Powering a daughterboard from a STM32F4 Discovery Board for prototype

[LMorr.3]

I need 16 DAC outputs for my project. I was planning on using Texas Instrument's DAC8168IAPW over I2C and making a daughter board to connect to the Disco board. I also plan on adding an IC to drive LEDs. Do I power the daughterboard using the Disco board's voltage regulator or should I power the daughterboard with it's own supply? Do I connect a wallwart to the Dicso board even though I still have it connected to my USB port? I don't want to damage my USB port or the board.

[FThie.1]

There's no easy answer to your question as there are a lot ok unknown points.

One thing is OK, you can add an external 5V to your disco board without risk for your USB.

However, if you plan to supply both the disco and daughterboard with a single 5V source, you'll have to take care your 5V will supply enough for both, especially with leds that can take a lot of mA.

3.3V regulator on disco board has only a capacity of 150mA, far enough for the board itself but maybe too weak for your leds (for the DAC only, it should be ok).

To resume, you have to evaluate your board consumption, block by block. When you will know how many mA you need, things will be much clearer.

[LMorr.3]

I see what you mean. If I build a daughterboard with its own voltage reg./power supply, and only connect it to the Disco board over 2 i2c wires? Would that still work well even though the daughterboard does not share a ground with the Disco board? If this is a viable option, I can also add an I2C enabled LED driver IC to the daughterboard.

[FThie.1]

You need to connect SDA, SCL and GND

[Tesla DeLorean]

The boards have schematics.

A lot of the designs use diodes to allow multiple supplies, you should review where the appropriate point(s) to inject power are, perhaps using your own diodes. As I recall most of the STM32F4 side runs at around 3.0V

One of the bigger headaches is ensuring the board resets properly, and the ST-LINK is happy.

The STM32F4-DISCO might be less than ideal, it's an old design, and there are better and newer boards that have more flexibility, and improved design.

You'd need to estimate how much current the added circuitry is going to take.

For I2C, I'd probably look to having the STM32 board side do the pull-ups.

[LMorr.3]

I'm thinking of building a daughterboard with it's own voltage regulator and power supply, and only connect to the Disco board using 3 wire I2C with shared ground. I hope this works out ok.

[LMorr.3]

What if I add a voltage regulator to my daughter board, and feed 5v into the DISCO board from the daughter board? That would ensure I have common ground and the roughly 200mA I need to run LEDs on the daughter board too. I would not have to worry about the DISCO's 100mA limit for the onboard regulator.

[Tesla DeLorean]

I'd probably take a 7V input, run it thru a 5V regulator, and then feed it into the F4-DISCO via a BAT60JFILM into the V5 rail at P2.3 and P2.4

https://www.st.com/resource/en/schematic_pack/mb997-f407vgt6-e01_schematic.pdf

[LMorr.3]

Ok thanks. I have a power supply board with 5V out powering the daughterboard so I'll feed that into a BAT60JFLIM and then into both P2.3 and P2.4.

Is the diode in case a wall-wart over 10VDC is connected to the DISCO's power connector? ( to protect the daughterboard's power supply? )

[LMorr.3]

I plan on building a power daughterboard with 5v and 3.3v regulators, as well as +-12v. The 5v and digital GND will feed into the DISCO's gnd, P2.3 and P2.4, and the 3.3v and +-12v, Digital GND and Analog GND will power 3 other 'daughterboards'.

What is the best way to connect from the power daughterboard to the 3 daughterboards? Should I just connect using screw headers and wires in a star pattern, or should I send the power and grounds in and out of the 1st daughterboard, into and out of the 2nd daughterboard into the 3rd? I would usually use make/female headers but cannot in this case.

I know Eurorack uses a ribbon cable to connect power to modules... I suspect using a ribbon cable like this for power is not recommended. Should I use molex connectors?

I want to make sure I use the right connectors/cables for ground planes/power to ensure I don't risk continuously resetting the DISCO board.

[S.Ma]

Because each board clips 5v to 3v3 through individual regulators, voltage droops are minimized. Now remains possible supply and ground bounce which comes only if you have high transiants. Physics suggests to minimize the strong fast signals to ground power loops areas (EMI and EMC related topics)

[LMorr.3]

Ok thanks. I'll send +-12v and 5v from the power daughterboard to all daughterboards and 5v to the DISCO board. I'll have a 3.3v regulator on all daughterboards.

Unlike Eurorack, I rather not use ribbon cable for sending power to daughterboards so I guess I'll use molex connectors and have PWR in and PWR out on each daughterboard to daisy-chain the power?