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TPS23756 and USB PD Design Questions

Jeffery Pfarr
Genius 14317 points
Other Parts Discussed in Thread: TPS23756, TPS23754, TPS23754EVM-383

Customer is looking at using the TPS23756 for their PoE PD design (Vout = 12 VDC, Iout = 2A+). Design requirements are:

- The power required exceeds the 12.9W available using standard PoE (IEEE 802.3af) and so requires the higher power available under IEEE 802.3at Type 2.

- The product is a Class 4 Powered Device (PD) which allows up 25.5W at the device using 100m max of Cat5e cable.

- Per IEEE 802.3at Type 2, the input voltage range will be 42.5V (min) to 57V (max) at the Exec2. PoE modes A and B are supported.

- 1500 V min. isolation.

- The Power supply design employs high reliability long life components. The Product Design life is 7 – 10 years. If used, electrolytic Capacitors should be long life, high temperature components operating at a voltage no greater than 50% of the rated  maximum.

Customer questions:

1. What is the life span of this device as it appears to be an older?  Is there a newer device we should consider?

2. Is there an Isolated Reference Design App Note available?

3. Are there efficiency curves and Input Power curves available for an Isolated design?

 

  • 0
    TI__Mastermind 41800 points
    Hi Jeff,

    I recommend looking at the TPS23754. This meets the power requirements above but also has an EVM designed for 12V/2A in the TPS23754EVM-383.

    1. TPS23754 is very robust PoE PD with a 100V abs max rating whereas some of our competitors have reliability issues with their ~70V processes. It's FIT curve is shown in the TPS23754 product page. If looking for Type 2 and high efficiency applications, this will be the best solution.

    2. I recommend looking at the TPS23754EVM-383 to start as there are some test data already in it's user's guide. They could even order an EVM to evaluate the performance under specific operating conditions that they are interested in.

    3. The EVM is an isolated active clamp forward converter. It's efficiency is shown in it's user's guide. ~90%.
  • 0 in reply to Darwin Fernandez
    TI__Genius 14317 points
    Thanks Darwin for the informative answers. Customer has a follow-on question: Is there any reason(s) that they should not use the TPS23756 for this application? Going EOL?, too Pricey?, Poor Efficiency?...or?
  • 0 in reply to Jeffery Pfarr
    TI__Mastermind 41800 points
    Hi Jeff,

    Looking at the 1K price online, the 756 is slightly more costly; mainly because it can operate at wider input voltage range (can be used with 12V adapter ORing at the primary where as the TPS23754 can be used for 24V adapter ORing at the primary) . However, since this a 12v application, if they were to have a 12V adapter, it would most likely be at the secondary since it would be more efficient and a smaller converter solution could be designed. These push more choosing the TPS23754. But if the customer insists on TPS23756, for the TPS23754EVM-383 design we recommended, you can switch the IC to the TPS23756 and it will still work.

    Regards,
    Darwin
  • 0 in reply to Jeffery Pfarr
    Prodigy 60 points

    Hi Jeffery,

    Please kindly advise if you have got a design for PoE+ at 24V @ 0.8A with an auxiliary power input from 18V-28V.

    Kind Regards, Bogdan 

  • 0 in reply to bogdan cojocariu
    TI__Mastermind 41800 points
    Hi Bogdan,

    Please see below link:
    e2e.ti.com/.../690037

    Unfortunately, this is designed for 48V adatpers. However, for a 24V output and ~24V adapters, it will more efficient to power the adapter directly at the secondary output with ORing diodes.