LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
LMH6738 Very Wideband, Low Distortion Triple Op Amp
Check for Samples: LMH6738
FEATURES
1
•
2
•
•
•
•
•
•
DESCRIPTION
750 MHz −3 dB small signal bandwidth
(AV = +1)
−85 dBc 3rd harmonic distortion (20 MHz)
2.3 nV/Hz input noise voltage
3300 V/μs slew rate
33 mA supply current (11.3 mA per op amp)
90 mA linear output current
0.02/0.01 Diff. Gain / Diff. Phase (RL = 150Ω)
The LMH6738 is a very wideband, DC coupled
monolithic operational amplifier designed specifically
for ultra high resolution video systems as well as wide
dynamic range systems requiring exceptional signal
fidelity. Benefiting from TI’s current feedback
architecture, the LMH6738 offers a gain range of ±1
to ±10 while providing stable, operation without
external compensation, even at unity gain. At a gain
of +2 the LMH6738 supports ultra high resolution
video systems with a 400 MHz 2 VPP –3 dB
Bandwidth. With 12-bit distortion levels through 30
MHz (RL = 100Ω), 2.3 nV/Hz input referred noise, the
LMH6738 is the ideal driver or buffer for high speed
flash A/D and D/A converters. Wide dynamic range
systems such as radar and communication receivers
requiring a wideband amplifier offering exceptional
signal purity will find the LMH6738 low input referred
noise and low harmonic distortion make it an
attractive solution.
APPLICATIONS
•
•
•
•
•
•
•
•
•
RGB video driver
High resolution projectors
Flash A/D driver
D/A transimpedance buffer
Wide dynamic range IF amp
Radar/communication receivers
DDS post-amps
Wideband inverting summer
Line driver
CONNECTION DIAGRAM
16-Pin SSOP
Top View
-IN A
1
+IN A
2
DIS B
3
-IN B
4
+IN B
5
DIS C
6
-IN C
7
+IN C
8
16
+
DIS A
15 +VS
14 OUT A
+
13 -VS
12 OUT B
11 +VS
+
10 OUT C
9
-VS
See Package Number DBQ0016A
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings
(1)
Supply Voltage (V+ - V–)
13.2V
IOUT
See Note
Common Mode Input Voltage
(2)
±VCC
Maximum Junction Temperature
+150°C
−65°C to +150°C
Storage Temperature Range
Soldering Information
Infrared or Convection (20 sec.)
235°C
Wave Soldering (10 sec.)
260°C
ESD Tolerance
(3)
Human Body Model
2000V
Machine Model
200V
−65°C to +150°C
Storage Temperature Range
(1)
(2)
(3)
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 ensured. For specifications, see the Electrical
Characteristics tables.
The maximum output current (IOUT) is determined by device power dissipation limitations. See the Power Dissipation section of the
Application Section for more details.
Human Body Model is 1.5 kΩ in series with 100 pF. Machine Model is 0Ω in series with 200 pF.
Operating Ratings
(1)
Thermal Resistance
Package
16-Pin SSOP
–
Supply Voltage (V - V )
(1)
2
(θJA)
120°C/W
−40°C to +85°C
Operating Temperature Range
+
(θJC)
36°C/W
8V to 12V
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 ensured. For specifications, see the Electrical
Characteristics tables.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
Electrical Characteristics
(1)
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Frequency Domain Performance
UGBW
-3 dB Bandwidth
Unity Gain, VOUT = 200 mVPP
750
SSBW
-3 dB Bandwidth
VOUT = 200 mVPP
480
VOUT = 2 VPP
400
LSBW
MHz
MHz
0.1 dB Bandwidth
VOUT = 2 VPP
150
MHz
GFPL
Peaking
DC to 75 MHz
0
dB
GFR1
Rolloff
DC to 150 MHz, VOUT = 2 VPP
0.1
dB
GFR2
Rolloff
@ 300 MHz, VOUT = 2 VPP
1.0
dB
Rise and Fall Time
(10% to 90%)
2V Step
0.9
5V Step
1.7
SR
Slew Rate
5V Step
3300
V/µs
ts
Settling Time to 0.1%
2V Step
10
ns
te
Enable Time
From Disable = rising edge.
7.3
ns
td
Disable Time
From Disable = falling edge.
4.5
ns
2nd Harmonic Distortion
2 VPP, 5 MHz
−80
HD2
2 VPP, 20 MHz
−71
HD2H
2 VPP, 50 MHz
−55
2 VPP, 5 MHz
−90
HD3
2 VPP, 20 MHz
−85
HD3H
2 VPP, 50 MHz
−65
Time Domain Response
TRS
TRL
ns
Distortion
HD2L
HD3L
3rd Harmonic Distortion
dBc
dBc
Equivalent Input Noise
VN
Non-Inverting Voltage
>1 MHz
2.3
nV/√Hz
ICN
Inverting Current
>1 MHz
12
pA/√Hz
NCN
Non-Inverting Current
>1 MHz
3
pA/√Hz
Video Performance
DG
Differential Gain
4.43 MHz, RL = 150Ω
.02
%
DP
Differential Phase
4.43 MHz, RL = 150Ω
.01
°
Static, DC Performance
(2)
VIO
Input Offset Voltage
IBN
Input Bias Current
(2)
Non-Inverting
IBI
Input Bias Current
(2)
Inverting
PSRR
Power Supply Rejection Ratio
CMRR
Common Mode Rejection Ratio
XTLK
Crosstalk
ICC
Supply Current
(2)
Supply Current Disabled V+
(1)
(2)
±2.5
±4.5
mV
−7
0
+5
µA
−2
±25
±35
μA
50
48.5
53
dB
46
44
50
dB
Input Referred, f=10MHz, Drive
channels A,C measure channel B
−80
dB
All three amps Enabled, No Load
32
35
40
mA
RL = ∞
1.9
2.2
mA
(2)
(2)
−15
−20
0.5
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. Performance is indicated in the electrical tables under conditions of internal self
heating where TJ> TA. See Applications Section for information on temperature de-rating of this device." Min/Max ratings are based on
product characterization and simulation. Individual parameters are tested as noted.
Parameter 100% production tested at 25°C.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
3
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
Electrical Characteristics (1) (continued)
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified.
Symbol
Parameter
Conditions
−
Supply Current Disabled V
Min
RL = ∞
Typ
Max
Units
1.1
1.3
mA
Miscellaneous Performance
RIN+
Non-Inverting Input Resistance
CIN+
Non-Inverting Input Capacitance
RIN−
Inverting Input Impedance
Output impedance of input buffer.
RO
Output Impedance
DC
VO
Output Voltage Range
(2)
1000
kΩ
.8
pF
30
Ω
0.05
Ω
RL = 100Ω
±3.25
±3.1
±3.5
RL = ∞
±3.65
±3.5
±3.8
±1.9
±1.7
±2.0
V
80
60
90
mA
V
CMIR
Common Mode Input Range
CMRR > 40 dB
IO
Linear Output Current
VIN = 0V, VOUT < ±30 mV
ISC
Short Circuit Current
VIN = 2V Output Shorted to Ground
160
mA
IIH
Disable Pin Bias Current High
Disable Pin = V+
10
μA
IIL
Disable Pin Bias Current Low
Disable Pin = 0V
−350
VDMAX
Voltage for Disable
Disable Pin ≤ VDMAX
VDMIM
Voltage for Enable
Disable Pin ≥ VDMIN
(3)
(4)
4
(2)
(3) (2)
(4)
μA
0.8
2.0
V
V
The maximum output current (IOUT) is determined by device power dissipation limitations. See the Power Dissipation section of the
Application Section for more details.
Short circuit current should be limited in duration to no more than 10 seconds. See the Power Dissipation section of the Application
Section for more details.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
Typical Performance Characteristics
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified).
Large Signal Frequency Response
1
0
0
-1
NORMALIZED GAIN (dB)
NORMALIZED GAIN (dB)
Large Signal Frequency Response
1
AV = 1, RF = 749:
-2
AV = 2, RF = 549:
-3
-4
AV = 5, RF = 459:
-5
AV = 10, RF = 332:
-6
-7
-8
-1
AV = -1, RF = 475:
-2
-3
AV = -2, RF = 450:
-4
AV = -5, RF = 400:
-5
AV = -10, RF = 500:
-6
-7
-8
VOUT = 2 VPP
VOUT = 2 VPP
-9
-9
10
100
10
1000
100
FREQUENCY (MHz)
Figure 2.
Small Signal Frequency Response
Frequency Response
vs.
VOUT
1
1
0
0
-1
-1
AV = 1, RF = 749:
-2
AV = 2, RF = 549:
-4
-5
AV = 5, RF = 459:
-6
VOUT = 4 VPP
-2
-3
-3
VOUT = 2 VPP
-4
-5
VOUT = 1 VPP
-6
-7
-7
-8
-8
VOUT = 0.25 VPP
10
100
1000
FREQUENCY (MHz)
VOUT = 0.5 VPP
AV = 2 V/V
RF = 549:
-9
10
-9
100
FREQUENCY (MHz)
Figure 3.
0.5
0
0.4
-1
0.3
NORMALIZED GAIN (dB)
NORMALIZED GAIN (dB)
Gain Flatness
1
VS = 7V
-2
-3
VS = 9V
-4
-5
VS = 12.5V
-6
-7
VOUT = 2 VPP
-9
10
100
1000
Figure 4.
Frequency Response
vs.
Supply Voltage
-8
1000
Figure 1.
GAIN (dB)
NORMALIZED GAIN (dB)
FREQUENCY (MHz)
1000
AV = 1
0.2
AV = 2
0.1
0
-0.1
-0.2
AV = 5
-0.3
-0.4
VOUT = 1 VPP
-0.5
10
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 5.
Figure 6.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
5
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
Typical Performance Characteristics (continued)
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified).
Frequency Response
vs.
Capacitive Load
Pulse Response
1.5
2
1
0
0.5
-2
CL = 4.7 pF, RS = 70:
GAIN (dB)
VOUT (V)
CL = 15 pF, RS = 44:
0
CL = 47 pF, RS = 24:
-4
CL = 100 pF, RS = 17:
-0.5
-6
-1
-8
VOUT = 1 VPP, CL || 1 k:
-1.5
-10
0
4
8
12
16
20
1
10
100
1000
FREQUENCY (MHz)
TIME (ns)
Figure 7.
Figure 8.
Series Output Resistance
vs.
Capacitive Load
Open Loop Gain and Phase
80
120
LOAD = 1 k: || CL
110
MAGNITUDE
60
50
40
30
20
100
90
80
0
70
-45
-90
60
PHASE
10
-135
50
0
0
20
40
60
80
100
120
40
0.01
-180
1000
100
FREQUENCY (MHz)
Figure 9.
Figure 10.
Distortion
vs.
Frequency
Distortion
vs.
Output Voltage
-40
-40
RL = 100:
f = 10 MHz
VOUT = 2 VPP
-45
-50
-50
-55
DISTORTION (dBc)
DISTORTION (dBc)
10
1
0.1
CAPACITIVE LOAD (pF)
-60
-65
HD2
-70
-75
-80
-85
-90
-60
HD3
-70
-80
HD2
-90
-100
-95
-100
HD3
-110
1
10
100
FREQUENCY (MHz)
0
1
2
3
4
5
6
7
8
VOUT (VPP)
Figure 11.
6
PHASE (°)
MAGNITUDE, |Z| (dB:)
RECOMMENDED RS (:)
70
Figure 12.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
Typical Performance Characteristics (continued)
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified).
Distortion
vs.
Supply Voltage
CMRR
vs.
Frequency
50
-65
VOUT = 2VPP
f = 10 MHz
HD2
-70
45
35
CMRR (dB)
DISTORTION (dBc)
40
-75
-80
HD3
-85
30
25
20
15
-90
10
-95
5
-100
0
6.8
7.6
8.4
9.2
0.01
10.8 11.6 12.4
10
Figure 13.
Figure 14.
PSRR
vs.
Frequency
Crosstalk
vs.
Frequency
1000
-30
60
CH A & C VOUT = 2 VPP
PSRR +
50
MEASURE CH B
-40
CROSSTALK (dBc)
PSRR 40
PSRR (dB)
100
FREQUENCY (MHz)
TOTAL SUPPLY VOLTAGE (V)
30
20
10
-50
-60
-70
-80
0
-90
0.1
1
10
100
1
1000
10
100
1000
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 15.
Figure 16.
Closed Loop Output Impedance |Z|
Disable Timing
0.6
100
AV = 2 V/V
0.4
VIN = 0V
VOUT
OUTPUT (V)
1
DISABLE (V)
0.2
10
|Z| (:)
10
1
0.1
0.0
-0.2
-0.4
-0.6
0.1
3
1
DISABLE
0.01
0.001 0.01
-1
0.1
1
10
100
1000
0
10
20
30
40
50
60
70
TIME (ns)
FREQUENCY (MHz)
Figure 17.
Figure 18.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
7
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
Typical Performance Characteristics (continued)
AV = +2, VCC = ±5V, RL = 100Ω, RF = 549Ω; unless otherwise specified).
DC Errors
vs.
Temperature
Input Noise
vs.
Frequency
1
6
1000
1000
0.6
2
0.4
0
VOS
0.2
-2
0
-4
-0.2
-6
-0.4
100
INVERTING CURRENT
NO
N
CU
RR
EN
T
10
10
-8
IBN
-0.6
-40
-IN
VER
TIN
G
100
CURRENT NOISE (pA/ Hz)
4
VOLTAGE NOISE (nV/ Hz)
0.8
BIAS CURRENT (PA)
OFFSET VOLTAGE (mV)
IBI
-10
-20
0
20
40
60
80
NON-INVERTING VOLTAGE
1
100
0.1
1
10
100
1
1k
10k
kHz
TEMPERATURE (°C)
Figure 19.
Figure 20.
Figure 21.
Disabled Channel Isolation
vs.
Frequency
-30
CROSSTALK (dBc)
-40
VIN = 2 VPP
VS = ±5V
-50
-60
-70
-80
-90
-100
0.1
1
10
100
1000
FREQUENCY (MHz)
8
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
APPLICATION INFORMATION
+5V
0.01 µF
VIN
RIN
+5V
6.8 µF
6.8 µF
AV = 1 +RF/RG = VOUT/VIN
0.01 µF
CPOS
VOUT
25:
-
+
CSS
0.1 µF
-
CNEG
0.01 µF
RG
=
VOUT
VIN
CPOS
+
CSS
0.1 µF
RF
AV =
RF
VIN
RG
RG
-5V
CNEG
0.01 µF
RT
6.8 µF
VOUT
6.8 µF
-5V
Figure 22. Recommended Non-Inverting Gain
Circuit
RF
SELECT RT TO
YIELD DESIRED
RIN = RT||RG
Figure 23. Recommended Inverting Gain Circuit
GENERAL INFORMATION
The LMH6738 is a high speed current feedback amplifier, optimized for very high speed and low distortion. The
LMH6738 has no internal ground reference so single or split supply configurations are both equally useful.
EVALUATION BOARDS
Texas Instruments provides the following evaluation boards as a guide for high frequency layout and as an aid in
device testing and characterization. Many of the data sheet plots were measured with these boards.
Device
Package
Evaluation Board
Part Number
LMH6738MQA
SSOP
LMH730275
FEEDBACK RESISTOR SELECTION
One of the key benefits of a current feedback operational amplifier is the ability to maintain optimum frequency
response independent of gain by using appropriate values for the feedback resistor (RF). The Electrical
Characteristics and Typical Performance plots specify an RF of 550Ω, a gain of +2 V/V and ±5V power supplies
(unless otherwise specified). Generally, lowering RF from it’s recommended value will peak the frequency
response and extend the bandwidth while increasing the value of RF will cause the frequency response to roll off
faster. Reducing the value of RF too far below it’s recommended value will cause overshoot, ringing and,
eventually, oscillation.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
9
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
800
RECOMMENDED RF (:)
700
600
NON-INVERTING (AV > 0)
500
400
300
INVERTING (AV < 0)
200
100
0
1
2
3
4
5
6
7
8
9
10
|GAIN| (V/V)
Figure 24. Recommended RF vs. Gain
See Figure 24, Recommended RF. vs Gain for selecting a feedback resistor value for gains of ±1 to ±10. Since
each application is slightly different it is worth some experimentation to find the optimal RF for a given circuit. In
general a value of RF that produces ~.1 dB of peaking is the best compromise between stability and maximal
bandwidth. Note that it is not possible to use a current feedback amplifier with the output shorted directly to the
inverting input. The buffer configuration of the LMH6738 requires a 750Ω feedback resistor for stable operation.
The LMH6738 was optimized for high speed operation. As shown in Figure 24 the suggested value for RF
decreases for higher gains. Due to the impedance of the input buffer there is a practical limit for how small RFcan
go, based on the lowest practical value of RG. This limitation applies to both inverting and non inverting
configurations. For the LMH6738 the input resistance of the inverting input is approximately 30Ω and 20Ω is a
practical (but not hard and fast) lower limit for RG. The LMH6738 begins to operate in a gain bandwidth limited
fashion in the region where RG is nearly equal to the input buffer impedance. Note that the amplifier will operate
with RG values well below 20Ω, however results may be substantially different than predicted from ideal models.
In particular the voltage potential between the Inverting and Non Inverting inputs cannot be expected to remain
small.
Inverting gain applications that require impedance matched inputs may limit gain flexibility somewhat (especially
if maximum bandwidth is required). The impedance seen by the source is RG || RT (RT is optional). The value of
RG is RF /Gain. Thus for an inverting gain of −7 V/V and an optimal value for RF the input impedance is equal to
50Ω. Using a termination resistor this can be brought down to match a 25Ω source, however, a 150Ω source
cannot be matched. To match a 150Ω source would require using a 1050Ω feedback resistor and would result in
reduced bandwidth.
For more information see Application Note OA-13 (SNOA366) which describes the relationship between RF and
closed-loop frequency response for current feedback operational amplifiers. The value for the inverting input
impedance for the LMH6738 is approximately 30Ω. The LMH6738 is designed for optimum performance at gains
of +1 to +10 V/V and −1 to −9 V/V. Higher gain configurations are still useful, however, the bandwidth will fall as
gain is increased, much like a typical voltage feedback amplifier.
ACTIVE FILTER
When using any current feedback Operational Amplifier as an active filter it is necessary to be careful using
reactive components in the feedback loop. Reducing the feedback impedance, especially at higher frequencies,
will almost certainly cause stability problems. Likewise capacitance on the inverting input should be avoided. See
Application Notes OA-07 (SNOA365) and OA-26 (SNOA387) for more information on Active Filter applications for
Current Feedback Op Amps.
10
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
When using the LMH6738 as a low pass filter the value of RF can be substantially reduced from the value
recommended in the RF vs. Gain charts. The benefit of reducing RF is increased gain at higher frequencies,
which improves attenuation in the stop band. Stability problems are avoided because in the stop band additional
device bandwidth is used to cancel the input signal rather than amplify it. The benefit of this change depends on
the particulars of the circuit design. With a high pass filter configuration reducing RF will likely result in device
instability and is not recommended.
X1
6.8 PF
+
C2
0.01 PF
RIN
51:
RG
550:
-
+
-
ROUT
51:
CL
10 pF
RL
1 k:
C1
RIN
75:
RF
550:
X1
VIN
+
RG
550:
-
+
VOUT
ROUT
75:
-
RF
550:
0.01 PF
C3
6.8 PF
C4
Figure 25. Typical Video Application
Figure 26. Decoupling Capacitive Loads
DRIVING CAPACITIVE LOADS
Capacitive output loading applications will benefit from the use of a series output resistor ROUT. Figure 26 shows
the use of a series output resistor, ROUT, to stabilize the amplifier output under capacitive loading. Capacitive
loads of 5 to 120 pF are the most critical, causing ringing, frequency response peaking and possible oscillation.
The charts “Suggested ROUT vs. Cap Load” give a recommended value for selecting a series output resistor for
mitigating capacitive loads. The values suggested in the charts are selected for .5 dB or less of peaking in the
frequency response. This gives a good compromise between settling time and bandwidth. For applications where
maximum frequency response is needed and some peaking is tolerable, the value of ROUT can be reduced
slightly from the recommended values.
An alternative approach is to place Rout inside the feedback loop as shown in Figure 27. This will preserve gain
accuracy, but will still limit maximum output voltage swing.
X1
+
+
RIN
51:
RG
550:
-
-
ROUT
51:
CL
10 pF
RL
1 k:
RF
550:
Figure 27. Series Output Resistor Inside
Feedback Loop
INVERTING INPUT PARASITIC CAPACITANCE
Parasitic capacitance is any capacitance in a circuit that was not intentionally added. It comes about from
electrical interaction between conductors. Parasitic capacitance can be reduced but never entirely eliminated.
Most parasitic capacitances that cause problems are related to board layout or lack of termination on
transmission lines. Please see the section on Layout Considerations for hints on reducing problems due to
parasitic capacitances on board traces. Transmission lines should be terminated in their characteristic
impedance at both ends.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
11
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
High speed amplifiers are sensitive to capacitance between the inverting input and ground or power supplies.
This shows up as gain peaking at high frequency. The capacitor raises device gain at high frequencies by
making RG appear smaller. Capacitive output loading will exaggerate this effect. In general, avoid introducing
unnecessary parasitic capacitance at both the inverting input and the output.
One possible remedy for this effect is to slightly increase the value of the feedback (and gain set) resistor. This
will tend to offset the high frequency gain peaking while leaving other parameters relatively unchanged. If the
device has a capacitive load as well as inverting input capacitance using a series output resistor as described in
DRIVING CAPACITIVE LOADS will help.
LAYOUT CONSIDERATIONS
Whenever questions about layout arise, use the evaluation board as a guide. The LMH730275 is the evaluation
board for the LMH6738.
To reduce parasitic capacitances ground and power planes should be removed near the input and output pins.
Components in the feedback loop should be placed as close to the device as possible. For long signal paths
controlled impedance lines should be used, along with impedance matching elements at both ends.
Bypass capacitors should be placed as close to the device as possible. Bypass capacitors from each rail to
ground are applied in pairs. The larger electrolytic bypass capacitors can be located farther from the device, the
smaller ceramic capacitors should be placed as close to the device as possible. The LMH6738 has multiple
power and ground pins for enhanced supply bypassing. Every pin should ideally have a separate bypass
capacitor. Sharing bypass capacitors may slightly degrade second order harmonic performance, especially if the
supply traces are thin and /or long. In Figure 22 and Figure 23 CSS is optional, but is recommended for best
second harmonic distortion. Another option to using CSS is to use pairs of .01 μF and 0.1 μF ceramic capacitors
for each supply bypass.
VIDEO PERFORMANCE
The LMH6738 has been designed to provide excellent performance with production quality video signals in a
wide variety of formats such as HDTV and High Resolution VGA. NTSC and PAL performance is nearly flawless.
Best performance will be obtained with back terminated loads. The back termination reduces reflections from the
transmission line and effectively masks transmission line and other parasitic capacitances from the amplifier
output stage. Figure 25 shows a typical configuration for driving a 75Ω Cable. The amplifier is configured for a
gain of two to make up for the 6 dB of loss in ROUT.
MAXIMUM POWER DISSIPATION (W)
2
1.8
225 LFPM FORCED AIR
1.6
1.4
1.2
1
STILL AIR
0.8
0.6
0.4
0.2
0
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
Figure 28. Maximum Power Dissipation
POWER DISSIPATION
The LMH6738 is optimized for maximum speed and performance in the small form factor of the standard SSOP16 package. To achieve its high level of performance, the LMH6738 consumes an appreciable amount of
quiescent current which cannot be neglected when considering the total package power dissipation limit. The
quiescent current contributes to about 40° C rise in junction temperature when no additional heat sink is used (VS
= ±5V, all 3 channels on). Therefore, it is easy to see the need for proper precautions to be taken in order to
make sure the junction temperature’s absolute maximum rating of 150°C is not violated.
12
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
LMH6738
www.ti.com
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
To ensure maximum output drive and highest performance, thermal shutdown is not provided. Therefore, it is of
utmost importance to make sure that the TJMAX is never exceeded due to the overall power dissipation (all 3
channels).
With the LMH6738 used in a back-terminated 75Ω RGB analog video system (with 2 VPP output voltage), the
total power dissipation is around 435 mW of which 340 mW is due to the quiescent device dissipation (output
black level at 0V). With no additional heat sink used, that puts the junction temperature to about 140° C when
operated at 85°C ambient.
To reduce the junction temperature many options are available. Forced air cooling is the easiest option. An
external add-on heat-sink can be added to the SSOP-16 package, or alternatively, additional board metal
(copper) area can be utilized as heat-sink.
An effective way to reduce the junction temperature for the SSOP-16 package (and other plastic packages) is to
use the copper board area to conduct heat. With no enhancement the major heat flow path in this package is
from the die through the metal lead frame (inside the package) and onto the surrounding copper through the
interconnecting leads. Since high frequency performance requires limited metal near the device pins the best
way to use board copper to remove heat is through the bottom of the package. A gap filler with high thermal
conductivity can be used to conduct heat from the bottom of the package to copper on the circuit board. Vias to a
ground or power plane on the back side of the circuit board will provide additional heat dissipation. A combination
of front side copper and vias to the back side can be combined as well.
Follow these steps to determine the Maximum power dissipation for the LMH6738:
1. Calculate the quiescent (no-load) power: PAMP = ICC* (VS) VS = V+-V−
2. Calculate the RMS power dissipated in the output stage:
– PD (rms) = rms ((VS - VOUT)*IOUT) where VOUT and IOUT are the voltage and current across the external
load and VS is the total supply current
3. Calculate the total RMS power: PT = PAMP+PD
The maximum power that the LMH6738, package can dissipate at a given temperature can be derived with the
following equation (See Figure 28):
PMAX = (150º – TAMB)/ θJA, where TAMB = Ambient temperature (°C) and θJA = Thermal resistance, from junction
to ambient, for a given package (°C/W). For the SSOP package θJA is 120°C/W.
ESD PROTECTION
The LMH6738 is protected against electrostatic discharge (ESD) on all pins. The LMH6738 will survive 2000V
Human Body model and 200V Machine model events.
Under closed loop operation the ESD diodes have no effect on circuit performance. There are occasions,
however, when the ESD diodes will be evident. If the LMH6738 is driven by a large signal while the device is
powered down the ESD diodes will conduct.
The current that flows through the ESD diodes will either exit the chip through the supply pins or will flow through
the device, hence it is possible to power up a chip with a large signal applied to the input pins. Shorting the
power pins to each other will prevent the chip from being powered up through the input.
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
13
LMH6738
SNOSAC1E – APRIL 2004 – REVISED MARCH 2013
www.ti.com
REVISION HISTORY
Changes from Revision D (March 2013) to Revision E
•
14
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 13
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LMH6738
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LMH6738MQ/NOPB
ACTIVE
SSOP
DBQ
16
95
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
LH67
38MQ
LMH6738MQX/NOPB
ACTIVE
SSOP
DBQ
16
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
LH67
38MQ
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
