AM335x
RTC/
Backup
battery
domain
PMIC
pmic_pwr_enable
Enable/NSleep
Wakeup
Internal FSM/control
SoC-Power-on-reset
SoC-Power-on-supplies
ext_wakeup0
RTC-Power-on-reset
RTC Power supply
Backup supply
Pushbutton
Main supply
Power, Reset, and Clock Management
Figure 8-5. High Level System View for RTC-only Mode
Wakeup from RTC-only mode can only be achieved using the ext_wakeup0 signal. Once a wakeup is
triggered using this signal, the device drives pmic_pwr_enable to initiate a power-up sequence by the
PMIC. The device must go through a full cold boot upon wakeup from RTC-only mode.
8.1.4.3.6 Internal RTC LDO
The device contains an internal LDO (low dropout) regulator which powers the RTC digital core.
Depending on your application, you may be able to disable this regulator to save power in low power use
cases.
If your application never uses the RTC functionality, connect RTC_KALDO_ENn to VDDS_RTC,
CAP_VDD_RTC to VDD_CORE, and RTC_PWRONRSTn to ground. These connections disable the
internal RTC LDO because RTC_KALDO_ENn is high, and they use the external VDD_CORE supply to
power the RTC digital core. The RTC LDO must be disabled for internal power sequencing even though
the RTC is not used. Grounding the reset signal will ensure the RTC stays in reset. Disabling the internal
LDO will allow the application to achieve lower power consumption in all the low power modes.
If your application uses the RTC functionality and never needs RTC-only mode, the hardware scenario is
similar to the previous description, but the RTC reset signal must be connected to the device
PWRONRSTn. This connection allows full functionality of the RTC subsystem without the internal RTC
LDO consuming power.
If your application uses the RTC functionality and requires RTC-only mode, the internal LDO is required to
enable proper wakeup signaling from the RTC domain. The proper wakeup signaling requires the following
connections:
•
RTC_KALDO_ENn is grounded
•
CAP_VDD_RTC is connected to 1uF decoupling capacitor to ground
•
RTC_PWRONRSTn is connected to 1.8V RTC power on reset
•
PMIC_POWER_EN is connected to power input of PMIC
•
EXT_WAKEUP0 is connected to a wakeup source
See the device datasheet for more information on these signals.
512
Power, Reset, and Clock Management (PRCM)
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated