Nxp Semiconductors OM11043 数据表
LPC1769_68_67_66_65_64_63
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Product data sheet
Rev. 9.5 — 24 June 2014
74 of 89
NXP Semiconductors
LPC1769/68/67/66/65/64/63
32-bit ARM Cortex-M3 microcontroller
15.3 XTAL and RTCX 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
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
must also be connected to the ground plain. Loops must be made as small as possible in
Fig 37. Oscillator modes and models: oscillation mode of operation and external crystal
model used for C
X1
/C
X2
evaluation
Table 23.
Recommended values for C
X1
/C
X2
in oscillation mode (crystal and external
components parameters): low frequency mode
Fundamental oscillation
frequency F
frequency F
OSC
Crystal load
capacitance C
capacitance C
L
Maximum crystal
series resistance R
series resistance R
S
External load
capacitors C
capacitors C
X1
/C
X2
1 MHz to 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 to 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 to 15 MHz
10 pF
< 160
18 pF, 18 pF
20 pF
< 60
39 pF, 39 pF
15 MHz to 20 MHz
10 pF
< 80
18 pF, 18 pF
Table 24.
Recommended values for C
X1
/C
X2
in oscillation mode (crystal and external
components parameters): high frequency mode
Fundamental oscillation
frequency F
frequency F
OSC
Crystal load
capacitance C
capacitance C
L
Maximum crystal
series resistance R
series resistance R
S
External load
capacitors C
capacitors C
X1
, C
X2
15 MHz to 20 MHz
10 pF
< 180
18 pF, 18 pF
20 pF
< 100
39 pF, 39 pF
20 MHz to 25 MHz
10 pF
< 160
18 pF, 18 pF
20 pF
< 80
39 pF, 39 pF
002aaf424
LPC1xxx
XTALIN
XTALOUT
CX2
CX1
XTAL
=
CL
CP
RS
L