LMV7235M5/NOPB National Semiconductor, LMV7235M5/NOPB Datasheet - Page 10

• Manufacturer Part Number: LMV7235M5/NOPB
• Description: IC COMPARATOR R-R INPUT SOT23-5
• Manufacturer: National Semiconductor
• Type: General Purposer

Specifications of LMV7235M5/NOPB

• Number Of Elements: 1
• Output Type: Open-Drain, Rail-to-Rail
• Voltage - Supply: 2.7 V ~ 5 V
• Mounting Type: Surface Mount
• Package / Case: SC-74A, SOT-753
• Comparator Type: General Purpose
• No. Of Comparators: 1
• Response Time: 45ns
• Ic Output Type: Open Drain / Push Pull
• Supply Current: 65µA
• Supply Voltage Range: 2.7V To 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMV7235M5; LMV7235M5TR

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NON-INVERTING COMPARATOR WITH HYSTERESIS
A non inverting comparator with hysteresis requires a two re-
sistor network, and a voltage reference (V
input. When V
to switch from low to high, V
V
When V
parator switch back to it's low state, V
before V
The hysteresis of this circuit is the difference between V
and V
Delta V
CIRCUIT LAYOUT AND BYPASSING
The LMV7235/LMV7239 require high speed layout. Follow
these layout guidelines:
1. Use printed circuit board with a good, unbroken low-induc-
tance ground plane.
2. Place a decoupling capacitor (0.1µF ceramic surface
mount capacitor) as close as possible to V
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 parasitic
feedback. A small capacitor (1000pF or less) placed between
the inputs can help eliminate oscillations in the transition re-
gion. This capacitor causes some degradation to t
source impedance is low.
6. The topside ground plane runs between the output and in-
puts.
IN1
FIGURE 2. Non-Inverting Comparator with Hysteresis
is calculated by.
IN2
IN
IN
.
A
= V
will again equal V
is high, the output is also high, to make the com-
V
CC
IN2
IN
R1/R2
V
is low, the output is also low. For the output
= (V
IN1
= R1*(V
REF
(R1+ R2) - V
REF
REF
IN
. V
/R2) + V
must rise up to V
IN
can be calculated by
CC
IN
R1)/R2
REF
REF
CC
must equal V
) at the inverting
pin.
PD
10135924
IN1
when the
where
10135920
REF
IN1
10
7. Ground trace from the ground pin runs under the device up
to the bypass capacitor, shielding the inputs from the outputs.
ZERO-CROSSING DETECTOR
The inverting input is connected to ground and the non-in-
verting input is connected to 100mVp-p signal. As the signal
at the non-inverting input crosses 0V, the comparator's output
changes state.
THRESHOLD DETECTOR
Instead of tying the inverting input to 0V, the inverting input
can be tied to a reference voltage. The non-inverting input is
connected to the input. As the input passes the V
old, the comparator's output changes state.
CRYSTAL OSCILLATOR
A simple crystal oscillator using the LMV7239 is shown below.
Resistors R1 and R2 set the bias point at the comparator's
non-inverting input. Resistors R3, R4 and C1 sets the invert-
ing input node at an appropriate DC average level based on
the output. The crystal's path provides resonant positive feed-
back and stable oscillation occurs. The output duty cycle for
this circuit is roughly 50%, but it is affected by resistor toler-
ances and to a lesser extent by the comparator offset.
FIGURE 3. Zero-Crossing Detector
FIGURE 4. Threshold Detector
FIGURE 5. Crystal Oscillator
10135921
10135922
10135918
REF
thresh-