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TPS23881: IEEE 802.3at support and POE voltage polarity

Part Number: TPS23881
Other Parts Discussed in Thread: TPS23882, TPS23861, TPS23861EVM-612, MSP430F5234

I have two questions:

1. Our application needs 8 POE ports that support either 802.3af or 802.3at power levels. TPS23881RTQR is advertised as a 4-port 802.3bt device. The datasheet is not very clear on this but it seems that It can be used to power eight 802.3at type POE ports (where each port can be programmed to be limited to  802.3af or 802.3at power levels).Please confirm.

2. The reference schematic on page 19 of SLVUBP0A EVM document VPWR (positive supply voltage) is connected to data pair 2 (pins 3&6 of the RJ45) but according to the POE standard it should be connected to data pair 1 (pins 1&2 of the RJ45). Similarly the PSE_Nx signal is connected to data pair 1 but should be connected to data pair 2. 

  • Hi Ufuk, 

    TPS23881 is a device can support both 2 pair 30W and 4 pair 90W applications. If you only need 30W, you can use TPS23882 which is designed for 30W only applications. You can program the port to allocate 30W or 15.4W.

    For the polarity, both type 1,  type 2 and type 3 PSEs allow the polarity designed with our EVM. 

    IEEE802.3at stanard:

    IEEE802.3bt stanard:

    Thanks,

    Penny

  • Thank You for the reply. TPS23882 is a better device for this application. How about if I need 10 ports of 802.3at type 2 (30W) instead of 8 ports, do I add the 4 port device TPS23861?

    How does power budgeting work when more than one device is sharing the total available POE power budget? I assume software has to keep monitoring the power usage on all ports and keep reprogramming both devices to change the power available for each device. That creates some delay in responding to power utilization changes and also complicates the Software. Do you have or are you working on a 12 port PSE controller?

  • Hi Ufuk,

    In your case, I think TPS23861 is a better solution for you since TPS23861 and TPS23882 have some differences in register setting. You can use 3 of TPS23861 devices. We have MSP430 reference code for multi-port power management applications(http://www.ti.com/product/TPS23861/toolssoftware). In TPS23861EVM-612 user's guide, you can find detailed flow chart of the port power management algorithm.   Thanks.

    Best regards,

    Penny

  • TPS23861 has an unusual slave address determination method that requires the part to be programmed with a slave address prior to use. I would probably use two TPS23882 devices instead. 

  • Hi Ufuk,

    TPS23861 only requires I2C address programming once during initial power up and the address would be stored in EEPROM forever.  If you use TPS23882, will you have an MCU or CPU in the system to load the SRAM code and control the PSE devices  through I2C? Thanks.

    Best regards,

    Penny

  • A multi-core CPU will be controlling the PSE devices. Can the PSE controller function with an un-programmed SRAM? Is the programming of the SRAM needed in order to run the power budget algorithm? If it is needed, who generates the loadable SRAM image and is it fixed?

    Regarding programming the I2C slave address, it is another step at manufacturing and maybe even some software to be written to perform that operation. I try to avoid extra  manufacturing step and extra SW work if possible. 

  • Hi Ufuk,

    It is recommended to program the SRAM code into TPS23882 if you want to pass compliance test. You can download SRAM code from TPS23882 mySecure folder(requesting access from http://www.ti.com/product/TPS23882). We have an tech note describes the steps to load SRAM and MSP430 reference code. Since you want to do power management with multiple PSE devices, you may be interested in the FirmPSE solution that we are offering today. It is a turnkey software solution written with MSP430F5234 and you only need to configure system level parameters such as power budget, port priority, number of ports and the SW would run automatically to manage the system power. You can get check the TIDA-050026-23882 here to see more details. 

    For TPS23861 I2C address programming, you don't need extra step to manually program the device. You can add a few lines of code in your system software to program the devices' I2C address. Upon power on, first check if the I2C address has been programmed, if not, go with programming I2C address. We have MSP430 reference code (including how to program I2C address) as well.  Thanks.

    Best regards,

    Penny

  • Hi Penny,

    Is FirmPSE source code written for MSP430 that we can use as reference when developing our own power management code? Is that included in the slvc790.zip file?

    Thanks,

    Ufuk

  • Hi Ufuk,

    We don't provide FirmPSE source code as this is a production ready software solution that host can configure the system through I2C or UART. However, you can refer to TPS23861 MSP430 reference code for power management algorithm and TPS23882 MSP430 reference code for TPS23882 register configurations which is slightly different than TPS23861 if you decide to use TPS23882 instead of TPS23861. Thanks. 

    Thanks,

    Penny