Datasheet

LPC408X_7X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 3.1 — 1 September 2014 115 of 138
NXP Semiconductors
LPC408x/7x
32-bit ARM Cortex-M4 microcontroller
In slave mode the input clock signal should be coupled by means of a capacitor of 100 pF
(Figure 40
), with an amplitude between 200 mV(RMS) and 1000 mV(RMS). This
corresponds to a square wave signal with a signal swing of between 280 mV and 1.4 V.
The XTALOUT pin in this configuration can be left unconnected.
External components and models used in oscillation mode are shown in Figure 41
and in
Table 34
and Table 35. Since the feedback resistance is integrated on chip, only a crystal
and the capacitances C
X1
and C
X2
need to be connected externally in case of
fundamental mode oscillation (the fundamental frequency is represented by L, C
L
and
R
S
). Capacitance C
P
in Figure 41 represents the parallel package capacitance and should
not be larger than 7 pF. Parameters F
OSC
, C
L
, R
S
and C
P
are supplied by the crystal
manufacturer.
Fig 41. Oscillator modes and models: oscillation mode of operation and external crystal
model used for C
X1
/C
X2
evaluation
Table 34. 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 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
002aah274
LPC40xx
XTALIN XTALOUT
C
X2
C
X1
XTAL
=
C
L
C
P
R
S
L