參數(shù)資料
型號: LMV7239
廠商: National Semiconductor Corporation
英文描述: 45ns, Ultra Low Power, Low Voltage, Rail-to-Rail Input Comparator with Open-Drain/Push-Pull Output
中文描述: 45ns,超低功耗,低電壓軌至軌輸入輸出比較器Open-Drain/Push-Pull
文件頁數(shù): 9/12頁
文件大?。?/td> 320K
代理商: LMV7239
Application Section
(Continued)
Non-Inverting Comparator with Hysteresis
A non inverting comparator with hysteresis requires a two
resistor network, and a voltage reference (V
) at the in-
verting input. When V
is low, the output is also low. For the
output to switch from low to high, V
IN
must rise up to V
IN1
where V
IN1
is calculated by.
V
IN1
= R1*(V
REF
/R2) + V
REF
When V
is high, the output is also high, to make the
comparator switch back to it’s low state, V
must equal V
before V
A
will again equal V
REF
. V
IN
can be calculated by
V
IN2
= (V
REF
(R1+ R2) - V
CC
R1)/R2
The hysteresis of this circuit is the difference between V
IN1
and V
IN2
.
Delta V
IN
= V
CC
R1/R2
Circuit Layout and Bypassing
The LMV7235/39 require high speed layout. Follow these
layout guidelines:
1. Use printed circuit board with a good, unbroken low-
inductance ground plane.
2. Place a decoupling capacitor (0.1μF ceramic surface
mount capacitor) as close as possible to V
CC
pin.
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 para-
sitic feedback. A small capacitor (1000pF or less) placed
between the inputs can help eliminate oscillations in the
transition region. This capacitor causes some degradation to
t
PD
when the source impedance is low.
6. The topside ground plane runs between the output and
inputs.
7. Ground trace from the ground pin runs under the device
up to the bypass capacitor, shielding the inputs from the
outputs.
10135919
FIGURE 1.
10135924
10135920
FIGURE 2. Non-Inverting Comparator with Hysteresis
L
www.national.com
9
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