6.1.1 Power Supply Slew Rate Requirement
To maintain the safe operating range of the internal ESD protection devices, TI recommends limiting the maximum slew rate for powering on the supplies to be less than 1.0E +5 V/s. For instance, as shown in Figure 6-1, TI recommends a value greater than 18 µs for the supply ramp slew for a 1.8-V supply.
A. RTC_PWRONRSTn should be asserted for at least 1 ms to provide enough time for the internal RTC LDO output to reach a valid level before RTC reset is released.
B. The CAP_VDD_RTC terminal operates as an input to the RTC core voltage domain when the internal RTC LDO is disabled by connecting the RTC_KALDO_ENn terminal to VDDS_RTC. If the internal RTC LDO is disabled, CAP_VDD_RTC should be sourced from an external 1.1-V power supply.
C. When using the ZCZ package option, VDD_MPU and VDD_CORE power inputs may be powered from the same source if the application only uses operating performance points (OPPs) that define a common power supply voltage for VDD_MPU and VDD_CORE. The ZCE package option has the VDD_MPU domain merged with the VDD_CORE domain.
D. If a USB port is not used, the respective VDDA1P8V_USB terminal may be connected to any 1.8-V power supply and the respective VDDA3P3V_USB terminal may be connected to any 3.3-V power supply. If the system does not have a 3.3-V power supply, the VDDA3P3V_USB terminal may be connected to ground.
E. If the system uses mDDR or DDR2 memory devices, VDDS_DDR can be ramped simultaneously with the other 1.8-V I/O power supplies.
F. VDDS_RTC should be ramped at the same time or before CAP_VDD_RTC, but these power inputs can be ramped independent of other power supplies if PMIC_POWER_EN functionality is not required. If CAP_VDD_RTC is ramped after VDD_CORE, there might be a small amount of additional leakage current on VDD_CORE. The power sequence shown provides the lowest leakage option.
G. To configure VDDSHVx [1-6] as 1.8 V, power up the respective VDDSHVx [1-6] to 1.8 V following the recommended sequence. To configure VDDSHVx [1-6] as 3.3 V, power up the respective VDDSHVx [1-6] to 3.3 V following the recommended sequence.
H. If all the 1.8-V supplies are not sourced from the same power supply, it is required to power up VDDS before other 1.8-V supplies. Further, it is also recommended to source VDDS and VDDSHvx [x = 1-6] when configured as 1.8V from the same power supply.
Figure 6-5 Power-Supply Sequencing With Internal RTC LDO Disabled