LPV7215MFX INTERSIL [Intersil Corporation], LPV7215MFX Datasheet - Page 14

• Manufacturer Part Number: LPV7215MFX
• Description: Micropower, CMOS Input, RRIO, 1.8V, Push-Pull Output Comparator
• Manufacturer: INTERSIL [Intersil Corporation]

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NON-INVERTING COMPARATOR WITH HYSTERESIS
A non-inverting comparator with hysteresis requires a two re-
sistor network, and a voltage reference (V
input. When V
to switch from low to high, V
V
As soon as V
than V
To make the comparator switch back to it’s low state, V
equal V
culated by
The hysteresis of this circuit is the difference between V
and V
IN1
FIGURE 4. Non-Inverting Comparator with Hysteresis
is calculated by.
IN2
REF
REF
.
, which is given by
before V
O
IN
switches to V
is low, the output is also low. For the output
A
ΔV
will again equal V
IN
= V
CC
IN
, V
CC
must rise up to V
R
A
will step to a value greater
1
/R
2
REF
REF
. V
) at the inverting
IN2
20123642
can be cal-
IN1
IN
20123635
where
must
IN1
14
ZERO CROSSING DETECTOR
In a zero crossing detector circuit, the inverting input is con-
nected to ground and the non-inverting input is connected to
a 100 mV
crosses 0V, the comparator’s output changes state.
To improve switching times and to center the input threshold
to ground a small amount of positive feedback is added to the
circuit. The voltage divider, R
voltage, V
tance, R
V
sistor, R
R
very small (ΔV
output voltage transitions. Diode D
inverting input terminal of the comparator never goes below
approximately −100 mV. As the input terminal goes negative,
D
approximately −700 mV. This sets up a voltage divider with
R
imum negative input overdrive is limited by the current han-
dling ability of D
2
5
1
2
, will be satisfied when V
). The resultant hysteresis established by this network is
will forward bias, clamping the node between R
and R
FIGURE 6. Zero Crossing Detector with Positive
6
1
3
PP
, is made very large with respect to R
1
plus R
preventing V
, at the positive input. By making the series resis-
FIGURE 5. Zero Crossing Detector
AC signal. As the signal at the non-inverting input
1
1
2
< 10 mV) but it is sufficient to insure rapid
.
equal to R
2
from going below ground. The max-
Feedback
IN
4
5
and R
= 0. The positive feedback re-
, the switching condition, V
1
5
is used to insure that the
, establishes a reference
20123649
5
(R
1
and R
6
20123629
= 2000
2
1
to
=