Datasheet

MCP6541/1R/1U/2/3/4
DS21696H-page 20 © 2002-2011 Microchip Technology Inc.
The easiest way to reduce surface leakage is to use a
guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin.
An example of this type of layout is shown in
Figure 4-9.
FIGURE 4-9: Example Guard Ring Layout
for Inverting Circuit.
1. Inverting Configuration (Figures 4-6 and 4-9):
a.Connect the guard ring to the non-inverting
input pin (V
IN
+). This biases the guard ring
to the same reference voltage as the
comparator (e.g., V
DD
/2 or ground).
b.Connect the inverting pin (V
IN
–) to the input
pad without touching the guard ring.
2. Non-inverting Configuration (Figure 4-4):
a.Connect the non-inverting pin (V
IN
+) to the
input pad without touching the guard ring.
b.Connect the guard ring to the inverting input
pin (V
IN
–).
4.9 Unused Comparators
An unused amplifier in a quad package (MCP6544)
should be configured as shown in Figure 4-10. This
circuit prevents the output from toggling and causing
crosstalk. It uses the minimum number of components
and draws minimal current (see Figure 2-15 and
Figure 2-18).
FIGURE 4-10: Unused Comparators.
4.10 Typical Applications
4.10.1 PRECISE COMPARATOR
Some applications require higher DC precision. An
easy way to solve this problem is to use an amplifier
(such as the MCP6041) to gain-up the input signal
before it reaches the comparator. Figure 4-11 shows an
example of this approach.
FIGURE 4-11: Precise Inverting
Comparator.
4.10.2 WINDOWED COMPARATOR
Figure 4-12 shows one approach to designing a win-
dowed comparator. The AND gate produces a logic ‘1’
when the input voltage is between V
RB
and V
RT
(where
V
RT
> V
RB
).
FIGURE 4-12: Windowed Comparator.
4.10.3 ASTABLE MULTIVIBRATOR
A simple astable multivibrator design is shown in
Figure 4-13. V
REF
needs to be between the power
supplies (V
SS
= GND and V
DD
) to achieve oscillation.
The output duty cycle changes with V
REF
.
FIGURE 4-13: Astable Multivibrator.
Guard Ring
V
SS
V
IN
-V
IN
+
¼ MCP6544
V
DD
–
+
V
REF
V
DD
V
DD
R
1
R
2
V
OUT
V
IN
V
REF
MCP6041
MCP654X
V
RT
MCP6542
V
RB
V
IN
1/2
MCP6542
1/2
MCP6541
V
DD
R
1
R
2
R
3
V
REF
C
1
V
OUT