SBOU275 April   2022 INA190-EP

 

  1.   Trademarks
  2. 1Overview
    1. 1.1 INA190-EP Kit Contents
    2. 1.2 Related Documentation From Texas Instruments
  3. 2INA190EPEVM Hardware
    1. 2.1 Features
  4. 3Quick Start Setup and Use
    1. 3.1 Measurements
  5. 4INA190EPEVM Circuit and Components
    1. 4.1 R2x, R3x, R5x, C2x, C3x
    2. 4.2 C1x
    3. 4.3 R1x
    4. 4.4 R6
    5. 4.5 R4x
    6. 4.6 U1x - INA190-EP
    7. 4.7 J0x, J1x
  6. 5Reference Voltage Setup
    1. 5.1 Unidirectional Mode
    2. 5.2 Bidirectional Mode
  7. 6Guarding Voltage - Using the "Guarded Inputs" Panel
  8. 7INA190EPEVM Schematics and PCB Layout
    1. 7.1 Schematics
    2. 7.2 PCB Layout
  9. 8Bill of Materials

6 Guarding Voltage - Using the "Guarded Inputs" Panel

One panel on the INA190EPEVM is labeled as "Guarded Inputs" because it includes extra circuitry to help guard the input traces going into the IN+ and IN– pins of the INA190A5. When measuring a small current, it is desirable to minimize the input bias currents of the device, which is in the nanoamps. The input bias current could increase due to leakage currents sinking into a nearby ground plane and this is simply due to finite resistance of PCB material and a voltage potential. This voltage potential only grows as common-mode voltage increases. Guard the input traces with an isolated guarding plane and fence that is at the same potential and any leakage currents from the input traces will be significantly reduced. This technique is more practical when dealing with currents in the picoamps level, but it is included to help evaluate any extreme cases: low-current or high common-mode voltage or both.

The guarding plane can be driven by an external voltage source using the VG test point, or by populating R6 with a 0-Ω resistor, which will automatically tie common-mode voltage at the inputs to the guarding plane. If using the VG test point, ensure the external source has a common ground with the INA190-EP.