Datasheet

LPC11U3X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 2.2 — 11 March 2014 56 of 77
NXP Semiconductors
LPC11U3x
32-bit ARM Cortex-M0 microcontroller
11.2 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 that the input be coupled 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, couple the input clock signal with a capacitor of 100 pF (Figure 29), with an
amplitude between 200 mV (RMS) and 1000 mV (RMS). This signal 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 30
and in
Table 18
and Table 19. 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 (L, C
L
and R
S
represent the fundamental frequency).
Capacitance C
P
in Figure 30 represents the parallel package capacitance and must not be
larger than 7 pF. Parameters F
OSC
, C
L
, R
S
and C
P
are supplied by the crystal
manufacturer.
Fig 29. Slave mode operation of the on-chip oscillator
Fig 30. Oscillator modes and models: oscillation mode of operation and external crystal
model used for C
X1
/C
X2
evaluation
LPC1xxx
XTALIN
C
i
100 pF
C
g
002aae788
002aaf424
LPC1xxx
XTALIN XTALOUT
C
X2
C
X1
XTAL
=
C
L
C
P
R
S
L