NSC LMH6658

LMH6657/LMH6658
270MHz Single Supply, Single & Dual Amplifiers
General Description
Features
The LMH6657/6658 are low-cost operational amplifiers that
operate from a single supply with input voltage range extending below the V−. Based on easy to use voltage feedback 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 (AV = +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.
VS = 5V, TA = 25˚C, RL = 100Ω (Typical values unless
specified)
n −3dB BW (AV = +1)
270MHz
n Supply voltage range
3V to 12V
n Slew rate, (VS = ± 5V)
700V/µs
n Supply current
6.2mA/amp
n Output current
+80/−90mA
n Input common mode volt. 0.5V beyond V−, 1.7V from V+
n Output voltage swing (RL = 2kΩ)
0.8V from rails
n Input voltage noise
11nV/
n Input current noise
2.1pA/
n DG error
0.03%
n DP error
0.10˚
n THD (5MHz)
−55dBc
n Settling time (0.1%)
37ns
n Fully characterized for 5V, and ± 5V
n Output overdrive recovery
18ns
n Output short circuit protected (Note 10)
n No output phase reversal with CMVR exceeded
Applications
n
n
n
n
n
CD/DVD ROM
ADC buffer amp
Portable video
Current sense buffer
Portable communications
Connection Diagrams
SOT23-5/SC70-5 (LMH6657)
SOIC-8/MSOP-8 (LMH6658)
20053261
20053263
Top View
© 2004 National Semiconductor Corporation
DS200532
www.national.com
LMH6657/LMH6658 270MHz Single Supply, Single & Dual Amplifiers
October 2004
LMH6657/LMH6658
Absolute Maximum Ratings (Note 1)
Wave Soldering (10 sec.)
Storage Temperature Range
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V+ – V−)
200V (Note 9)
Output Short Circuit Duration
(Note 3), (Note 11)
+
−
Supply Voltage (V - V )
Voltage at Input/Output pins
SC70
12.6V
V+ +0.8V, V− −0.8V
Soldering Information
Infrared or Convection (20 sec.)
−40˚C to +85˚C
Package Thermal Resistance (θJA)(Note 4)
± 10mA
Input Current
3V to 12V
Operating Temperature Range
(Note 4)
± 2.5V
VIN Differential
+150˚C
Operating Ratings (Note 1)
2KV(Note 2)
Machine Model
−65˚C to +150˚C
Junction Temperature (Note 4)
ESD Tolerance
Human Body Model
260˚C
235˚C
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 TJ = 25˚C, V+ = 5V, V− = 0V, VCM = VO = V+/2, and RL = 100Ω (or as
specified) tied to V+/2. Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
GB
Gain Bandwidth Product
VOUT < 200mVPP
SSBW
−3dB BW
AV = +1, VOUT = 200mVPP
Min
(Note 6)
Typ
(Note 5)
140
220
270
AV = +2 or −1, VOUT = 200mVPP
100
Max
(Note 6)
Units
MHz
MHz
GFP
Frequency Response Peaking
AV = +2, VOUT = 200mVPP,
DC to 100MHz
1.5
GFR
Frequency Response Rolloff
AV = +2, VOUT = 200mVPP,
DC to 100MHz
0.5
LPD1˚
1˚ Linear Phase Deviation
AV = +2, VOUT = 200mVPP, ± 1˚
30
MHz
GF0.1dB
0.1dB Gain Flatness
AV = +2, ± 0.1dB, VOUT = 200mVPP
13
MHz
dB
dB
PBW
Full Power Bandwidth
−1dB, VOUT = 3VPP, AV = −1
55
MHz
DG
Differential Gain
NTSC, VCM = 2V, RL = 150Ω to
V+/2, Pos. Video Only
0.03
%
DP
Differential Phase
NTSC, VCM = 2V, RL=150Ω to V+/2
Pos. Video Only
0.1
deg
AV = +2, VOUT = 500mVPP
3.3
ns
AV = −1, VOUT = 500mVPP
3.4
Time Domain Response
tr
Rise and Fall Time
OS
Overshoot, Undershoot
AV = +2, VOUT = 500mVPP
18
%
ts
Settling Time
VO = 2VPP, ± 0.1%, RL = 500Ω to
V+/2, AV = −1
37
ns
SR
Slew Rate (Note 8)
AV = −1, VO = 3VPP (Note 13)
470
AV = +2, VO = 3VPP (Note 13)
420
V/µs
Distortion and Noise Response
HD2
2nd Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−70
dBc
HD3
3rd Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−57
dBc
THD
Total Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−55.5
dBc
Vn
Input-Referred Voltage Noise
f = 100KHz
11
f = 1KHz
19
f = 100KHz
2.1
f = 1KHz
7.5
f = 5MHz, RL (SND) = 100Ω
RCV: RF = RG = 1k
69
In
XTLKA
Input-Referred Current Noise
Cross-Talk Rejection
(LMH6658)
Static, DC Performance
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2
nV/
pA/
dB
(Continued)
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = 0V, VCM = VO = V+/2, and RL = 100Ω (or as
specified) tied to V+/2. Boldface limits apply at the temperature extremes.
Symbol
AVOL
CMVR
Parameter
Large Signal Voltage Gain
Input Common-Mode Voltage
Range
Conditions
Min
(Note 6)
Typ
(Note 5)
VO = 1.25V to 3.75V,
RL = 2k to V+/2
85
95
VO = 1.5V to 3.5V,
RL = 150Ω to V+/2
75
85
VO = 2V to 3V,
RL = 50Ω to V+/2
70
80
−0.2
−0.1
−0.5
3.0
2.8
3.3
CMRR ≥ 50dB
± 1.1
VOS
Input Offset Voltage
TC VOS
Input Offset Voltage Average
Drift
(Note 12)
±2
IB
Input Bias Current
(Note 7)
−5
Input Bias Current Average
Drift
(Note 12)
0.01
TC
IB
IOS
Input Offset Current
50
CMRR
Common Mode Rejection
Ratio
VCM Stepped from 0V to 3.0V
72
82
+PSRR
Positive Power Supply
Rejection Ratio
V+ = 4.5V to 5.5V, VCM = 1V
72
82
IS
Supply Current (per channel)
No load
6.2
Max
(Note 6)
Units
dB
V
±5
±7
mV
µV/C
−20
−30
µA
nA/˚C
300
500
nA
dB
dB
8.5
10
mA
Miscellaneous Performance
VOH
VOL
Output Swing
High
Output Swing
Low
RL = 2k to V+/2
4.10
3.8
4.25
RL = 150Ω to V+/2
4.00
3.70
4.19
RL = 75Ω to V+/2
3.85
3.50
4.15
RL = 2k to V+/2
900
1100
800
RL = 150Ω to V+/2
970
1200
870
= 75Ω to V+/2
990
1250
885
R
L
IOUT
Output Current
VOUT = 1V from either rail
± 40
+85, −105
ISC
Output Short CircuitCurrent
(Note 10)
Sourcing to V+/2
100
80
155
Sinking to V+/2
100
80
220
RIN
Common Mode Input
Resistance
3
CIN
Common Mode Input
Capacitance
1.8
ROUT
Output Impedance
f = 1MHz, AV = +1
0.06
3
V
mV
mA
mA
MΩ
pF
Ω
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LMH6657/LMH6658
5V Electrical Characteristics
LMH6657/LMH6658
± 5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = −5V, VCM = VO, and RL = 100Ω (or as specified) tied to 0V. Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
GB
Gain Bandwidth Product
VOUT < 200mVPP
SSBW
−3dB BW
AV = +1, VOUT = 200mVPP
Min
(Note 6)
Typ
(Note 5)
220
270
Max
(Note 6)
140
AV = +2 or −1, VOUT = 200mVPP
100
Units
MHz
MHz
GFP
Frequency Response Peaking
AV = +2, VOUT = 200mVPP,
DC to 100MHz
1.0
GFR
Frequency Response Rolloff
AV = +2, VOUT = 200mVPP,
DC to 100MHz
0.9
LPD1˚
1˚ Linear Phase Deviation
AV = +2, VOUT = 200mVPP, ± 1˚
30
MHz
20
MHz
30
MHz
dB
dB
GF0.1dB
0.1dB Gain Flatness
AV = +2, ± 0.1dB, VOUT = 200mVPP
PBW
Full Power Bandwidth
−1dB, VOUT = 8VPP, AV = −1
DG
Differential Gain
NTSC, RL = 150Ω, Pos. or Neg.
Video
0.03
%
DP
Differential Phase
NTSC,RL = 150Ω, Pos. or Neg.
Video
0.1
deg
AV = +2, VOUT = 500mVPP
3.3
AV = −1, VOUT = 500mVPP
3.3
Time Domain Response
tr
Rise and Fall Time
ns
OS
Overshoot, Undershoot
AV = +2, VOUT = 500mVPP
16
%
ts
Settling Time
VO = 5VPP, ± 0.1%, RL =500Ω,
AV = −1
35
ns
SR
Slew Rate (Note 8)
AV = −1, VO = 8VPP
700
AV = +2, VO = 8VPP
500
V/µs
Distortion and Noise Response
HD2
2nd Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−70
dBc
HD3
3rd Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−57
dBc
THD
Total Harmonic Distortion
f = 5MHz, VO = 2VPP, AV = -1
−55.5
dBc
Vn
Input-Referred Voltage Noise
f = 100KHz
11
f = 1KHz
19
f = 100KHz
2.1
f = 1KHz
7.5
f = 5MHz, RL (SND) = 100Ω
RCV: RF = RG = 1k
69
In
XTLKA
Input-Referred Current Noise
Cross-Talk Rejection
(LMH6658)
nV/
pA/
dB
Static, DC Performance
AVOL
CMVR
Large Signal Voltage Gain
Input Common-Mode Voltage
Range
VO = −3.75V to 3.75V, RL = 2k
87
VO = −3.5V to 3.5V, RL = 150Ω
80
90
VO = −3V to 3V, RL = 50Ω
75
85
−5.2
−5.1
−5.5
3.0
2.8
3.3
CMRR ≥ 50dB
100
± 1.0
VOS
Input Offset Voltage
TC VOS
Input Offset Voltage Average
Drift
(Note 12)
±2
IB
Input Bias Current
(Note 7)
−5
TCIB
Input Bias Current Average
Drift
(Note 12)
0.01
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4
dB
V
±5
±7
mV
µV/C
−20
−30
µA
nA/˚C
(Continued)
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = −5V, VCM = VO, and RL = 100Ω (or as specified) tied to 0V. Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
Typ
(Note 5)
Max
(Note 6)
50
300
500
Units
IOS
Input Offset Current
CMRR
Common ModeRejection Ratio VCM Stepped from −5V to 3.0V
75
84
dB
+PSRR
Positive Power Supply
Rejection Ratio
V+ = 4.5V to 5.5V, VCM = −4V
75
82
dB
−PSRR
Negative Power Supply
Rejection Ratio
V− = −4.5V to −5.5V
78
85
dB
IS
Supply Current (per channel)
No load
6.5
9.0
11
nA
mA
Miscellaneous Performance
VOH
VOL
Output Swing
High
Output Swing
Low
RL = 2k
4.10
3.80
4.25
RL = 150Ω
4.00
3.70
4.20
RL = 75Ω
3.85
3.50
4.18
RL = 2k
−4.05
−3.80
−4.19
RL = 150Ω
−3.90
−3.65
−4.05
= 75Ω
−3.80
−3.50
−4.00
R
L
IOUT
Output Current
VOUT = 1V from either rail
± 45
+100, −110
ISC
Output Short Circuit Current
(Note 10)
Sourcing to Ground
120
100
180
Sinking to Ground
120
100
230
RIN
Common Mode Input
Resistance
4
CIN
Common Mode Input
Capacitance
1.8
ROUT
Output Impedance
f = 1MHz, AV = +1
0.06
5
V
V
mA
mA
MΩ
pF
Ω
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LMH6657/LMH6658
± 5V Electrical Characteristics
LMH6657/LMH6658
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, 1.5kΩ 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 TJ(MAX), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is
PD = (TJ(MAX) - TA)/ 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, 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 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
SC70-5
LMH6657MG
3k Units Tape and Reel
A76
1k Units Tape and Reel
LMH6657MGX
SOIC-8
LMH6658MA
LMH6658MA
LMH6658MAX
MSOP-8
LMH6658MM
Rails
M08A
2.5k Units Tape and Reel
A88A
1k Units Tape and Reel
LMH6658MMX
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MAA05A
3k Units Tape and Reel
3.5k Units Tape and Reel
6
MUA08A
LMH6657/LMH6658
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. VCM
20053223
20053241
7
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LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
Phase Margin vs. VCM
Output vs. Input
20053204
20053242
Output vs. Input
CMRR vs. Frequency
20053206
20053203
PSRR vs. Frequency
DG/DP vs. IRE
20053201
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20053211
8
LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
Noise vs. Frequency
Crosstalk Rejection vs. Frequency
20053205
20053202
Output Impedance vs. Frequency
HD vs. VOUT
20053210
20053213
HD vs. VOUT
THD vs. VOUT
20053212
20053253
9
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LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
HD vs. Frequency
HD vs. Frequency
20053214
20053215
VOUT vs. ISOURCE
VOUT vs. ISINK
20053243
20053244
VOUT vs. ISOURCE
VOUT vs. ISINK
20053245
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20053246
10
LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
Short Circuit Current
Short Circuit Current
20053230
20053231
Settling Time vs. Output Step Amplitude
Settling Time vs. Output Step Amplitude
20053207
20053208
∆VOS vs. VOUT
0.1% Settling Time vs. Cap Load
20053209
20053240
11
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LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
∆VOS vs. VOUT
IS /Amp vs. VS
20053232
20053239
IS/Amp vs. VCM
IS/Amp vs. VCM
20053237
20053238
VOS vs. VS (for 3 Representative Units)
VOS vs. VS (for 3 Representative Units)
20053234
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20053233
12
LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
VOS vs. VS (for 3 Representative Units)
VOS vs. VCM (A Typical Unit)
20053236
20053235
|IB| vs. VS
IOS vs. VS
20053228
20053229
Small Signal Step Response
Small Signal Step Response
20053222
20053220
13
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LMH6657/LMH6658
Typical Performance Characteristics
(Continued)
Small Signal Step Response
Small Signal Step Response
20053221
20053216
Large Signal Step Response
Large Signal Step Response
20053217
20053219
Large Signal Step Response
20053218
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14
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.
LARGE SIGNAL BEHAVIOR
The LMH6657/6658 is specially designed to handle large
output swings, such as those encountered in video waveforms, 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 conventional limitation imposed by slew rate limit.
The LMH6657/6658 input stage is designed to provide excess 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 conditions. 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:
The following plots aid in predicting the output transition time
based on the amount of swing required for a given gain
setting.
20053251
FIGURE 2. Output 20%-80% Transition vs. Output
Voltage Swing (Non-Inverting Gain)
20053250
FIGURE 1. Plot Showing the Relationship Between
Slew Rate and Input Overdrive
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 (Typical Performance Characteristics section), with a 30MHz signal and 7VPP input signal, it can be seen that the output will
be limited to a swing of 6.9VPP. From the frequency Response 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 1.9VPP differential input
voltage corresponding to 650V/µs of slew rate from Figure 1,
above (SR = VO(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 frequency
• Amplifier configuration (inverting or non-inverting)
20053252
FIGURE 3. Output 20%-80% Transition vs. Output
Voltage Swing (Inverting Gain)
Beyond a gain of 5 or so, the LMH6657/6658 output transition 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.
15
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LMH6657/LMH6658
Application Section
LMH6657/LMH6658
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
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 output 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 temperature 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 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.
20053249
FIGURE 6. Output Overload Recovery
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 applications, 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 Ratings of the device could however damage or otherwise adversely effect the reliability or life of the device.
20053247
FIGURE 4. VOUT vs. ISOURCE (for Various Overdrive)
DRIVING CAPACITIVE LOADS
The LMH6657/6658 can drive moderate values of capacitance by utilizing a series isolation resistor between the
output and the capacitive load. Typical Performance Characteristics section shows the settling time behavior for various capacitive loads and 20Ω of isolation resistance. Capacitive load tolerance will improve with higher closed loop
gain values. Applications such as ADC buffers, among others, 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 application.
20053248
DISTORTION
Applications with demanding distortion performance requirements 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
FIGURE 5. VOUT vs. ISINK (for Various Overdrive)
The LMH6657/6658 output stage is designed to swing within
approximately one diode drop of each supply voltage by
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16
evaluation boards as a guide for high frequency layout and
as an aid in device testing and characterization:
(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 configuration is at a further disadvantage of having to contend with the
input common voltage range. There is also a strong relationship between output loading and distortion performance (i.e.
1kΩ vs. 100Ω distortion 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 reduced HD3 term and thus improves THD.
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. Another 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 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 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.
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
17
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LMH6657/LMH6658
Output Characteristics
LMH6657/LMH6658
Physical Dimensions
inches (millimeters) unless otherwise noted
5-Pin SOT23
NS Package Number MF05A
SC70-5
NS Package Number MAA05A
www.national.com
18
LMH6657/LMH6658
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
8-Pin SOIC
NS Package Number M08A
8-Pin MSOP
NS Package Number MUA08A
19
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LMH6657/LMH6658 270MHz Single Supply, Single & Dual Amplifiers
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.
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