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LMV7235 Datasheet(PDF) 9 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor. Click here to check the latest version.
Part No. LMV7235
Description  45ns, Ultra Low Power, Low Voltage, Rail-to-Rail Input Comparator with Open-Drain/Push-Pull Output
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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LMV7235 Datasheet(HTML) 9 Page - National Semiconductor (TI)

 
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Application Section (Continued)
Non-Inverting Comparator with Hysteresis
A non inverting comparator with hysteresis requires a two
resistor network, and a voltage reference (V
REF) at the in-
verting input. When V
IN is low, the output is also low. For the
output to switch from low to high, V
IN must rise up to VIN1
where V
IN1 is calculated by.
V
IN1 = R1*(VREF/R2) + VREF
When V
IN is high, the output is also high, to make the
comparator switch back to it’s low state, V
IN must equal VREF
before V
A will again equal VREF.VIN can be calculated by
V
IN2 =(VREF (R1+ R2) - VCCR1)/R2
The hysteresis of this circuit is the difference between V
IN1
and V
IN2.
Delta V
IN =VCCR1/R2
Circuit Layout and Bypassing
The LMV7235/39 require high speed layout. Follow these
layout guidelines:
1. Use printed circuit board with a good, unbroken low-
inductance ground plane.
2. Place a decoupling capacitor (0.1µF ceramic surface
mount capacitor) as close as possible to V
CC pin.
3. On the inputs and the output, keep lead lengths as short
as possible to avoid unwanted parasitic feedback around the
comparator. Keep inputs away from output.
4. Solder the device directly to the printed circuit board rather
than using a socket.
5. For slow moving input signals, take care to prevent para-
sitic feedback. A small capacitor (1000pF or less) placed
between the inputs can help eliminate oscillations in the
transition region. This capacitor causes some degradation to
t
PD when the source impedance is low.
6. The topside ground plane runs between the output and
inputs.
7. Ground trace from the ground pin runs under the device
up to the bypass capacitor, shielding the inputs from the
outputs.
10135919
FIGURE 1.
10135924
10135920
FIGURE 2. Non-Inverting Comparator with Hysteresis
www.national.com
9


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