PIC16F648A-I Datasheet, PDF (16/34 Pages) Microchip Technology – Push-Pull Output Sub-Microamp Comparators

MCP6541/1R/1U/2/3/4
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.
V_DD
V_IN
V_DD
MCP654X
V_OUT
R₂
R₃
R_F
FIGURE 4-6:
Hysteresis.
Inverting Circuit With
V_DD
V_OH
V_OUT
Low-to-High
High-to-Low
V_OL
V_SS
V_SS
V_TLH V_THL
V_IN
V_DD
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, R₂ and R₃ can be
simplified to the Thevenin equivalent circuit with
respect to V_DD, as shown in Figure 4-8.
V_DD
-
MCP654X
+
V_SS
V_OUT
V₂₃
R₂₃
R_F
FIGURE 4-8:
Thevenin Equivalent Circuit.
Where:
R₂₃
=
----^R---²---^R----³----
R₂ + R₃
V₂₃
=
-------^R----³-------
R₂ + R₃
×
V_DD
Using this simplified circuit, the trip voltage can be
calculated using the following equation:
EQUATION 4-2:
V_THL
=
V_O
H
⎛
⎜
⎝
R----₂^---₃^{-R---+-2--3--R----F--}_{⎠⎟⎞}
+
V₂₃
⎛
⎝
R----₂^---₃^{-R---+-F----R----}_F^{-⎠⎞}
V_TLH
=
V_O
L
⎛
⎜
⎝
R----₂^---₃^{-R---+-2--3--R----F--}_{⎠⎟⎞}
+ V_{23⎝⎛R----2}---₃-R---+-^F----R----_F-_⎠⎞
V_TLH = trip voltage from low to high
V_THL = trip voltage from high to low
Figure 2-20 and Figure 2-23 can be used to determine
typical values for V_OH and V_OL.
4.5 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.
4.6 Capacitive Loads
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.
4.7 Battery Life
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.
DS21696E-page 16
© 2006 Microchip Technology Inc.