• 0
hcadam

Arty A7 Schematic Error?

Question

Hi all,

I was looking at the schematic for the Arty A7, more specifically the REG5V0/VBUS switching circuit, and thought something seemed odd about the REG5V0 mosfet. The schematic symbol for the CSD25310Q2 seems correct, but wouldn't that make it backwards in the circuit, always conducting through the body diode, or am I missing something? Thanks!

Share this post


Link to post
Share on other sites

2 answers to this question

Recommended Posts

  • 0

Hi @hcadam,

I have asked one of our design Engineers about this forum thread. If I were to take a guess,  I am thinking that we are using the p channel mosfet to make a synchronous rectifier. Using the mosfet’s internal diode. So it’s basically a diode with a transistor across it. The transistor is turned on when it is known the diode should be conducting. This lowers the voltage drop across the diode making the switching circuit more efficient. 

thank you,

Jon

Share this post


Link to post
Share on other sites
  • 0

Hi @hcadam,

The design engineer responded that CSD25310Q2 is labeled correctly, and that I was wrong, it is not used as a synchronous rectifier. "The CSD25310Q2 is part of an ideal diode oring circuit used to or together the two different sources for the VCC5V0 rail. One source is the regulated 5V output, which is derived from an external power supply plugged into J13 and the other is VBUS from the JTAG/UART USB header. The MP8756GD regulator doesn’t like a voltage being applied to it’s output pins (SW, FB, VOUT) when there is no voltage applied to its VIN pin, which is why we have all of that extra circuitry around Q8, which keeps it in the off state when either VU (external supply) is not present or the 5V regulator output is not ready. IC13 is there to prevent the onboard 5V regulator from back powering an upstream USB port on your hub or PC."

Hope this helps,

Jon

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now