Datasheet

LPC11U3X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 2.2 — 11 March 2014 59 of 77
NXP Semiconductors
LPC11U3x
32-bit ARM Cortex-M0 microcontroller
11.5 Reset pad configuration
11.6 ADC effective input impedance
A simplified diagram of the ADC input channels can be used to determine the effective
input impedance seen from an external voltage source. See Figure 33
.
The effective input impedance, R
in
, seen by the external voltage source, V
EXT
, is the
parallel impedance of ((1/f
s
x C
ia
) + R
mux
+ R
sw
) and (1/f
s
x C
io
), and can be calculated
using Equation 1
with
f
s
= sampling frequency
C
ia
= ADC analog input capacitance
R
mux
= analog mux resistance
R
sw
= switch resistance
C
io
= pin capacitance
(1)
Fig 32. Reset pad configuration
V
SS
reset
002aaf274
V
DD
V
DD
V
DD
R
pu
ESD
ESD
20 ns RC
GLITCH FILTER
PIN
Fig 33. ADC input channel
C
ia
R
s
V
SS
V
EXT
002aah615
ADC
COMPARATOR
ADC Block
R
in
C
io
R
mux
R
sw
Source
<2 kΩ <1.3 kΩ
R
in
1
f
s
C
ia

------------------
R
mux
R
sw
++


1
f
s
C
io

------------------



=