Datasheet

LPC82x All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 1 — 1 October 2014 67 of 81
NXP Semiconductors
LPC82x
32-bit ARM Cortex-M0+ microcontroller
14. Application information
14.1 XTAL input
The input voltage to the on-chip oscillators is limited to 1.8 V. If the oscillator is driven by a
clock in slave mode, it is recommended to couple the input through a capacitor with C
i
=
100 pF. To limit the input voltage to the specified range, choose an additional capacitor to
ground C
g
which attenuates the input voltage by a factor C
i
/(C
i
+ C
g
). In slave mode, a
minimum of 200 mV(RMS) is needed.
In slave mode the input clock signal should be coupled with 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 27
and Table 28. Since the feedback resistance is integrated on chip, only a crystal
and the capacitances C
X1
and C
X2
must 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 (see Table 27
).
Fig 40. Slave mode operation of the on-chip oscillator
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