Datasheet

LPC1311_13_42_43 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 5 — 6 June 2012 61 of 74
NXP Semiconductors
LPC1311/13/42/43
32-bit ARM Cortex-M3 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
order to keep the noise coupled in via the PCB as small as possible. Also parasitics
should stay as small as possible. Values of C
x1
and C
x2
should be chosen smaller
accordingly to the increase in parasitics of the PCB layout.
Table 21. 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 Ω 18 pF, 18 pF
20 pF < 300 Ω 39 pF, 39 pF
30 pF < 300 Ω 57 pF, 57 pF
5 MHz - 10 MHz 10 pF < 300 Ω 18 pF, 18 pF
20 pF < 200 Ω 39 pF, 39 pF
30 pF < 100 Ω 57 pF, 57 pF
10 MHz - 15 MHz 10 pF < 160 Ω 18 pF, 18 pF
20 pF < 60 Ω 39 pF, 39 pF
15 MHz - 20 MHz 10 pF < 80 Ω 18 pF, 18 pF
Table 22. 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 Ω 18 pF, 18 pF
20 pF < 100 Ω 39 pF, 39 pF
20 MHz - 25 MHz 10 pF < 160 Ω 18 pF, 18 pF
20 pF < 80 Ω 39 pF, 39 pF