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TPS2051B in HOST mode

Aska
Intellectual 740 points

Hi,

          The Figure 33. Typical One-Port USB Host / Self-Powered Hub in datasheet page.20.

          The capacitor 120uf whether necessary? How is this calculated? can using a smaller capacitor? Thank you.

  • 0
    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 original text can be found under USB.org  here:  http://www.usb.org/developers/docs/