MCP6541/1R/1U/2/3/4
Where:
4.4.2
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.
R2R3
R23 = ------------------
R2 + R3
R3
------------------
VDD
V23
=
× VDD
R2 + R3
VIN
Using this simplified circuit, the trip voltage can be
calculated using the following equation:
VDD
VOUT
MCP654X
R2
R3
EQUATION 4-2:
R23
RF
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎝
⎞
⎠
----------------------
---------------------
R23 + RF
VTHL = VOH
+ V
+ V
RF
23
R
23 + R
F
R23
RF
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎝
⎞
⎠
----------------------
---------------------
VTLH = VOL
23
R
23 + R
R23 + RF
F
FIGURE 4-6:
Hysteresis.
Inverting Circuit With
V
TLH = trip voltage from low to high
VTHL = trip voltage from high to low
VOUT
Figure 2-20 and Figure 2-23 can be used to determine
typical values for VOH and VOL
VDD
VOH
.
Low-to-High
High-to-Low
4.5
Bypass Capacitors
With this family of comparators, the power supply pin
(VDD 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.
VIN
VOL
VSS
VSS
VTLH VTHL
VDD
FIGURE 4-7:
Hysteresis Diagram for the
Inverting Circuit.
4.6
Capacitive Loads
In order to determine the trip voltages (VTHL and VTLH
)
Reasonable capacitive loads (e.g., logic gates) have
little impact on propagation delay (see Figure 2-31).
The supply current increases with increasing toggle
frequency (Figure 2-19), especially with higher
capacitive loads.
for the circuit shown in Figure 4-6, R2 and R3 can be
simplified to the Thevenin equivalent circuit with
respect to VDD, as shown in Figure 4-8.
VDD
4.7
Battery Life
-
MCP654X
In order to maximize battery life in portable
applications, use large resistors and small capacitive
loads. Avoid toggling the output more than necessary.
Do not use Chip Select (CS) frequently to conserve
start-up power. Capacitive loads will draw additional
power at start-up.
VOUT
+
VSS
V23
R23
RF
Thevenin Equivalent Circuit.
FIGURE 4-8:
DS21696E-page 16
© 2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
