參數(shù)資料
型號: LMV7271MGX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 比較器
英文描述: Single & Dual, 1.8V Low Power Comparators with Rail-to-Rail Input
中文描述: COMPARATOR, 4000 uV OFFSET-MAX, PDSO5
封裝: SC-70, 5 PIN
文件頁數(shù): 14/16頁
文件大?。?/td> 494K
代理商: LMV7271MGX
Typical Applications
(Continued)
NEGATIVE PEAK DETECTOR
For the negative detector, the output transistor of the com-
parator acts as a low impedance current sink. Since there is
no pull-up resistor, the only discharge path will be the 1M
resistor and any load impedance used. Decay time is
changed by varying the 1M
resistor.
SQUARE WAVE GENERATOR
A typical application for a comparator is as a square wave
oscillator. The circuit below generates a square wave whose
period is set by the RC time constant of the capacitor C
1
and
resistor R
4
. The maximum frequency is limited by the large
signal propagation delay of the comparator, and by the ca-
pacitive loading at the output, which limits the output slew
rate.
To analyze the circuit, consider it when the output is high.
That implies that the inverted input (V
C
) is lower than the
non-inverting input (V
). This causes the C
to get charged
through R
and the voltage V
increases till it is equal to the
non-inverting input. The value of V
A
at this point is
If R
1
= R
2
= R
3
then V
A1
= 2V
CC
/3
At this point the comparator switches pulling down the output
to the negative rail. The value of V
A
at this point is
If R
1
= R
2
= R
3
then V
A2
= V
CC
/3
The capacitor C
now discharges through R
, and the volt-
age V
decreases till it is equal to V
, at which point the
comparator switches again, bringing it back to the initial
stage. The time period is equal to twice the time it takes to
discharge C
from 2V
/3 to V
/3, which is given by
R
4
C
1
.ln2. Hence the formula for the frequency is:
F = 1/(2·R
4
·C
1
·ln2)
20064055
FIGURE 9. Negative Peak Detector
20064056
20064057
FIGURE 10. Squarewave Oscillator
L
www.national.com
14
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