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powering BMP388/BMP390
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

powering BMP388/BMP390

by bastler59 on Fri Dec 03, 2021 3:29 am

Hi,

some centuries ago first voltage regulators were these L7805 or µA7805 (for 5V output) and for audio circuits you use larger capacitors on input and output to get a voltage with less noise.

In datasheets you find often a diode parallel to voltage regulator, so current can flow from output to input. The explanation - this one is from ST datasheet - tells:
Application with high capacitance loads and an output voltage greater than 6 volts
need an external diode to protect the device against input short circuit. In this case the input
voltage falls rapidly while the output voltage decrease slowly. The capacitance
discharges by means of the base-emitter junction of the series pass transistor in
the regulator. If the energy is sufficiently high, the transistor may be destroyed.
The external diode by-passes the current from the IC to ground.


Today you find a voltage regulator AP211K on sensor boards with BMP388 or BMP390 (Product ID: 3966 and 4816). You can power these boards with 5V, if you are using an Arduino board. Other MCUs are working with 3.3V and 5V will kill GPIOs.

So what will happen, if you power sensor board on the 3.3V pin?
I see a "... you can use it with a 3V or 5V logic microcontroller without worry" in description. But is it really harmless for the regulator? In datasheet, I don't see a remark about this condition.

Bye
Jürgen

bastler59
 
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Re: powering BMP388/BMP390

by jps2000 on Fri Dec 03, 2021 5:09 am

You are mixing 2 things.
The protection diode story is valid for these dino regulators (I am also from that decades). It is meant to protect these regulators.
Modern regulators do not have such problems unless mentioned in the spec.
The second problem is how to interface 3vlogic and 5v Logic.
best is always check schematics of boards.
Using just qwiic interface does not make problems. For more advanced wiring you need some electronic know how.
Voltage dividers, Open collector( drain) circuits with pullups, diodes level converter ic etc are feasible solutions.
Underrecognized problems even with identical VCC may occur if you switch off power on parts of the electronic.
Thinking and measuring is key

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Re: powering BMP388/BMP390

by bastler59 on Fri Dec 03, 2021 5:29 am

jps2000 wrote: Thinking and measuring is key

Are you always so "friendly" to other forum users?

bastler59
 
Posts: 18
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Re: powering BMP388/BMP390

by jps2000 on Fri Dec 03, 2021 6:34 am

Verstehe nicht warum sie da eingeschnappt sind.
Ich hab nicht gemeint sie sollen besser nachdenken sondern man muss das überlegen.

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Re: powering BMP388/BMP390

by adafruit_support_carter on Mon Dec 06, 2021 2:19 pm

So what will happen, if you power sensor board on the 3.3V pin?

Result may vary from board to board depending on other details, but in general, that pin is an output. Just apply power, 5V or 3.3V, to VIN. The vregs used are LDO so generally don't need to worry about trying to bypass.

Please don't respond negatively to someone simply trying to help.

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Please be positive and constructive with your questions and comments.