Nxp Semiconductors OM11043 Data Sheet

LPC1769_68_67_66_65_64_63

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© NXP Semiconductors N.V. 2014. All rights reserved.

 

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 
(

), 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 

 and in 

 and 

. 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

 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.

USB-B
connector

33 

Ω

33 

Ω

USB_UP_LED

USB_CONNECT

V

DD

V

DD

D+

D

−

USB_D+

USB_D

−

V

BUS

V

BUS

V

SS 

XTAL1

Ci
100 pF

Cg