TIDUEB8C July   2018  – March 2021 TPS274160

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 LM5165
      2. 2.2.2 TLC59282
      3. 2.2.3 TPS4H160-Q1
      4. 2.2.4 INA253
      5. 2.2.5 TIOL111
    3. 2.3 System Design Theory
      1. 2.3.1 IO-Link PHY
      2. 2.3.2 Current Sink
      3. 2.3.3 Power Supply for L+
      4. 2.3.4 Power Supply
      5. 2.3.5 Pinouts
    4. 2.4 Software Frame Handler
      1. 2.4.1 PRU-ICSS IO-Link Frame-Handler
        1. 2.4.1.1 Performance Advantages and Benefits
        2. 2.4.1.2 Principle of Operation
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Software
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 IO-Link Wake-Up Pulse
        2. 3.2.2.2 L+ Turnon Behavior
        3. 3.2.2.3 Current Sink on CQ
        4. 3.2.2.4 Residue Voltage
        5. 3.2.2.5 IO-Link Physical Layer Test Summary
        6. 3.2.2.6 Current Sense on Each Port
        7. 3.2.2.7 TPS4H160 Thermal Behavior
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7About the Author
  13. 8Revision History

2.3.3 Power Supply for L+

An IO-Link master has to power the L+ line with a current capability of at least 200 mA and 400 mA pulse for 50 ms. The specification states this as shown in Table 2-4.

Table 2-4 Specification for L+ Supply
PropertyDesignationMinimumTypicalMaximumUnitRemark
VSMSupply voltage for devices202430VSee Voltage level definitions in IO-Link Interface and System Specification Version 1.1.22
ISMSupply current for devices200N/AN/AmAExternal supply required for > 200 mA
ISIRMCurrent pulse capability for devices400N/AN/AmAMaster supply current capability for a minimum of 50 ms at 18 V after power-on of the port supply

To supply this, a TPS4H160 device is used. This quad-channel, high-side switch provides a programmable current limit and has a current sense output that is connected to the MCU. So each channel is short-circuit protect and can be observed by the MCU to measure the current on each port and detect faults.

Meeting the requirements for the ISm is rather easy and can be achieved with any device with a low enough R(DS)on. However, the ISIRm is more difficult to achieve, since the power dissipation from the junction to the ambient is a limiting factor here. When the output is shorted, or a large capacitor has to be charged, the power dissipation in the device is up to 400 mA × 30 V = 12 W for a short time. This can be even more, when the design drives more than the minimum current of 400 mA.

Charging a capacitor on the L+ line with a static load (which is a realistic scenario for an IO-Link device) relaxes this a bit, since the L+ line voltage increases, the voltage drop in the FET decreases and also the power dissipation decreases.

However, since the power does not propagate that fast to the PCB or a heat sink, mainly the package of the device is the limiting factor.

See the Maximum Device consumption at power-up table in Section 4.4 of the IO-Link Package 2015 & Corrigendum Version 1.0 for detailed specifications and the definition of a charge of 400 mA in the first 50 ms after power up, resulting in 20 mAs.

Due to this extension of the specification, the testing of the output on the L+ line is defined to be a large capacitor of 1000 µF in parallel with a 150-Ω resistor. This load simulates a device with a static load and a large input capacitor.

GUID-5A036C4A-89AE-4B1F-B2DF-DDA0C1A586E4-low.svgFigure 2-10 High-Side Switch Schematic

The high-side switch is configured to limit the current at 0.6 A. This current is selected to meet the requirements for the turn on behavior. At a higher current, the package cannot handle the power dissipation during charging the capacitor and the device switches off to cool down and restart again.

The current sense is configured to go up to 0.7 A at a maximum output voltage of 1.8 V (which is given by the ADC in the AM4379 device on the IDK used here). This results in the schematic seen in Figure 2-10. The TPS4H160 device can be set to two different behaviors after a thermal error occurred: it can switch off or retry automatically, here it is configured to switch off until it is enabled again.

If other requirements are necessary or a turn on behavior with interruption is acceptable, a higher current of 1 A per port is feasible and working when turned on.