Datasheet

 2009-2013 Microchip Technology Inc. DS22143D-page 19
MCP6566/6R/6U/7/9
4.3.2 INVERTING CIRCUIT
Figure 4-6 shows an inverting circuit for single-supply
using three resistors. The resulting hysteresis diagram
is shown in Figure 4-7.
FIGURE 4-6: Inverting Circuit with
Hysteresis.
FIGURE 4-7: Hysteresis Diagram for the
Inverting Circuit.
In order to determine the trip voltages (V
THL
and V
TLH
)
for the circuit shown in Figure 4-6, R
2
and R
3
can be
simplified to the Thevenin equivalent circuit with
respect to V
DD
, as shown in Figure 4-8.
FIGURE 4-8: Thevenin Equivalent Circuit.
Where:
Using this simplified circuit, the trip voltage can be
calculated using the following equation:
EQUATION 4-2:
Figure 2-21 and Figure 2-24 can be used to determine
typical values for V
OH
and V
OL
.
4.4 Bypass Capacitors
With this family of comparators, the power supply pin
(V
DD
for single supply) should have a local bypass
capacitor (i.e., 0.01 µF to 0.1 µF) within 2 mm for good
edge rate performance.
4.5 Capacitive Loads
Reasonable capacitive loads (e.g., logic gates) have
little impact on propagation delay (see Figure 2-32).
The supply current increases with increasing toggle
frequency (Figure 2-20), especially with higher
capacitive loads. The output slew rate and propagation
delay performance will be reduced with higher
capacitive loads.
V
IN
V
OUT
V
DD
R
2
R
F
R
3
V
DD
V
PU
R
PU
MCP656X
V
OUT
High-to-LowLow-to-High
V
DD
V
OH
V
OL
V
SS
V
SS
V
DD
V
TLH
V
THL
V
IN
V
23
V
OUT
V
DD
R
23
R
F
+
-
V
SS
V
PU
R
PU
MCP656X
R
23
R
2
R
3
R
2
R
3
+
-------------------=
V
23
R
3
R
2
R
3
+
-------------------V
DD
 =
V
THL
V
OH
R
23
R
23
R
F
+
-----------------------



V
23
R
F
R
23
R
F
+
----------------------


+=
V
TLH
V
OL
R
23
R
23
R
F
+
-----------------------



V
23
R
F
R
23
R
F
+
----------------------


+=
Where:
V
TLH
= trip voltage from low-to-high
V
THL
= trip voltage from high-to-low