• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 2131 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2501 USB Output Capacitor

Dennis Larson
Prodigy 30 points
Other Parts Discussed in Thread: TPS2501

I have a design using the TPS2501 and limiting USB charge current to 500 mA. Our design only uses 10 uF output capacitor, but I found several mentions that 120 uF minimum is required. We are somewhat space constrained so using a 120 uF capacitor is a challenge. What can I expect for effects if I only use 10 uF? If I can use a 22 uF capacitor will that improve things?

  • 0
    Mastermind 7395 points

    Acc. the datasheet, the capacitor is not a requirement of the device. It is used because "many USB applications require that downstream-facing ports be bypassed with a

    minimum of 120uF, low ESR capacitance" (datasheet p. 25)

  • 0
    Prodigy 30 points

    As I said I am using in a USB charging application, so I understand the TPPS2501 doesn't require it.

  • 0 in reply to Avi Chami1
    TI__Expert 7990 points

    The USB2.0 standard requries a minimum of 120uF in the hub in support of the downstream ports.  The wording is not straight forward, but I beleive the 120uF can be shared between multiple ports.  I think the concept is that, given the upstream-facing port (device that plugs in) can have up to 10uF on plugin, the capacitive divider (with the hub) assures integrity of hub operation (maintains Vbus source voltage integrity).  Many designers put 120uF on each port either as a conservative approach, experience with control of voltage droops, or as a defense against the wording in the spec.  Another consideration is that sometimes several ports share the same power switch and the concern is that plugging one port in may effect the operation of an previously attached device.

    The TPS2501 switch section has a UVLO (under-voltage lockout) of 4.21V (falling).  Insufficient buffer capacitance might trigger a UVLO, with a turnoff and restart.  Eventually it would be expected that the load would start.  If the switch is powering just that one load, this is probably not a problem.

     

  • 0 in reply to Martin Patoka
    Prodigy 30 points

    I only have a single charging port. Based on the information you provided, it seems I should get as much capacitance as I can given the space I have.

    Thanks for your help.