Datasheet

LPC55S6x All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2019. All rights reserved.
Product data sheet Rev. 1.0 — 26 February 2019 109 of 123
NXP Semiconductors
LPC55S6x
32-bit ARM Cortex-M33 microcontroller
Although C
Parasitic
can be ignored in general, the actual board layout and placement of
external components influences the optimal values of external load capacitors. Therefore,
it is recommended to fine tune the values of external load capacitors on actual hardware
board to get the accurate clock frequency. For fine tuning, output the RTC Clock to one of
the GPIOs and optimize the values of external load capacitors for minimum frequency
deviation.
13.4.1 RTC Printed Circuit Board (PCB) design guidelines
• Connect the crystal and external load capacitors on the PCB as close as possible to
the oscillator input and output pins of the chip.
• The length of traces in the oscillation circuit should be as short as possible and must
not cross other signal lines.
• Ensure that the load capacitors CX1, CX2, and CX3, in case of third overtone crystal
usage, have a common ground plane.
• Loops must be made as small as possible to minimize the noise coupled in through
the PCB and to keep the parasitics as small as possible.
• Lay out the ground (GND) pattern under crystal unit.
• Do not lay out other signal lines under crystal unit for multi-layered PCB.