LMC6772AIN National Semiconductor, LMC6772AIN Datasheet - Page 10

• Manufacturer Part Number: LMC6772AIN
• Description: IC COMP DUAL MICRPWR CMOS 8-DIP
• Manufacturer: National Semiconductor
• Type: General Purposer

Specifications of LMC6772AIN

• Number Of Elements: 2
• Output Type: Open Drain
• Voltage - Supply: 2.7 V ~ 15 V, ±1.35 V ~ 7.5 V
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LMC6772AIN

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Application Information
1.0 INPUT COMMON-MODE VOLTAGE RANGE
At supply voltages of 2.7V, 5V and 15V, the LMC6772 has an
input common-mode voltage range which exceeds both sup-
plies. As in the case of operational amplifiers, CMVR is de-
fined by the V
mode range of the device. A CMRR (ΔV
(typical) implies a shift of < 1 mV over the entire common-
mode range of the device. The absolute maximum input
voltage at V
temperature.
FIGURE 1. An Input Signal Exceeds the LMC6772 Power
A wide input voltage range means that the comparator can be
used to sense signals close to ground and also to the power
supplies. This is an extremely useful feature in power supply
monitoring circuits.
An input common-mode voltage range that exceeds the sup-
plies, 20 fA input currents (typical), and a high input
impedance makes the LMC6772 ideal for sensor applica-
tions. The LMC6772 can directly interface to sensors without
the use of amplifiers or bias circuits. In circuits with sensors
which produce outputs in the tens to hundreds of millivolts,
the LMC6772 can compare the sensor signal with an appro-
priately 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.
Supply Voltages with No Output Phase Inversion
+
= 5V is 200 mV beyond either supply rail at room
OS
shift of the comparator over the common-
OS
/ΔV
CM
1234724
) of 75 dB
10
FIGURE 2. Even at Low-Supply Voltage of 2.7V, an Input
Signal which Exceeds the Supply Voltages Produces No
At V
μs with overdrives of 100 mV. Please refer to the performance
curves for more extensive characterization.
3.0 OUTPUT SHORT CIRCUIT CURRENT
The LMC6772 has short circuit protection of 40 mA. However,
it is not designed to withstand continuous short circuits, tran-
sient voltage or current spikes, or shorts to any voltage be-
yond 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 hysteresis.
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:
•
•
•
and many more characteristics as listed on the macromodel
disk.
FIGURE 3. Canceling the Effect of Input Capacitance
Input common-mode voltage range
Quiescent and dynamic supply current
Input overdrive characteristics
+
= 2.7V, propagation delays are t
Phase Inversion at the Output
PLH
= 4 μs and t
1234725
PHL
1234726
= 4