LPC1763 datasheet(71/86 Pages) PHILIPS

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LPC1769_68_67_66_65_64_63

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Product data sheet

Rev. 9.3 — 8 January 2014

71 of 86

NXP Semiconductors

LPC1769/68/67/66/65/64/63

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

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.

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 23 and Table 24. 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 35 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.

Fig 33. USB device port configuration

LPC17xx

USB-B

connector

002aad943

USB_UP_LED

USB_CONNECT

VDD

D+

−

USB_D+

USB_D

−

VBUS

VSS

Fig 34. Slave mode operation of the on-chip oscillator

LPC1xxx

XTAL1

100 pF

002aae835

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