LMC7211AIMX NSC [National Semiconductor], LMC7211AIMX Datasheet - Page 9

• Manufacturer Part Number: LMC7211AIMX
• Description: Tiny CMOS Comparator with Rail-to-Rail Input and Push-Pull Output
• Manufacturer: NSC [National Semiconductor]

Application Information
R
R
6.0 Input Protection
If input signals are like to exceed the common mode range of
the LMC7211, or it is likely that signals may be present when
power is off, damage to the LMC7211 may occur. Large
value (100 k
hood of damage by limiting the input currents. Since the
LMC7211 has very low input leakage currents, the effect on
accuracy will be small. Additional protection may require the
use of diodes, as shown in Figure 7 . Note that diode leakage
F
F
@
@
R
R
FIGURE 4. Positive Feedback for Hysteresis
1
2
and
to M ) input resistors may reduce the likeli-
Without Positive Feedback
With Positive Feedback
(Hysteresis or Memory)
(No Hysteresis)
FIGURE 5.
FIGURE 6.
(Continued)
DS012337-9
DS012337-10
DS012337-11
9
current may affect accuracy during normal operation. The
R-C time constant of R
also slow response time.
7.0 Layout Considerations
The LMC7211 is not an especially fast comparator, so high
speed design practices are not required. The LMC7211 is
capable of operating with very high impedance inputs, so
precautions should be taken to reduce noise pickup with
high impedance ( 100 k and greater) designs and in elec-
trically noisy environments.
Keeping high value resistors close to the LMC7211 and mini-
mizing the size of the input nodes is a good practice. With
multilayer designs, try to avoid long loops which could act as
inductors (coils). Sensors which are not close to the com-
parator may need twisted pair or shielded connections to re-
duce noise.
8.0 Open Drain Output, Dual Versions
The LMC7221 is a comparator similar to the LMC7211, but
with an open drain output which allows the output voltage to
be different (higher or lower) than the supply voltage. The
open drain output is like the open collector output of a logic
gate. This makes the LMC7221 very useful for mixed voltage
systems. Many systems will have different voltages for the
analog and microprocessor sections. Please see the
LMC7221 datasheet for details.
The performance of the LMC7211 is available in dual de-
vices. Please see the LMC6762 datasheet for details on a
dual push-pull output device. For a dual device with open
drain outputs, please see the LMC6772 datasheet.
Rail-to-Rail Input Low Power Comparators —
LMC7211
LMC6762
LMC7221
LMC6772
Push-Pull Output
Open Drain Output
SOT23-5, SO-8
SO-8, DIP
SOT23-5, SO-8
SO-8, DIP
IN
FIGURE 7.
and the diode capacitance may
DS012337-12
Single
Dual
Single
Dual
www.national.com