© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 01 — 15 August 2005
265
17.1 Features
•
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
REF
(typically 3 V; not to exceed V
DDA
voltage level).
•
10 bit conversion time
≥
2.44
µ
s.
•
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).
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
gives a brief summary of each of ADC related pins.
UM10139
Chapter 17: Analog-to-Digital Converter (ADC)
Rev. 01 — 15 August 2005
User manual
Table 253: ADC pin description
Pin
Type
Description
AD0.7:6, AD0.4:1
&
AD1.7:0
(LPC2144/6/8)
Input
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
3A
at any time. Otherwise, A/D converter readings will be invalid. If the A/D
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
), the analog multiplexing in the ADC block is not. More than
3.3 V (V
DDA
) +10 % should not be applied to any pin that is selected as an ADC input,
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.
V
REF
Reference
Voltage Reference. This pin is provides a voltage reference level for the A/D
converter(s).
V
DDA
, V
SSA
Power
Analog Power and Ground. These should be nominally the same voltages as V
DD
and V
SS
, but should be isolated to minimize noise and error.