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RMas
Visitor II
December 13, 2022
Question

UCPD Schematic review on G4

  • December 13, 2022
  • 1 reply
  • 1140 views

I want to create a power distribution system that can accept up to three supplied (AC/DC, USB, and Battery. At the end of VBUS will be the management system that will choose the highest voltage and use that as primary supply.

Would like some suggestions on any changes my UCPD sink may require. I've used these guides as reference (SNK1M1, TCPP01-M12, USB, G434)

I'm wanted to implement dead battery and want the TCPP to only disable after is gets 3.3V from VBUS (chose the LDO from SNK1M1). The MCU will be powered from VCC after power management. My thought is this will keep protection intact in case USB is plugged in when the system is already powered. here are my questions.

  1. TCPP01 section 6.6.3 mentions Sink Capacitance, but i see no other reference to it in this or any other guide or schematic. How is this calculated
  2. TCPP01 section 6.6.6 mentions VBUS detect. Want to make sure this is only optional?
  3. TCPP01 section 6.6.4 mentions the value range of C1 C2, but the SNK1M1 didn't seem clear as to how exactly they are chosen. i went with the value from SNK1M1
  4. Same question in G431 section 5.3.7 about CL1 and CL2 around the HSE
  5. SNK1M1 section 1.2.2 what is the importance of Rds(on) and how might if effect this circuit?
  6. I would like to add an LED indicator TCPP01 FLT when it drops low. Datasheet states when active low the resistance is 250ohm. Would like to know if this 150ohm resistor in series would be safe?
  7. Would SNK1M1 Figure 9 be suitable for adding indicators at these locations?
  8. For deadbattery condition are the DB pins tied to ground or to CCx pins for this setup? i see both in the docs.

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    1 reply

    M
    MROUV.1
    ST Employee
    January 9, 2023

    Hello,

    Thanks for sharing your case and your questions.

      

    1- Sink capacitance is fixed by Universal Serial Bus Power Delivery Specification table 7 : cSnkBulk

    0693W00000Y7kUMQAZ.pngWe suggest to select 2.2µF

    2- Vbus detect

    It is mandatory to measure Vbus voltages across various steps (attach, detach, …).

    3- CC line capacitance

    CC line capacitance is fixed by Universal Serial Bus Power Delivery Specification Table 5-19 : cReceiver

    0693W00000Y7kVyQAJ.pngValue chosen in X-NUCLEO-SNK1M1 (330pF) considers STM32 and TCPP01-M12 capacitances in parallel to match with standard requirement.

    4- CL1 and CL2

    The application note AN2867 details all oscillator capacitor selection for STM8/STM32.

    5- Rds_ON of CC lines switches

    A too high Rds_ON of CC lines switches should degrades eyes diagram of the digital communication.

    STM32 UCPD and TCPP are co-design and works together.

    They have been validated together by an USB-IF independent certification that includes an eye diagram.

    6- LED on open drain flag

    OD output grants VOL < 0.4V at 1mA for STM32.

    Nevertheless, I recommand to use 1kOhm on 3.3V and maintains current lower and 3mA.

    7- Indication LED

    1kOhm resistor on 3.3V + SMD LED can be placed in parallel of pull-up resistor (if used) for FLG indication.

    8- DBCC connection

    DBCC PIN of STM32 can be used as GPIO because TCPP01 present Dead Battery when battery is fully depleted.

    Best regards,

    Mathieu

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