1.0 Input Common-Mode Voltage

LMC6772 can compare the sensor signal with an appropri-

ately small reference voltage. This reference voltage can be

close to ground or the positive supply rail.

2.0 Low Voltage Operation

Comparators are the common devices by which analog sig-

nals interface with digital circuits. The LMC6772 has been

designed to operate at supply voltages of 2.7V, without sac-

rificing performance, to meet the demands of 3V digital sys-

tems.

At supply voltages of 2.7V, the common-mode voltage range

extends 200 mV (guaranteed) below the negative supply.

This feature, in addition to the comparator being able to

sense signals near the positive rail, is extremely useful in low

voltage applications.

At V

4 µs with overdrives of 100 mV. Please refer to the perfor-

mance curves for more extensive characterization.

3.0 Output Short Circuit Current

The LMC6772 has short circuit protection of 40 mA. How-

ever, it is not designed to withstand continuous short circuits,

transient voltage or current spikes, or shorts to any voltage

beyond the supplies. A resistor is series with the output

should reduce the effect of shorts. For outputs which send

signals off PC boards additional protection devices, such as

diodes to the supply rails, and varistors may be used.

4.0 Hysteresis

If the input signal is very noisy, the comparator output might

trip several times as the input signal repeatedly passes

through the threshold. This problem can be addressed by

making use of hysteresis as shown below.

The capacitor added across the feedback resistor increases

the switching speed and provides more short term hyster-

esis. This can result in greater noise immunity for the circuit.

5.0 Spice Macromodel

A Spice Macromodel is available for the LMC6772. The

model includes a simulation of:

•

Input common-mode voltage range

•

Quiescent and dynamic supply current

•

Input overdrive characteristics

and many more characteristics as listed on the macromodel

disk.

Contact the National Semiconductor Customer Response

Center at 1-800-272-9959 to obtain an operational amplifier

spice model library disk.

Typical Applications

Universal Logic Level Shifter

The output of the LMC6772 is the uncommitted drain of the

output NMOS transistor. Many drains can be tied together to

provide an output OR’ing function. An output pullup resistor

can be connected to any available power supply voltage

within the permitted power supply range.

The two 1 k

Ω resistors bias the input to half of the power

supply voltage. The pull-up resistor should go to the output

logic supply. Due to its wide operating range, the LMC6772

is ideal for the logic level shifting applications.

DS012347-25

FIGURE 2. Even at Low-Supply Voltage of 2.7V, an

Input Signal which Exceeds the Supply Voltages

Produces No Phase Inversion at the Output

DS012347-26

FIGURE 3. Canceling the Effect of Input Capacitance

DS012347-27

FIGURE 4. Universal Logic Level Shifter

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