hi,
we completed the schematic of our low cost STM32-H407 board and I'm looking forward to hear your comments:
schematic: http://www.olimex.com/dev/ARM/ST/STM32-H407/STM32-H407_Rev_A.pdf
board layout http://www.olimex.com/dev/ARM/ST/STM32-H407/STM32-H407-BRD.gif
This is open source hardware project, the cad files will be uploaded on GitHub when we complete the routing.
Best regards
Tsvetan
nplayle
Member
Hi Tvestan,
It looks like a nice board, but I agree with Thomas on the input voltage is very restrictive. I regularly power my boards from a 2 cell lipo (7.4v) so having a higher input voltage is a must. Have you looked at the REG104 series from TI? I've used them on a few projects and they are quite nice (but linear regulators, not switching), but can take up to 15V in at 1A, though I've only used mine to about 9v at 250mA.
Nick
gbulmer
Moderator
I agree on the power input, higher would be nice. We might use 6 NiMh for 7.2V
The other 'nice to haves' might be either USART1 or USART2 on an FTDI 3.3V Serial compatible header, so that the bootloader can be put on without JTAG.
It is exciting to have two USB's, and one is a 'proper' Host - great for talking to Android devices.
Overall, a very impressive looking board.
I agree having wider power supply is nice, but it cost money :-)
this board have 2 USB hosts which should be able to provide up to 0.5A to devices, then there is provision for external RAM and processor for at least 0.5A more, so we have to have input power supply providing at least 2A (to be on safe side with reserves), this makes Linear voltage regulator no-choice.
Adding DCDC which allow 6-16VDC power supply input will add EUR 3 to the final price, this is 10% price increase.
5V power supply adapters are widely available, of course if the board should be used with battery pack 6-16V DC-DC is must.
siy
Member
Well, since you don't use 2-step conversion (Input->5V->3.3V), there is no need to source USB devices from on-board regulator. This significantly reduces requirements to this regulator. In other words, as long as single-step conversion is used (Input->3.3V), there is no need to provide 2A.
P.S. I wonder how did you discover SY8008...
siy
Member
Of course, external 5V supply will be necessary in this case. But actually current STM32-H407 schematic built exactly by this scheme - single step conversion and requirement for +5V only external supply. From the other hand I understand reasons for using this approach. Two step conversion with wide range of input voltages (especially at low end) requires use of SEPIC or buck/bust DC/DC regulator in order to allow input voltages close or below 5V. Such a regulators are more complicated and definitely more expensive than simple buck or boost.
siy
Member
@olimexino, By the way, perhaps it worth to consider following approach: instead of using chained voltage regulators, use two independent regulators. One is 3.3V regulator which automatically selects source between VBUS and external source +4-12V (12V is just an example). Second is 5V regulator which works from external +6-12V (12V again is just an example) supply and sources only VBUS-es. This would enable various use cases mentioned above. As long as there is no need to source VBUS (in many cases there is no need for USB HOST/OTG, having USB device is enough), first external voltage source input can be used. In cases when USB HOST/OTG is necessary, can be used second input or both inputs. I understand that this approach might not fit into board budget, so I'm not proposing to implement it in STM32-H407, but I'd like to know your opinion (as well as opinion of other community members) in regard to it.
gbulmer
Moderator
Maybe a useful add-on, which would give folks (me:-) what they want, and allow Olimex to make a bit of money is a separate switch mode supply board?
Something smaller than the board, that could take a 2-pin 'molex' for power (and a socket for JST RC-battery plugs)
by putting two voltage regultors on the board everybody will pay for them no matter if use them or not, many probably do not use batteries but 5V adapters
I like the gbulmer idea - one small DCDC with input for 6-16VDC and output 5V on plug jack, and who ever want to use batteries or other power supply can use this adapter between the battery and STM32-H407
siy
Member
@olimexino, as I've mentioned, I'm not proposing to add it to your board, I'm just discussing idea in general (to be fair, I'm just considering options for my board with 100-pin chip). IMHO, having Host/OTG support without ability to properly source it is not the best combination, that's why I'm thinking about different combinations for on-board regulator.
our engineers just found way to bring all Ethernet signals to the arduino platform, so we will make small "ethernet shield" later for those who want to have Ethernet connectivity with this board!
also after lot of thinking we decide to put DCDC on the input stage also, so now this board will take 6-16VDC power supply
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