SBOS820A September   2019  – June 2020 TMCS1100

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Typical Application
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Power Ratings
    6. 7.6  Insulation Specifications
    7. 7.7  Safety-Related Certifications
    8. 7.8  Safety Limiting Values
    9. 7.9  Electrical Characteristics
    10. 7.10 Typical Characteristics
      1. 7.10.1 Insulation Characteristics Curves
  8. Parameter Measurement Information
    1. 8.1 Accuracy Parameters
      1. 8.1.1 Sensitivity Error
      2. 8.1.2 Offset Error and Offset Error Drift
      3. 8.1.3 Nonlinearity Error
      4. 8.1.4 Power Supply Rejection Ratio
      5. 8.1.5 Common-Mode Rejection Ratio
      6. 8.1.6 Reference Voltage Rejection Ratio
      7. 8.1.7 External Magnetic Field Errors
    2. 8.2 Transient Response Parameters
      1. 8.2.1 Slew Rate
      2. 8.2.2 Propagation Delay and Response Time
      3. 8.2.3 Current Overload Parameters
      4. 8.2.4 CMTI, Common Mode Transient Immunity
    3. 8.3 Safe Operating Area
      1. 8.3.1 Continuous DC or Sinusoidal AC Current
      2. 8.3.2 Repetitive Pulsed Current SOA
      3. 8.3.3 Single Event Current Capability
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Current Input
      2. 9.3.2 Input Isolation
      3. 9.3.3 High-Precision Signal Chain
        1. 9.3.3.1 Temperature Stability
        2. 9.3.3.2 Lifetime and Environmental Stability
        3. 9.3.3.3 Frequency Response
        4. 9.3.3.4 Transient Response
      4. 9.3.4 External Reference Voltage Input
      5. 9.3.5 Current-Sensing Measurable Ranges
    4. 9.4 Device Functional Modes
      1. 9.4.1 Power-Down Behavior
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Total Error Calculation Examples
        1. 10.1.1.1 Room Temperature Error Calculations
        2. 10.1.1.2 Full Temperature Range Error Calculations
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Development Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

Detailed Design Procedure

The TMCS1100 application design procedure has two key design parameters: the sensitivity version chosen (A1-A4) and the reference voltage input. Further consideration of noise and integration with an ADC can be explored, but is beyond the scope of this application design example. The TMCS1100 transfer function is effectively a transimpedance with a variable offset set by VREF, defined by Equation 28.

Equation 28. TMCS1100 eq_ideal_transfer_sbos820.gif

Design of the sensing solution first focuses on maximizing the sensitivity of the device while maintaining linear measurement over the expected current input range. The linear output voltage range is constrained by the TMCS1100 linear swing to ground, SwingGND, and swing to supply, SwingVS. With the previous parameters, the maximum linear output voltage range is the range between VOUT,max and VOUT,min, as defined by Equation 29 and Equation 30.

Equation 29. TMCS1100 eq_voutmax_noadc_sbos820.gif
Equation 30. TMCS1100 eq_voutmin_noadc_sbos820.gif

For a bidirectional current-sensing application, a sufficient linear output voltage range is required from VREF to both ground and the power supply. Design parameters for this example application are shown in Table 4 along with the calculated output range.

Table 4. Example Application Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
SwingVS 0.2 V
SwingGND 0.05 V
VOUT,max 4.7 V
VOUT,min 0.05 V
VOUT,max - VOUT,min 4.65 V

These design parameters result in a maximum linear output voltage swing of 4.65 V. To determine which sensitivity variant of the TMCS1100 most fully uses this linear range, calculate the maximum current range by Equation 31 for a unidirectional current (IU,MAX), andEquation 32 for a bidirectional current (IB,MAX).

Equation 31. TMCS1100 eq_imax_uni_sbos820.gif
Equation 32. TMCS1100 eq_imax_bi_sbos820.gif

where

  • SA<x> is the sensitivity of the relevant A1-A4 variant.

Table 5 shows such calculation for each gain variant of the TMCS1100 with the appropriate sensitivities.

Table 5. Maximum Full-Scale Current Ranges With 4.65-V Output Range

SENSITIVITY VARIANT SENSITIVITY IU,MAX IB,MAX
TMCS1100A1 50 mV/A 93 A ±46.5 A
TMCS1100A2 100 mV/A 46.5 A ±23.2A
TMCS1100A3 200 mV/A 23.2 A ±11.6A
TMCS1100A4 400 mV/A 11.6 A ±5.8 A

In general, select the highest sensitivity variant that provides for the desired full-scale current range. For the design parameters in this example, the TMCS1100A2 with a sensitivity of 0.1 V/A is the proper selection because the maximum-calculated ±23.2 A linear measurable range is sufficient for the desired ±20-A full-scale current.

After selecting the appropriate sensitivity variant for the application, the zero-current reference voltage defined by the VREF input pin is defined. Manipulating Equation 28 and using the linear range defined by VOUT,max, VOUT,min, and the full-scale input current, IIN,FS, calculate the maximum and minimum VREF voltages allowed to remain within the linear measurement range, shown in Equation 33 and Equation 34.

Equation 33. TMCS1100 eq_vrefmax_sbos820.gif
Equation 34. TMCS1100 eq_vrefmin_sbos820.gif

Any value of VREF can be chosen between VREF,max and VREF,min to maintain the required linear sensing range. If the allowable VREF range is not wide enough or does not include a desired VREF voltage, the analysis must be repeated with a lower sensitivity variant of the TMCS1100. Equation 28 can be manipulated to solve for the maximum allowable current in either direction by using the selected VREF voltage and the maximum linear voltage ranges as in Equation 35 and Equation 36.

Equation 35. TMCS1100 eq_i_in_fsp_sbos820.gif
Equation 36. TMCS1100 eq_i_in_fsn_sbos820.gif

Table 6 shows the respective values for the example design parameters in Table 4. In this case, a VREF of 2.5 V has been selected such that the zero current output is half of the nominal power supply. This example VREF design value provides a linear input current-sensing range of –24.5 A to +22 A, with the positive current defined as current flowing into the IN+ pin.

Table 6. Example VREF Limits and Associated Current Ranges

REFERENCE PARAMETER EXAMPLE VALUE MAXIMUM LINEAR CURRENT SENSING RANGE
IMAX+ IMAX–
VREF,min 2.05 V 26.5 A –20 A
VREF,max 2.7 V 20 A –26.5 A
Selected VREF 2.5 V 22 A –24.5 A

The transfer function of the TMCS1100 linear sensing range for these design parameters is shown in Figure 49.

TMCS1100 D001_SBOS820.gifFigure 49. Application Example Design Transfer Curve

After selecting a VREF for the application design, an appropriate source must be defined. Multiple implementations are possible, but could include:

  • Resistor divider from the supply voltage
  • Resistor divider from an ADC full-scale reference
  • Dedicated or preexisting voltage reference IC
  • DAC or reference voltage from a system microcontroller

Each of these options has benefits, and the error terms, noise, simplicity, and cost of each implementation must be weighed. In the current design example, any of these options are potentially available as a 2.5-V VREF is midrail of the power supply, a common IC reference voltage, and might already be available in the system. If the primary consideration for the current application design is to maximize precision while minimizing temperature drift and noise, a dedicated voltage reference must be chosen. For this case, the LM4030C-2.5 can be chosen for to optimize system accuracy without significant cost addition. Figure 50 depicts the current-sense system design as discussed.

TMCS1100 system_reference_solution_sbos820.gifFigure 50. TMCS1100 Example Current-Sense System Design