LMV321M7 National Semiconductor, LMV321M7 Datasheet - Page 16

• Manufacturer Part Number: LMV321M7
• Description: OPERATIONAL AMPLIFIER OP AMP IC
• Manufacturer: National Semiconductor

Specifications of LMV321M7

• No. Of Amplifiers: 1
• Slew Rate: 1V/µs
• No. Of Pins: 5
• Peak Reflow Compatible (260 C): No
• Leaded Process Compatible: No
• Amplifier Type: Operational
• Package / Case: 5-SC-70
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Notes
Note that the single-op-amp active filters are used in to the
applications that require low quality factor, Q( ≤ 10), low
frequency (≤ 5 kHz), and low gain (≤ 10), or a small value for
the product of gain times Q (≤ 100). The op amp should have
an open loop voltage gain at the highest frequency of inter-
est at least 50 times larger than the gain of the filter at this
frequency. In addition, the selected op amp should have a
slew rate that meets the following requirement:
where ω
output peak-to-peak voltage.
4.4.2 Sallen-Key 2nd-Order Active Low-Pass Filter
The Sallen-Key 2nd-order active low-pass filter is illustrated
in Figure 13. The dc gain of the filter is expressed as
FIGURE 12. Frequency Response of Simple Low-Pass
FIGURE 11. Simple Low-Pass Active Filter
Slew Rate ≥ 0.5 x (ω
H
is the highest frequency of interest, and V
Active Filter in Figure 11
H
V
10006037
OPP
(Continued)
) x 10
−6
10006015
V/µsec
10006014
opp
is the
(1)
16
Its transfer function is
The following paragraphs explain how to select values for
R
as A
The standard form for a 2nd-order low pass filter is
where
Comparison between the Equation (2) and Equation (3)
yields
To reduce the required calculations in filter design, it is
convenient to introduce normalization into the components
and design parameters. To normalize, let ω
and C
Equation (4) and Equation (5). From Equation (4), we obtain
From Equation (5), we obtain
1
Q: Pole Quality Factor
ω
FIGURE 13. Sallen-Key 2nd-Order Active Low-Pass
, R
C
LP
: Corner Frequency
2
, R
1
, Q, and f
= C
3
, R
2
4
, C
= C
1
c
, and C
.
n
= 1F, and substitute these values into
2
for given filter requirements, such
Filter
C
= ω
10006016
n
= 1rad/s,
(2)
(3)
(4)
(5)
(6)
(7)