SBAA551 June   2022 ADS8661 , ADS8665 , ADS8671 , ADS8675 , ADS8681 , ADS8685 , ADS8689 , ADS8691 , ADS8695 , ADS8699 , INA823 , INA826 , LM317L , LM337L , MUX509 , TPS2661 , TPS560430

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Circuit Description
    1. 2.1 Input Stage
    2. 2.2 Multiplexer Stage
    3. 2.3 Instrumentation Amplifier
    4. 2.4 Analog-to-Digital Converter
    5. 2.5 Power Supply
  5. 3Results
    1. 3.1 Accuracy and Noise Performance
    2. 3.2 Common-Mode Rejection of Input Signal
    3. 3.3 Input Impedance
    4. 3.4 Settling Time
    5. 3.5 Input Protection
  6. 4Summary
  7. 5References

3.5 Input Protection

Another important requirement of an analog input module is the ability to tolerate mis-wiring. A connection of the PLC supply voltage of up to ±33 V is tolerated (permanently) in voltage mode as the series resistors R3 and R8 (see Figure 2-1) limit the current into MUX. In current mode the TPS26611 limits the current to 30 mA, turns-off, and retries.

Table 3-4 Current Input During Overvoltage Due to Mis-wiring
Setup INx+ IN0– IIN INx+ Comment
Positive
voltage input overdrive ch 0		 +30 V GND 4.1 mA R3, R8 resistors limit current into MUX
Negative
voltage input overdrive ch 0		 -30 V GND -4.1 mA R3, R8 resistors limit current into MUX
Positive
current input overdrive ch 0		 +30 V GND 30 mA TPS26611 limits, turns-off and retries
Negative
current input overdrive ch 0		 -30 V GND -30 mA TPS26611 limits, turns-off and retries