775V IN+141311R 1LIN 10V REG V+7.5V to 36VType K1N414850Ω5.2kΩ100Ω1MΩ (1)2kΩR G1kΩ432R GR GV IN–I RETXTR1069BQ 1C OUT0.01µFE8Lin I OPolarity 7126I O = 4mA + V IN • (40)R GV REG (pin 1)I O4-20 mAV OR L+V PS–NOTE: (1) For burn-out indication.0.01µFFIGURE 7. Thermocouple Low Offset, Low Drift Loop Measurement with Diode Cold-Junction Compensation.BridgeSensor2.5V– +R BR GV REF 55432V REF 2.5V IN+14V+R GXTR106 BR G–V INI RET6V REG13 R LIN11110LinPolarity12I OE7981N4148I O = 4-20mA0.01µF+12V1µFSee ISO124 data sheetif isolation is needed.1610113 1215RCV42014213541µFV O = 0V to 5VNOTE: Lin Polarity shown connected to correct positive bridgenonlinearity. See Figure 3b to correct negative bridge nonlinearity.–12VFIGURE 8. ±12V-Powered Transmitter/Receiver Loop.XTR106 15SBOS092Awww.ti.com
Page 3 and 4: PIN CONFIGURATIONTop ViewV REGV - I
Page 5 and 6: TYPICAL PERFORMANCE CURVESAt T A =
Page 7 and 8: TYPICAL PERFORMANCE CURVES (CONT)At
Page 9 and 10: APPLICATIONS INFORMATIONFigure 1 sh
Page 11 and 12: Figure 4, but not peaking exactly a
Page 13: to the upper and lower sides of the
Page 19: IMPORTANT NOTICETexas Instruments I

XTR106: 4-20mA Current Transmitter with Bridge Excitation And ...

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