LPC1111FDH20SLASH002 datasheet(97/127 Pages) NXP

97 / 127 page

LPC111X

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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

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 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 CX1 and CX2 need to be connected externally in case of

Fig 49. Slave mode operation of the on-chip oscillator

LPC1xxx

XTALIN

100 pF

002aae788

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