Datasheet

Z
LOAD
+
-
R
F
R
F
R
S
V
+
R
G
R
G
FREQUENCY (Hz)
GAIN (dB)
10
0
-10
-20
-30
-40
1k 10k 100k
FILTER A
FILTER B
COMBINED
FILTER
LMV841, LMV842, LMV844
SNOSAT1G –OCTOBER 2006–REVISED FEBRUARY 2013 www.ti.com
Figure 41. Active Filter Curve
The responses of filter A and filter B are shown as the thin lines in Figure 41; the response of the combined filter
is shown as the thick line. Shifting the center frequencies of the separate filters farther apart, will result in a wider
band; however, positioning the center frequencies too far apart will result in a less flat gain within the band. For
wider bands more band-pass filters can be cascaded.
Tip: Use the WEBENCH internet tools at www.ti.com for your filter application.
HIGH-SIDE CURRENT SENSING
The rail-to-rail input and the low V
OS
features make the LMV841/LMV842/LMV844 ideal op amps for high-side
current sensing applications.
To measure a current, a sense resistor is placed in series with the load, as shown in Figure 42. The current
flowing through this sense resistor will result in a voltage drop, that is amplified by the op amp.
Suppose it is necessary to measure a current between 0A and 2A using a sense resistor of 100mΩ, and convert
it to an output voltage of 0 to 5V. A current of 2A flowing through the load and the sense resistor will result in a
voltage of 200mV across the sense resistor. The op amp will amplify this 200mV to fit the current range to the
output voltage range. Use the formula:
V
OUT
= R
F
/R
G
* V
SENSE
(20)
to calculate the gain needed. For a load current of 2A and an output voltage of 5V the gain would be V
OUT
/
V
SENSE
= 25.
If the feedback resistor, R
F
, is 100kΩ, then the value for R
G
will be 4kΩ. The tolerance of the resistors has to be
low to obtain a good common-mode rejection.
Figure 42. High-Side Current Sensing
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Product Folder Links: LMV841 LMV842 LMV844