UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
476 of 515
NXP Semiconductors
UM11029
Chapter 28: LPC84x Analog comparator
28.5.1 Reference voltages
The voltage ladder can use two reference voltages, from the VDDCMP or the VDD pin.
The voltage ladder selects one of 32 steps between the pin voltage and VSS inclusive.
The voltage on VDDCMP should not exceed that on VDD.
28.5.2 Settling times
After the voltage ladder is powered on, it requires stabilization time until comparisons
using it are accurate. Much shorter settling times apply after the LADSEL value is
changed and when either or both voltage sources are changed. Software can deal with
these factors by repeatedly reading the comparator output until a number of readings yield
the same result.
28.5.3 Interrupts
The interrupt output comes from edge detection circuitry in this module. Rising edges,
falling edges, or both edges can set the COMPEDGE bit and thus request an interrupt.
COMPEDGE and the interrupt request are cleared when software writes a 1 to
EDGECLR.
Fig 63. Comparator block diagram
0
7
31
0
0
7
0
1
V
DD
ext. VDDCMP
LADREF
LADEN & nACOMP_PD
LADSEL
COMP_VP_SEL
+
-
HYS
COMP_VM_SEL
ACMP_I1
ACMP_I2
internal bandgap reference voltage
VOLTAGE
LADDER OUT
ACOMP_PD
D Q
buf
0
1
D Q
SYNC
2 OF 3
SAMPLING
EDGE DETECT
S Q
R
COMPSA
EDGESEL
EDGECLR or
ACOMP_RST_N
COMPEDGE
(to INTERRUPT)
buf
COMPSTAT
to ACMP_O
CONTROL / STATUS REGISTER BITS
ACOMP_RST_N
ACMP_I3
ACMP_I4
ACMP_I5
DACOUT0
n.c.