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Im using STM32F103C8T6 with sl4432 as small radio beacon. It's working fine, but range much shorter than suppose to be. Sl4432 require max 85 mAh for 20dbm transmit, but how much STM32F103C8T6 3.3v pin can give at max? I can't find that info in datasheet and it's not GPIO pin anyway.


To be more specific, I power up STM32F103C8T6 from blue circle. And power up my sl4432 from green circle. [pinout]

here what board is that

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closed as unclear what you're asking by brhans, Chris Stratton, RoyC, Elliot Alderson, Dwayne Reid Oct 20 '18 at 5:31

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Are you connecting your Sl4432's power supply pin to a GPIO output from your STM32? \$\endgroup\$ – brhans Oct 18 '18 at 18:51
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    \$\begingroup\$ Are you talking about the microcontroller's VDD pins? Those consume current, they do not supply it. The current comes from your power supply. Do you have the facilities to measure the output power from your board? At those frequencies, board design and component choice is going to have a critical effect on whether the chip develops the power that's promised. \$\endgroup\$ – TimWescott Oct 18 '18 at 18:53
  • \$\begingroup\$ I will upload image... Sec. \$\endgroup\$ – Cookins Oct 18 '18 at 19:09
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    \$\begingroup\$ The actual subject of your question is not the MCU but an unidentified board containing it. You will need to obtain the specifications from the manufacturer and use the lesser of that or the upstream power source's capability. Or provide the exact identification of the regulator used on the board. It's fairly unlikely that this is the source of your problem. That's more likely to be insufficient point-of-load capacitors, misconfiguration of the radio, receiver problems, a noisy environment (or noisy receiver power), poorly chosen radio scheme bad antennas or unrealistic expectations. \$\endgroup\$ – Chris Stratton Oct 18 '18 at 19:19
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The 3V3 pin in your dev board is not an actual MCU pin but the output of an onboard 3.3V linear regulator. Also, both your green and blue pins are internally connected, so the max current you can source out of that pin is the max current your power source can provide.

I would recommend removing the onboard LDO if you are providing the 3.3V externally.

You can check out the schematic at the stm32duino wiki for the Blue Pill:

https://wiki.stm32duino.com/index.php?title=Blue_Pill

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The STM32F103 series does not contain a 3.3V regulator.

If you're referring to a pin labelled "3.3V" on a development board, this pin is probably fed by a linear regulator on the board. You will need to refer to the specifications on that part for information on its current capacity.

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It is the BluePill. This 3.3V is actually a part of the SWD programming port and if is used to source the current it takes it from the small LDO on board. Use 5V port with a proper LDO.

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    \$\begingroup\$ Only a small fraction of the world's SOT23-5 regulators would be unable to supply 85 mA in addition to the current required by an STM32. 100 mA and below ratings do exist in this package, but they're not the common ones. This isn't like the on-chip regulator of an Arduino derivative's USB interface chip which can only spare a few tens of milliamps. \$\endgroup\$ – Chris Stratton Oct 18 '18 at 20:10
  • \$\begingroup\$ Adding some capacitors at the radio (if they don't already exist on its board) might not be a bad idea. But the real problem is probably something else. \$\endgroup\$ – Chris Stratton Oct 18 '18 at 20:17
  • \$\begingroup\$ @ChrisStratton 5V is connected directly to the USB VDD. He will need to use his own LDO + capacitors. \$\endgroup\$ – P__J__ Oct 18 '18 at 21:00
  • \$\begingroup\$ No, because the regulator feeding the 3v3 pin he is presently using probably has sufficient capacity. That this was a power problem at all was only ever a wild guess; if it is power related (and it probably isn't) then explanation is more likely lack of capacitance at the point of load, not the regulator. \$\endgroup\$ – Chris Stratton Oct 18 '18 at 21:11
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    \$\begingroup\$ I'm powering it NOT from usb. I showed that on picture. As far as 3.3v pin going directly from powering pin then it's not power related. Thanks all for helping to find out it. \$\endgroup\$ – Cookins Oct 18 '18 at 23:27

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