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TUSB8020B: Design Questions

d_zero
Genius 4955 points

Part Number: TUSB8020B

Hi all,

we have few questions regarding TUSB8020B:

1) Can the TUSB8020B work in standalone mode ( without I2C or SMBUS) connection ? 

2) In standalone mode the pins should be:

2 SCL/SMBCLK -> left unconnected

3 SDA/SMBDAT -> left unconnected

22 SMBUSz/SS_DN2 -> left unconnected

3) What is the benefit to have an I2C EEPROM vs standalone mode?

4) if we want Full power management of downstream ports and Individual control of downstream port power switch then ?

pin 36 needs a pull-down

pin 35 needs a pull-down

5)Can we control the GRSTz (pin11) with PG pin (combined) from VDD33 and VDD regulator or is there no need for this and only a CAP is required on GRSTz to meet the power-up  sequence  on page 7 ?

6) We want  to use TPS25210A ( auto-Retray) for load switch for the DFP ports

to do so 

6a) because the EN pin on TPS25210A is active high, we should set a pull-down on pin 21 PWRCTL_POL?

6b) we should connect pins 4 and 6 from TUSB8020B to TPS25210A  En pin?

6c) the pin 4 and 6 should have a pull-down in order to set Battery charging not supported ? what is the recommended value of those pull-down if we have res divider on EN of TPS25210A for UVLO?

6d) can we use PG pin from TPS25210A to connect to pin 5 OVERCUR1z and 8 OVERCUR2z of the TUSB8020B ?

6e) would you recommend TPS25210L over TPS25210A  for this application

Best Regards,

David.

  • 0
    TI__Guru 60870 points

    Hi David,

    1) Yes, I2C and SMBUS are NOT required

    2) Yes, unused SCL/SDA/SMBUSz should be unconnected when unused

    3) Section 8.5 describes the possible register configuration options available with I2C / SMSBUS

    4) pin 36 needs a pull-down - YES

    pin 35 needs a pull-down - YES

    5) GRSTz can be controlled with just an external capacitor or a PG from one of the regulators.

    6a)  Yes, or you can rely on the internal pulldown.

    6b) Yes, PWRCTL is routed to the EN.

    6c) The PWRCTL_BATEN pins have internal pulldowns (~22K) so that they default to battery charging OFF.

    6d) / 6e) - I'm moving this thread to the team that supports TPS25210 to answer.

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Guru 57737 points

    HI JMMN,

    I will get back to you tomorrow with difference between TPS25210L over TPS25210A.

  • +1 in reply to Praveen GD
    TI__Guru 57737 points

    Hi David,

    Please see my response below,

    6d) The PG pin of TPS25210 will not accurately convey the over current condition. During an overcurrent event, the device limits the current in the path to the set current limit value (Ilim). The output voltage during current limit is now = (Ilim x Rout). This means the output voltage is a function of the output load resistance (amount of overcurrent) during current limit operation.

    The PG pin asserts HIGH(If PGTH pin voltage > VPGTH(R)) and asserts LOW (If PGTH pin voltage < VPGTH(F))

    So, the amount of overcurrent/ the load resistance decides if the PG stays HIGH or pulls LOW during the current limit operation. If the over current persists for longer duration, the device may turn off due to thermal protection. The device may or may not turn off due to thermal protection depending on the power loss in the FET, Ambient Temperature and Layout (RQJA). Also, PG asserts low various other instances like Reverse current, ILM Pin Open or Shorted to GND, Input Reverse Polarity, Undervoltage, Overvoltage (OVC).Therefore, I think using PG for overcurrent indication may not be the right approach. 

    6e) TPS25210L : Latches OFF after a Fault event whereas TPS25210A auto retries. You can find the information in the table below.

    I may not be able to comment on which variant of the device is suitable for this application. So, assigning the thread back to JMMN.

  • 0 in reply to Praveen GD
    TI__Guru 60870 points

    When an overcurrent event is reported to the USB hub via the overcurrent input, it will report it to the host which will typically disable all the downstream ports.  Having the port latched off after a fault event is preferable so that the port is not powered on until the host re-enables it.

    Regards,

    JMMN