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TPS2388: Power injector with 4-pairs(45W) using Single-port. (TPS23861 or TPS2388)

BJ Han
Expert 2035 points
Part Number: TPS2388
Other Parts Discussed in Thread: TPS23861,

Hi Penny,

I would like to develop a 1-port four-pair power injector using two of the four outputs of the TPS23861 or TPS2388.

I have questions about PSE and PD compatibility testing.

As far as I know, PD knows that there are LLDP(1-PD) and FORCED(2-PDs) methods.

Do you need an MCU to satisfy the two methods?

Do you need to control using semi auto mode?

If control is needed, do you need to control only the LLPD method?

In case of FORCED method, it is not necessary to control because there are 2-PDs.

  • 0
    TI__Genius 9230 points
    Hey BJ,

    I just assigned the thread to Penny. She should see this soon.

    Thanks,
    Tom
  • 0
    TI__Intellectual 1695 points
    Hi BJ,

    Generally, for 60W UPoE forced PD applications the auto mode can be used.
    But if you use TPS2388, you need MCU to control in both PD methods for there is no auto mode in TPS2388 and the semi-auto mode is used for both.
    In LLDP the MCU is needed to realize classification, power allocation in two channels, and power enable command.
    In forced PD, the two channels can implement detect and class for two PDs individually and MCU is used to configure the ICUT and power on command.

    If you use TPS23861, you will need MCU to control in LLDP for the same reason like TPS2388.
    But for forced PD, the auto mode can be used.

    Thank you
    Best Regards
    Jack Chen
  • 0 in reply to Jack CCY
    Expert 2035 points

    Hi Jack,

    Thanks for your details explanation. It’s quite clear to me.

    I have additional questions. (TPS23861)

    Can I change the Current-Sensing Resistor value?(0.255-> 0.15Ω)

    I changed the Current-Sensing Resistor value to achieve higher output power.

    The reason for this is to produce a non-standard 45W output.

    Is there any side impact when changing?

    Thank you.

  • 0 in reply to BJ Han
    TI__Intellectual 1695 points
    Hi BJ,

    It is not recommended to change the current-sensing resistor because it is related to class and ICUT ILIM setting.
    If you want to change the sensing resistor, you have to change the class resistor too for correct classification and modify the ICUT, ILIM register for correct current limit.
    You can use ICUT and POEPn register to set the ICUT current to 920mA which make the port 45W for single channel.

    Thank you so much.
    Best Regards
    Jack Chen