MCP6549-ESLASHST datasheet(14/32 Pages) MICROCHIP

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

DS21714E-page 14

FIGURE 4-3:

The MCP6546/7/8/9

comparators’ internal hysteresis eliminates

output chatter caused by input noise voltage.

4.2

Open-Drain Output

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 cur-

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

when the output changes state. See Figures 2-15, 2-18

and 2-37 through 2-41, for more information.

4.3

MCP6548 Chip Select (CS)

The MCP6548 is a single comparator with a Chip

Select (CS) pin. 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 VDD pin,

as 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.

4.4

Externally Set Hysteresis

Greater flexibility in selecting hysteresis, or input trip

points, is achieved by using external resistors.

Input offset voltage (VOS) is the center (average) of the

(input-referred) low-high and high-low trip points. Input

hysteresis voltage (VHYST) is the difference between

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).

4.4.1

INVERTING CIRCUIT

Figure 4-4 shows an inverting circuit for a single-supply

application using three resistors, besides the pull-up

resistor. The resulting hysteresis diagram is shown in

Figure 4-5.

FIGURE 4-4:

Inverting circuit with

hysteresis.

FIGURE 4-5:

Hysteresis diagram for the

inverting circuit.

In order to determine the trip voltages (VTHL and VTLH)

for the circuit shown in Figure 4-4, R2 and R3 can be

simplified to the Thevenin equivalent circuit with

respect to VDD, as shown in Figure 4-6.

FIGURE 4-6:

Thevenin Equivalent Circuit.

-3

-2

-1

Time (100 ms/div)

-30

-25

-20

-15

-10

-5

VOUT

VIN–

VDD = 5.0V

Hysteresis

VIN

VOUT

MCP654X

VDD

VPU

RPU

VDD

IOL

IRF

IPU

VOUT

High-to-Low

Low-to-High

VOH

VOL

VSS

VDD

VTLH VTHL

VIN

VPU

VTLH = trip voltage from low to high

VTHL = trip voltage from high to low

V23

VOUT

MCP654X

VPU

R23

RPU

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