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DC / DC Converter Shutdown when Load not Present

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I have a DC / DC converter feeding a powered USB port. I want the DC / DC to shutoff when no USB device is connected but turn on when one is.

Any suggestions?

Thanks
 

You can't shutdown VUSB if you want to recognize devices plugged to the USB. So there must be at least a low-power VUSB when the main supply is shut down.
 
You can use a mechanical switch that will sit on the USB port and when a device is plugged in it will push the switch and activate the converter. This way when the converter will turn on the device will be detected.
 
YanivS said:
You can use a mechanical switch that will sit on the USB port and when a device is plugged in it will push the switch and activate the converter. This way when the converter will turn on the device will be detected.
Click to expand...
This works in the sense that you detect a cable insertion, but not an actual device. As FvM said, identifying an actual device requires communicating with the device, which requires the supply voltage. So you have to at least enable the power whenever you want to poll for devices.
 
True. However by detecting the cable insertion you will enable the power and then the usb will be powered and hence will be detected.
 
I'd suggest looking for DC-DCs that offer better-enough
light load efficiency that you can tolerate the current
drain. I've seen some advertised as low as tens of uA
(but don't recall specifics) with pulse-skipping for low
load / no load. A hysteretic converter might be good
here, you get pulse-skip for free more or less.
 
One way might be to put "sniff" of DC on the pin (say via a !M) then sample this point with a high impedance amp. Working on the basis that without an external USB plugged in you get the full voltage, with a device plugged in the voltage falls. The reason for the 1M is so any residual DC will have no effect on the digital signal as it should be below 10mV.
Frank
 
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