Hello all,
Our customer measured TPS65218 by using theirs EVM. When VIN is forced, DCDC3 is 0v to 0.7V, 0.7V to 0v and DCDC3 is ramped.
It's strange behavior. TPS65218 goes to ACTIVE mode with no issue. When INT_LDO is remained above 0.6V, strange behavior is occurd. When INT_LDO below 0.6V, strange behavior isn't occurd.
Is strange behavior OK? Or Do you have any solution? I attachied strange behavior 
wave. CH1: VIN CH2: LDO1 CH3:DCDC3 CH4:INT_LDO
Best Rgards.,
M.Iwasaki
I have attempted to re-create your issue on a TPS65218EVM-100 board and it appears that the reason for your issue is because IN_BIAS is not connected directly to VSYS. There is a delay between VSYS and INT_LDO on your scope shot, and INT_LDO is generated from IN_BIAS.
When I tested, I captured my signals on the same channels as in your testing, but the scope converts channel 1 from Yellow to Dark Blue.
You can see that Channel 4 (INT_LDO) in my scope shot rises at the same time as VSYS (Ch. 1):
Yes, IN_BIAS should be connected directly to the main "System Power" supply, which you labeled VIN on your scope shot.
IN_BIAS is a sense pin for UVLO in addition to being the supply for INT_LDO and the bias voltage for all DC-DC converters. The PMIC does not expect the IN_DCDCx, IN_BU, or AC_DET signals to ramp before IN_BIAS.
The Typical Application Schematic (Figure 6-3 on page 93 of datasheet) shows all the inputs that should be connected directly to the "2.7-V to 5.5-V system power" supply:
