TPS23751: Driver requirements for LTC0266-50 in PMP8812 PoE Design (12V/2A output with 18-40V adapter)

Namith HL

Part Number: TPS23751
Other Parts Discussed in Thread: TPS23752,

Hello,

Im planning to design 12V/2A POE+ design for input voltage 42.5v to57v and adpter voltage range 18 to 40 v,i had refereed several ti design upon which PMP8812 was suitable to me. but i had question over LTC0266-50 transformer driver requirement...please suggest me to resolve my doubt.

over 6 years ago

0 Thomas Amlee over 6 years ago

TI__Genius 9230 points

Hi,

Can you highlight some of your doubts? I can take a closer look early next week.

Thanks,
Tom A.

0 Namith HL over 6 years ago in reply to Thomas Amlee

Intellectual 570 points

I referred couple of ti design using TPS23751 ,example : 5V/4.5A(TPS23751EVM)

Input range 42.5V to 57V and Adapter range 21V to 57V

Another Ti design using TPS23751 ex: PMP8812 reference design(12V/2.1A) with same input voltage range.

when compared to two design PMP8812 reference design contains LTC0266-50 transformer driver for gate control pin of TPS23752

Questions: 1) How to set adapter input voltage range b/w 18V to 40V

2)what is the purpose of using LTC0266-50 for 12V/2.1A design ,can i connect similar to 5V/4.5A

3)can i use 5v/4.5A design for 12V/2.1A only by changing transformer that can support 12V/2.1A ?

4) Is any other changes to be required for 12V/2.1A ,when compared to 5V/4.5A ti design?

0 Thomas Amlee over 6 years ago in reply to Namith HL

TI__Genius 9230 points

Hi Namith,

Sorry for the delay:

1. To design for a lower voltage adapter, I would start from section 2.2 of this app note: www.ti.com/.../slva305c.pdf and work your way forward.

2. In the TPS23751EVM-104 board, the gate driver transformer is packaged with the flyback transformer. This was likely a custom part developed by Coilcraft for the purpose of this EVM design. Using LTC0266-50 would be appropriate for the 12V design, given that the secondary side FET circuit is similar. I would tread carefully when changing output voltages.

3. Your feedback circuit & secondary side will likely change. See this app note for design help: www.ti.com/.../slva305c.pdf

Overall, I would take care in redesigning your circuit from the ground up since you desire a different output voltage. See the app note I've linked to above.

- Tom

0 Namith HL over 6 years ago in reply to Thomas Amlee

Intellectual 570 points

Thank you for reply,

POE i/p range: 42V-57V

Adapter I/P range :18V-40V

O/P Voltage: 12V/2A ( Output power will not be 24W)

kindly consider this specification and suggest me suitable POE+ reference design from TI

Regards,

Namith

0 Thomas Amlee over 6 years ago in reply to Namith HL

TI__Genius 9230 points

Hi Namith,

Try PMP6659: http://www.ti.com/tool/PMP6659

- Tom

0 Namith HL over 6 years ago in reply to Thomas Amlee

Intellectual 570 points

kindly note, adapter input is dc 18t o 40v

0 Thomas Amlee over 6 years ago in reply to Namith HL

TI__Genius 9230 points

Namith,

This the closest design I could locate. There is another that works with 20V, but not 18V. Would you be interested in that one? Keep in mind that you can use your 18V adapter with this design.

Thanks,
Tom

0 Namith HL over 6 years ago in reply to Thomas Amlee

Intellectual 570 points

yea please share link,

0 Thomas Amlee over 6 years ago in reply to Namith HL

TI__Genius 9230 points

PMP5008 (20V minimum input, 12V/2A output):

PMP5008_RevA_SCH.pdf

PMP5008_RevA_BOM.xls

PMP5008_RevA_Test Data.doc

0 Namith HL over 6 years ago in reply to Thomas Amlee

Intellectual 570 points

Hello,'

following are our main requirement regarding poe

please suggest me what is main consideration for design?

1) It shall consist of a PoE deriving a nominal 28V and secondary DC supply of 21-30V
shall be diode OR’d with PoE supply as an alternative means of powering the unit.

2) According to the loading on the Power Amplifier 2 modes of PoE operation are
required – 802.3af (PoE) and 802.3at (PoE+).

Regards,

Namith HL

0 Darwin Fernandez over 6 years ago in reply to Namith HL

TI__Mastermind 40560 points

Hi Namith,

As 28V is not a common output voltage for PoE, it'll be difficult to find an off the shelf PoE transformer. Why not design with a 24V output to OR with your DC adapter at the secondary since it's within the adapter range?

Please see below link that describes how to modify the TPS23754EVM (.at power level) to output 24V.
e2e.ti.com/.../690037

Regards,
Darwin

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TPS23751: Driver requirements for LTC0266-50 in PMP8812 PoE Design (12V/2A output with 18-40V adapter)