Datasheet

LPC11U6x All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 1.2 — 26 May 2014 78 of 96
NXP Semiconductors
LPC11U6x
32-bit ARM Cortex-M0+ microcontroller
14.4 XTAL input and crystal oscillator 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 through a capacitor of 100 pF
(Figure 41
), 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.
Fig 40. USB interface for low-speed, XTAL-less operation
V
DD
R1
1.5 kΩ
USB-B
connector
USB_DP
USB_DM
USB_VBUS
V
SS
R
S
= 33 Ω
R
S
= 10 Ω
R
S
= 10 Ω
R
S
= 33 Ω
USB
USB_CONNECT
D+
D-
USBCLKDIV
/8
USB PLL
SYSCON
USB main clock
= 6 MHz
12 MHz
IRC
48 MHz
aaa-011021
Fig 41. Slave mode operation of the on-chip oscillator
LPC1xxx
XTALIN
C
i
100 pF
C
g
002aae788