SNVAA25A January   2022  – July 2022 DP83TD510E , ESDS302 , LM5155 , LM66100 , MSP430FR2476 , TL431LI , TLV3012

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 10BASE-T1L (IEEE 802.3cg) PoDL Overview
    2. 1.2 PoDL PSE Types and Power Classes
  4. 2Terminology
  5. 3PD Design
    1. 3.1 PD Design Overview
    2. 3.2 Coupling and Decoupling Network (CDN)
    3. 3.3 VID Circuit
    4. 3.4 SCCP Communication
    5. 3.5 Protection Features
    6. 3.6 Power and Scalability
  6. 4References
  7. 5Revision History

3.3 VID Circuit

The voltage identification function is a mandatory feature of PD. Before the PSE applies full power to the link, it will test the link with a 9-mA to 16-mA constant current pulse and must detect a signature voltage from 4.05 V to 4.55 V. If the PSE detects a valid voltage signature, the PSE recognizes the device as PoDL compliant and can now supply full power to this link.

Table 3-2 details the PD detection parameters.

Table 3-2 PD Detection
Signature disable voltage (rising edge): 4.6 V to 5.75 V
Signature enable voltage (falling edge): 3.6 V to 4.3 V
Valid signature voltage 4.05 V to 4.55 V
PD current 7 mA to 17 mA

On the PD board, this voltage is generated using the eComp module integrated into the MSP430FR2476 microcontroller and a TL431 shunt reference. The shunt reference is configured to output approximately 3.6 V. Additional voltage drop over the rectifier diodes will increase the overall drop of the PD to be in the range of 4.05 - 4.55 V. The microcontroller is supplied from the 3.3-V rail and has an internal 1.2-V reference. The microcontroller checks the voltage on the connector, disconnects the shunt reference with the Q1 MOSFET when the input voltage rises above the signature disable threshold, and connects the TL431 reference U1 again when the input voltage falls below the signature enable threshold.

Figure 3-3 shows the PD VID circuit realized with the comparator and reference internal in theMSP430.



Figure 3-3 PD VID Circuit

Figure 3-4 shows the test results of the voltage signature circuit. The black line is seen to be within the 4.05-V and 4.55-V bounds when tested with a 7-mA to 17-mA signal. Note that the voltage drop across the rectifier bridge had to be taken into account in the calculation of resistors R1 through R7.

Figure 3-4 PD Signature Voltage Test Results