Datasheet

LPC1759_58_56_54_52_51 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 8.5 — 24 June 2014 67 of 80
NXP Semiconductors
LPC1759/58/56/54/52/51
32-bit ARM Cortex-M3 microcontroller
15.2 Crystal oscillator XTAL input and component selection
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 the input clock signal should be coupled by means of a capacitor of 100 pF
(Figure 34
), 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 35
and in
Table 22
and Table 23. 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 35 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 33. LPC1759/58/56/54/52/51 USB device port configuration
LPC17xx
USB-B
connector
33 Ω
33 Ω
002aad943
USB_UP_LED
USB_CONNECT
V
DD
V
DD
D+
D−
USB_D+
USB_D−
V
BUS
V
BUS
V
SS
Fig 34. Slave mode operation of the on-chip oscillator
LPC1xxx
XTAL1
C
i
100 pF
C
g
002aae835