ZHCSW26B September   2000  – April 2024 INA117

PRODUCTION DATA  

  1.   1
  2. 特性
  3. 应用
  4. 说明
  5. Pin Configuration and Functions
  6. 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. Typical Characteristics
  8. Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Common-mode Rejection
      2. 7.1.2 Transfer Function
      3. 7.1.3 Measuring Current
      4. 7.1.4 Noise Performance
  9. Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 接收文档更新通知
    3. 8.3 支持资源
    4. 8.4 Trademarks
    5. 8.5 静电放电警告
    6. 8.6 术语表
  10. Revision History
  11. 10Mechanical, Packaging, and Orderable Information

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)
  • D|8
  • P|8
  • LMC|8
散热焊盘机械数据 (封装 | 引脚)
订购信息

Measuring Current

The INA117 can be used to measure a current by sensing the voltage drop across a series resistor, RS. Figure 7-4 shows the INA117 used to measure the supply currents of a device under test. The circuit in Figure 7-5 measures the output current of a power supply. If the power supply has a sense connection, the power supply can be connected to the output side of RS to eliminate the voltage-drop error. Another common application is current-to-voltage conversion, as shown in Figure 7-6.

INA117 CMR Trim Circuit Figure 7-3 CMR Trim Circuit
INA117 Measuring Supply Currents of
                    Device Under Test Figure 7-4 Measuring Supply Currents of Device Under Test
INA117 Measuring Power Supply Output
                    Current

*RC not needed if RS is less than 20Ω – see text.

Figure 7-5 Measuring Power Supply Output Current
INA117 Current to Voltage
                    Converter Figure 7-6 Current to Voltage Converter

In all cases, the sense resistor imbalances the input resistor matching of the INA117, degrading the CMR. Also, the input impedance of the INA117 loads RS, causing gain error in the voltage-to-current conversion. Both of these errors can be easily corrected.

The CMR error can be corrected with the addition of a compensation resistor, RC, equal in value to RS as shown in Figure 7-4, Figure 7-5, and Figure 7-6. If RS is less than 20Ω, the degradation in CMR is negligible and RC can be omitted. If RS is larger than approximately 2kΩ, trimming RC can be required to achieve greater than 86dB CMR. This trim is because the actual INA117 input impedances have 1% typical mismatch. If RS is more than approximately 100Ω, the gain error is greater than the 0.05% specification of the INA117. This gain error can be corrected by slightly increasing the value of RS. The corrected value, RS', can be calculated by:

Equation 1. R S ' = R S × 380 k Ω 380 k Ω - R S  

Example: For a 1V/mA transfer function, the nominal, uncorrected value for RS is 1kΩ. A slightly larger value, RS' = 1002.6Ω, compensates for the gain error due to loading.

The 380kΩ term in the equation for RS' has a tolerance of ±25%, so sense resistors above approximately 400Ω can require trimming to achieve gain accuracy better than 0.05%.

Of course, if a buffer amplifier is added as shown in Figure 7-7, both inputs see a low source impedance, and the sense resistor is not loaded. As a result, there is no gain error or CMR degradation. The buffer amplifier can operate as a unity gain buffer or as an amplifier with non-inverting gain. Gain added ahead of the INA117 improves both CMR and signal-to-noise. Added gain also allows a lower voltage drop across the sense resistor. The OPA1013 is a good choice for the buffer amplifier since both the input and output can swing close to the negative power supply.

INA117 Current Sensing With Input
                    Buffer Figure 7-7 Current Sensing With Input Buffer

Figure 7-8 shows very high input impedance buffer used to measure low leakage currents. Here, the buffer operational amplifier is powered with an isolated, split-voltage power supply. Using an isolated power supply allows full ±200V common-mode input range.