SLVAEX0 October   2020 TPS1H000-Q1 , TPS1H100-Q1 , TPS1H200A-Q1 , TPS1HA08-Q1 , TPS1HB16-Q1 , TPS1HB50-Q1 , TPS2HB16-Q1 , TPS2HB50-Q1 , TPS4H000-Q1 , TPS4H160-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Normal Operation Diagnostics
    1. 2.1 Configuring Diagnostics With SEL/SELx Pin
      1. 2.1.1 Diagnostics Select Pin: SEL1
      2. 2.1.2 Diagnostics Select Pin: SELx
    2. 2.2 Operating Current Measurements Using the SNS/CS Pin
      1. 2.2.1 Internal/External Factor: Load Current Through Device
      2. 2.2.2 External Factor: Analog-to-Digital Converter (ADC)
      3. 2.2.3 External Factor: Probe Ground Termination
      4. 2.2.4 External Factor: Component Tolerances
    3. 2.3 Device Temperature on the Sense (SNS) Pin
  5. 3Fault State Diagnostics
    1. 3.1 Fault Behavior Configurations: Latch/THER/Delay Pin
      1. 3.1.1 Latch Pin
      2. 3.1.2 THER Pin
      3. 3.1.3 Delay Pin
    2. 3.2 Open Load Fault
    3. 3.3 Short to Battery Fault
    4. 3.4 Thermal Shutdown
    5. 3.5 Loss of Ground or Power Supply
    6. 3.6 Summary
  6. 4References

2.2.2 External Factor: Analog-to-Digital Converter (ADC)

For each of the configuration of the SNS pin, whether it is configured for measuring load current or device temperature, the voltage needs to be interpreted by the system. This can be done by measuring with an Analog-to-Digital Converter (ADC). With a digital system, it is common to use an ADC to measure analog signals such as the one outputted on the SNS pin. As a result of being an intermediate step for reading the CS pin, the ADC becomes a limiting factor in the accuracy of reading the voltage output on the CS or SNS pin.

Ultimately, the factors that should be taken into account by an engineer regarding the ADC is the resolution and the reference voltage. These are factors that are determined by the designer and allow the user to interpret the ADC reading with their judgement. An example of the effect of the choice in a 16 versus 8 bit ADC can be seen in Table 2-6.

Table 2-6 Comparison of Accuracy in 8-Bit ADC and 16-Bit ADC With 3.3 V Reference
Number of Bits CS or SNS Resistor [Ω] Current [A] Current Sense Ratio Sense Current [A] Sense Voltage [V] ADC Measured Value Measured Sense Voltage [V]
8 3.01k 1.5 1500 0.001 3.010 233 3.003
16 3.01k 1.5 1500 0.001 3.010 5977 3.009

As shown, the 16-Bit ADC can read the output voltage with the less error, due to having a tighter voltage step than the 8-bit ADC per bit, and reduce the amount of error that occurs when converting the voltage back to the current. More details and examples to configure the ADC and sense resistor can be seen in Automotive Load Short-Circuit Reliability and Accurate Current Sensing Reference Design. As the ADC is an external factor, it is up to the engineer on how to take advantage of the ADC.