Datasheet

LPC178X_7X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 5 — 9 September 2014 103 of 122
NXP Semiconductors
LPC178x/7x
32-bit ARM Cortex-M3 microcontroller
In slave mode the input clock signal should be coupled by means of a capacitor of 100 pF
(Figure 36
), 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 37
and in
Table 32
and Table 33. 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 37 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 36. Slave mode operation of the on-chip oscillator
Fig 37. Oscillator modes and models: oscillation mode of operation and external crystal
model used for C
X1
/C
X2
evaluation
Table 32. 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
LPC1xxx
XTAL1
C
i
100 pF
C
g
002aae835
002aaf424
LPC1xxx
XTALIN XTALOUT
C
X2
C
X1
XTAL
=
C
L
C
P
R
S
L