LMV7235_06 NSC [National Semiconductor], LMV7235_06 Datasheet - Page 9

• Manufacturer Part Number: LMV7235_06
• Description: 45 nsec, Ultra Low Power, Low Voltage, Rail-to-Rail Input Comparator with Open-Drain/Push-Pull Output
• Manufacturer: NSC [National Semiconductor]

Application Information
The LMV7235/LMV7239 are single supply comparators with
45ns of propagation delay and only 65µA of supply current.
The LMV7235/LMV7239 are rail-to-rail input and output. The
typical input common mode voltage range of −0.2V below
the ground to 0.2V above the supply. The LMV7235/
LMV7239 use a complimentary PNP and NPN input stage in
which the PNP stage senses common mode voltage near V
and the NPN stage senses common mode voltage near V
If either of the input signals falls below the negative common
mode limit, the parasitic PN junction formed by the substrate
and the base of the PNP will turn on resulting in an increase
of input bias current.
If one of the input goes above the positive common mode
limit, the output will still maintain the correct logic level as
long as the other input stays within the common mode range.
However, the propagation delay will increase. When both
inputs are outside the common mode voltage range, current
saturation occurs in the input stage, and the output becomes
unpredictable.
The propagation delay does not increase significantly with
large differential input voltages. However, large differential
voltages greater than the supply voltage should be avoided
to prevent damage to the input stage.
The LMV7239 has a push-pull output. When the output
switches, there is a direct path between V
causing high output sinking or sourcing current during the
transition. After the transition, the output current decreases
and the supply current settles back to about 65µA at 5V, thus
conserving power consumption.
The LMV7235 has an open drain that requires a pull-up
resistor to a positive supply voltage for the output to switch
properly. When the internal output transistor is off, the output
voltage will be pulled up to the external positive voltage.
CC
and ground,
+
−
.
9
COMPARATOR WITH HYSTERESIS
The basic comparator configuration may oscillate or produce
a noisy output if the applied differential input voltage is near
the comparator’s offset voltage. This usually happens when
the input signal is moving very slowly across the compara-
tor’s switching threshold. This problem can be prevented by
the addition of hysteresis or positive feedback.
INVERTING COMPARATOR WITH HYSTERESIS
The inverting comparator with hysteresis requires a three
resistor network that is referenced to the supply voltage V
of the comparator, as shown in Figure 1. When V
inverting input is less than V
inverting node of the comparator (V
voltage is high (for simplicity assume V
V
R1||R3 in series with R2. The lower input trip voltage V
defined as
When V
low, very close to ground. In this case the three network
resistors can be presented as R2||R3 in series with R1. The
upper trip voltage V
The total hysteresis provided by the network is defined as
To assure that the comparator will always switch fully to V
and not be pulled down by the load the resistors, values
should be chosen as follow:
CC
). The three network resistors can be represented as
V
V
Delta V
R
IN
A1
A2
PULL-UP
is greater than V
= V
= V
A
CC
CC
= V
<<
R2 / ((R1||R3) + R2)
(R2||R3) / ((R1+ (R2||R3)
A1
A2
R
- V
LOAD
is defined as
A2
A
(V
IN
A
, the voltage at the non-
>
V
A
), the output voltage is
IN
O
switches as high as
<
V
A
), the output
www.national.com
IN
at the
A1
CC
CC
is