Datasheet

LPC11CX2_CX4 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3.1 — 15 May 2013 51 of 62
NXP Semiconductors
LPC11Cx2/Cx4
32-bit ARM Cortex-M0 microcontroller
11.3 XTAL Printed Circuit Board (PCB) layout guidelines
The crystal should be connected on the PCB as close as possible to the oscillator input
and output pins of the chip. Take care that the load capacitors C
x1
, C
x2
, and C
x3
in case of
third overtone crystal usage have a common ground plane. The external components
must also be connected to the ground plain. Loops must be made as small as possible in
Fig 24. Oscillator modes and models: oscillation mode of operation and external crystal
model used for C
X1
/C
X2
evaluation
Table 19. Recommended values for C
X1
/C
X2
in oscillation mode (crystal and external
components parameters) low frequency mode
Fundamental oscillation
frequency F
OSC
Crystal load
capacitance C
L
Maximum crystal
series resistance R
S
External load
capacitors C
X1
, C
X2
1 MHz - 5 MHz 10 pF < 300  18 pF, 18 pF
20 pF < 300  39 pF, 39 pF
30 pF < 300  57 pF, 57 pF
5 MHz - 10 MHz 10 pF < 300  18 pF, 18 pF
20 pF < 200  39 pF, 39 pF
30 pF < 100  57 pF, 57 pF
10 MHz - 15 MHz 10 pF < 160  18 pF, 18 pF
20 pF < 60  39 pF, 39 pF
15 MHz - 20 MHz 10 pF < 80  18 pF, 18 pF
Table 20. Recommended values for C
X1
/C
X2
in oscillation mode (crystal and external
components parameters) high frequency mode
Fundamental oscillation
frequency F
OSC
Crystal load
capacitance C
L
Maximum crystal
series resistance R
S
External load
capacitors C
X1
, C
X2
15 MHz - 20 MHz 10 pF < 180  18 pF, 18 pF
20 pF < 100  39 pF, 39 pF
20 MHz - 25 MHz 10 pF < 160  18 pF, 18 pF
20 pF < 80  39 pF, 39 pF
002aaf424
LPC1xxx
XTALIN XTALOUT
C
X2
C
X1
XTAL
=
C
L
C
P
R
S
L