General
Review and verify the following for
the custom schematic design:
- The sections above, including
relevant application notes and FAQ links
- Pin attributes, signal
description, and electrical specifications
- Electrical characteristics,
timing parameters, and any additional available information
- Selection of WKUP clock input
source - crystal or oscillator
- 32.768kHz is the WKUP clock
input frequency supported, refer to the processor-specific data sheet for
supported clock input frequency
- Selection of the crystal load
versus data sheet recommendations
- Selection of load capacitor
versus data sheet recommendations
- WKUP_LFOSC0 has limited use
cases, provide provisions to ground the XI input when the clock option is
not used
Schematic Review
Follow the below for the custom
schematic design:
- Connections of the clock
circuit (WKUP_LFOSC0), as per the data sheet recommendations
- Selection of crystal load and
load capacitance, with the load capacitance being twice the crystal
load
- Connection of the clock
circuit when external oscillator is used (XO is grounded)
- Connection of the XI input
when the WKUP_LFOSC0 is unused (XI is grounded)
Additional
- Crystal load capacitance versus
LFOSC0 registers. The only LFOSC0 register bits users change are BP_C, PD_C, and
CTRLMMR_WKUP_LFXOSC_TRIM[18:16], where PD_C is reset (0) to enable the
oscillator and the BP_C bit is only set (1) to place the oscillator in bypass
mode when using an LVCMOS clock source. The CTRLMMR_WKUP_LFXOSC_TRIM[18:16] bits
are set based on the actual capacitance load applied to the crystal, as defined
by the Load Capacitance Equation.
- Refer to the processor data sheet for the recommended circuit configuration
during preproduction PCB and the production PCB