Datasheet LMV7255M7, LMV7255M5X, LMV7255M5, LMV7251M7X, LMV7251M5X Datasheet (NSC)

January 2001

LMV7251/LMV7255

1.8V Low Voltage Comparator with Rail-to-Rail Input

LMV7251/LMV7255 1.8V Low Voltage Comparator with Rail-to-Rail Input

General Description

The LMV7251/LMV7255 are rail-to-rail input low voltage
comparators, which can operate at supply voltage range of

1.8V to 5.0V. The LMV7251/LMV7255 are available in space
saving SC-70 or SOT23-5 packages. These comparators
are ideal for low voltage and space critical designs.

The LMV7251featuresapush-pull output stage. This feature
allows operation with minimum power consumption when
driving a load.

The LMV7255 features an open drain output. This allows the
connection of an external resistor at the output. The output of
the comparator can be used as a level shifter.

The IC’s are built with National Semiconductor’s advance
Submicron Silicon-Gate BiCMOS process. The
LMV7251/LMV7255 have bipolar inputs for improved noise
performance and CMOS outputs for better rail-to-rail output
performance.

Features

(VS= 1.8V, TA= 25˚C, Typical values unless specified).

n Single or Dual Supplies
n Low supply voltage 1.8V to 5.0V
n Ultra low supply current 11µA
n Low input bias current 14nA
n Low input offset current 200pA
n Low input offset voltage +/−0.3mV
n Response time 670ns (20mV overdrive)
n Input common mode voltage 0.1V beyond rails

Applications

n Mobile communications
n Laptops and PDA’s
n Battery powered electronics
n General purpose low voltage applications

Typical Circuit Connection Diagram

DS200057-1

Top View

DS200057-2

FIGURE 1. Threshold Detector

© 2001 National Semiconductor Corporation DS200057 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/

Wave Soldering (10 sec.) 260˚C
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) +150˚C

Distributors for availability and specifications.

ESD Tolerance 1KV (Note 2)

LMV7251/LMV7255

V

Differential +/−Supply Voltage

IN

Supply Voltage (V
Voltage at Input/Output pins V

+-V−

) 5.5V

+

+0.1V, V−−0.1V

Soldering Information

Infrared or Convection (20

200V (Note 6)

Operating Ratings (Note 1)

Supply Voltage V
Junction Temperature Range (Note

3) −40˚C to +85˚C

Package Thermal Resisance (Note 3)

SOT23-5 325˚C/W

SC-70 265˚C/W

+

sec.) 235˚C

1.8V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 1.8V, V−= 0V. Boldface limits apply at the temperature
extremes.

Symbol Parameter Condition Typ

(Note 4)

V

OS

TC V
I

B

I

OS

I

S

I

SC

Input Offset Voltage 0.3 6

Input Offset Average Drift VCM= 0.9V (Note 7) 10 uV/C

OS

Input Bias Current 14 nA
Input Offset Current 200 pA
Supply Current 11 15

Output Short Circuit Current Sourcing, VO= 0.9V

(LMV7251 only)

= 0.9V 11.6 5

O

300 pA

I

LEAKAGE

Sinking, V

Output Leakage Current VO= 1.8V

(LMV7255 only)

V

OH

Output Voltage High IO= 1.5mA

1.72 1.675 V

(LMV7251 only)

V

OL

V

CM

CMRR Common Mode Rejection Ratio 0

PSRR Power Supply Rejection Ratio V

Output Voltage Low IO= −1.5mA 65 125 mV

Input Common Voltage Range CMRR>45 dB 1.9 V

<

<

V

1.8V 72 47 dB

CM

+

= 1.8V to 5V 79 55 dB

84

Limits

(Note 5)

8

17

−0.1 V

1.8V to 5.0V

Units

mV

max

µA

max

mA

min

min

max

max

min

min

min

1.8V AC Electrical Characteristics

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 1.8V, V−= 0V, VCM= 0.5V, VO=V+/2. Boldface limits
apply at the temperature extremes.

Symbol Parameter Condition Typ

t

PHL

Propagation Delay
(High to Low)

Input Overdrive = 20mV
Load = 50pF//5kΩ

Input Overdrive = 50mV
Load = 50pF//5kΩ

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(Note 5)

720 ns

380 ns

Limits

(Note 6)

Units

1.8V AC Electrical Characteristics (Continued)

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 1.8V, V−= 0V, VCM= 0.5V, VO=V+/2. Boldface limits
apply at the temperature extremes.

Symbol Parameter Condition Typ

(Note 5)

t

PLH

Propagation Delay
(Low to High)

Input Overdrive = 20mV
Load = 50pF//5kΩ

Input Overdrive = 50mV

670 ns

400 ns

Limits

(Note 6)

Load = 50pF//5kΩ

2.7V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 2.7V, V−= 0V. Boldface limits apply at the temperature
extremes.

Symbol Parameter Conditions Typ

(Note 5)

V

OS

TC V
I

B

I

OS

I

S

I

SC

Input Offset Voltage 0.03 6

Input Offset Average Drift VCM= 1.35V (Note 7) 10 µV/C

OS

Input Bias Current 15 nA
Input offset Current 210 pA
Supply Current 11 18

Output Short Circuit Current Sourcing, VO= 1.35V

(LMV7251 only)

I

LEAKAGE

Sinking, V

Output Leakage Current VO= 2.7V,

= 1.35V 28 15

O

320 pA

(LMV7255 only)

V

OH

Output Voltage High IO= 2mA

2.63 2.575 V

(LMV7251 only)

V

OL

V

CM

CMRR Common Mode Rejection Ratio 0

PSRR Power Supply Rejection Ratio V

Output Voltage Low IO= −2mA 61 125 mV

Input Common Voltage Range CMRR>45dB 2.8 V

<

<

V

2.7V 75 46 dB

CM

+

= 1.8V to 5V 79 55 dB

28 15

Limits

(Note 6)

8

22

−0.1 V

LMV7251/LMV7255

Units

Units

mV

max

µA

max

mA

min

max

max

min

min

min

2.7V AC Electrical Characteristics

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 2.7V, V−= 0V.Boldface limits apply at the temperature
extremes.

Symbol Parameter Condition Typ

(Note 5)

t

PHL

Propagation Delay
(High to Low)

Input Overdrive = 20mV
Load = 50pF//5kΩ

Input Overdrive = 50mV

830 ns

430 ns

Load = 50pF//5kΩ

t

PLH

Propagation Delay
(Low to High)

Input Overdrive = 20mV
Load = 50pF//5kΩ

Input Overdrive = 50mV

730 ns

410 ns

Load = 50pF//5kΩ

Limits

(Note 6)

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Units

5V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for TJ= 25˚C, V+= 5V, V−= 0V. Boldface limits apply at the temperature ex­tremes.

Symbol Parameter Conditions Typ

(Note 5)

V

OS

Input Offset Voltage 0.03 6

LMV7251/LMV7255

TC V
I

B

I

OS

I

S

I

SC

I

LEAKAGE

V

OH

V

OL

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.

Note 2: Human body model, 1.5kΩ in series with 100pF.
Note 3: The maximum power dissipation is a function of T

=(T

P

D

Note 4: Typical values represent the most likely parametric norm.
Note 5: All limits are guaranteed by testing or statistical analysis.
Note 6: Machine Model, 0Ω in series with 200pF.
Note 7: Offset Voltage average drift determined by dividing the change in V

Input Offset Average Drift VCM= 2.5V (Note 7) 10 µV/C

OS

Input Bias Current 16 nA
Input Offset Current 220 pA
Supply Current 12 20

Output Short Circuit Current Sourcing, VO= 2.5V

82 50

(LMV7251 only)
Sinking, V

Output Leakage Current VO= 5V,

= 2.5V 78 50

O

375 pA

(LMV7255 only)

Output Voltage High IO= 4mA 4.9 4.82 V

Output Voltage Low IO= −4mA 90 180 mV

, θJA, and TA. The maximum allowable power dissipation at any ambient temperature is

J(max)-TA

)/θJA. All numbers apply for packages soldered directly into a PC board.

J(max)

at temperature extremes into the total temperature change.

OS

Limits

(Note 6)

8

25

Units

mV

max

µA

max

mA
min

min

max

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LMV7251/LMV7255

Typical Performance Characteristics (T

Short Circuit Current vs. Supply Voltage

DS200057-3

Output Voltage vs. Supply Voltage

= 25˚C, Unless otherwise specified).

A

Supply Current vs. Supply Voltage

Output Voltage vs. Supply Voltage

DS200057-4

DS200057-5

Output Voltage vs. Output Current@1.8V Supply
Voltage

DS200057-7

DS200057-6

Output Voltage vs. Output Current@1.8V Supply
Voltage

DS200057-8

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Typical Performance Characteristics (T

= 25˚C, Unless otherwise specified). (Continued)

A

Output Voltage vs. Output Current
Voltage

LMV7251/LMV7255

Response Time for Various Input Overdrives - t

@

2.7V Supply

DS200057-9

PLH

Output Voltage vs. Output Current@2.7V Supply
Voltage

DS200057-10

Response Time for Various Input Overdrives - t

PHL

DS200057-11

Response Time for Various Input Overdrives - t

PLH

DS200057-13

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DS200057-12

Response Time for Various Input Overdrives - t

DS200057-14

PHL

Application Info

Basic Comparators

A comparator is quite often used to convert an analog signal
to a digital signal. The comparator compares an input volt­age (V
(V
(V
output voltage (V

) at the non-inverting pin to the reference voltage

IN

) at the inverting pin. If VINis less than V

REF

) is low (VOL). However, if VINis greater than V

O

) is high (VOH).

O

REF

LMV7251

DS200057-15

LMV7255

the output

, the

REF

hysteresis causes one input to effectively move quickly pass
the other. Thus, effectively moving the input out of region that
oscillation may occur.

Hysteresis can easily be added to a comparator in a
non-inverting configuration with two resistors and positive
feedback
when V

The output will switch from high to low when V
where V

The Hysteresis is the difference between V
∆V

R2)-V

Figure 3

rises up to V

IN

V

=(V

IN1

IN2

V

IN2

IN=VIN1-VIN2

CC

REF

is calculated by
=(V

REF

R1) / R2) = VCCR1/ R2.

. The output will switch from low to high

, where V

IN1

is calculated by

IN1

(R1 + R2))/ R2

falls to V

IN

IN2

(R1+R2)-VCCR1)/R2

= ((V

(R1 + R2)) / R2) - ((V

REF

IN1

and V

REF

.

IN2

(R1 +

LMV7251/LMV7255

,

DS200057-16

Input/Output

DS200057-17

FIGURE 2. Basic Comparator

Hysteresis

The basic comparator configuration may oscillate or produce
a noisy output if the applied differential input is near the
comparator’s input offset voltage. This tends to occur when
the voltage on the input is equal or very close to the other
input voltage. Adding hysteresis can prevent this problem.
Hysteresis creates two switching thresholds (one for the
rising input voltage and the other for the falling input volt­age). Hysteresis is the voltage difference between the two
switching thresholds. When both inputs are nearly equal,

DS200057-18

DS200057-19

FIGURE 3. Non-Inverting Comparator Configuration —

LMV7251

For an inverting configured comparator, hysteresis can be
added with a three resistor network and positive feedback.
When input voltage (V
non-inverting node (V

) at the inverting node is less than

IN

), the output is high. The equivalent

T

circuit for the three resistor network is R1 in parallel with R3
and in series with R2. The lower threshold voltage V

T1

calculated by:

V

= ((VCCR2) / ((R1 R3) / (R1+ R3)) + R2)

T1

When V

is greater than VT, the output voltage is low. The

IN

equivalent circuit for the three resistor network is R2 in
parallel with R3 and in series with R1. The upper threshold
voltage V

V

T2=VCC

is calculated by:

T2

((R2 R3) / (R2 + R3)) / ((R1 + ((R2 R3) / (R2 +

R3))
The hysteresis is defined as
∆V

IN=VT1-VT2

(V

((R2 R3) / (R2 + R3)) / ((R1 + ((R2 R3) / (R2 + R3)))

CC

= ((VCCR2) / ((R1 R3) / (R1+ R3)) + R2) –

is

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Application Info (Continued)

LMV7251/LMV7255

DS200057-20

Power supply decoupling is critical and improves stability.
Place decoupling capacitors 0.1µF as close as possible to

+

the V

pin. For split supply applications, place decoupling

capacitors 0.1µF on both the V

+

and V−pins. The decoupling
capacitors will help keep the comparator from oscillating
under various load conditions.

DS200057-21

FIGURE 4. Inverting Configured Comparator —

LMV7255

Input Stage

The LMV7251 and LMV7255 have rail-to-rail input stages.
The input common mode voltage range is from −100mV to
(V

+ 100mV).

CC

Output Stage

The LMV7251 has a push-pull CMOS output stage. Large
push-pull output drivers allows rail-to-rail output swings with
load currents in the miliampere range.

The LMV7255 has a open drain CMOS output stage. This
requires an external pull-up resistor connected between the
positive supply voltage and the output. The external pull-up
resistor should be high enough resistance so to avoid exces­sive power dissipation. In addition, the pull-up resistor
should be low enough resistance to enable the comparator
to switch with the load circuitry connected.

Power Supply Considerations

The LMV7251/LMV7255 are well suited for many battery­powered applications. The LMV7251/LMV7255 can operate
from single power supply of +1.8V to +5V. The device typi­cally consumes only 11µA with a 2.7V supply. With a high
power supply rejection ratio (PSRR) of 79 dB (typical), the
comparator is well suited for operating under conditions of a
decaying battery voltage.

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Ordering Information

Package Ordering Info Pkg Marking Supplied As NSC Drawing

5-Pin SOT23-5 LMV7251M5 C16A 1k Units Tape and Reel MF05A

LMV7251M5X C16A 3k units Tape and Reel

LMV7255M5 C18A 1k Units Tape and Reel

LMV7255M5X C18A 3k units Tape and Reel

5-Pin SC-70 LMV7251M7 C17 1k Units Tape and Reel MAA05A

LMV7251M7X C17 3k units Tape and Reel

LMV7255M7 C19 1k Units Tape and Reel

LMV7255M7X C19 3k units Tape and Reel

LMV7251/LMV7255

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Physical Dimensions inches (millimeters) unless otherwise noted

LMV7251/LMV7255

5-Pin SC70-5

NS Package Number MAA05A

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Physical Dimensions inches (millimeters) unless otherwise noted

LMV7251/LMV7255 1.8V Low Voltage Comparator with Rail-to-Rail Input

5-Pin SOT23-5

NS Package Number MF05A

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