USB power

This topic has 3 replies, 2 voices, and was last updated 6 years, 2 months ago by Neeraj Dantu.

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- September 21, 2018 at 1:53 am #6469
  tmatsuzawa
  Participant
  Hello.
  I am using PocketBeagle for my prototype, and now looking into the following and others to learn USB devie (connected to PocketBagle) power current.
  I am adding 2nd (USB1) USB port to the board.
  I am currnetly using the power switch TPS2051 suggested on the example. I believe it has overcurrent detection.
  OSD335x Lesson 2: USB Circuitry
  I also looked into OSD3358-SM-RED, and it also is using TPS2051. SM-RED schematics also states that “Only 500 mA is supplied for all 4 ports. Therefore, battery carging is disabled for all ports.”
  I think this limitation is due to USB2.0 spec (current limited to 500 mA), and also SM-RED USB hub is drawing VBUS current from SYS-VOUT?
  Q) What if I want more current for my USB1 VBUS?
  Just changing TPS2051 to the other power switch which has larger OC limit?
  (I am feeding 5V for VBUS from external source, not from SIP SYS-VOUT, so doing so I should have no 500 mA limit (as long as SYS-VOUT is concerned?)
  I may look into USB power source circuit examples from TI, but since I am integrating it with PocketBeagle (or OSD3358) and if you have any suggestion or points to consider, I highly appreiate hearing it.
- September 21, 2018 at 6:16 pm #6470
  Neeraj Dantu
  Moderator
  Hey T,
  The following things can be implemented to achieve higher current on USB host terminal:
  – Switch TPS2051 current switch as you mentioned with a switch with a higher capacity.
  – You are also right that you would have to move the supply voltage rail for VBUS to an different 5V supply other than SYS.
  Best,
  Neeraj
- September 24, 2018 at 8:47 pm #6474
  tmatsuzawa
  Participant
  Thank you for your suggestion.
  And I have additional one question which may be obvious (though I want to make sure).
  “USB Host” diagram, I can see two ferrite beads: FB1 and FB2. They read like the follows.
  FB1: 0.1 Ohm. 0805
  FB2: 150 Ohm, 800 mA
  Can I interpret that both are the same part (like, DC resistance 0.1 Ohm, size 0805, impedance at 100 Mhz 150 Ohms, current 800 mA)?
- September 25, 2018 at 9:43 am #6475
  Neeraj Dantu
  Moderator
  These are Ferrite beads that help with noise reduction on the power rail. The values depend on the board and are chosen as needed. For this particular board, we used the following components:
  FB1: MPZ2012S601AT000
  FB2: BLM21AG151SN1D
  Hope that helps.
  Best,
  Neeraj
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