Datasheet
LPC111X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 9.2 — 26 March 2014 97 of 127
NXP Semiconductors
LPC1110/11/12/13/14/15
32-bit ARM Cortex-M0 microcontroller
12. Application information
12.1 ADC usage notes
The following guidelines show how to increase the performance of the ADC in a noisy
environment beyond the ADC specifications listed in Table 18
:
• The ADC input trace must be short and as close as possible to the
LPC1110/11/12/13/14/15 chip.
• The ADC input traces must be shielded from fast switching digital signals and noisy
power supply lines.
• Because the ADC and the digital core share the same power supply, the power supply
line must be adequately filtered.
• To improve the ADC performance in a very noisy environment, put the device in Sleep
mode during the ADC conversion.
12.2 Use of ADC input trigger signals
For applications that use trigger signals to start conversions and require a precise sample
frequency, ensure that the period of the trigger signal is an integral multiple of the period
of the ADC clock.
12.3 XTAL input
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 49
), 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 50
and in
Table 30
and Table 31. 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
Fig 49. Slave mode operation of the on-chip oscillator
LPC1xxx
XTALIN
C
i
100 pF
C
g
002aae788