USB Power-Bus supply RIPPLE - How much??

[Alexandre Heil Franca]

Hi there!

I am building a device that should include a USB-Host. As a USB-Host, it
should supply 5V x 500mA. I hasn't been able to find any reference about
the max. ripple for the power-bus.
In reality I am not sure, if all clients must include a power supply it
self, or at least any kind a filter at the input of the power-bus. If any
of these options is true, I don't need to care about ripple. Does anyone
could point me any reference? Does anyone know how much it should be?

Thanks in advance!

Best regards,

Alexandre