Backplane Rev C Errata

[ppannuto]

• [x] USB !BUSPWR is wrong: Currently tied to GND, which states that the hub and all downstream devices are powered from the upstream port. Should be tied high, stating that the hub has an "external" power supply. In both modes, the hub still will perform overcurrent and poweroff protections.
  • Symptom: This limits the hub to 500mA max total draw, as each downstream port has a minimum 100mA allotment (USB spec), so the hub disables higher ports (cannot use USB in Module 5 or Module 7 slot)
  • Remedy: Cut trace at pin 10 (!BUSPWR) and short pins 10 and 9.

[ppannuto]

• [ ] Between power module and backplane isolation circuitry, something needs to protect against shorts.
  • Currently, the power module has a limiter downstream of the regulator, which protects the regulator by limiting to no more than 2A (?) sustained draw. The backplane module power switches are rated for 1.5A (?), so shorting a module will cause the isolation to blow.