The hardware manual for the startKIT is very clear on the matter of powering the board from the USB connector.
However, this is inconvenient when trying to deploy a prototype solution based on the startKIT.
From examination of the schematics, the only difference between USB VBUS and onboard 5V rail is a single ferrite bead and a 2.2uF cap.
Can anyone explain why power could not be provided via a 5V pin (e.g. J6) with a similar set of components?
Is it possible to have external 5v Power source to startKIT?
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Hagrid
- Active Member
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mon2
- XCore Legend
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- Joined: Thu Jun 10, 2010 11:43 am
Hagrid, after a review of the same schematics of the Startkit, see no offending reason why you cannot use the referenced J6 5 volt pad to power this board.
Of course, remove the USB connector if you proceed with this method of powering this kit so that you are not supplying the same external power rail back to your PC. The 2.2 uf cap which is not much of a filter but is intentionally small to avoid the in rush current on the VBus rail. Likely you have a beefy power supply of say 1A or perhaps more(?) so will not hurt to stuff a local 10uf or 22uf when using the external power source. Just remove the same extra filter bulk cap if using the original USB host port as your power source.
By USB spec, each compliant USB port is required to feature a short circuit / excessive port protection (ie. shut down the power rail on such faults without damage to the related ports). Often throgh the use of polymer fuse (effectively a thermal fuse which self-heals when OFF) which we do not agree are capable of fast enough turn off time and also that they derate over time; on/off cycling. We did a review for a very large OEM (with 2 letters in their name) for a custom design of a USB host adapter that is pending and found that the majority of the competing models on the market do not offer this mandatory feature !! That is, under similar conditions of using an external power source AND applying the USB connector to the host PC would literally fry the Vbus trace on the host adapter. There is no current limit circuit on the majority of the add-on USB host adapters so be cautious. Nasty stuff out there if you are not careful - the PC industry is too driven by lower and lower bill of material costs / resales at the expense of creating more garbage for the dump.
<End of my rant> :).
Of course, remove the USB connector if you proceed with this method of powering this kit so that you are not supplying the same external power rail back to your PC. The 2.2 uf cap which is not much of a filter but is intentionally small to avoid the in rush current on the VBus rail. Likely you have a beefy power supply of say 1A or perhaps more(?) so will not hurt to stuff a local 10uf or 22uf when using the external power source. Just remove the same extra filter bulk cap if using the original USB host port as your power source.
By USB spec, each compliant USB port is required to feature a short circuit / excessive port protection (ie. shut down the power rail on such faults without damage to the related ports). Often throgh the use of polymer fuse (effectively a thermal fuse which self-heals when OFF) which we do not agree are capable of fast enough turn off time and also that they derate over time; on/off cycling. We did a review for a very large OEM (with 2 letters in their name) for a custom design of a USB host adapter that is pending and found that the majority of the competing models on the market do not offer this mandatory feature !! That is, under similar conditions of using an external power source AND applying the USB connector to the host PC would literally fry the Vbus trace on the host adapter. There is no current limit circuit on the majority of the add-on USB host adapters so be cautious. Nasty stuff out there if you are not careful - the PC industry is too driven by lower and lower bill of material costs / resales at the expense of creating more garbage for the dump.
<End of my rant> :).