SGLS174J September   2003  – August 2018 INA138-Q1 , INA168-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Circuit
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Voltage Range
      2. 7.3.2 Bandwidth
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Operation
    2. 8.2 Typical Applications
      1. 8.2.1 Buffering Output to Drive an ADC
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Selecting RS and RL
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Output Filter
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curve
      3. 8.2.3 Offsetting the Output Voltage
      4. 8.2.4 Bipolar Current Measurement
        1. 8.2.4.1 Application Curve
      5. 8.2.5 Bipolar Current Measurement Using Differential Input of an ADC
      6. 8.2.6 Multiplexed Measurement Using Logic Signal for Power
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Related Links
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.1.1 Operation

Figure 9 illustrates the basic circuit diagram for both the INA138-Q1 and INA168-Q1. Load current IS is drawn from supply VP through shunt resistor RS. The voltage drop in the shunt resistor is forced across RG1 by the internal op amp, causing current to flow into the collector of Q1. External resistor RL converts the output current, IO, to a voltage, VOUT, at the OUT pin. The transfer function for the INA1x8-Q1 is shown in Equation 3:

Equation 3. IO = gm (VIN+ − VIN−)

where

  • gm = 200 μA/V

In the circuit of Figure 9, the input voltage, (VIN+ − VIN−), is equal to IS × RS. The output voltage, VOUT, is equal to IO × RL. The transconductance, gm, of the INA1x8-Q1 is 200 μA/V. The complete transfer function for the current measurement amplifier in this application is shown in Equation 4:

Equation 4. VOUT = (IS) (RS) (200 μA/V) (RL)

The maximum differential input voltage for accurate measurements is 0.5 V, producing a 100-μA output current. A differential input voltage of up to 2 V does not cause damage. Differential measurements (VIN+ and VIN− pins) must be unipolar, with a more-positive voltage applied to the VIN+ pin. If a more-negative voltage is applied to the VIN+ pin, IO goes to zero, but no damage occurs.

INA138-Q1 INA168-Q1 basic_circuit_connections_sgls174.gif
1. Maximum VP and V+ voltage is 60 V with INA168-Q1.
Figure 9. Basic Circuit Connections

Table 1. Voltage Gains and Corresponding Load-Resistor Values

VOLTAGE GAIN EXACT RL (kΩ) NEAREST 1% RL (kΩ)
1 5 4.99
2 10 10
5 25 24.9
10 50 49.9
20 100 100
50 250 249
100 500 499