LPC1769 View Datasheet(PDF) - NXP Semiconductors.
Part Name
Description
MFG CO.
'LPC1769' PDF : 79 Pages View PDF
NXP Semiconductors
LPC1769/68/67/66/65/64/63
32-bit ARM Cortex-M3 microcontroller
VDD
USB_UP_LED
LPC17xx
VDD
USB_CONNECT
USB_D+
33 Ω
USB_D−
33 Ω
VBUS
VSS
D+
D−
VBUS
USB-B
connector
Fig 32. USB device port configuration
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14.2 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
Ci = 100 pF. To limit the input voltage to the specified range, choose an additional
capacitor to ground Cg which attenuates the input voltage by a factor Ci/(Ci + Cg). In slave
mode, a minimum of 200 mV(RMS) is needed.
LPC1xxx
XTAL1
Ci
Cg
100 pF
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Fig 33. Slave mode operation of the on-chip oscillator
In slave mode the input clock signal should be coupled by means of a capacitor of 100 pF
(Figure 33), 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 34 and in
Table 22 and Table 23. Since the feedback resistance is integrated on chip, only a crystal
and the capacitances CX1 and CX2 need to be connected externally in case of
fundamental mode oscillation (the fundamental frequency is represented by L, CL and
RS). Capacitance CP in Figure 34 represents the parallel package capacitance and should
not be larger than 7 pF. Parameters FOSC, CL, RS and CP are supplied by the crystal
manufacturer.
LPC1769_68_67_66_65_64_63
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 7 — 5 April 2011
© NXP B.V. 2011. All rights reserved.
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