Seed power supply

Hardware Development
#1

Hi, just been looking at the Daisy Seed schematics. Am I right in thinking the Seed can be completely powered by the USB, or is it advisable to use a separate Vin? Is there any problem having both plugged in, or will the regulators take care of this?

I can see there that onboard the Seed there is a TPS6217 step down converter generating +3.3V_D which powers the RAM, flash memory and is used for the Reset/Boot Flash switches, and a LP2985 linear regulator for +3.3V_A used for the codec and ADC reference. What is supplying the +3.3V for the STM32 VDD?

Thanks in advance!

#2

USB is sufficient to power the Seed. The 3.3V_D is powering the STM. 3.3V_A is also connected as a reference voltage (for the STM’s ADCs?).

#3

Thanks for confirming, that’s what I thought.

If both USB and Vin were plugged in however, would you get Vin + VBUS (5v) at the input to the TPS6217? If so then perhaps the maximum allowed Vin should be 12v, as the max recommended Vin from the TPS6217 data sheet is 17v? Please correct me if I’ve got this wrong!

https://www.ti.com/lit/ds/symlink/tps62172.pdf?ts=1594740480657&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FTPS62172

#4

I would see the choice of regulator as a way by Electro Smith to ensure that you don’t fry your Daisy Seed if you accidentally plug both VIN and power the USB … but I would not do this on purpose.

If you design something that powers the VIN maybe make the VIN a jumper.

#5

From the schematics:
“Diodes D1 & D2 are for isolation between VBUS and 5V reg”
You can power both inputs, the UNREGULATED_VCC will use the highest available voltage to feed the regulators.