Power Pi Pico by applying 5 V to VSYS—any experiences with or thoughts on additional safety measures?
Asked 7 days ago
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The official Pico datasheet chapter 4.5 suggests using either a Schottky diode or a P-channel MOSFET (P-FET; or a combination of both) when powering the Pico from an external power source (at least if you want to keep the option of simultaneously connecting a computer via USB).
As a suitable P-MOSFET, they suggest Diodes DMG2305UX. However, I couldn’t find this one in online stores here in Germany.
I wondered whether some of you have experiences with one or both of the options and could elaborate what good solutions are and which common diode/MOSFET models are the most suitable for the job (the job being in this case, to power the Pico).
From VSYS and the adjacent GND pin, I power an AirLift FeatherWing to provide the Pico with WLAN, as described in this example. It needs up to 250 mA during Wifi use. Moreover, I want to connect 2 GY-BME280 using i2c and 2 DS18B20 on GPIO 16. These should use something of the magnitude of 1 mA per sensor, which, I guess, is negligible.
The power source will be this 5 V 12 W power supply transforming 230 V 50 Hz AC to 5 V DC.
I attached two images from the original Pi Pico datasheet depicting both versions.
This is their version using the Schottky diode:
This is their version using the MOSFET:
They added: “For inputs that have a low minimum input voltage, or if the P- FET gate is expected to change slowly (e.g. if any capacitance is added to VBUS) a secondary Schottky diode across the P-FET (in the same direction as the body diode) is recommended.”
asked Sep 13 at 14:22
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- (1) For Pico with WiFi, I would suggest to use Pico W: (a) New Pi Pico W- WiFi Features, Specs & Pinout Simplified – etechnophiles etechnophiles.com/raspberry-pi-pico-w-wifi-specs-pinout – tlfong01 Sep 15 at 8:14
- (2) Pico W’s power cct is similar to Pico, so your question need lttle modification: imgur.com/a/vRC5e3U – tlfong01 Sep 15 at 8:19
- (3) BME280 is a bit out of date. I would suggest to instead use BME680: (3.1) bosch-sensortec.com/products/environmental-sensors/gas-sensors/… (3.2) bosch-sensortec.com/media/boschsensortec/downloads/datasheets/… (3.3) bosch-sensortec.com/media/boschsensortec/downloads/… (3.4) pt.aliexpress.com/item/… – tlfong01 Sep 16 at 3:29
- (4) I surveyed Schottky diodes and found 1N5822 good (only 0.4V drop at 1A): imgur.com/a/8AVLt4O – tlfong01 Sep 18 at 4:19
- (5) For P-MOSFET, I m thinking of trying this: IRF9540N datasheet – infineon infineon.com/dgdl/… – tlfong01 2 days ago
- (6) irf9540n summary: imgur.com/a/17nb9Fe.. IRF9540N vgs(th) max is 4V, so should be OK if Vgs = Vusb = 5V. – tlfong01 2 days ago
- Now I have bought the BME280 and irf9540n. Next step is testing them: imgur.com/a/Qrbvxxu – tlfong01 yesterday
- (7) Now my first test is to use the P-channel power MOSFET IRF9540N as a high side switch to switch on/off power to RpiPico W. Reference: Low side vs High side switch – James Lewis, BaldEngineer baldengineer.com/low-side-vs-high-side-transistor-switch.html – tlfong01 yesterday
- (8) IRF9540 P-channel power MOSFET as high side switch for external 5V power to RPi Pico W: imgur.com/a/aGDaNP4 – tlfong01 15 hours ago
- (9) Next step is measuring IRF9540N Vgs(th) 5V and RsOn values: imgur.com/a/DCo6EUs – tlfong01 41 secs ago Edit
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Although your question is call for sharing experience, I also have interpreted it as asking for help with realizing the circuits from datasheet. Since you cannot get the MOSFET referenced, you may want simply try alternatives that are on stock in Germany:
- This one has lower drain current (2.8 instead of 4.2), though with 12W supply it should be good enough. It also has insignificantly (i.e. 50mV) higher gate threshold voltage (450 mV instead of 400mV).
- This one has 100 mV lower threshold voltage should not matter neither, and lower drain-source breakdown (-12V instead of -20V), since you use it with 5V circuit, you won’t ever exceed 12V, so should be fine too.
- Finally, this is very close to the original, with very high current rating (13.4 A). It has slightly less standard packaging, which may or may not matter to you.
There are a lot more alternatives at (e.g. Mouser) especially with leg-less SMD packaging.
Note: I only checked catalog values which on rare occasions may not mach to the datasheets. It is a good idea to double-check datasheets before buying and using components
answered Sep 15 at 10:02
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