I am bringing up a new AM437X board and my TPS65218 PMIC is cycling on and off. The captures below show Vdcdc6 (1 Yellow), Vdcdc5 (2 Green), PGOOD_BU (3 Blue) and PWR_EN (4 Pink). First capture shows 500ms cycling, and second shows the same but zoomed in on the power up sequence.
IN_DCDC1, IN_DCDC2, IN_DCDC3, IN_DCDC4, IN_DCDC5, IN_DCDC6, AC_DET, IN_BIAS, IN_BU, and PB are all connected to 5V. CC battery is at 2.5V. PFI is 4.0V. The voltage at INT_LDO is a steady 2.5V.
All control registers are at their default values. No I2C commands have been sent to the PMIC.
The voltage at SYS_BU is a steady 0V (*** Supposed to be either IN_BU or the CC voltage but isn't ***).
PGOOD_BU pulses low for 400ns at about the same time as Vdcdc6 and Vdcdc5 go into the high impedance state when the power up sequence fails.
The power up sequence does not make it past powering up DCDC6 and DCDC5 and when it stops it seems to go into a high impedance state instead of starting a power down sequence.
As shown in the captures, DCDC5 only reaches 0.5V, but if I add a 10mA load it reaches the proper 1V with no change in the cycling.
What is causing the power up sequence to fail?
