LMV821M7 National Semiconductor, LMV821M7 Datasheet - Page 15

• Manufacturer Part Number: LMV821M7
• Description: Operational Amplifier (Op-Amp) IC
• Manufacturer: National Semiconductor

Specifications of LMV821M7

• No. Of Amplifiers: 1
• Bandwidth: 5MHz
• Slew Rate: 2V/µs
• No. Of Pins: 5
• Single Supply Voltage Min (+v): 2.7V
• Peak Reflow Compatible (260 C): No
• Input Offset Voltage Max: 3.5mV
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Note
To simplify the design process, certain components are set
equal to each other. Refer to Figure 10 and Figure 11. These
equal component values help to simplify the design equa-
tions as follows:
To illustrate the design process/implementation, a 3 kHz,
Butterworth response, low-pass filter DAAF (Figure 10) is
designed as follows:
1. Choose C
2. Choose R
3. Calculate R
4. Calculate R
Butterworth (Maximally Flat) response is 0.707 (45 degrees
into the s-plane). R
1
4
= R
a
= C
3
and R
for the desired Q. The desired Q for a
3
5
3
= C = 1 nF
= 1 kΩ
calculates as follows:
2
for the desired Fc as follows:
(Continued)
15
Notice that R
The circuit was implemented and its cutoff frequency mea-
sured. The cutoff frequency measured at 2.92 kHz.
The circuit also showed good repeatability. Ten different
LMV822 samples were placed in the circuit. The correspond-
ing change in the cutoff frequency was less than a percent.
TRI-LEVEL VOLTAGE DETECTOR
The tri-level voltage detector of Figure 13 provides a type of
window comparator function. It detects three different input
voltage ranges: Min-range, Mid-range, and Max-range. The
output voltage (V
clamped at GND for the Mid-range. For the Max-range, V
at V
the circuit of Figure 13.
Its operation is as follows: V
the diode bridge to absorb I
tion (V
diode bridge. When this limit is reached, the clamping effect
stops and the op amp responds open loop. The design
equation directly preceding Figure 14, shows how to deter-
mine the clamping range. The equation solves for the input
voltage band on each side GND. The mid-range is twice this
voltage band.
ee
. Figure 14 shows a V
O
= 0V). Eventually, I
3
could also be calculated as 0.707 of R
O
) is at V
IN
IN
O
I
CC
to maintain a clamped condi-
vs. V
deviating from GND, causes
reaches the bias limit of the
for the Min-range. V
I
oscilloscope photo per
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a
or R
O
O
is
is
2.