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Gms-u1LP: does it make any sense to supply USB-Vcc when Vcc is not supplied?

Started by Horsa, April 14, 2011, 10:47:57 AM

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Q: GlobalTop Gms-u1LP: does it make any sense to supply the USB-Vcc pin 20 when the Vcc pin 1 is not supplied?

No, it does not.

The USB-VCC pin 20 is used to supply power the USB function only, but the main VCC pin 1 still needs to be connected for the
entire module to function.

There is no point in supplying USB-VCC power when the module is off, because the main processor is not accepting any input anyway when the module is off, even in power periodic mode's sleep state.

The reason why USB-VCC is now independent in Gms-u1LP (with regards to previous GlobalTop modules) is because GlobalTop wanted to lower the power consumption as much as possible, and USB is actually still drawing a couple mA of power even when it is not used (like in PA6B). This in turn offers more power saving capabilities and allows for a more flexible design.