LMV7291MG/NOPB National Semiconductor, LMV7291MG/NOPB Datasheet - Page 10

• Manufacturer Part Number: LMV7291MG/NOPB
• Description: IC COMPARATOR 1.8V R-R LP SC70-5
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: General Purposer

Specifications of LMV7291MG/NOPB

• Number Of Elements: 1
• Output Type: CMOS, Push-Pull, Rail-to-Rail
• Voltage - Supply: 1.8 V ~ 5 V, ±0.9 V ~ 2.5 V
• Mounting Type: Surface Mount
• Package / Case: 6-TSSOP (5 lead), SC-88A, SOT-353
• Comparator Type: General Purpose
• No. Of Comparators: 1
• Response Time: 880ns
• Ic Output Type: Push Pull
• Supply Current: 14µA
• Supply Voltage Range: 1.8V To 5V
• Amplifier Case Style: SC-70
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LMV7291MG; LMV7291MGTR

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Application Notes
BASIC COMPARATOR
A comparator is often used to convert an analog signal to a
digital signal. As shown in Figure 2, the comparator com-
pares an input voltage (V
RAIL-TO-RAIL INPUT STAGE
The LMV7291 has an input common mode voltage range
(V
achieved by using paralleled PNP and NPN differential input
pairs. When the V
PNP pair is off. When the V
and the PNP pair is on. The crossover point between the
NPN and PNP input stages is around 950mV from V
each input stage has its own offset voltage (V
the comparator becomes a function of the V
for V
tion. In application design, it is recommended to keep the
V
wide input voltage range makes LMV7291 ideal in power
supply monitoring circuits, where the comparators are used
to sense signals close to gnd and power supplies.
OUTPUT STAGE
The LMV7291 has a push-pull output stage. This output
stage keeps the total system power consumption to the
absolute minimum. The only current consumed is the low
supply current and the current going directly into the load.
When output switches, both PMOS and NMOS at the output
stage are on at the same time for a very short time. This
allows current to flow directly between V
output transistors. The result is a short spike of current
(shoot-through current) drawn from the supply and glitches
in the supply voltages. The glitches can spread to other parts
of the board as noise. To prevent the glitches in supply lines,
power supply bypass capacitors must be installed. See sec-
tion for supply bypassing in the Application Notes for details.
CM
CM
OS
) of −0.1V below the V
away from the crossover point to avoid problems. The
vs. V
CM
in Typical Performance Characteristics sec-
CM
is near V
IN
LMV7291
) to a reference voltage (V
CM
−
is near V
+
, the NPN pair is on and the
to 0.1V above V
−
, the NPN pair is off
20080025
+
FIGURE 2. LMV7291 Basic Comparator
and V
CM
OS
. See curves
), the V
+
−
. This is
+
through
REF
. Since
OS
). If
of
10
V
is greater than V
HYSTERESIS
It is a standard procedure to use hysteresis (positive feed-
back) around a comparator, to prevent oscillation, and to
avoid excessive noise on the output because the comparator
is a good amplifier of its own noise.
Inverting Comparator with Hysteresis
The inverting comparator with hysteresis requires a three
resistor network that are referenced to the supply voltage
V
input is less than V
the comparator (V
simplicity assume V
network resistors can be represented as R
R
When V
low and very close to ground. In this case the three network
resistors can be presented as R
upper trip voltage V
The total hysteresis provided by the network is defined as
A good typical value of ∆V
mV. This is easily obtained by choosing R
times (R
(R
IN
CC
2
1
. The lower input trip voltage V
||R
is less than V
of the comparator (Figure 3). When V
2
) for 1.8V operation.
IN
1
||R
is greater than V
2
) for 5V operation, or as 300 to 30 times
REF
REF
A
IN
, the voltage at the non-inverting node of
A2
O
, the output voltage (V
, the output (V
<
∆V
switches as high as V
is defined as
V
A
A
A
= V
A
), the output voltage is high (for
would be in the range of 5 to 50
(V
A1
IN
2
>
- V
//R
A1
O
V
A2
3
) is low. However, if V
is defined as
A
), the output voltage is
in series with R
1
IN
3
||R
O
) is high.
as 1000 to 100
at the inverting
CC
3
in series with
). The three
20080017
1
. The
IN