SBOSAA6 May   2024 INA790B

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Integrated Shunt Resistor
      2. 6.3.2 Safe Operating Area
      3. 6.3.3 Short-Circuit Duration
      4. 6.3.4 Temperature Stability
      5. 6.3.5 Enhanced PWM Rejection Operation
    4. 6.4 Device Functional Modes
      1. 6.4.1 Adjusting the Output With the Reference Pin
        1. 6.4.1.1 Reference Pin Connections for Unidirectional Current Measurements
        2. 6.4.1.2 Ground Referenced Output
        3. 6.4.1.3 Reference Pin Connections for Bidirectional Current Measurements
        4. 6.4.1.4 Output Set to Mid-Supply Voltage
      2. 6.4.2 Adjustable Gain Set Using External Resistors
        1. 6.4.2.1 Adjustable Unity Gain
      3. 6.4.3 Thermal Alert Function
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Calculating Total Error
        1. 7.1.1.1 Error Sources
        2. 7.1.1.2 Reference Voltage Rejection Ratio Error
        3. 7.1.1.3 External Adjustable Gain Error
        4. 7.1.1.4 Total Error Example 1
        5. 7.1.1.5 Total Error Example 2
        6. 7.1.1.6 Total Error Example 3
    2. 7.2 Typical Applications
      1. 7.2.1 High-Side, High-Drive, Solenoid Current-Sense Application
        1. 7.2.1.1 Design Requirements
      2. 7.2.2 Speaker Enhancements and Diagnostics Using Current Sense Amplifier
        1. 7.2.2.1 Design Requirements
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.4.2 Adjustable Gain Set Using External Resistors

The INA790x features adjustable gain with two external resistor network. The default gain is 20mV/A, and with added external adjustable gain resistor network, total gain (G) can range up to 400mV/A. Figure 6-7 shows two external resistors RFB1 and RFB2 configured for added external gain. Equation 2 can be used for calculating external adjustable gain and Equation 3 shows the total gain of the system with external adjustable gain. The REF pin and one end of resistor RFB2 is connected to external reference based on needed voltage at OUT pin as described in Adjusting the Output With the Reference Pin.

INA790B Adjustable Gain Setting With External Resistor Divider Figure 6-7 Adjustable Gain Setting With External Resistor Divider
Equation 2. A d j u s t a b l e   G a i n = ( 1 + R F B 1 R F B 2 )
Equation 3. G = 20 m A V × ( 1 + R F B 1 R F B 2 )

The FB pin in INA790x has associated bias current, which can add to error when large values of adjustable gain resistor, RFB1, is used. Alternatively, very low values of adjustable gain resistors load the output of the sense amplifier limiting the capability of the sense amplifier to get close to the supply rail. Keeping the sum of external resistors RFB1 and RFB2 between 10kΩ and 40kΩ is recommended when external adjustable gain is higher than 1. Table 6-1 shows recommended values of external gain resistors for the most common gains.

Table 6-1 Recommended Values of External Resistors Setting Adjustable Gain
External Adjustable Gain RFB1 RFB2 Total Gain (G)
1 0Ω (short) Open 20mV/A
2 20kΩ 20kΩ 40mV/A
4 30kΩ 10kΩ 80mV/A
5 20kΩ 5kΩ 100mV/A