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| USB memory stick voltage |
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| Simon:
well i will go back to the supplier and see what they say. ultimately I can't fix stuff here and the under voltage units are out of warranty. |
| SiliconWizard:
--- Quote from: Simon on February 26, 2019, 08:39:45 am ---but if the device is powered directly off the battery this will vary from around 4V fully charged to lower voltages. So would it be reasonable to expect a memory chip that has the built in USB interface to work? --- End quote --- Would it be reasonable to expect any device to work out of spec? Whereas we can reasonably expect all of these to be internally powered at 3.3V, given their size and cost, it's very likely they use a linear regulator. Given again the cost factor, it's also very likely they include lousy LDOs that are not that low drop-out at all. A very common "LDO" that we can see in many cheap devices is the ubiquitous AMS1117 which is dead cheap, for instance. It has over 1V of drop-out voltage, so given that for most of the useful life of a LiPo battery, the voltage is around 3.7V-3.8V, you'd end up with 2.7V or less. So not only may some ICs misbehave, but one of the most problematic point I see would be a significant mismatch in the logic 'high' voltage between the host and the memory stick, potentially causing problems with the USB data lines. The power supply stage of those memory sticks is likely to be pretty different from one device to another. Powering USB devices directly from a LiPo battery looks like a pretty lousy design here IMO. |
| Simon:
i really don't know why anyone thinks there are any voltage regulators in here. The 3.9V has not come through a "LDO" or it would be hardly 3V. I suspect the circuitry is 3.3-5V tolerant but the memory stick maybe not. |
| ogden:
--- Quote from: Simon on February 26, 2019, 05:40:48 pm ---well i will go back to the supplier and see what they say. ultimately I can't fix stuff here and the under voltage units are out of warranty. --- End quote --- Manufacturer shall fix problems anyway, thou make sure that your tests confirm/demonstrate voltage problem and other potential controller/disk_size/file_system/file_naming software/compatibility problems are excluded from suspicions. --- Quote from: Simon on February 26, 2019, 06:14:22 pm ---i really don't know why anyone thinks there are any voltage regulators in here. --- End quote --- Flash sticks receive 5V from USB but controllers are 3.3V+1.8V IC's. Indeed there is some regulator, in the flash drive - separate or IC-integrated. |
| Simon:
So you think there might be a regulator in the memory stick that drops the voltage to 3.3V which may be hard to achieve with 3.9V in the first place? |
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