TPS65217: Not working, sys5v is outputting 0.35V

Samer,

It would be helpful if you share your schematic. Some previous issues we've had when designers "copy" the BBB (BEAGLEBK) include:

• PWR_EN pin on PMIC(PMIC_PWR_EN signal on processor) not driven by the processor or not connected at all
  • Result: PWR_EN low will allow the PMIC to turn on for 5s, then it will turn off and SYS will go low
• BAT not used,or wired the same as it was wired on the BBB design
  • TPS65217x Schematic Checklist
  • Designing Robust TPS65217x Systems for VIN Brownout Application Note
  • These documents touch on the fact that it was never intended for BAT pins to be left floating, and the adverse effects this can have
• Over-voltage or under-voltage on AC- would cause the system to shut off and the PMIC may not recover automatically
  • typically, a push-button press (PB_IN) would test to see if the system is still operational after a fault on AC supply, but many customers remove the push-button from the final design which makes debug more difficult

The approach I would take is to monitor the first power-on of the system closely with an oscilloscope (measure VAC, PWR_EN, VSYS, and LDO1) to get a better understanding of which type of problem we are facing.

If LDO1 does turn on and everything else looks good, then I would start looking for a short on the board. You can do this by following the power-up sequence shown in the Powering AM335x with TPS65217x User's Guide and measuring to see which DCDC or LDO regulator fails to turn on.

If LDO1 != 1.8V, this is the reason PWR_EN cannot turn on.

My recommendation is to remove power from your board completely for at least 5 seconds, re-apply power and monitor SYS and LDO1 closely during power-up.

VSYS should be 5V (VSYS ~= VAC), but it will be ~1.3V when it gets back-fed through VIO. This means some other supply in your design is generating 1.8V, where 1.8V - Vd (diode drop) = 1.29V, which is connected to VIO prior to the application of VAC. Instead of a cold boot, you are starting the system from an unknown state.

If BAT pins are floating, then VBAT = VSYS, and this could cause the PMIC to not recognize when you apply power at AC input. It appears that a battery is connected, even if it is a very low voltage with minimal current capability, and it is enough to keep the digital alive inside the PMIC and cause detection/removal issues on the AC/USB supplies.