Datasheet

LPC1102_1104 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 7 — 26 September 2013 35 of 43
NXP Semiconductors
LPC1102/1104
32-bit ARM Cortex-M0 microcontroller
11. Application information
11.1 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 6
:
• The ADC input trace must be short and as close as possible to the LPC1102/1104
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.
11.2 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 20
), 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.
11.3 Standard I/O pad configuration
Figure 21 shows the possible pin modes for standard I/O pins with analog input function:
• Digital output driver
• Digital input: Pull-up enabled/disabled
• Digital input: Pull-down enabled/disabled
• Digital input: Repeater mode enabled/disabled
• Analog input
Fig 20. Slave mode operation of the on-chip oscillator
LPC1xxx
XTALIN
C
i
100 pF
C
g
002aae788