LMH6657,LMH6658
LMH6657/LMH6658 270MHz Single Supply, Single & Dual Amplifiers
Literature Number: SNOSA35E
LMH6657/LMH6658
270MHz Single Supply, Single & Dual Amplifiers
General Description
The LMH6657/6658 are low-cost operational amplifiers that
operate from a single supply with input voltage range ex-
tending below the V
−
. Based on easy to use voltage feed-
back topology and boasting fast slew rate (700V/µs) and
high speed (140MHz GBWP), the LMH6657 (Single) and
LMH6658 (dual) can be used in high speed large signal
applications. These applications include instrumentation,
communication devices, set-top boxes, etc.
With a -3dB BW of 100MHz (A
V
= +2) and DG & DP of 0.03%
& 0.10˚ respectively, the LMH6657/6658 are well suited for
video applications. The output stage can typically supply
80mA into the load with a swing of about 1V from either rail.
For Industrial applications, the LMH6657/6658 are excellent
cost-saving choices. Input referred voltage noise is low and
the input voltage can extend below V
−
to ease amplification
of low level signals that could be at or near the system
ground. With low distortion and fast settling, LMH6657/6658
can provide buffering for A/D and D/A applications.
The LMH6657/6658 versatility and ease of use is extended
even further by offering these high slew rate , high speed Op
Amps in miniature packages such as SOT23-5, SC70,
SOIC-8, and MSOP-8. Refer to the Ordering Information
section for packaging options available for each device.
Features
V
S
=5V,T
A
= 25˚C, R
L
= 100Ω(Typical values unless
specified)
n−3dB BW (A
V
= +1) 270MHz
nSupply voltage range 3V to 12V
nSlew rate, (V
S
=±5V) 700V/µs
nSupply current 6.2mA/amp
nOutput current +80/−90mA
nInput common mode volt. 0.5V beyond V
−
, 1.7V from V
+
nOutput voltage swing (R
L
=2kΩ) 0.8V from rails
nInput voltage noise 11nV/
nInput current noise 2.1pA/
nDG error 0.03%
nDP error 0.10˚
nTHD (5MHz) −55dBc
nSettling time (0.1%) 37ns
nFully characterized for 5V, and ±5V
nOutput overdrive recovery 18ns
nOutput short circuit protected (Note 10)
nNo output phase reversal with CMVR exceeded
Applications
nCD/DVD ROM
nADC buffer amp
nPortable video
nCurrent sense buffer
nPortable communications
Connection Diagrams
SOT23-5/SC70-5 (LMH6657) SOIC-8/MSOP-8 (LMH6658)
20053261
Top View 20053263
October 2004
LMH6657/LMH6658 270MHz Single Supply, Single & Dual Amplifiers
© 2004 National Semiconductor Corporation DS200532 www.national.com
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 Model 2KV(Note 2)
Machine Model 200V (Note 9)
V
IN
Differential ±2.5V
Output Short Circuit Duration (Note 3), (Note 11)
Input Current ±10mA
Supply Voltage (V
+
-V
−
) 12.6V
Voltage at Input/Output pins V
+
+0.8V, V
−
−0.8V
Soldering Information
Infrared or Convection (20 sec.) 235˚C
Wave Soldering (10 sec.) 260˚C
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) +150˚C
Operating Ratings (Note 1)
Supply Voltage (V
+
–V
−
) 3Vto12V
Operating Temperature Range
(Note 4) −40˚C to +85˚C
Package Thermal Resistance (θ
JA
)(Note 4)
SC70 478˚C/W
SOT23–5 265˚C/W
MSOP-8 235˚C/W
SOIC-8 190˚C/W
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
L
= 100Ω(or as
specified) tied to V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
GB Gain Bandwidth Product V
OUT
<200mV
PP
140 MHz
SSBW −3dB BW A
V
= +1, V
OUT
= 200mV
PP
220 270 MHz
A
V
=+2or−1,V
OUT
= 200mV
PP
100
GFP Frequency Response Peaking A
V
= +2, V
OUT
= 200mV
PP
,
DC to 100MHz
1.5 dB
GFR Frequency Response Rolloff A
V
= +2, V
OUT
= 200mV
PP
,
DC to 100MHz
0.5 dB
LPD
1˚
1˚ Linear Phase Deviation A
V
= +2, V
OUT
= 200mV
PP
,±1˚ 30 MHz
GF
0.1dB
0.1dB Gain Flatness A
V
= +2, ±0.1dB, V
OUT
= 200mV
PP
13 MHz
PBW Full Power Bandwidth −1dB, V
OUT
=3V
PP
,A
V
= −1 55 MHz
DG Differential Gain NTSC, V
CM
= 2V, R
L
= 150Ωto
V
+
/2, Pos. Video Only
0.03 %
DP Differential Phase NTSC, V
CM
= 2V, R
L
=150Ωto V
+
/2
Pos. Video Only
0.1 deg
Time Domain Response
t
r
Rise and Fall Time A
V
= +2, V
OUT
= 500mV
PP
3.3 ns
A
V
= −1, V
OUT
= 500mV
PP
3.4
OS Overshoot, Undershoot A
V
= +2, V
OUT
= 500mV
PP
18 %
t
s
Settling Time V
O
=2V
PP
,±0.1%, R
L
= 500Ωto
V
+
/2, A
V
=−1
37 ns
SR Slew Rate (Note 8) A
V
= −1, V
O
=3V
PP
(Note 13) 470 V/µs
A
V
= +2, V
O
=3V
PP
(Note 13) 420
Distortion and Noise Response
HD2 2
nd
Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −70 dBc
HD3 3
rd
Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −57 dBc
THD Total Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −55.5 dBc
V
n
Input-Referred Voltage Noise f = 100KHz 11 nV/
f = 1KHz 19
I
n
Input-Referred Current Noise f = 100KHz 2.1 pA/
f = 1KHz 7.5
XTLKA Cross-Talk Rejection
(LMH6658)
f = 5MHz, R
L
(SND) = 100Ω
RCV: R
F
=R
G
=1k
69 dB
Static, DC Performance
LMH6657/LMH6658
www.national.com 2
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
L
= 100Ω(or as
specified) tied to V
+
/2. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
A
VOL
Large Signal Voltage Gain V
O
= 1.25V to 3.75V,
R
L
=2ktoV
+
/2
85 95
dB
V
O
= 1.5V to 3.5V,
R
L
= 150Ωto V
+
/2
75 85
V
O
=2Vto3V,
R
L
=50Ωto V
+
/2
70 80
CMVR Input Common-Mode Voltage
Range
CMRR ≥50dB −0.2
−0.1
−0.5
V
3.0
2.8
3.3
V
OS
Input Offset Voltage ±1.1 ±5
±7mV
TC V
OS
Input Offset Voltage Average
Drift
(Note 12) ±2 µV/C
I
B
Input Bias Current (Note 7) −5 −20
−30 µA
TC
IB
Input Bias Current Average
Drift
(Note 12) 0.01 nA/˚C
I
OS
Input Offset Current 50 300
500 nA
CMRR Common Mode Rejection
Ratio
V
CM
Stepped from 0V to 3.0V 72 82 dB
+PSRR Positive Power Supply
Rejection Ratio
V
+
= 4.5V to 5.5V, V
CM
=1V 72 82 dB
I
S
Supply Current (per channel) No load 6.2 8.5
10 mA
Miscellaneous Performance
V
OH
Output Swing
High
R
L
=2ktoV
+
/2 4.10
3.8
4.25
V
R
L
= 150Ωto V
+
/2 4.00
3.70
4.19
R
L
=75Ωto V
+
/2 3.85
3.50
4.15
V
OL
Output Swing
Low
R
L
=2ktoV
+
/2 900
1100
800
mV
R
L
= 150Ωto V
+
/2 970
1200
870
R
L
=75Ωto V
+
/2 990
1250
885
I
OUT
Output Current V
OUT
= 1V from either rail ±40 +85, −105 mA
I
SC
Output Short CircuitCurrent
(Note 10)
Sourcing to V
+
/2 100
80
155
mA
Sinking to V
+
/2 100
80
220
R
IN
Common Mode Input
Resistance
3MΩ
C
IN
Common Mode Input
Capacitance
1.8 pF
R
OUT
Output Impedance f = 1MHz, A
V
= +1 0.06 Ω
LMH6657/LMH6658
www.national.com3
±5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= −5V, V
CM
=V
O
, and R
L
= 100Ω(or as speci-
fied) tied to 0V. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
GB Gain Bandwidth Product V
OUT
<200mV
PP
140 MHz
SSBW −3dB BW A
V
= +1, V
OUT
= 200mV
PP
220 270 MHz
A
V
=+2or−1,V
OUT
= 200mV
PP
100
GFP Frequency Response Peaking A
V
= +2, V
OUT
= 200mV
PP
,
DC to 100MHz
1.0 dB
GFR Frequency Response Rolloff A
V
= +2, V
OUT
= 200mV
PP
,
DC to 100MHz
0.9 dB
LPD
1˚
1˚ Linear Phase Deviation A
V
= +2, V
OUT
= 200mV
PP
,±1˚ 30 MHz
GF
0.1dB
0.1dB Gain Flatness A
V
= +2, ±0.1dB, V
OUT
= 200mV
PP
20 MHz
PBW Full Power Bandwidth −1dB, V
OUT
=8V
PP
,A
V
= −1 30 MHz
DG Differential Gain NTSC, R
L
= 150Ω, Pos. or Neg.
Video
0.03 %
DP Differential Phase NTSC,R
L
= 150Ω, Pos. or Neg.
Video
0.1 deg
Time Domain Response
t
r
Rise and Fall Time A
V
= +2, V
OUT
= 500mV
PP
3.3 ns
A
V
= −1, V
OUT
= 500mV
PP
3.3
OS Overshoot, Undershoot A
V
= +2, V
OUT
= 500mV
PP
16 %
t
s
Settling Time V
O
=5V
PP
,±0.1%, R
L
=500Ω,
A
V
=−1
35 ns
SR Slew Rate (Note 8) A
V
= −1, V
O
=8V
PP
700 V/µs
A
V
= +2, V
O
=8V
PP
500
Distortion and Noise Response
HD2 2
nd
Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −70 dBc
HD3 3
rd
Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −57 dBc
THD Total Harmonic Distortion f = 5MHz, V
O
=2V
PP
,A
V
= -1 −55.5 dBc
V
n
Input-Referred Voltage Noise f = 100KHz 11 nV/
f = 1KHz 19
I
n
Input-Referred Current Noise f = 100KHz 2.1 pA/
f = 1KHz 7.5
XTLKA Cross-Talk Rejection
(LMH6658)
f = 5MHz, R
L
(SND) = 100Ω
RCV: R
F
=R
G
=1k
69 dB
Static, DC Performance
A
VOL
Large Signal Voltage Gain V
O
= −3.75V to 3.75V, R
L
= 2k 87 100
dBV
O
= −3.5V to 3.5V, R
L
= 150Ω80 90
V
O
= −3V to 3V, R
L
=50Ω75 85
CMVR Input Common-Mode Voltage
Range
CMRR ≥50dB −5.2
−5.1
−5.5
V
3.0
2.8
3.3
V
OS
Input Offset Voltage ±1.0 ±5
±7mV
TC V
OS
Input Offset Voltage Average
Drift
(Note 12) ±2 µV/C
I
B
Input Bias Current (Note 7) −5 −20
−30 µA
TC
IB
Input Bias Current Average
Drift
(Note 12) 0.01 nA/˚C
LMH6657/LMH6658
www.national.com 4
±5V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at T
J
= 25˚C, V
+
= 5V, V
−
= −5V, V
CM
=V
O
, and R
L
= 100Ω(or as speci-
fied) tied to 0V. Boldface limits apply at the temperature extremes.
Symbol Parameter Conditions Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
Units
I
OS
Input Offset Current 50 300
500 nA
CMRR Common ModeRejection Ratio V
CM
Stepped from −5V to 3.0V 75 84 dB
+PSRR Positive Power Supply
Rejection Ratio
V
+
= 4.5V to 5.5V, V
CM
= −4V 75 82 dB
−PSRR Negative Power Supply
Rejection Ratio
V
−
= −4.5V to −5.5V 78 85 dB
I
S
Supply Current (per channel) No load 6.5 9.0
11 mA
Miscellaneous Performance
V
OH
Output Swing
High
R
L
= 2k 4.10
3.80
4.25
V
R
L
= 150Ω4.00
3.70
4.20
R
L
=75Ω3.85
3.50
4.18
V
OL
Output Swing
Low
R
L
= 2k −4.05
−3.80
−4.19
V
R
L
= 150Ω−3.90
−3.65
−4.05
R
L
=75Ω−3.80
−3.50
−4.00
I
OUT
Output Current V
OUT
= 1V from either rail ±45 +100, −110 mA
I
SC
Output Short Circuit Current
(Note 10)
Sourcing to Ground 120
100
180
mA
Sinking to Ground 120
100
230
R
IN
Common Mode Input
Resistance
4MΩ
C
IN
Common Mode Input
Capacitance
1.8 pF
R
OUT
Output Impedance f = 1MHz, A
V
= +1 0.06 Ω
LMH6657/LMH6658
www.national.com5
Note 1: 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 "worst case" 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: Drift determined by dividing the change in parameter at temperature extremes by the total temperature change.
Note 13: Output Swing not limited by Slew Rate limit.
Ordering Information
Package Part Number Package Marking Transport Media NSC Drawing
SOT23-5 LMH6657MF A85A 1k Units Tape and Reel MF05A
LMH6657MFX 3k Units Tape and Reel
SC70-5 LMH6657MG A76 1k Units Tape and Reel MAA05A
LMH6657MGX 3k Units Tape and Reel
SOIC-8 LMH6658MA LMH6658MA Rails M08A
LMH6658MAX 2.5k Units Tape and Reel
MSOP-8 LMH6658MM A88A 1k Units Tape and Reel MUA08A
LMH6658MMX 3.5k Units Tape and Reel
LMH6657/LMH6658
www.national.com 6
Typical Performance Characteristics
Non-Inverting Frequency Response,
Gain
Inverting Frequency Response,
Gain
20053226 20053224
Non-Inverting Frequency Response, Phase Inverting Frequency Response, Phase
20053227 20053225
Open Loop Gain/Phase vs. Frequency Unity Gain Frequency vs. V
CM
20053223
20053241
LMH6657/LMH6658
www.national.com7
Typical Performance Characteristics (Continued)
Phase Margin vs. V
CM
Output vs. Input
20053242 20053204
Output vs. Input CMRR vs. Frequency
20053203 20053206
PSRR vs. Frequency DG/DP vs. IRE
20053201 20053211
LMH6657/LMH6658
www.national.com 8
Typical Performance Characteristics (Continued)
Noise vs. Frequency Crosstalk Rejection vs. Frequency
20053202 20053205
Output Impedance vs. Frequency HD vs. V
OUT
20053210 20053213
HD vs. V
OUT
THD vs. V
OUT
20053212 20053253
LMH6657/LMH6658
www.national.com9
Typical Performance Characteristics (Continued)
HD vs. Frequency HD vs. Frequency
20053214 20053215
V
OUT
vs. I
SOURCE
V
OUT
vs. I
SINK
20053243 20053244
V
OUT
vs. I
SOURCE
V
OUT
vs. I
SINK
20053245 20053246
LMH6657/LMH6658
www.national.com 10
Typical Performance Characteristics (Continued)
Short Circuit Current Short Circuit Current
20053230 20053231
Settling Time vs. Output Step Amplitude Settling Time vs. Output Step Amplitude
20053208 20053207
0.1% Settling Time vs. Cap Load ∆V
OS
vs. V
OUT
20053209 20053240
LMH6657/LMH6658
www.national.com11
Typical Performance Characteristics (Continued)
∆V
OS
vs. V
OUT
I
S
/Amp vs. V
S
20053239 20053232
I
S
/Amp vs. V
CM
I
S
/Amp vs. V
CM
20053238 20053237
V
OS
vs. V
S
(for 3 Representative Units) V
OS
vs. V
S
(for 3 Representative Units)
20053234 20053233
LMH6657/LMH6658
www.national.com 12
Typical Performance Characteristics (Continued)
V
OS
vs. V
S
(for 3 Representative Units) V
OS
vs. V
CM
(A Typical Unit)
20053235 20053236
|I
B
| vs. V
S
I
OS
vs. V
S
20053228 20053229
Small Signal Step Response Small Signal Step Response
20053222 20053220
LMH6657/LMH6658
www.national.com13
Typical Performance Characteristics (Continued)
Small Signal Step Response Small Signal Step Response
20053216 20053221
Large Signal Step Response Large Signal Step Response
20053217 20053219
Large Signal Step Response
20053218
LMH6657/LMH6658
www.national.com 14
Application Section
LARGE SIGNAL BEHAVIOR
The LMH6657/6658 is specially designed to handle large
output swings, such as those encountered in video wave-
forms, without being slew rate limited. With 5V supply, the
LMH6657/6658 slew rate limit is larger than that might be
necessary to make full allowable output swing excursions.
Therefore, the large signal frequency response is dominated
by the small signal characteristics, rather than the conven-
tional limitation imposed by slew rate limit.
The LMH6657/6658 input stage is designed to provide ex-
cess overdrive when needed. This occurs when fast input
signal excursions cannot be followed by the output stage. In
these situations, the device encounters larger input signals
than would be encountered under normal closed loop con-
ditions. The LMH6657/6658 input stage is designed to take
advantage of this "input overdrive" condition. The larger the
amount of this overdrive, the greater is the speed with which
the output voltage can change. Here is a plot of how the
output slew rate limitation varies with respect to the amount
of overdrive imposed on the input:
To relate the explanation above to a practical example,
consider the following application example. Consider the
case of a closed loop amplifier with a gain of −1 amplifying a
sinusoidal waveform. From the plot of Output vs. Input (Typi-
cal Performance Characteristics section), with a 30MHz sig-
nal and 7V
PP
input signal, it can be seen that the output will
be limited to a swing of 6.9V
PP
. From the frequency Re-
sponse plot it can be seen that the inverting gain of −1 has a
−32˚ output phase shift at this frequency. It can be shown
that this setup will result in about 1.9V
PP
differential input
voltage corresponding to 650V/µs of slew rate from Figure 1,
above (SR = V
O
(pp)*π*f = 650V/µs). Note that the amount of
overdrive appearing on the input for a given sinusoidal test
waveform is affected by the following:
•Output swing
•Gain setting
•Input/output phase relationship for the given test fre-
quency
•Amplifier configuration (inverting or non-inverting)
Due to the higher frequency phase shift between input and
output, there is no closed form solution to input overdrive for
a given input. Therefore, Figure 1 is not very useful by itself
in determining the output swing.
The following plots aid in predicting the output transition time
based on the amount of swing required for a given gain
setting.
Beyond a gain of 5 or so, the LMH6657/6658 output transi-
tion would be limited by bandwidth. For example, with a gain
of 5, the −3dB BW would be around 30MHz corresponding to
a rise time of about 12ns (10% - 90%). Assuming a near
linear transition, the 20%-80% transition time would be
around 9ns which matches the measured results as shown
in Figure 2.
When the output is heavily loaded, output swing may be
limited by current capability of the device. Refer to "Output
Current Capability" section, below, for more details.
20053250
FIGURE 1. Plot Showing the Relationship Between
Slew Rate and Input Overdrive
20053251
FIGURE 2. Output 20%-80% Transition vs. Output
Voltage Swing (Non-Inverting Gain)
20053252
FIGURE 3. Output 20%-80% Transition vs. Output
Voltage Swing (Inverting Gain)
LMH6657/LMH6658
www.national.com15
Output Characteristics
OUTPUT CURRENT CAPABILITY
The LMH6657/6658 output swing for a given load can be
determined by referring to the Output Voltage vs. Output
Current plots (Typical Performance Characteristics section).
Characteristic Tables show the output current when the out-
put is 1V from either rail. The plots and table values can be
used to predict closed loop continuous value of current for a
given load. If left unchecked, the output current capability of
the LMH6657/6658 could easily result in junction tempera-
ture exceeding the maximum allowed value specified under
Absolute Maximum Ratings. Proper heat sinking or other
precautions are required if conditions as such, exist.
Under transient conditions, such as when the input voltage
makes a large transition and the output has not had time to
reach its final value, the device can deliver output currents in
excess of the typical plots mentioned above. Plots shown in
Figure 5 and below, depict how the output current capability
improves under higher input overdrive voltages:
The LMH6657/6658 output stage is designed to swing within
approximately one diode drop of each supply voltage by
utilizing specially designed high speed output clamps. This
allows adequate output voltage swing even with 5V supplies
and yet avoids some of the issues associated with rail-to-rail
output operational amplifiers. Some of these issues are:
•Supply current increases when output reaches saturation
at or near the supply rails
•Prolonged recovery when output approaches the rails
The LMH6657/6658 output is exceedingly well-behaved
when it comes to recovering from an overload condition. As
can be seen from Figure 6 below, the LMH6657/6658 will
typically recover from an output overload condition in about
18ns, regardless of the duration of the overload.
OUTPUT PHASE REVERSAL
This is a problem with some operational amplifiers. This
effect is caused by phase reversal in the input stage due to
saturation of one or more of the transistors when the inputs
exceed the normal expected range of voltages. Some appli-
cations, such as servo control loops among others, are
sensitive to this kind of behavior and would need special
safeguards to ensure proper functioning. The LMH6657/
6658 is immune to output phase reversal with input overload.
With inputs exceeded, the LMH6657/6658 output will stay at
the clamped voltage from the supply rail. Exceeding the
input supply voltages beyond the Absolute Maximum Rat-
ings of the device could however damage or otherwise ad-
versely effect the reliability or life of the device.
DRIVING CAPACITIVE LOADS
The LMH6657/6658 can drive moderate values of capaci-
tance by utilizing a series isolation resistor between the
output and the capacitive load. Typical Performance Char-
acteristics section shows the settling time behavior for vari-
ous capacitive loads and 20Ωof isolation resistance. Ca-
pacitive load tolerance will improve with higher closed loop
gain values. Applications such as ADC buffers, among oth-
ers, present complex and varying capacitive loads to the Op
Amp; best value for this isolation resistance is often found by
experimentation and actual trial and error for each applica-
tion.
DISTORTION
Applications with demanding distortion performance require-
ments are best served with the device operating in the
inverting mode. The reason for this is that in the inverting
configuration, the input common mode voltage does not vary
20053247
FIGURE 4. V
OUT
vs. I
SOURCE
(for Various Overdrive)
20053248
FIGURE 5. V
OUT
vs. I
SINK
(for Various Overdrive)
20053249
FIGURE 6. Output Overload Recovery
LMH6657/LMH6658
www.national.com 16
Output Characteristics (Continued)
with the signal and there is no subsequent ill effects due to
this shift in operating point and the possibility of additional
non-linearity. Moreover, under low closed loop gain settings
(most suited to low distortion), the non-inverting configura-
tion is at a further disadvantage of having to contend with the
input common voltage range. There is also a strong relation-
ship between output loading and distortion performance (i.e.
1kΩvs. 100Ωdistortion improves by about 20dB @100KHz)
especially at the lower frequency end where the distortion
tends to be lower. At higher frequency, this dependence
diminishes greatly such that this difference is only about 4dB
at 10MHz. But, in general, lighter output load leads to re-
duced HD3 term and thus improves THD.
PRINTED CIRCUIT BOARD LAYOUT AND COMPONENT
VALUES SECTIONS
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). 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
LMH6657MF SOT23-5 CLC730068
LMH6657MG SC-70 NA
LMH6658MA 8-Pin SOIC CLC730036
LMH6658MM 8-Pin MSOP CLC730123
These free evaluation boards are shipped when a device
sample request is placed with National Semiconductor. An-
other important parameter in working with high speed/high
performance amplifiers, is the component values selection.
Choosing external resistors that are large in value will effect
the closed loop behavior of the stage because of the inter-
action 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 interac-
tion to a large extent. On the other hand, choosing very low
value resistors will load down nodes and will contribute to
higher overall power dissipation.
LMH6657/LMH6658
www.national.com17
Physical Dimensions inches (millimeters) unless otherwise noted
5-Pin SOT23
NS Package Number MF05A
SC70-5
NS Package Number MAA05A
LMH6657/LMH6658
www.national.com 18
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Pin SOIC
NS Package Number M08A
8-Pin MSOP
NS Package Number MUA08A
LMH6657/LMH6658
www.national.com19
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 certifies that the products and packing materials 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.
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
LMH6657/LMH6658 270MHz Single Supply, Single & Dual Amplifiers
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