On their design, there is a solder pad jumper, located on the left side of the microUSB port. I wish I had a 3.3V version but only have 5V version. In the design file, it says close the jumper SJ1 for 5V version and keep it open for 3.3V version. The photos confirm the design:
I imagine that the regulator on 5V board and 3.3V board are different. Correct? Otherwise it makes no sense.
Also, the 5V version I got is a clone. It comes with a 16MHz crystal so I assume 5V. On the other hand, the solder jumper SJ1 is unsoldered. I checked, on my PC USB port, VCC=4.6V, RAW=4.7V. Is this just sloppiness of the clone makers? Why not closing the jumper?
Thanks.
If the clone follows the Sparkfun schematic and the jumper is open, then the Vcc reading of 4.6 volts is very plausible for a 5v regulator being fed at 5v via the usb. If the jumper was closed, the regulator would be bypassed and you would see the full usb voltage.
What you see at the RAW input is the usb voltage drop over a Schottky? diode.
Thanks. I wanted this module to also provide power to a raspberry pi zero w. Pro micro enumerates as a high-power module needing 500mA so that is enough for it and rpi 0w. But if I could control the current to stay below 100mA during the first 100ms of USB insertion, that would be OK. Maybe using a low on-resistance MOSFET to turn on rpi instead of tying 5V of pro micro and rpi together.
There are purpose made high side load switches for such an application, for example TPS27081A.
You could also do something similar with a P channel mosfet.
6v6gt:
There are purpose made high side load switches for such an application, for example TPS27081A.
You could also do something similar with a P channel mosfet.
Interesting their ‘Page 1, Simplified Schematic’ doesn’t match their ‘7.2 Functional Block Diagram’
larryd:
Interesting their ‘Page 1, Simplified Schematic’ doesn’t match their ‘7.2 Functional Block Diagram’
The simplified schematic illustrates the mosfets as "Basic enhancemment insulated gate FET
(MOSFET) no bulk semiconductor", so the source arrow is reversed. I wasn't aware of that distinction before, but found these terms here:
Thanks 6v6gt for the part recommendation! Definitely will investigate it, maybe even for other projects where I need to switch 5V with 3.3V logic.
Just so I understand, the simplified schematic means the part is like an N-MOSFET couple with a P-MOSEFT, something I would use for high-side switching when the switching logic has a lower voltage than the switched power (up to 8V for this part). Am I correct?
