Datasheet LMH6647MAX, LMH6647MA, LMH6645MF, LMH6645MA, LMH6645MFX Datasheet (NSC)

LMH6645/46/47

2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output
Amplifiers with Shutdown Option

February 2002

LMH6645/46/47 2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output Amplifiers with Shutdown

Option

General Description

The LMH6645 (single) and LMH6646 (dual), rail-to-rail input
and output voltage feedback amplifiers, offer high speed
(55MHz), and low voltage operation (2.7V) in addition to
micro-power shutdown capability (LMH6647, single).

Input common modevoltage range exceeds either supply by

0.3V, enhancing ease of use in multitude of applications
where previously only inferior devices could be used. Output
voltage range extends to within 20mV of either supply rails,
allowing wide dynamic range especially in low voltage appli­cations. Even with low supply current of 650µA/amplifier,
output current capability is kept at a respectable
driving heavier loads. Important device parameters such as
BW, Slew Rate and output current are kept relatively inde­pendent of the operating supply voltage by a combination of
process enhancements and design architecture.

In portable applications, the LMH6647 provides shutdown
capability while keeping the turn-off current to less than
50µA. Both turn-on and turn-off characteristics are well be­haved with minimal output fluctuations during transitions.
This allows the part to be used in power saving mode, as
well as multiplexing applications. Miniature packages
(SOT23, MSOP-8, and SO-8) are further means to ease the
adoption of these low power high speed devices in applica­tions where board area is at a premium.

±

20mA for

Connection Diagrams

Features

(VS= 2.7V, TA= 25˚C, RL=1kΩto V+/2, AV= +1. Typical
values unless specified).

n −3dB BW 55MHz
n Supply voltage range 2.5V to 12V
n Slew rate 22V/µs
n Supply current 650µA/channel
n Output short circuit current 42mA
n Linear output current
n Input common mode voltage 0.3V beyond rails
n Output voltage swing 20mV from rails
n Input voltage noise 17nV/

n Input current noise 0.75pA/

±

20mA

Applications

n Active filters
n High speed portable devices
n Multiplexing applications (LMH6647)
n Current sense buffer
n High speed transducer amp

SOT23-5 (LMH6645) SOT23-6 (LMH6647) SOIC-8 (LMH6645)

Top View

20020259

© 2002 National Semiconductor Corporation DS200202 www.national.com

Top View

20020260

Top View

20020261

Connection Diagrams (Continued)

SOIC-8 (LMH6647)

LMH6645/46/47

SOIC-8 and MSOP-8

(LMH6646)

20020263

Top View

20020262

Top View

Ordering Information

Package Part Number Package Marking Transport Media NSC Drawing

5-Pin SOT-23 LMH6645MF A68A 1k Units Tape and Reel MF05A

LMH6645MFX 3k Units Tape and Reel

6-Pin SOT-23 LMH6647MF A69A 1k Units Tape and Reel MF06A

LMH6647MFX 3k Units Tape and Reel

SOIC-8 LMH6645MA LMH6645MA 95 Units Rails M08A

LMH6645MAX 2.5k Units Tape and Reel

LMH6646MA LMH6646MA 95 Units Rails

LMH6646MAX 2.5k Units Tape and Reel

LMH6647MA LMH6647MA 95 Units Rails

LMH6647MAX 2.5k Units Tape and Reel

MSOP-8 LMH6646MM A70A 1k Units Tape and Reel MUA08A

LMH6646MMX 3.5k Units Tape and Reel

www.national.com 2

LMH6645/46/47

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

ESD Tolerance

Human Body 2KV (Note 2)
Machine Model 200V (Note 9)

V

Differential

IN

Output Short Circuit Duration (Note 3, 11)
Supply Voltage (V
Voltage at Input/Output pins V

+-V−

) 12.6V

+

+0.8V, V−−0.8V
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) +150˚C

±

2.5V

Soldering Information

Infrared or Convection (20 sec) 235˚C
Wave Soldering (10 sec) 260˚C

Operating Ratings (Note 1)

Supply Voltage (V
Junction Temperature Range (Note 4) −40˚C to +85˚C

Package Thermal Resistance (Note 4) (θ

SOT23-5 265˚C/W
SOT23-6 265˚C/W
SOIC-8 190˚C/W
MSOP-8 235˚C/W

+–V−

) 2.5V to 12V

)

JA

2.7V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 2.7V, V−= 0V, VCM=VO=V+/2, and Rf=2kΩ, and R
=1kΩto V+/2. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)

BW −3dB BW A

e

n

Input-Referred Voltage Noise f = 100kHz 17

V

V

CM

= +1, V

= 0.7V

= 200mVPP,

OUT

f = 1kHz 25

i

n

Input-Referred Current Noise f = 100kHz 0.75

f = 1kHz 1.20

CT Rej. Cross-Talk Rejection

(LMH6646 only)

SR Slew Rate A

f = 5MHz, Receiver:
R

= 510Ω,AV=+2

f=Rg

= −1, VO=2V

V

PP

(Note 8, 13)

T

ON

Turn-On Time
(LMH6647 only)

T

OFF

Turn-Off Time
(LMH6647 only)

TH

SD

Shutdown Threshold

IS≤ 50µA 1.95 2.30

(LMH6647 only)

I

SD

Shutdown Pin Input Current

(Note 7) −20 µA

(LMH6647 only)

V

OS

TC V
I

B

I

OS

R

IN

Input Offset Voltage 0V ≤ VCM≤ 2.7V −3

Input Offset Average Drift (Note 12)

OS

Input Bias Current VCM= 2.5V (Note 7) 0.40 2

= 0.5V (Note 7) −0.68 −2

V

CM

Input Offset Current 0V ≤ VCM≤ 2.7V 1 500 nA
Common Mode Input

Resistance

C

IN

Common Mode Input
Capacitance

CMVR Input Common-Mode Voltage

CMRR ≥ 50dB −0.5 −0.3

Range

40 55 MHz

15 22 V/µs

−4

3.0

2.8

Typ

(Note 5)

Max

(Note 6)

Units

nV/

pA/

47 dB

250 ns

560 ns

±

13

4

±

5 µV/˚C

2.2

−2.2

3MΩ

2pF

−0.1

3.2

L

V

mV

µA

V

www.national.com3

2.7V Electrical Characteristics (Continued)

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 2.7V, V−= 0V, VCM=VO=V+/2, and Rf=2kΩ, and R
=1kΩto V+/2. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

LMH6645/46/47

CMRR Common Mode Rejection

Ratio

A

VOL

V

O

Large Signal Voltage Gain VO= 0.35V to 2.35V 76

Output Swing

High

Output Swing

Low

I

I

SC

OUT

Output Short Circuit Current Sourcing to V

Output Current V

PSRR Power Supply Rejection Ratio V

I

S

Supply Current (per channel) Normal Operation 650 1250

V

Stepped from 0V to 2.7V 46 77

CM

Stepped from 0V to 1.55V 58 76

V

CM

RL=1ktoV+/2 2.55 2.66

= 10k to V+/2 2.68

R

L

R

=1ktoV+/2 40 150

L

= 10k to V+/2 20

R

L

−

VID= 200mV (Note 10)
Sinking to V

+

VID= −200mV (Note 10)

= 0.5V from rails

OUT
+

= 2.7V to 3.7V or

−

=0Vto−1V

V

Shutdown Mode (LMH6647 only) 15 50

(Note 6)

74

75 83 dB

Typ

(Note 5)

Max

(Note 6)

87 dB

43

42

±

20 mA

L

Units

dB

V

mV

mA

µA

5V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 5V, V−= 0V, VCM=VO=V+/2, and Rf=2kΩ, and R
=1kΩto V+/2. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)
BW −3dB BW A
e

n

Input-Referred Voltage Noise f = 100kHz 17

= +1, V

V

OUT

= 200mV

PP

f = 1kHz 25

i

n

Input-Referred Current Noise f = 100kHz 0.75

f = 1kHz 1.20

CT Rej. Cross-Talk Rejection

(LMH6646 only)

SR Slew Rate A

f = 5MHz, Receiver:
R

= 510Ω,AV=+2

f=Rg

= −1, VO=2V

V

PP

(Note 8, 13)
T
T
TH

ON
OFF

SD

Turn-On Time (LMH6647 only) 210 ns
Turn-Off Time (LMH6647 only) 500 ns
Shutdown Threshold

IS≤ 50µA 4.25 4.60 V

(LMH6647 only)

I

SD

Shutdown Pin Input Current

(Note 7)

(LMH6647 only)

V

OS

TC V
I

B

I

OS

R

IN

Input Offset Voltage 0V ≤ VCM≤ 5V −3

Input Offset Average Drift (Note 12)

OS

Input Bias Current VCM= 4.8V (Note 7)

= 0.5V (Note 7)

V

CM

Input Offset Current 0V ≤ VCM≤ 5V 1 500 nA
Common Mode Input

Resistance

40 55 MHz

15 22

−4

Typ

(Note 5)

Max

(Note 6)

nV/

pA/

47 dB

−20 µA

±

1

±

5 µV/C

+0.36

−0.68

3

4

+2

−2.2

−2

−2.2

3MΩ

L

Units

V/µs

mV

µA

www.national.com 4

5V Electrical Characteristics (Continued)

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 5V, V−= 0V, VCM=VO=V+/2, and Rf=2kΩ, and R
=1kΩto V+/2. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)

C

IN

Common Mode Input
Capacitance

CMVR Input Common-Mode Voltage

CMRR ≥ 50dB −0.5 −0.3

Range

CMRR Common Mode Rejection

Ratio

A

VOL

V

O

Large Signal Voltage Gain VO= 1.5V to 3.5V 76

Output Swing

High

Output Swing

Low

I

SC

Output Short Circuit Current Sourcing to V

Stepped from 0V to 5V 56 82

V

CM

Stepped from 0V to 3.8V 66 85

V

CM

RL=1ktoV+/2 4.80 4.95

= 10k to V+/2 4.98

R

L

R

=1ktoV+/2 50 200

L

= 10k to V+/2 20

R

L

−

VID= 200mV (Note 10)
Sinking to V

+

VID= −200mV (Note 10)

I

OUT

Output Current V
PSRR Power Supply Rejection Ratio V
I

S

Supply Current (per channel) Normal Operation 700 1400

= 0.5V From rails

OUT
+

=5Vto6VorV−= 0V to −1V 75 95 dB

Shutdown Mode (LMH6647 only) 10 50

5.3

5.1

74

Typ

(Note 5)

Max

(Note 6)

2pF

−0.1

5.5

85

55

53

±

20 mA

LMH6645/46/47

L

Units

V

dB

dB

V

mV

mA

µA

±

5V Electrical Characteristics

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 5V, V−= −5V, VCM=VO= 0V, Rf=2kΩ, and RL=
1kΩ to GND. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

(Note 6)
BW −3dB BW A
e

n

Input-Referred Voltage Noise f = 100kHz 17

= +1, V

V

OUT

= 200mV

PP

40 55 MHz

Typ

(Note 5)

Max

(Note 6)

f = 1kHz 25

i

n

Input-Referred Current Noise f = 100kHz 0.75

f = 1kHz 1.20

CT Rej. Cross-Talk Rejection

(LMH6646 only)
SR Slew Rate A
T
T
TH

ON
OFF

SD

Turn-On Time (LMH6647 only) 200 ns

Turn-Off Time (LMH6647 only) 700 ns

Shutdown Threshold

(LMH6647 only)
I

SD

Shutdown Pin Input Current

f = 5MHz, Receiver:
R

= 510Ω,AV=+2

f=Rg

= −1, VO=2VPP(Note 8) 15 22 V/µs

V

IS≤ 50µA

47 dB

4.25 4.60

(Note 7) −20 µA

(LMH6647 only)
V

OS

TC V

Input Offset Voltage −5V ≤ VCM≤ 5V −3

Input Offset Average Drift (Note 12)

OS

−4

±

1

±

5 µV/˚C

3

4

Units

nV/

pA/

V

mV

www.national.com5

±

5V Electrical Characteristics (Continued)

Unless otherwise specified, all limits guaranteed for at TJ= 25˚C, V+= 5V, V−= −5V, VCM=VO= 0V, Rf=2kΩ, and RL=
1kΩ to GND. Boldface limits apply at the temperature extremes.

Symbol Parameter Conditions Min

LMH6645/46/47

I

B

I

OS

R

IN

Input Bias Current VCM= 4.8V (Note 7)

= −4.5V (Note 7)

V

CM

Input Offset Current −5V ≤ VCM≤ 5V 3 500 nA
Common Mode Input

(Note 6)

Typ

(Note 5)

+0.40

−0.65

Max

(Note 6)

+2

+2.2

−2

−2.2

3MΩ

Resistance

C

IN

Common Mode Input

2pF

Capacitance

CMVR Input Common-Mode Voltage

Range

CMRR ≥ 50dB −5.5 −5.3

−5.1

5.3

5.5

5.1

CMRR Common Mode Rejection

Ratio

A

VOL

Large Signal Voltage Gain VO= −2V to 2V 76

Stepped from −5V to 5V 60 84

V

CM

Stepped from −5V to 3.5V 66 104

V

CM

85

74

V

O

I

SC

I

OUT

PSRR Power Supply Rejection Ratio V
I

S

Output Swing

High

Output Swing

Low

Output Short Circuit Current Sourcing to V

Output Current V

RL=1kΩ 4.70 4.92

= 10kΩ 4.97

R

L

R

=1kΩ −4.93 −4.70

L

= 10kΩ −4.98

R

L

VID= 200mV (Note 10)
Sinking to V

VID= −200mV (Note 10)

OUT
+

=5Vto6VorV−= −5V to −6V 76 95 dB

−

+

= 0.5V from rails

66

61

±

20 mA

Supply Current (per channel) Normal Operation 725 1600

Shutdown Mode (LMH6647 only) 10 50

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: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the

maximum allowed junction temperature of 150˚C.
Note 4: The maximum power dissipation is a function of T

=(T

P

D

J(MAX)-TA

Note 5: Typical values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: Positive current corresponds to current flowing into the device.
Note 8: Slew rate is the average of the rising and falling slew rates.
Note 9: Machine Model, 0Ω in series with 200pF.
Note 10: Short circuit test is a momentary test. See Note 11.
Note 11: Output short circuit duration is infinite for V
Note 12: Offset voltage average drift determined by dividing the change in V
Note 13: Guaranteed based on characterization only.

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

<

6V at room temperature and below. For V

S

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

J(MAX)

>

6V, allowable short circuit duration is 1.5ms.

at temperature extremes into the total temperature change.

OS

S

Units

µA

V

dB

dB

V

V

mA

µA

www.national.com 6

LMH6645/46/47

Typical Performance Characteristics At T

Closed Loop Frequency Response for Various

Temperature Frequency Response for Various A

20020249

Open Loop Gain/Phase vs. Frequency for Various

Temperature THD vs. Output Swing

= 25˚C. Unless otherwise specified.

J

V

20020248

20020250 20020253

THD vs. Output Swing Output Swing vs. Frequency

20020254 20020255

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Typical Performance Characteristics At T

Settling Time vs. Step Size Noise vs. Frequency

LMH6645/46/47

20020252 20020234

V

from V+vs. I

OUT

SOURCE

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

J

V

from V−vs. I

OUT

SINK

20020237

20020238

Output Swing from V+vs. RL(tied to VS/2) Output Swing from V+vs. RL(tied to VS/2)

20020202 20020206

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LMH6645/46/47

Typical Performance Characteristics At T

Output Swing from V

Output Swing from V−vs. RL(tied to VS/2) Output Swing from V−vs. RL(tied to VS/2)

+

vs. RL(tied to VS/2) Output Swing from V−vs. RL(tied to VS/2)

20020204 20020203

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

J

20020207

Cap Load Tolerance and Setting Time vs. Closed Loop

Gain Z

20020201 20020216

vs. Frequency

OUT

20020205

www.national.com9

Typical Performance Characteristics At T

PSRR vs. Frequency CMRR vs. Frequency

LMH6645/46/47

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

J

20020247

Crosstalk Rejection vs. Frequency (Output to Output)

(LMH6646) V

20020257

VOSvs. VS(A Typical Unit) VOSvs. V

Distribution

OS

(A Typical Unit)

OUT

20020251

20020225

20020218

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20020228

LMH6645/46/47

Typical Performance Characteristics At T

V

vs. V

OS

VOSvs. VCM(A Typical Unit) VOSvs. VCM(A Typical Unit)

(A Typical Unit) VOSvs. VCM(A Typical Unit)

OUT

20020229 20020231

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

J

IBvs. V

CM

20020230 20020232

IBvs. V

20020226 20020219

CM

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Typical Performance Characteristics At T

I

vs. V

B

S

LMH6645/46/47

20020227 20020223

IS(mA) (per channel) ISvs. V

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

J

ISvs. V

CM

SHUTDOWN

(LMH6647)

20020224 20020221

ISvs. V

SHUTDOWN

(LMH6647) ISvs. V

20020220

www.national.com 12

SHUTDOWN

(LMH6647)

20020222

LMH6645/46/47

Typical Performance Characteristics At T

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

J

Shutdown Pin and Supply Current vs. Shutdown Voltage Small Signal Step Response

20020208

Large Signal Step Response Large Signal Step Response

20020243

Output Overload Recovery

20020244 20020245

20020246

www.national.com13

Application Notes

Circuit Description:

The LMH6645/6646/6647 family is based on National Semi­conductor’s proprietary VIP10 dielectrically isolated bipolar
process.

LMH6645/46/47

This device family architecture features the following:

Complimentary bipolar devices with exceptionally high f

•

(∼8GHz) even under low supply voltage (2.7V) and low
Collector bias current.

Rail-to-Rail input which allows the input common mode

•

voltage to go beyond either rail by about 0.5V typically.
A class A-B “turn-around” stage with improved noise,

•

offset, and reduced power dissipation compared to simi­lar speed devices (patent pending).

Common Emitter push-pull output stage capable of 20mA

•

output current (at 0.5V from the supply rails) while con­suming only ∼700µA of total supply current per channel.
This architecture allows output to reach within milli-volts
of either supply rail at light loads.

Consistent performance from any supply voltage

•

(2.7V-10V) with little variation with supply voltage for the
most important specifications (e.g. BW, SR, I

Application Hints:

The total input common mode voltage range, which extends
from below V
a NPN stage. The NPN stage is switched on whenever the
input is less than 1.2V from V
rest of the range. In terms of the input voltage, there is an
overlapping region where both stages are processing the
input signal. This region is about 0.5V from beginning to the
end. As far as the device application is concerned, this
transition is a transparent operation. However, keep in mind
that the input bias current value and direction will depend on
which input stage is operating (see typical performance
characteristics for plots). For low distortion applications, it is
best to keep the input common mode voltage from transvers­ing this transition point. Low gain settling applications, which
generally encounter larger peak-to-peak input voltages,
could be configured as inverting stages to eliminate common
mode voltage fluctuations.

In terms of the output, when the output swing approaches
either supply rail, the output transistor will enter a
Quasi-saturated state. A subtle effect of this operational
region is that there is an increase in supply current in this
state (up to 1mA). The onset of Quasi-saturation region is a
function of output loading (current) and varies from 100mV at
no load to about 1V when output is delivering 20mA, as
measured from supplies. Both input common mode voltage
and output voltage level effect the supply current (see typical
performance characteristics for plot).

With 2.7V supplies and a common mode input voltage range
that extends beyond either supply rail, the
LMH6645/6646/6647 family is well suited to many low
voltage/low power applications. Even with 2.7V supplies, the

−

to beyond V+, is covered by both a PNP and

+

and the PNP stage covers the

OUT

, etc.)

−3dB BW (

@

AV= +1) is typically 55MHz with a tested limit
of 45MHz. Production testing guarantees that process varia­tions will not compromise speed.

This device family is designed to avoid output phase rever­sal. With input over-drive, the output is kept near the supply

t

rail (or as close to it as mandated by the closed loop gain
setting and the input voltage).

Figure 1

, below, shows the
input and output voltage when the input voltage significantly
exceeds the supply voltages:

20020233

FIGURE 1. Input/Output Shown with Exceeded Input

CMVR

As can be seen, the output does not exhibit any phase
reversal as some op amps do. However, if the input voltage
range is exceeded by more than a diode drop beyond either
rail, the internal ESD protection diodes will start to conduct.
The current flow in these ESD diodes should be externally
limited.

LMH6647
Micro-power Shutdown

The LMH6647 can be shutdown to save power and reduce
its supply current to less than 50µAguaranteed, by applying
a voltage to the SD pin. The SD pin is “active high” and
needs to be tied to V
current (
to V

<

20µA, 4pF equivalent capacitance) and a resistor

−

(≤20kΩ) will result in normal operation. Shutdown is

guaranteed when SD pin is 0.4V or less from V

−

for normal operation. This input is low

+

at any

operating supply voltage and temperature.
In the shutdown mode, essentially all internal device biasing

is turned off in order to minimize supply current flow and the
output goes into Hi-Z (high impedance) mode. Complete
device Turn-on and Turn-off times vary considerably relative
to the output loading conditions, output voltage, and input
impedance, but is generally limited to less than 1µs (see
tables for actual data).

www.national.com 14

Application Notes (Continued)

During shutdown, the input stage has an equivalent circuit as
shown below in

FIGURE 2. LMH6647 Equivalent Input in Shutdown

As can be seen above, in shutdown, there may be current
flow through the internal diodes shown, caused by input
potential, if present. This current may flow through the exter­nal feedback resistor and result in an apparent output signal.
In most shutdown applications the presence of this output is
inconsequential. However, if the output is “forced” by another
device such as in a multiplexer, the other device will need to
conduct the current described in order to maintain the output
potential.

To keep the output at or near ground during shutdown when
there is no other device to hold the output low, a switch
(transistor) could be used to shunt the output to ground.

Figure 3

the output near ground (∼80mV):

Figure 2

20020256

Mode

shows a circuit where a NPN bipolar is used to keep

Figure 4

shows the output waveform.

20020236

FIGURE 4. Output Held Low by Active Pull-Down

Circuit

If bipolar transistor power dissipation is not tolerable, the
switch could be by a N-channel enhancement mode MOS­FET.

2.7V Single Supply RRIO 2:1 MUX:

The schematic show in

Figure 5

will function as a 2:1 MUX
operating on a single 2.7V power supply, by utilizing the
shutdown feature of the LMH6647:

LMH6645/46/47

20020264

FIGURE 3. Active Pull-Down Schematic

20020258

FIGURE 5. 2:1 MUX Operating off a 2.7V Single Supply

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Application Notes (Continued)

Figure 6

1MHz sine and a 250KHz triangular waveform.

LMH6645/46/47

As can be seen in
there are no spikes or glitches due to the switching. Switch­ing times are approximately around 500ns based on the time
when the output is considered “valid”.

Printed Circuit Board Layout, Component Values Selec­tion, and Evaluation Boards:

Generally, a good high-frequency layout will keep power
supply and ground traces away from the inverting input and
output pins. Parasitic capacitances on these nodes to

shows the MUX output when selecting between a

20020235

FIGURE 6. 2:1 MUX Output

Figure 6

, the output is well behaved and

ground will cause frequency response peaking and possible
circuit oscillations (see Application Note OA-15 for more
information).

Another important parameter in working with high
speed/high performance amplifiers, is the component values
selection. Choosing large valued external resistors, will ef­fect the closed loop behavior of the stage because of the
interaction of these resistors with parasitic capacitances.
These capacitors could be inherent to the device or a
by-product of the board layout and component placement.
Either way, keeping the resistor values lower, will diminish
this interaction. On the other hand, choosing very low value
resistors could load down nodes and will contribute to higher
overall power dissipation.

National Semiconductor suggests the following evaluation
boards as a guide for high frequency layout and as an aid in
device testing and characterization:

Device Package Evaluation

Board PN

LMH6645MF SOT23-5 CLC730068
LMH6645MA 8-Pin SOIC CLC730027
LMH6646MA 8-Pin SOIC CLC730036
LMH6646MM 8-Pin MSOP CLC730123
LMH6647MA 8-Pin SOIC CLC730027
LMH6647MF SOT23-6 CLC730116

These free evaluation boards are shipped when a device
sample request is placed with National Semiconductor.

LMH6647 Evaluation:

For normal operation, tie the SD pin to V

−

.

www.national.com 16

Physical Dimensions inches (millimeters) unless otherwise noted

LMH6645/46/47

5-Pin SOT23

NS Package Number MF05A

6-Pin SOT23

NS Package Number MF06A

www.national.com17

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LMH6645/46/47

8-Pin SOIC

NS Package Number M08A

8Pin MSOP

NS Package Number MUA08A

www.national.com 18

Notes

LMH6645/46/47 2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output Amplifiers with Shutdown

Option

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
significant injury to the user.

National Semiconductor
Corporation

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Email: [e-mail]

www.national.com

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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