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From: Mahen K on 29 Apr 2010 08:58
Hi

The schematic below is from ISP150x application note. The OTG
application uses external charge pump to source 5V(a)100ma in the host
mode. If the OTG application role is changed from Host to Device/
Peripheral powered from the connected USB Host, the VBUS line receives
5V from the host. The charge pump is in disabled state but since its
output is connected directly to the VBUS on which we have 5V supplied
by the host will it not cause any damage to the charge pump IC? Any
suggestions or reference schematic for interfacing external charge
pump with OTG controllers.

Schematic : http://picasaweb.google.com/mahen.jnk/OTG#
Full Application note : http://www.stericsson.com/technical_documents/CD00222782.pdf

Thanks
-Mahen J
From: Michael Karas on 29 Apr 2010 10:33
In article <dc1bb3a1-e54b-4944-806e-
bd50714f278c(a)h20g2000prn.googlegroups.com>, mahen.jnk(a)gmail.com says...
>
> Hi
>
> The schematic below is from ISP150x application note. The OTG
> application uses external charge pump to source 5V(a)100ma in the host
> mode. If the OTG application role is changed from Host to Device/
> Peripheral powered from the connected USB Host, the VBUS line receives
> 5V from the host. The charge pump is in disabled state but since its
> output is connected directly to the VBUS on which we have 5V supplied
> by the host will it not cause any damage to the charge pump IC? Any
> suggestions or reference schematic for interfacing external charge
> pump with OTG controllers.
>
> Schematic : http://picasaweb.google.com/mahen.jnk/OTG#
> Full Application note : http://www.stericsson.com/technical_documents/CD00222782.pdf
>
> Thanks
> -Mahen J

Seems that you would have to look closely at how the charge pump
IC works. The data sheet for the part you are using should shed
some light on the characteristics of the part and whether the
output of the part is susceptible to back feed when it is
disabled.

--
- mkaras
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