MCP6546RT-ESLASHMS datasheet(13/32 Pages) MICROCHIP

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DS21714E-page 13

MCP6546/6R/6U/7/8/9

4.0

APPLICATIONS INFORMATION

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.

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

VSS. They also clamp any voltages that go too far

above VDD; 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 VIN+ and VIN– 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

(VIN+ and VIN–) from going too far below ground, and

the resistors R1 and R2 limit the possible current drawn

out of the input pin. Diodes D1 and D2 prevent the input

pin (VIN+ and VIN–) from going too far above VDD.

When implemented as shown, resistors R1 and R2 also

limit the current through D1 and D2.

FIGURE 4-2:

Protecting the Analog Inputs.

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 2-42. Applications that are

high impedance may need to limit the useable 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 VDD

and 0.3V below VSS. The input offset voltage is

measured at both VSS - 0.3V and VDD + 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 µVP-P). Figure 4-3 illustrates

this capability.

Bond

Pad

Bond

Pad

Bond

Pad

VDD

VIN+

VSS

Input

Stage

Bond

Pad

VIN–

MCP6G0X

VDD

R1 ≥

VSS – (minimum expected V1)

2mA

VOUT

–

R2 ≥

VSS – (minimum expected V2)

2mA

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