SLVAEW6 December   2020 TPS2661

 

  1.   Trademarks
  2. 1Introduction
  3. 2Protection Required for Current Inputs in Analog Input Modules
    1. 2.1 Over-Current Protection from Miswiring to Field Power Supplies
    2. 2.2 Over-Voltage Protection from Miswiring to Field Power Supplies
  4. 3Typical Discrete Circuit for Protection of Current Input
    1. 3.1 Protection Provided by Discrete Circuit
      1. 3.1.1 Over-Current Protection with Discrete Circuit
      2. 3.1.2 Over-voltage Protection with Discrete Circuit
    2. 3.2 Heating and Temperature Rise with Discrete Circuit
    3. 3.3 Reverse Leakage Current of Zener Diodes and Current Measurement Accuracy
  5. 4TPS26610 for Analog Current Loop Protection
    1. 4.1 Current Input Protection with TPS26610
    2. 4.2 Accurate Current Limiting with TPS26610
    3. 4.3 Leakage Current of TPS26610 and Current Measurement Accuracy
    4. 4.4 Protection from Mis-wiring to Field Power Supplies
    5. 4.5 Heating and Temperature Rise with TPS26610
    6. 4.6 Reduction in PCB Size with TPS26610 for Current Input Protection
  6. 5Conclusion

3.3 Reverse Leakage Current of Zener Diodes and Current Measurement Accuracy

As described in Section 3.1.1, a Zener diode with power rating more than 2W is required for protection in current input. Zener diode with a higher power rating has higher reverse leakage currents. Reverse leakage current of Zener diode cause an error in current measurements, Figure 3-8 illustrates the reverse leakage current in a 7.5 V and 2W Zener diode and the corresponding error in 20mA current measurement. As the ambient temperature goes above 60°C, the error contributed by reverse leakage current is more than 0.1% and this starts degrading the overall current measurement accuracy. A higher value of RBurden is usually preferred for lower noise in current measurements. The reverse leakage current increases with voltage drop across RBurden and it becomes difficult to achieve accuracy better than 0.25% with higher value of burden resistors.

GUID-20201210-CA0I-G2Q8-BTVF-4JS7DWB3G1JF-low.svg Figure 3-8 Reverse Leakage Current in a 7.5 V and 2W Zener Diode