Datasheet

© 2002-2012 Microchip Technology Inc. DS21714G-page 15
MCP6546/6R/6U/7/8/9
4.0 APPLICATIONS INFORMATION
The MCP6546/6R/6U/7/8/9 family of push-pull output
comparators are fabricated on Microchip’s state-of-the-
art CMOS process. They are suitable for a wide range
of applications requiring very low power consumption.
4.1 Comparator Inputs
4.1.1 PHASE REVERSAL
The MCP6546/6R/6U/7/8/9 comparator family uses
CMOS transistors at the input. They are designed to
prevent phase inversion when the input pins exceed
the supply voltages. Figure 2-3 shows an input voltage
exceeding both supplies with no resulting phase
inversion.
4.1.2 INPUT VOLTAGE AND CURRENT
LIMITS
The ESD protection on the inputs can be depicted as
shown in Figure 4-1. This structure was chosen to pro-
tect the input transistors, and to minimize input bias
current (IB). The input ESD diodes clamp the inputs
when they try to go more than one diode drop below
V
SS
. They also clamp any voltages that go too far
above V
DD
; their breakdown voltage is high enough to
allow normal operation, and low enough to bypass ESD
events within the specified limits.
FIGURE 4-1: Simplified Analog Input ESD
Structures.
In order to prevent damage and/or improper operation
of these amplifiers, the circuits they are in must limit the
currents (and voltages) at the V
IN
+ and V
IN
– pins (see
Absolute Maximum Ratings † at the beginning of
Section 1.0 “Electrical Characteristics”). Figure 4-3
shows the recommended approach to protecting these
inputs. The internal ESD diodes prevent the input pins
(V
IN
+ and V
IN
–) from going too far below ground, and
the resistors R
1
and R
2
limit the possible current drawn
out of the input pin. Diodes D
1
and D
2
prevent the input
pin (V
IN
+ and V
IN
–) from going too far above V
DD
.
When implemented as shown, resistors R
1
and R
2
also
limit the current through D
1
and D
2
.
FIGURE 4-2: Protecting the Analog
Inputs.
It is also possible to connect the diodes to the left of
resistors R
1
and R
2
. In this case, the currents through
diodes D
1
and D
2
need to be limited by some other
mechanism. The resistor then serves as in-rush current
limiter; the DC current into the input pins (V
IN
+ and
V
IN
–) should be very small.
A significant amount of current can flow out of the
inputs when the common mode voltage (V
CM
) is below
ground (V
SS
); see Figure 2-42. Applications that are
high impedance may need to limit the usable voltage
range.
4.1.3 NORMAL OPERATION
The input stage of this family of devices uses two
differential input stages in parallel, one operates at low
input voltages, and the other at high input voltages.
With this topology, the input voltage is 0.3V above V
DD
and 0.3V below V
SS
. The input offset voltage is
measured at both V
SS
- 0.3V and V
DD
+ 0.3V to ensure
proper operation.
The MCP6546/6R/6U/7/8/9 family has internally-set
hysteresis that is small enough to maintain input offset
accuracy (<7 mV), and large enough to eliminate
output chattering caused by the comparator’s own
input noise voltage (200 µV
P-P
). Figure 4-3 illustrates
this capability.
Bond
Pad
Bond
Pad
Bond
Pad
V
DD
V
IN
+
V
SS
Input
Stage
Bond
Pad
V
IN
–
V
1
MCP6G0X
R
1
V
DD
D
1
R
1
≥
V
SS
– (minimum expected V
1
)
2mA
V
OUT
V
2
R
2
R
3
D
2
+
–
R
2
≥
V
SS
– (minimum expected V
2
)
2mA