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17.1 Features
17.2 Description
Basic clocking for the A/D converters is provided by the VPB clock. A programmable
divider is included in each converter, to scale this clock to the 4.5 MHz (max) clock
needed by the successive approximation process. A fully accurate conversion requires 11
of these clocks.
17.3 Pin description
Table 253
Table 253: ADC pin description
Pin
Type
AD0.7:6, AD0.4:1
Input
&
AD1.7:0
(LPC2144/6/8)
V
Reference
REF
V
, V
Power
DDA
SSA
User manual
UM10139
Chapter 17: Analog-to-Digital Converter (ADC)
Rev. 01 — 15 August 2005
•
10 bit successive approximation analog to digital converter (one in LPC2141/2 and
two in LPC2144/6/8).
•
Input multiplexing among 6 or 8 pins (ADC0 and ADC1).
•
Power-down mode.
•
Measurement range 0 V to V
10 bit conversion time ≥ 2.44 µs.
•
•
Burst conversion mode for single or multiple inputs.
•
Optional conversion on transition on input pin or Timer Match signal.
•
Global Start command for both converters (LPC2144/6/8 only).
gives a brief summary of each of ADC related pins.
Description
Analog Inputs. The ADC cell can measure the voltage on any of these input signals.
Note that these analog inputs are always connected to their pins, even if the Pin
function Select register assigns them to port pins. A simple self-test of the ADC can be
done by driving these pins as port outputs.
Note: if the ADC is used, signal levels on analog input pins must not be above the
level of V
at any time. Otherwise, A/D converter readings will be invalid. If the A/D
3A
converter is not used in an application then the pins associated with A/D inputs can be
used as 5 V tolerant digital IO pins.
Warning: while the ADC pins are specified as 5 V tolerant (see
description" on page
3.3 V (V
) +10 % should not be applied to any pin that is selected as an ADC input,
DDA
or the ADC reading will be incorrect. If for example AD0.0 and AD0.1 are used as the
ADC0 inputs and voltage on AD0.0 = 4.5 V while AD0.1 = 2.5 V, an excessive voltage
on the AD0.0 can cause an incorrect reading of the AD0.1, although the AD0.1 input
voltage is within the right range.
Voltage Reference. This pin is provides a voltage reference level for the A/D
converter(s).
Analog Power and Ground. These should be nominally the same voltages as V
and V
, but should be isolated to minimize noise and error.
SS
Rev. 01 — 15 August 2005
(typically 3 V; not to exceed V
REF
69), the analog multiplexing in the ADC block is not. More than
User manual
voltage level).
DDA
Table 58 "Pin
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
DD
265
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