SBAS734A March 2017  – July 2017 AMC1306E05 , AMC1306E25 , AMC1306M05 , AMC1306M25

PRODUCTION DATA. 

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and 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: AMC1306x05
    10. 7.10Electrical Characteristics: AMC1306x25
    11. 7.11Switching Characteristics
    12. 7.12Insulation Characteristics Curves
    13. 7.13Typical Characteristics
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
    3. 8.3Feature Description
      1. 8.3.1Analog Input
      2. 8.3.2Modulator
      3. 8.3.3Isolation Channel Signal Transmission
      4. 8.3.4Digital Output
      5. 8.3.5Manchester Coding Feature
    4. 8.4Device Functional Modes
      1. 8.4.1Fail-Safe Output
      2. 8.4.2Output Behavior in Case of a Full-Scale Input
  9. Application and Implementation
    1. 9.1Application Information
      1. 9.1.1Digital Filter Usage
    2. 9.2Typical Applications
      1. 9.2.1Frequency Inverter Application
        1. 9.2.1.1Design Requirements
        2. 9.2.1.2Detailed Design Procedure
        3. 9.2.1.3Application Curve
      2. 9.2.2Isolated Voltage Sensing
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2Detailed Design Procedure
        3. 9.2.2.3Application Curve
      3. 9.2.3Do's and Don'ts
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1Layout Guidelines
    2. 11.2Layout Example
  12. 12Device and Documentation Support
    1. 12.1Device Support
      1. 12.1.1Device Nomenclature
        1. 12.1.1.1Isolation Glossary
    2. 12.2Documentation Support
      1. 12.2.1Related Documentation
    3. 12.3Related Links
    4. 12.4Receiving Notification of Documentation Updates
    5. 12.5Community Resources
    6. 12.6Trademarks
    7. 12.7Electrostatic Discharge Caution
    8. 12.8Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DWV|8
Orderable Information

Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

Application Information

Digital Filter Usage

The modulator generates a bitstream that is processed by a digital filter to obtain a digital word similar to a conversion result of a conventional analog-to-digital converter (ADC). A very simple filter, built with minimal effort and hardware, is a sinc3-type filter, as shown in Equation 2:

Equation 2. AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 q_hz_sbas734.gif

This filter provides the best output performance at the lowest hardware size (count of digital gates) for a second-order modulator. All the characterization in this document is also done with a sinc3 filter with an oversampling ratio (OSR) of 256 and an output word width of 16 bits.

The effective number of bits (ENOB) is often used to compare the performance of ADCs and ΔΣ modulators. Figure 55 shows the ENOB of the AMC1306 with different oversampling ratios. In this document, this number is calculated from the SNR by using Equation 3:

Equation 3. AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 q_snr_sbas734.gif
AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 D040_SBAS734.gif
Figure 55. Measured Effective Number of Bits versus Oversampling Ratio

An example code for implementing a sinc3 filter in an FPGA is discussed in the Combining the ADS1202 with an FPGA Digital Filter for Current Measurement in Motor Control Applications application note, available for download at www.ti.com.

Typical Applications

Frequency Inverter Application

Isolated ΔΣ modulators are being widely used in frequency inverter designs because of their high ac and dc performance. Frequency inverters are critical parts of industrial motor drives, photovoltaic inverters (string and central inverters), uninterruptible power supplies (UPS), electrical and hybrid electrical vehicles, and other industrial applications.

Figure 56 shows a simplified schematics of the AMC1306Mx in a typical frequency inverter application as used in industrial motor drives with shunt resistors (RSHUNT) used for current sensing. Depending on the system design, either all three or only two motor phase currents are sensed.
The Manchester coded bitstream output of the AMC1306Ex minimizes the wiring efforts of the connection between the power board and the control board; see Figure 57. This bitstream output also allows the clock to be generated locally on the power board without the having to adjust the propagation delay time of each DOUT connection to fulfill the setup and hold time requirements of the microcontroller.

In both examples, an additional fourth AMC1306 is used to support isolated voltage sensing of the dc link. This high voltage is reduced using a high-impedance resistive divider and is sensed by the device across a smaller resistor. The value of this resistor can degrade the performance of the measurement, as described in the Isolated Voltage Sensing section.

AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 ai_inv_bas734.gif Figure 56. The AMC1306Mx in a Frequency Inverter Application
AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 ai_invM_bas734.gif Figure 57. The AMC1306Ex in a Frequency Inverter Application

Design Requirements

Table 1 lists the parameters for the typical application in the Frequency Inverter Application section.

Table 1. Design Requirements

PARAMETERVALUE
High-side supply voltage3.3 V or 5 V
Low-side supply voltage3.3 V or 5 V
Voltage drop across the shunt for a linear response±250 mV (maximum)

Detailed Design Procedure

The high-side power supply (AVDD) for the AMC1306 device is derived from the power supply of the upper gate driver. Further details are provided in the Power Supply Recommendations section.

The floating ground reference (AGND) is derived from one of the ends of the shunt resistor that is connected to the negative input of the AMC1306 (AINN). If a four-pin shunt is used, the inputs of the device are connected to the inner leads and AGND is connected to one of the outer shunt leads.

Use Ohm's Law to calculate the voltage drop across the shunt resistor (VSHUNT) for the desired measured current: VSHUNT = I × RSHUNT.

Consider the following two restrictions to choose the proper value of the shunt resistor RSHUNT:

  • The voltage drop caused by the nominal current range must not exceed the recommended differential input voltage range: VSHUNT ≤ ±250 mV
  • The voltage drop caused by the maximum allowed overcurrent must not exceed the input voltage that causes a clipping output: |VSHUNT| ≤ |VClipping|

The typically recommended RC filter in front of a ΔΣ modulator to improve signal-to-noise performance of the signal path is not required for the AMC1306. By design, the input bandwidth of the analog front-end of the device is limited as specified in the Electrical Characteristics table.

For modulator output bitstream filtering, a device from TI's TMS320F2807x family of low-cost microcontrollers (MCUs) or TMS320F2837x family of dual-core MCUs is recommended. These families support up to eight channels of dedicated hardwired filter structures that significantly simplify system level design by offering two filtering paths per channel: one providing high accuracy results for the control loop and one fast response path for overcurrent detection.

Application Curve

In motor control applications, a very fast response time for overcurrent detection is required. The time for fully settling the filter in case of a step-signal at the input of the modulator depends on the filter order; that is, a sinc3 filter requires three data updates for full settling (with fDATA = fCLK / OSR). Therefore, for overcurrent protection, filter types other than sinc3 can be a better choice; an alternative is the sinc2 filter. Figure 58 compares the settling times of different filter orders.

The delay time of the sinc filter with a continuous signal is half of the settling time.

AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 D041_SBAS734.gif
Figure 58. Measured Effective Number of Bits versus Settling Time

Isolated Voltage Sensing

The AMC1306 is optimized for usage in current-sensing applications using low-impedance shunts. However, the device can also be used in isolated voltage-sensing applications if the affect of the (usually higher) impedance of the resistor used in this case is considered.

AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 ai_v-sensing_bas734.gif Figure 59. Using the AMC1306 for Isolated Voltage Sensing

Design Requirements

Figure 59 shows a simplified circuit typically used in high-voltage-sensing applications. The high impedance resistors (R1 and R2) are used as voltage dividers and dominate the current value definition. The resistance of the sensing resistor R3 is chosen to meet the input voltage range of the AMC1306. This resistor and the differential input impedance of the device (the AMC1306x25 is 22 kΩ, the AMC1306x05 is 4.9 kΩ) also create a voltage divider that results in an additional gain error. With the assumption of R1, R2, and RIN having a considerably higher value than R3, the resulting total gain error can be estimated using Equation 4, with EG being the gain error of the AMC1306.

Equation 4. AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 q_egtot_sbas655.gif

This gain error can be easily minimized during the initial system-level gain calibration procedure.

Detailed Design Procedure

As indicated in Figure 59, the output of the integrated differential amplifier is internally biased to a common-mode voltage of 1.9 V. This voltage results in a bias current IIB through the resistive network R4 and R5 (or R4' and R5') used for setting the gain of the amplifier. The value range of this current is specified in the Electrical Characteristics table. This bias current generates additional offset error that depends on the value of the resistor R3. The initial system offset calibration does not minimize this effect because the value of the bias current depends on the actual common-mode amplitude of the input signal (as illustrated in Figure 60). Therefore, in systems with high accuracy requirements, a series resistor is recommended to be used at the negative input (AINN) of the AMC1306 with a value equal to the shunt resistor R3 (that is, R3' = R3 in Figure 59) to eliminate the effect of the bias current.

This additional series resistor (R3') influences the gain error of the circuit. The effect can be calculated using Equation 5 with R5 = R5' = 50 kΩ and R4 = R4' = 2.5 kΩ (for the AMC1306x05) or 12.5 kΩ (for the AMC1306x25).

Equation 5. AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 q_eg_percent_sbas734.gif

Application Curve

Figure 60 shows the dependency of the input bias current on the common-mode voltage at the input of the AMC1306.

AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25 D005_SBAS734.gif
Figure 60. Input Bias Current vs Common-Mode Input Voltage

Do's and Don'ts

Do not leave the inputs of the AMC1306 unconnected (floating) when the device is powered up. If both modulator inputs are left floating, the input bias current drives these inputs to the output common-mode of the analog front-end of approximately 2 V. If that voltage is above the specified input common-mode range, the front gain diminishes and the modulator outputs a bitstream resembling a zero input differential voltage.