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MCP6561

1.8V Low Power Push-Pull Output Comparator

Microchip Technology 

MCP6561/1R/1U/2/4

It is also possible to connect the diodes to the left of the

resistors R1 and R2. In this case, the currents through

the diodes D1 and D2 need to be limited by some other

mechanism. The resistor then serves as in-rush current

limiter; the DC current into the input pins (VIN+ and

VIN–) should be very small.

A significant amount of current can flow out of the

inputs when the common mode voltage (VCM) is below

ground (VSS); see Figure 2-32. Applications that are

high impedance may need to limit the usable voltage

range.

4.1.3 PHASE REVERSAL

The MCP6561/1R/1U/2/4 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.

4.2 Push-Pull Output

The push-pull output is designed to be compatible with

CMOS and TTL logic, while the output transistors are

configured to give rail-to-rail output performance. They

are driven with circuitry that minimizes any switching

current (shoot-through current from supply-to-supply)

when the output is transitioned from high-to-low, or

from low-to-high (see Figure 2-15 and Figure 2-18 for

more information).

4.3 Externally Set Hysteresis

Greater flexibility in selecting hysteresis (or input trip

points) is achieved by using external resistors.

Hysteresis reduces output chattering when one input is

slowly moving past the other. It also helps in systems

where it is best not to cycle between high and low

states too frequently (e.g., air conditioner thermostatic

control). Output chatter also increases the dynamic

supply current.

4.3.1 NON-INVERTING CIRCUIT

Figure 4-4 shows a non-inverting circuit for single-

supply applications using just two resistors. The

resulting hysteresis diagram is shown in Figure 4-5.

VREF

VDD

-

MCP656X

+

VOUT

VIN

R1

RF

FIGURE 4-4:

Non-Inverting Circuit with

Hysteresis for Single-Supply.

VDD

VOH

VOUT

High-to-Low

Low-to-High

VOL

VSS

VSS

VTHL VTLH

VIN

VDD

FIGURE 4-5:

Hysteresis Diagram for the

Non-Inverting Circuit.

The trip points for Figure 4-4 and Figure 4-5 are:

EQUATION 4-1:

VTLH

=

⎛

VREF⎝⎜

1

+

-R----1-

RF

⎞

⎟

⎠

–

VO

L⎝⎜⎛R-R---F-1-

⎞

⎟

⎠

VTHL

=

⎛

VREF⎝⎜

1

+

-R----1-

RF

⎞

⎟

⎠

–

VOH⎝⎜⎛R-R---F-1-

⎞

⎟

⎠

Where:

VTLH = trip voltage from low to high

VTHL = trip voltage from high to low

DS22139B-page 16

© 2009 Microchip Technology Inc.

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