RTC: 32.768-kHZ Clock is Gating Off
Revisions Affected 1.0
Details The RTC has a clock gating issue that stops the internal 32.768-kHz clock when the
VDD_CORE voltage domain drops below the recommended operating range or the
PWRONRSTn input terminal is held low. This issue has the following side effects:
• The RTC counters stop incrementing when the 32.768-kHz clock is gated. This
causes the RTC to lose time while the clock is gated.
• A wakeup event applied to the EXT_WAKEUP input terminal is masked if the
EXT_WAKEUP_DB_EN bit in the RTC PMIC register (0x98) is set to 1 which enables
the de-bounce function for the EXT_WAKEUP input. This occurs because the
32.768-kHz clock is being used to clock the de-bounce circuit.
Workarounds Do not turn off the VDD_CORE power source or source a logic low to the PWRONRSTn input while expecting RTC to keep an accurate time.
Do not enable the de-bounce circuit on the EXT_WAKEUP input if an external wakeup
event needs to be detected while the 32.768-kHz clock is gated.
USB
• The AM335x USB0_ID and USB1_ID terminals should never be connected to any external voltage source. These terminals should be open-circuit when the respective USB port is configured to operate in USB peripheral mode, or should be connected to ground when the respective USB port is configured to operate in USB host mode.
• USBx_DP and USB_DM should never have any series resistors or capacitance on these signals. These signals should be straight traces to the connector with no stubs or test points.
• Typical connections for a USB peripheral:
o USBx_DP and USBx_DM are connected directly to the USB connector
o USBx_CE can be used if supporting charging. This generally would be connected to the enable of a charging source for the battery.
o USBx_ID can be left unconnected
o USBx_DRVVBUS is not used and can be left unconnected
o USBx_VBUS should be connected directly to the VBUS pin on the USB connector
• Typical connections for a USB host:
o USBx_DP and USBx_DM are connected directly to the USB connector
o USBx_CE is typically not used and can be left unconnected
o USDx_ID should be grounded
o USBx_DRVVBUS should be connected to the enable of the 5V VBUS power source.
o USBx_VBUS should be connected to the output of the 5V VBUS power source
• Typical connections for a USB host with USB hub:
o USBx_DP and USBx_DM are connected directly to the USB hub upstream port. The hub then distributes these signals to the downstream ports as needed.
o USBx_CE is typically not used and can be left unconnected
o USDx_ID should be grounded to enable host mode.
o USBx_DRVVBUS should be connected to the enable of the 5V VBUS power source.
o USBx_VBUS should be connected to the output of the 5V VBUS power source. It is also connected to the VBUS detect on the hub, which then allows the hub to selectively enable/disable typically through a power switch to each downstream port.
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