AN1740 Freescale Semiconductor / Motorola, AN1740 Datasheet - Page 17

• Manufacturer Part Number: AN1740
• Description: Applications Using the Analog Subsystem on MC68HC05JJ/JP Series Microcontrollers
• Manufacturer: Freescale Semiconductor / Motorola

AN1740
MOTOROLA
V
V
P
P
= V
= V
N
N
+ V
– V
IO
IO
V
V
N
N
A — INITIAL INPUT OFFSET POSITIVE
–
+
–
+
+
+
IN ALL CASES, THE OUTPUT (X) RISES WHEN THE (+) INPUT RISES ABOVE THE (–) INPUT.
V
V
IO
IO
–
–
comparator input, but results in the addition or subtraction from the same
external input to the comparator. This inversion action is performed by
the INV bit in the AMUX register.
The INV bit, therefore, can be used to check for an input condition where
the difference between the inputs is less than the offset voltage or for the
case where one input is within the offset voltage of V
case B in
respect to the internal negative input of the comparator, then:
Therefore, the comparator output will not change states, since the V
must be at least 5 mV below V
However, if we invert, the sense of the comparator is inverted using the
INV bit, then V
positive input of the comparator. The 10-mV input offset is still with
respect to the internal negative input, but now is “moved” to the external
V
Figure 8. Inverted Comparator Offset Model
P
Freescale Semiconductor, Inc.
+
+
–
–
so that:
For More Information On This Product,
IDEAL
COMPARATOR
IDEAL
COMPARATOR
INV = 0
INV = 1
Figure 8
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V
V
N
P
P
will still be at 5 mV, but it is now connected to the internal
= V
= V
where V
N
X
X
N
+ V
– V
V
V
P
P
IO
= V
IO
= V
N
N
N
is 5 mV above V
+ V
= 5 mV + 10 mV = + 15 mV
– V
= 5 mV – 10 mV = – 5 mV
SS
IO
V
IO
V
N
.
N
+
–
B — INITIAL INPUT OFFSET NEGATIVE
+
–
+
+
V
V
IO
IO
–
–
SS
+
–
and V
+
–
IDEAL
COMPARATOR
SS
IDEAL
COMPARATOR
Voltage Comparators
. For example, in
INV = 1
IO
INV = 0
is 10 mV with
Application Note
X
P
X
17