LMH6645,LMH6646,LMH6647
LMH6645/46/47 2.7V, 650A, 55MHz, Rail-to-Rail Input and Output Amplifiers
with Shutdown Option
Literature Number: SNOS970B
LMH6645/46/47
2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output
Amplifiers with Shutdown Option
General Description
The LMH™6645 (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 mode voltage 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 appli-
cations. Even with low supply current of 650µA/amplifier,
output current capability is kept at a respectable ±20mA for
driving heavier loads. Important device parameters such as
BW, Slew Rate and output current are kept relatively inde-
pendent 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 be-
haved 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 applica-
tions where board area is at a premium.
Features
(V
S
= 2.7V, T
A
= 25˚C, R
L
=1kΩto V
+
/2, A
V
= +1. Typical
values unless specified).
n−3dB BW 55MHz
nSupply voltage range 2.5V to 12V
nSlew rate 22V/µs
nSupply current 650µA/channel
nOutput short circuit current 42mA
nLinear output current ±20mA
nInput common mode voltage 0.3V beyond rails
nOutput voltage swing 20mV from rails
nInput voltage noise 17nV/
nInput current noise 0.75pA/
Applications
nActive filters
nHigh speed portable devices
nMultiplexing applications (LMH6647)
nCurrent sense buffer
nHigh speed transducer amp
Connection Diagrams
SOT23-5 (LMH6645) SOT23-6 (LMH6647) SOIC-8 (LMH6645)
20020259
Top View
20020260
Top View 20020261
Top View
LMH™is a trademark of National Semiconductor Corporation.
June 2005
LMH6645/46/47 2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output Amplifiers with Shutdown
Option
© 2005 National Semiconductor Corporation DS200202 www.national.com
SOIC-8 (LMH6647)
SOIC-8 and MSOP-8
(LMH6646)
20020262
Top View
20020263
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
LMH6645/46/47
www.national.com 2
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
IN
Differential ±2.5V
Output Short Circuit Duration (Note 3, 11)
Supply Voltage (V
+
-V
−
) 12.6V
Voltage at Input/Output pins V
+
+0.8V, V
−
−0.8V
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) +150˚C
Soldering Information
Infrared or Convection (20 sec) 235˚C
Wave Soldering (10 sec) 260˚C
Operating Ratings (Note 1)
Supply Voltage (V
+
–V
−
) 2.5V to 12V
Temperature Range (Note 4) −40˚C to +85˚C
Package Thermal Resistance (Note 4) (θ
JA
)
SOT23-5 265˚C/W
SOT23-6 265˚C/W
SOIC-8 190˚C/W
MSOP-8 235˚C/W
2.7V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 2.7V, V
−
= 0V, V
CM
=V
O
=V
+
/2, and R
f
=2kΩ, and R
L
=1kΩto V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
BW −3dB BW A
V
= +1, V
OUT
= 200mV
PP
,
V
CM
= 0.7V
40 55 MHz
e
n
Input-Referred Voltage Noise f = 100kHz 17 nV/
f = 1kHz 25
i
n
Input-Referred Current Noise f = 100kHz 0.75 pA/
f = 1kHz 1.20
CT Rej. Cross-Talk Rejection
(LMH6646 only)
f = 5MHz, Receiver:
R
f
=R
g
= 510Ω,A
V
=+2
47 dB
SR Slew Rate A
V
= −1, V
O
=2V
PP
(Note 8, 13)
15 22 V/µs
T
ON
Turn-On Time
(LMH6647 only)
250 ns
T
OFF
Turn-Off Time
(LMH6647 only)
560 ns
TH
SD
Shutdown Threshold
(LMH6647 only)
I
S
≤50µA 1.95 2.30 V
I
SD
Shutdown Pin Input Current
(LMH6647 only)
(Note 7) −20 µA
V
OS
Input Offset Voltage 0V ≤V
CM
≤2.7V −3
−4
±13
4
mV
TC V
OS
Input Offset Average Drift (Note 12) ±5 µV/˚C
I
B
Input Bias Current V
CM
= 2.5V (Note 7) 0.40 2
2.2 µA
V
CM
= 0.5V (Note 7) −0.68 −2
−2.2
I
OS
Input Offset Current 0V ≤V
CM
≤2.7V 1 500 nA
R
IN
Common Mode Input
Resistance
3MΩ
C
IN
Common Mode Input
Capacitance
2pF
CMVR Input Common-Mode Voltage
Range
CMRR ≥50dB −0.5 −0.3
−0.1 V
3.0
2.8
3.2
LMH6645/46/47
www.national.com3
2.7V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 2.7V, V
−
= 0V, V
CM
=V
O
=V
+
/2, and R
f
=2kΩ, and R
L
=1kΩto V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
CMRR Common Mode Rejection
Ratio
V
CM
Stepped from 0V to 2.7V 46 77 dB
V
CM
Stepped from 0V to 1.55V 58 76
A
VOL
Large Signal Voltage Gain V
O
= 0.35V to 2.35V 76
74
87 dB
V
O
Output Swing
High
R
L
=1ktoV
+
/2 2.55 2.66 V
R
L
= 10k to V
+
/2 2.68
Output Swing
Low
R
L
=1ktoV
+
/2 40 150 mV
R
L
= 10k to V
+
/2 20
I
SC
Output Short Circuit Current Sourcing to V
−
V
ID
= 200mV (Note 10)
43
mA
Sinking to V
+
V
ID
= −200mV (Note 10)
42
I
OUT
Output Current V
OUT
= 0.5V from rails ±20 mA
PSRR Power Supply Rejection Ratio V
+
= 2.7V to 3.7V or
V
−
=0Vto−1V
75 83 dB
I
S
Supply Current (per channel) Normal Operation 650 1250 µA
Shutdown Mode (LMH6647 only) 15 50
5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= 0V, V
CM
=V
O
=V
+
/2, and R
f
=2kΩ, and R
L
=1kΩto V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
BW −3dB BW A
V
= +1, V
OUT
= 200mV
PP
40 55 MHz
e
n
Input-Referred Voltage Noise f = 100kHz 17 nV/
f = 1kHz 25
i
n
Input-Referred Current Noise f = 100kHz 0.75 pA/
f = 1kHz 1.20
CT Rej. Cross-Talk Rejection
(LMH6646 only)
f = 5MHz, Receiver:
R
f
=R
g
= 510Ω,A
V
=+2 47 dB
SR Slew Rate A
V
= −1, V
O
=2V
PP
(Note 8, 13) 15 22 V/µs
T
ON
Turn-On Time (LMH6647 only) 210 ns
T
OFF
Turn-Off Time (LMH6647 only) 500 ns
TH
SD
Shutdown Threshold
(LMH6647 only)
I
S
≤50µA 4.25 4.60 V
I
SD
Shutdown Pin Input Current
(LMH6647 only)
(Note 7) −20 µA
V
OS
Input Offset Voltage 0V ≤V
CM
≤5V −3
−4 ±13
4mV
TC V
OS
Input Offset Average Drift (Note 12) ±5 µV/C
I
B
Input Bias Current V
CM
= 4.8V (Note 7) +0.36 +2
−2.2 µA
V
CM
= 0.5V (Note 7) −0.68 −2
−2.2
I
OS
Input Offset Current 0V ≤V
CM
≤5V 1 500 nA
R
IN
Common Mode Input
Resistance
3MΩ
LMH6645/46/47
www.national.com 4
5V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= 0V, V
CM
=V
O
=V
+
/2, and R
f
=2kΩ, and R
L
=1kΩto V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
C
IN
Common Mode Input
Capacitance
2pF
CMVR Input Common-Mode Voltage
Range
CMRR ≥50dB −0.5 −0.3
−0.1 V
5.3
5.1
5.5
CMRR Common Mode Rejection
Ratio
V
CM
Stepped from 0V to 5V 56 82 dB
V
CM
Stepped from 0V to 3.8V 66 85
A
VOL
Large Signal Voltage Gain V
O
= 1.5V to 3.5V 76
74
85 dB
V
O
Output Swing
High
R
L
=1ktoV
+
/2 4.80 4.95 V
R
L
= 10k to V
+
/2 4.98
Output Swing
Low
R
L
=1ktoV
+
/2 50 200 mV
R
L
= 10k to V
+
/2 20
I
SC
Output Short Circuit Current Sourcing to V
−
V
ID
= 200mV (Note 10) 55
mA
Sinking to V
+
V
ID
= −200mV (Note 10) 53
I
OUT
Output Current V
OUT
= 0.5V From rails ±20 mA
PSRR Power Supply Rejection Ratio V
+
=5Vto6VorV
−
= 0V to −1V 75 95 dB
I
S
Supply Current (per channel) Normal Operation 700 1400 µA
Shutdown Mode (LMH6647 only) 10 50
±5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= −5V, V
CM
=V
O
= 0V, R
f
=2kΩ, and R
L
=
1kΩto GND. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
BW −3dB BW A
V
= +1, V
OUT
= 200mV
PP
40 55 MHz
e
n
Input-Referred Voltage Noise f = 100kHz 17 nV/
f = 1kHz 25
i
n
Input-Referred Current Noise f = 100kHz 0.75 pA/
f = 1kHz 1.20
CT Rej. Cross-Talk Rejection
(LMH6646 only)
f = 5MHz, Receiver:
R
f
=R
g
= 510Ω,A
V
=+2 47 dB
SR Slew Rate A
V
= −1, V
O
=2V
PP
(Note 8) 15 22 V/µs
T
ON
Turn-On Time (LMH6647 only) 200 ns
T
OFF
Turn-Off Time (LMH6647 only) 700 ns
TH
SD
Shutdown Threshold
(LMH6647 only)
I
S
≤50µA 4.25 4.60 V
I
SD
Shutdown Pin Input Current
(LMH6647 only)
(Note 7) −20 µA
V
OS
Input Offset Voltage −5V ≤V
CM
≤5V −3
−4 ±13
4mV
TC V
OS
Input Offset Average Drift (Note 12) ±5 µV/˚C
LMH6645/46/47
www.national.com5
±5V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= −5V, V
CM
=V
O
= 0V, R
f
=2kΩ, and R
L
=
1kΩto GND. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
I
B
Input Bias Current V
CM
= 4.8V (Note 7) +0.40 +2
+2.2 µA
V
CM
= −4.5V (Note 7) −0.65 −2
−2.2
I
OS
Input Offset Current −5V ≤V
CM
≤5V 3 500 nA
R
IN
Common Mode Input
Resistance
3MΩ
C
IN
Common Mode Input
Capacitance
2pF
CMVR Input Common-Mode Voltage
Range
CMRR ≥50dB −5.5 −5.3
−5.1 V
5.3
5.1
5.5
CMRR Common Mode Rejection
Ratio
V
CM
Stepped from −5V to 5V 60 84 dB
V
CM
Stepped from −5V to 3.5V 66 104
A
VOL
Large Signal Voltage Gain V
O
= −2V to 2V 76
74
85 dB
V
O
Output Swing
High
R
L
=1kΩ4.70 4.92 V
R
L
= 10kΩ4.97
Output Swing
Low
R
L
=1kΩ−4.93 −4.70 V
R
L
= 10kΩ−4.98
I
SC
Output Short Circuit Current Sourcing to V
−
V
ID
= 200mV (Note 10) 66
mA
Sinking to V
+
V
ID
= −200mV (Note 10) 61
I
OUT
Output Current V
OUT
= 0.5V from rails ±20 mA
PSRR Power Supply Rejection Ratio V
+
=5Vto6VorV
−
= −5V to −6V 76 95 dB
I
S
Supply Current (per channel) Normal Operation 725 1600 µA
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, 1.5kΩin 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 TJ(MAX),θJA, and TA. The maximum allowable power dissipation at any ambient temperature is
PD=(T
J(MAX) -T
A)/ θJA . All numbers apply for packages soldered directly onto a PC board.
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, 0Ωin series with 200pF.
Note 10: Short circuit test is a momentary test. See Note 11.
Note 11: Output short circuit duration is infinite for VS<6V at room temperature and below. For VS>6V, allowable short circuit duration is 1.5ms.
Note 12: Offset voltage average drift determined by dividing the change in VOS at temperature extremes into the total temperature change.
Note 13: Guaranteed based on characterization only.
LMH6645/46/47
www.national.com 6
Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified.
Closed Loop Frequency Response for Various
Temperature Frequency Response for Various A
V
20020249
20020248
Open Loop Gain/Phase vs. Frequency for Various
Temperature THD vs. Output Swing
20020250 20020253
THD vs. Output Swing Output Swing vs. Frequency
20020254 20020255
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
Settling Time vs. Step Size Noise vs. Frequency
20020252 20020234
V
OUT
from V
+
vs. I
SOURCE
V
OUT
from V
−
vs. I
SINK
20020237 20020238
Output Swing from V
+
vs. R
L
(tied to V
S
/2) Output Swing from V
+
vs. R
L
(tied to V
S
/2)
20020202 20020206
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
Output Swing from V
+
vs. R
L
(tied to V
S
/2) Output Swing from V
−
vs. R
L
(tied to V
S
/2)
20020204 20020203
Output Swing from V
−
vs. R
L
(tied to V
S
/2) Output Swing from V
−
vs. R
L
(tied to V
S
/2)
20020207 20020205
Cap Load Tolerance and Setting Time vs. Closed Loop
Gain Z
OUT
vs. Frequency
20020201 20020216
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
PSRR vs. Frequency CMRR vs. Frequency
20020247 20020251
Crosstalk Rejection vs. Frequency (Output to Output)
(LMH6646) V
OS
Distribution
20020257 20020225
V
OS
vs. V
S
(A Typical Unit) V
OS
vs. V
OUT
(A Typical Unit)
20020218 20020228
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
V
OS
vs. V
OUT
(A Typical Unit) V
OS
vs. V
CM
(A Typical Unit)
20020229 20020231
V
OS
vs. V
CM
(A Typical Unit) V
OS
vs. V
CM
(A Typical Unit)
20020230 20020232
I
B
vs. V
CM
I
B
vs. V
CM
20020226 20020219
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
I
B
vs. V
S
I
S
vs. V
CM
20020227 20020223
I
S
(mA) (per channel) I
S
vs. V
SHUTDOWN
(LMH6647)
20020224 20020221
I
S
vs. V
SHUTDOWN
(LMH6647) I
S
vs. V
SHUTDOWN
(LMH6647)
20020220 20020222
LMH6645/46/47
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Typical Performance Characteristics At T
J
= 25˚C. Unless otherwise specified. (Continued)
Shutdown Pin and Supply Current vs. Shutdown Voltage Small Signal Step Response
20020208
20020243
Large Signal Step Response Large Signal Step Response
20020244 20020245
Output Overload Recovery
20020246
LMH6645/46/47
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Application Notes
CIRCUIT DESCRIPTION
The LMH6645/6646/6647 family is based on National Semi-
conductor’s proprietary VIP10 dielectrically isolated bipolar
process.
This device family architecture features the following:
•Complimentary bipolar devices with exceptionally high f
t
(∼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 simi-
lar speed devices (patent pending).
•Common Emitter push-pull output stage capable of 20mA
output current (at 0.5V from the supply rails) while con-
suming 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
OUT
, etc.)
APPLICATION HINTS
The total input common mode voltage range, which extends
from below V
−
to beyond V
+
, is covered by both a PNP and
a NPN stage. The NPN stage is switched on whenever the
input is less than 1.2V from V
+
and the PNP stage covers the
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 transvers-
ing 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 volt-
age 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 −3dB BW (@A
V
=
+1) is typically 55MHz with a tested limit of 45MHz. Produc-
tion testing guarantees that process variations will not com-
promise speed.
This device family is designed to avoid output phase rever-
sal. With input over-drive, the output is kept near the supply
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:
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 50µA guaranteed, by applying
a voltage to the SD pin. The SD pin is “active high” and
needs to be tied to V
−
for normal operation. This input is low
current (<20µA, 4pF equivalent capacitance) and a resistor
to V
−
(≤20kΩ) will result in normal operation. Shutdown is
guaranteed when SD pin is 0.4V or less from V
+
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).
20020233
FIGURE 1. Input/Output Shown with Exceeded Input
CMVR
LMH6645/46/47
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Application Notes (Continued)
During shutdown, the input stage has an equivalent circuit as
shown below in Figure 2
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 exter-
nal 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 shows a circuit where a NPN bipolar is used to keep
the output near ground (∼80mV):
Figure 4 shows the output waveform.
If bipolar transistor power dissipation is not tolerable, the
switch could be by a N-channel enhancement mode MOS-
FET.
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:
20020256
FIGURE 2. LMH6647 Equivalent Input in Shutdown
Mode
20020264
FIGURE 3. Active Pull-Down Schematic
20020236
FIGURE 4. Output Held Low by Active Pull-Down
Circuit
20020258
FIGURE 5. 2:1 MUX Operating off a 2.7V Single Supply
LMH6645/46/47
www.national.com15
Application Notes (Continued)
Figure 6 shows the MUX output when selecting between a
1MHz sine and a 250KHz triangular waveform.
As can be seen in Figure 6, the output is well behaved and
there are no spikes or glitches due to the switching. Switch-
ing 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
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 selec-
tion. 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 capaci-
tors 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 dis-
sipation.
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
−
.
20020235
FIGURE 6. 2:1 MUX Output
LMH6645/46/47
www.national.com 16
Physical Dimensions inches (millimeters) unless otherwise noted
5-Pin SOT23
NS Package Number MF05A
6-Pin SOT23
NS Package Number MF06A
LMH6645/46/47
www.national.com17
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Pin SOIC
NS Package Number M08A
8Pin MSOP
NS Package Number MUA08A
LMH6645/46/47
www.national.com 18
Notes
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.
For the most current product information visit us at www.national.com.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL 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 labeling, can be reasonably expected to result
in a significant injury to the user.
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.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
Leadfree products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: ap.support@nsc.com
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
LMH6645/46/47 2.7V, 650µA, 55MHz, Rail-to-Rail Input and Output Amplifiers with Shutdown
Option
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