General
Review and verify the following for
the custom schematic design:
- Above sections, 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 LFOSC0 clock input source - crystal
or oscillator
- 32.768kHz is the LFOSC0 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
- 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 (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 LFOSC0 is
unused (XI is grounded)
Additional
- Crystal load capacitance versus LFOSC0 registers.
The only LFOSC0 register bits board designers 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-specific data sheet for
the recommended circuit configuration during preproduction
PCB and the production PCB