MCP6549 Microchip Technology, MCP6549 Datasheet - Page 12

• Manufacturer Part Number: MCP6549
• Description: (MCP6546 - MCP6549) Open-Drain Output Sub-Microamp Comparators
• Manufacturer: Microchip Technology

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MCP6546/7/8/9
3.0
The MCP6546/7/8/9 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.
3.1
The MCP6546/7/8/9 comparator family uses CMOS
transistors at the input. They are designed to prevent
phase inversion when the input pins exceed the supply
voltages.
exceeding both supplies with no resulting phase
inversion.
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
and 0.3V below V
voltage is measured at both V
to ensure proper operation.
The maximum operating input voltages that can be
applied are V
inputs that exceed this absolute maximum rating can
cause excessive current to flow and permanently
damage the device. In applications where the input pin
exceeds the specified range, external resistors can be
used to limit the current below ±2 mA, as shown in
Figure 3-1.
FIGURE 3-1:
should be used to limit excessive input current if
either of the inputs exceeds the absolute
maximum specification.
3.2
The open-drain output is designed to make level-
shifting and wired-OR logic easy to implement. The
output can go as high as 10V for 9V battery-powered
applications. The output stage minimizes switching
current (shoot-through current from supply-to-supply)
when the output changes state. See Figures 2-15, 2-17
and 2-32 through 2-36, for more information.
DS21714C-page 12
V
IN
R
APPLICATIONS INFORMATION
Comparator Inputs
R IN
Open-Drain Output
IN
Figure 2-37
SS
--------------------------------------------------------------------------------- -
R
V SS
----------------------------------------------------------------------------- -
Maximum expected V
- 0.3V and V
IN
–
SS
Minimum expected V IN
An input resistor (R
. Therefore, the input offset
MCP654X
shows
2 mA
2 mA
DD
SS
+ 0.3V. Voltages on the
- 0.3V and V
an
IN
–
input
V
DD
IN
DD
V
)
OUT
voltage
+ 0.3V
DD
3.3
The MCP6548 is a single comparator with a chip select
(CS) option. When CS is pulled high, the total current
consumption drops to 20 pA (typ). 1 pA (typ) flows
through the CS pin, 1 pA (typ) flows through the output
pin and 18 pA (typ) flows through the V
shown in Figure 1-1. When this happens, the
comparator output is put into a high-impedance state.
By pulling CS low, the comparator is enabled. If the CS
pin is left floating, the comparator will not operate
properly. Figure 1-1 shows the output voltage and
supply current response to a CS pulse.
The internal CS circuitry is designed to minimize
glitches when cycling the CS pin. This helps conserve
power, which is especially important in battery-powered
applications.
3.4
Greater flexibility in selecting hysteresis, or input trip
points, is achieved by using external resistors.
Input offset voltage (V
(input-referred) low-high and high-low trip points. Input
hysteresis voltage (V
the same trip points. Hysteresis reduces output
chattering when one input is slowly moving past the
other, thus reducing dynamic supply current. It also
helps in systems where it is best not to cycle between
states too frequently (e.g., air conditioner thermostatic
control). The MCP6546/7/8/9 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 µVp-p).
FIGURE 3-2:
comparators’ internal hysteresis eliminates
output chatter caused by input noise voltage.
-1
-2
-3
9
8
7
6
5
4
3
2
1
0
0
V
V
Externally Set Hysteresis
DD
IN
MCP6548 Chip Select (CS)
+ = 2.75V
100
= 5.0V
V
OUT
200
V
IN
300
–
Time (100 ms/div)
HYST
OS
The MCP6546/7/8/9
400
) is the center (average) of the
2003 Microchip Technology Inc.
) is the difference between
500
Hysteresis
600
700
800
DD
900
pin, as
1000
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30