LMH6642 [NSC]
3V, Low Power, 130MHz, 75mA Rail-to-Rail Output Amplifiers; 3V ，低功耗，为130MHz ， 75毫安轨到轨输出放大器
| 型号： | LMH6642 |
| 厂家： | 
National Semiconductor |
| 描述： | 3V, Low Power, 130MHz, 75mA Rail-to-Rail Output Amplifiers |
| 文件： | 总22页 (文件大小：950K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 2003
LMH6642/6643/6644
3V, Low Power, 130MHz, 75mA Rail-to-Rail Output
Amplifiers
in single (LMH6642), dual (LMH6643), and quad (LMH6644)
options. See ordering information for packages offered.
General Description
The LMH664X family true single supply voltage feedback
amplifiers offer high speed (130MHz), low distortion
(−62dBc), and exceptionally high output current (approxi-
mately 75mA) at low cost and with reduced power consump-
tion when compared against existing devices with similar
performance.
Features
(VS
=
5V, TA = 25˚C, RL = 2kΩ, AV = +1. Typical values
unless specified).
n −3dB BW (AV = +1)
130MHz
3V to 12.8V
130V/µs
Input common mode voltage range extends to 0.5V below V−
and 1V from V+. Output voltage range extends to within
40mV of either supply rail, allowing wide dynamic range
especially desirable in low voltage applications. The output
stage is capable of approximately 75mA in order to drive
heavy loads. Fast output Slew Rate (130V/µs) ensures large
peak-to-peak output swings can be maintained even at
higher speeds, resulting in exceptional full power bandwidth
of 40MHz with a 3V supply. These characteristics, along with
low cost, are ideal features for a multitude of industrial and
commercial applications.
n Supply voltage range
n Slew rate (Note 8), (AV = −1)
n Supply current (no load)
n Output short circuit current
n Linear output current
2.7mA/amp
+115mA/−145mA
75mA
n Input common mode volt. 0.5V beyond V−, 1V from V+
n Output voltage swing
n Input voltage noise (100kHz)
n Input current noise (100kHz)
40mV from rails
17nV/
0.9pA/
n THD (5MHz, RL = 2kΩ, VO = 2VPP, AV = +2)
n Settling time
−62dBc
68ns
Careful attention has been paid to ensure device stability
under all operating voltages and modes. The result is a very
well behaved frequency response characteristic (0.1dB gain
flatness up the 12MHz under 150Ω load and AV = +2) with
minimal peaking (typically 2dB maximum) for any gain set-
ting and under both heavy and light loads. This along with
fast settling time (68ns) and low distortion allows the device
to operate well in ADC buffer, and high frequency filter
applications as well as other applications.
n Fully characterized for 3V, 5V, and 5V
n Overdrive recovery
100ns
n Output short circuit protected (Note 11)
n No output phase reversal with CMVR exceeded
Applications
n Active filters
n CD/DVD ROM
n ADC buffer amp
n Portable video
n Current sense buffer
This device family offers professional quality video perfor-
mance with low DG (0.01%) and DP (0.01˚) characteristics.
Differential Gain and Differential Phase characteristics are
also well maintained under heavy loads (150Ω) and through-
out the output voltage range. The LMH664X family is offered
Closed Loop Gain vs. Frequency for Various Gain
Large Signal Frequency Response
20018547
20018535
© 2003 National Semiconductor Corporation
DS200185
www.national.com
Absolute Maximum Ratings (Note 1)
Infrared or Convection Reflow(20 sec)
Wave Soldering Lead Temp.(10 sec)
235˚C
260˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Ratings (Note 1)
Supply Voltage (V+ – V−)
ESD Tolerance
2KV (Note 2)
200V (Note 9)
2.5V
3V to 12.8V
Junction Temperature Range (Note 4)
−40˚C to +85˚C
VIN Differential
Package Thermal Resistance (Note 4) (θJA
)
Output Short Circuit Duration
Supply Voltage (V+ - V−)
Voltage at Input/Output pins
Input Current
(Note 3), (Note 11)
SOT23-5
SOIC-8
265˚C/W
190˚C/W
235˚C/W
145˚C/W
155˚C/W
13.5V
V+ +0.8V, V− −0.8V
10mA
MSOP-8
SOIC-14
TSSOP-14
Storage Temperature Range
Junction Temperature (Note 4)
Soldering Information
−65˚C to +150˚C
+150˚C
3V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 3V, V− = 0V, VCM = VO = V+/2, and RL = 2kΩ to V+/2.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
80
Typ
(Note 5)
115
Max
(Note 6)
Units
BW
−3dB BW
AV = +1, VOUT = 200mVPP
AV = +2, −1, VOUT = 200mVPP
AV = +2, RL = 150Ω to V+/2,
RL = 402Ω, VOUT = 200mVPP
AV = +1, −1dB, VOUT = 1VPP
f = 100kHz
MHz
MHz
46
BW0.1dB
0.1dB Gain Flatness
19
PBW
en
Full Power Bandwidth
40
17
MHz
Input-Referred Voltage Noise
nV/
pA/
dBc
f = 1kHz
48
in
Input-Referred Current Noise
Total Harmonic Distortion
Differential Gain
f = 100kHz
0.90
3.3
−48
f = 1kHz
THD
DG
f = 5MHz, VO = 2VPP, AV = −1,
RL = 100Ω to V+/2
VCM = 1V, NTSC, AV = +2
RL =150Ω to V+/2
RL =1kΩ to V+/2
0.17
%
0.03
0.05
DP
Differential Phase
VCM = 1V, NTSC, AV = +2
RL =150Ω to V+/2
RL =1kΩ to V+/2
deg
dB
ns
0.03
47
CT Rej.
TS
Cross-Talk Rejection
Settling Time
f = 5MHz, Receiver:
Rf = Rg = 510Ω, AV = +2
VO = 2VPP
VS = 5V
,
0.1%, 8pF Load,
68
SR
Slew Rate (Note 8)
Input Offset Voltage
AV = −1, VI = 2VPP
90
120
1
V/µs
mV
VOS
5
7
TC VOS
IB
Input Offset Average Drift
Input Bias Current
(Note 12)
(Note 7)
5
µV/˚C
µA
−1.50
−2.60
−3.25
800
IOS
RIN
CIN
Input Offset Current
20
3
nA
1000
Common Mode Input
Resistance
MΩ
Common Mode Input
Capacitance
2
pF
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2
3V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 3V, V− = 0V, VCM = VO = V+/2, and RL = 2kΩ to V+/2.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
Typ
(Note 5)
−0.5
Max
(Note 6)
−0.2
Units
CMVR
Input Common-Mode Voltage
Range
CMRR ≥ 50dB
−0.1
V
1.8
1.6
72
2.0
95
96
82
CMRR
AVOL
Common Mode Rejection
Ratio
VCM Stepped from 0V to 1.5V
dB
Large Signal Voltage Gain
VO = 0.5V to 2.5V
RL = 2kΩ to V+/2
80
75
dB
VO = 0.5V to 2.5V
RL = 150Ω to V+/2
74
70
VO
Output Swing
High
RL = 2kΩ to V+/2, VID = 200mV
RL = 150Ω to V+/2, VID = 200mV
RL = 2kΩ to V+/2, VID = −200mV
RL = 150Ω to V+/2, VID = −200mV
Sourcing to V+/2
2.90
2.80
2.98
2.93
25
V
Output Swing
Low
75
mV
75
150
ISC
Output Short Circuit Current
50
35
55
40
95
VID = 200mV (Note 10)
Sinking to V+/2
mA
110
VID = −200mV (Note 10)
VOUT = 0.5V from either supply
V+ = 3.0V to 3.5V, VCM = 1.5V
IOUT
Output Current
65
85
mA
dB
+PSRR
Positive Power Supply
Rejection Ratio
75
IS
Supply Current (per channel)
No Load
2.70
4.00
mA
4.50
5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = 0V, VCM = VO = V+/2, and RL = 2kΩ to V+/2.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
90
Typ
(Note 5)
120
Max
(Note 6)
Units
BW
−3dB BW
AV = +1, VOUT = 200mVPP
AV = +2, −1, VOUT = 200mVPP
AV = +2, RL = 150Ω to V+/2,
Rf = 402Ω, VOUT = 200mVPP
AV = +1, −1dB, VOUT = 2VPP
f = 100kHz
MHz
46
BW0.1dB
0.1dB Gain Flatness
15
MHz
MHz
PBW
en
Full Power Bandwidth
22
17
Input-Referred Voltage Noise
nV/
pA/
dBc
f = 1kHz
48
in
Input-Referred Current Noise
f = 100kHz
0.90
3.3
−60
f = 1kHz
THD
DG
Total Harmonic Distortion
Differential Gain
f = 5MHz, VO = 2VPP, AV = +2
NTSC, AV = +2
RL =150Ω to V+/2
RL =1kΩ to V+/2
0.16
0.05
0.05
0.01
47
%
DP
Differential Phase
NTSC, AV = +2
RL =150Ω to V+/2
deg
RL =1kΩ to V+/2
CT Rej.
TS
Cross-Talk Rejection
Settling Time
f = 5MHz, Receiver:
Rf = Rg = 510Ω, AV = +2
dB
ns
VO = 2VPP
,
0.1%, 8pF Load
68
3
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5V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = 0V, VCM = VO = V+/2, and RL = 2kΩ to V+/2.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
95
Typ
(Note 5)
125
Max
(Note 6)
Units
SR
Slew Rate (Note 8)
Input Offset Voltage
AV = −1, VI = 2VPP
V/µs
mV
VOS
5
1
5
7
TC VOS
IB
Input Offset Average Drift
Input Bias Current
(Note 12)
(Note 7)
µV/˚C
µA
−2.60
−3.25
800
−1.70
IOS
Input Offset Current
20
3
nA
1000
RIN
Common Mode Input
Resistance
MΩ
CIN
Common Mode Input
Capacitance
pF
2
CMVR
Input Common-Mode Voltage
Range
CMRR ≥ 50dB
−0.2
−0.5
4.0
95
98
82
−0.1
V
3.8
3.6
CMRR
AVOL
Common Mode Rejection
Ratio
VCM Stepped from 0V to 3.5V
dB
72
Large Signal Voltage Gain
VO = 0.5V to 4.50V
RL = 2kΩ to V+/2
86
82
dB
VO = 0.5V to 4.25V
RL = 150Ω to V+/2
76
72
VO
Output Swing
High
RL = 2kΩ to V+/2, VID = 200mV
RL = 150Ω to V+/2, VID = 200mV
RL = 2kΩ to V+/2, VID = −200mV
RL = 150Ω to V+/2, VID = −200mV
Sourcing to V+/2
4.90
4.65
4.98
4.90
25
V
Output Swing
Low
100
150
mV
100
ISC
Output Short Circuit Current
55
40
70
55
115
VID = 200mV (Note 10)
Sinking to V+/2
mA
140
70
VID = −200mV (Note 10)
VO = 0.5V from either supply
V+ = 4.0V to 6V
IOUT
Output Current
mA
dB
+PSRR
Positive Power Supply
Rejection Ratio
79
90
IS
Supply Current (per channel)
No Load
4.25
2.70
mA
5.00
5V Electrical Characteristics
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = −5V, VCM = VO = 0V and RL = 2kΩ to ground.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
95
Typ
(Note 5)
130
Max
(Note 6)
Units
BW
−3dB BW
AV = +1, VOUT = 200mVPP
AV = +2, −1, VOUT = 200mVPP
AV = +2, RL = 150Ω to V+/2,
Rf = 806Ω, VOUT = 200mVPP
AV = +1, −1dB, VOUT = 2VPP
f = 100kHz
MHz
46
BW0.1dB
0.1dB Gain Flatness
12
MHz
MHz
PBW
en
Full Power Bandwidth
24
17
48
Input-Referred Voltage Noise
nV/
f = 1kHz
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4
5V Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for at TJ = 25˚C, V+ = 5V, V− = −5V, VCM = VO = 0V and RL = 2kΩ to ground.
Boldface limits apply at the temperature extremes.
Symbol
Parameter
Conditions
Min
(Note 6)
Typ
(Note 5)
0.90
Max
(Note 6)
Units
in
Input-Referred Current Noise
f = 100kHz
pA/
f = 1kHz
3.3
THD
DG
Total Harmonic Distortion
Differential Gain
f = 5MHz, VO = 2VPP, AV = +2
NTSC, AV = +2
RL =150Ω to V+/2
RL =1kΩ to V+/2
NTSC, AV = +2
RL =150Ω to V+/2
RL =1kΩ to V+/2
f = 5MHz, Receiver:
Rf = Rg = 510Ω, AV = +2
−62
dBc
%
0.15
0.01
0.04
0.01
47
DP
Differential Phase
deg
CT Rej.
TS
Cross-Talk Rejection
Settling Time
dB
ns
VO = 2VPP
,
0.1%, 8pF Load,
68
135
1
VS = 5V
SR
Slew Rate (Note 8)
Input Offset Voltage
AV = −1, VI = 2VPP
100
V/µs
mV
VOS
5
7
TC VOS
IB
Input Offset Average Drift
Input Bias Current
(Note 12)
(Note 7)
5
µV/˚C
µA
−2.60
−3.25
800
−1.60
IOS
Input Offset Current
20
3
nA
1000
RIN
Common Mode Input
Resistance
MΩ
CIN
Common Mode Input
Capacitance
pF
2
CMVR
Input Common-Mode Voltage
Range
CMRR ≥ 50dB
−5.2
−5.5
4.0
95
96
82
−5.1
V
3.8
3.6
CMRR
AVOL
Common Mode Rejection
Ratio
VCM Stepped from −5V to 3.5V
dB
74
Large Signal Voltage Gain
VO = −4.5V to 4.5V,
RL = 2kΩ
88
84
dB
VO = −4.0V to 4.0V,
RL = 150Ω
78
74
VO
Output Swing
High
RL = 2kΩ, VID = 200mV
RL = 150Ω, VID = 200mV
RL = 2kΩ, VID = −200mV
RL = 150Ω, VID = −200mV
Sourcing to Ground
VID = 200mV (Note 10)
Sinking to Ground
4.90
4.65
4.96
4.80
V
V
Output Swing
Low
−4.96
−4.80
−4.90
−4.65
ISC
Output Short Circuit Current
60
35
85
65
75
115
145
mA
VID = −200mV (Note 10)
IOUT
Output Current
VO = 0.5V from either supply
mA
dB
PSRR
Power Supply Rejection Ratio (V+, V−) = (4.5V, −4.5V) to (5.5V,
−5.5V)
78
90
IS
Supply Current (per channel)
No Load
4.50
2.70
mA
5.50
5
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5V Electrical Characteristics (Continued)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics.
Note 2: Human body model, 1.5kΩ in series with 100pF.
Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the
maximum allowed junction temperature of 150˚C.
Note 4: The maximum power dissipation is a function of T
, θ , and T . The maximum allowable power dissipation at any ambient temperature is
J(MAX)
JA
A
P
= (T - T )/ θ . All numbers apply for packages soldered directly onto a PC board.
J(MAX) A JA
D
Note 5: Typical values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: Positive current corresponds to current flowing into the device.
Note 8: Slew rate is the average of the rising and falling slew rates.
Note 9: Machine Model, 0Ω in series with 200pF.
Note 10: Short circuit test is a momentary test. See Note 11.
<
>
6V, allowable short circuit duration is 1.5ms.
Note 11: Output short circuit duration is infinite for V
6V at room temperature and below. For V
S
S
Note 12: Offset voltage average drift determined by dividing the change in V
at temperature extremes by the total temperature change.
OS
Connection Diagrams
SOIC-8 and MSOP-8
(LMH6643)
SOT23-5 (LMH6642)
SOIC-8 (LMH6642)
20018561
20018562
Top View
Top View
20018563
Top View
SOIC-14 and TSSOP-14
(LMH6644)
20018568
Top View
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6
Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified.
Closed Loop Frequency Response for Various Supplies
Closed Loop Gain vs. Frequency for Various Gain
20018557
20018551
Closed Loop Frequency Response for Various
Temperature
Closed Loop Gain vs. Frequency for Various Gain
20018550
20018535
Closed Loop Frequency Response for Various
Temperature
Closed Loop Gain vs. Frequency for Various Supplies
20018548
20018534
7
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Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
Closed Loop Small Signal Frequency Response for
Large Signal Frequency Response
Various Supplies
20018546
20018547
Closed Loop Frequency Response for Various Supplies
0.1dB Gain Flatness for Various Supplies
20018544
20018545
<
<
VOUT (VPP) for THD 0.5%
VOUT (VPP) for THD 0.5%
20018509
20018508
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8
Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
<
VOUT (VPP) for THD 0.5%
Open Loop Gain/Phase for Various Temperature
20018532
20018510
Open Loop Gain/Phase for Various Temperature
HD2 (dBc) vs. Output Swing
20018533
20018514
HD3 (dBc) vs. Output Swing
HD2 vs. Output Swing
20018504
20018515
9
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Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
HD3 vs. Output Swing
THD (dBc) vs. Output Swing
20018505
20018506
Settling Time vs. Input Step Amplitude
(Output Slew and Settle Time)
Input Noise vs. Frequency
20018512
20018513
VOUT from V+ vs. ISOURCE
VOUT from V− vs. ISINK
20018518
20018519
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10
Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
VOUT from V+ vs. ISOURCE
VOUT from V− vs. ISINK
20018516
20018517
Swing vs. VS
Short Circuit Current (to VS/2) vs. VS
20018529
20018531
Output Sinking Saturation Voltage vs. IOUT
Output Sourcing Saturation Voltage vs. IOUT
20018520
20018501
11
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Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
Closed Loop Output Impedance vs. Frequency AV = +1
PSRR vs. Frequency
20018502
20018503
Crosstalk Rejection vs. Frequency
(Output to Output)
CMRR vs. Frequency
20018507
20018511
VOS vs. VOUT (Typical Unit)
VOS vs. VCM (Typical Unit)
20018527
20018530
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12
Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
VOS vs. VS (for 3 Representative Units)
VOS vs. VS (for 3 Representative Units)
20018522
20018523
VOS vs. VS (for 3 Representative Units)
IB vs. VS
20018525
20018524
IOS vs. VS
IS vs. VCM
20018528
20018526
13
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Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
IS vs. VS
Small Signal Step Response
20018553
20018521
Large Signal Step Response
Large Signal Step Response
20018541
20018539
Small Signal Step Response
Small Signal Step Response
20018556
20018536
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14
Typical Performance Characteristics At TJ = 25˚C, V+ = +5, V− = −5V, RF = RL = 2kΩ. Unless
otherwise specified. (Continued)
Small Signal Step Response
Small Signal Step Response
20018552
20018538
Large Signal Step Response
Large Signal Step Response
20018537
20018554
Large Signal Step Response
20018560
15
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This device family was designed to avoid output phase
reversal. With input overdrive, the output is kept near supply
rail (or as closed to it as mandated by the closed loop gain
setting and the input voltage). See Figure 1:
Application Notes
CIRCUIT DESCRIPTION:
The LMH664X family is based on National Semiconductor’s
proprietary VIP10 dielectrically isolated bipolar process.
This device family architecture features the following:
•
•
•
Complimentary bipolar devices with exceptionally high ft
(∼8GHz) even under low supply voltage (2.7V) and low
bias current.
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-push output stage capable of
75mA output current (at 0.5V from the supply rails) while
consuming only 2.7mA of total supply current per chan-
nel. This architecture allows output to reach within milli-
volts of either supply rail.
•
•
Consistent performance from any supply voltage (3V-
10V) with little variation with supply voltage for the most
important specifications (e.g. BW, SR, IOUT, etc.)
20018542
Significant power saving (∼40%) compared to competi-
tive devices on the market with similar performance.
FIGURE 1. Input and Output Shown with CMVR
Exceeded
However, if the input voltage range of −0.5V to 1V from V+ is
exceeded by more than a diode drop, the internal ESD
protection diodes will start to conduct.The current in the
diodes should be kept at or below 10mA.
Application Hints:
This Op Amp family is a drop-in replacement for the AD805X
family of high speed Op Amps in most applications. In addi-
tion, the LMH664X will typically save about 40% on power
dissipation, due to lower supply current, when compared to
competition. All AD805X family’s guaranteed parameters are
included in the list of LMH664X guaranteed specifications in
order to ensure equal or better level of performance. How-
ever, as in most high performance parts, due to subtleties of
applications, it is strongly recommended that the perfor-
mance of the part to be evaluated is tested under actual
operating conditions to ensure full compliance to all specifi-
cations.
Output overdrive recovery time is less than 100ns as can be
seen from Figure 2 plot:
With 3V supplies and a common mode input voltage range
that extends 0.5V below V−, the LMH664X find applications
in low voltage/low power applications. Even with 3V sup-
@
plies, the −3dB BW ( AV = +1) is typically 115MHz with a
tested limit of 80MHz. Production testing guarantees that
process variations with not compromise speed. High fre-
quency response is exceptionally stable confining the typical
-3dB BW over the industrial temperature range to 2.5%.
As can be seen from the typical performance plots, the
LMH664X output current capability (∼75mA) is enhanced
compared to AD805X. This enhancement, increases the
output load range, adding to the LMH664X’s versatility.
20018543
FIGURE 2. Overload Recovery Waveform
Because of the LMH664X’s high output current capability
attention should be given to device junction temperature in
order not to exceed the Absolute Maximum Rating.
www.national.com
16
Amp input capacitance and Q1 equivalent collector capaci-
tance together (CIN) will cause additional phase shift to the
signal fed back to the inverting node. Cf will function as a
zero in the feedback path counter-acting the effect of the CIN
and acting to stabilized the circuit. By proper selection of Cf
such that the Op Amp open loop gain is equal to the inverse
of the feedback factor at that frequency, the response is
optimized with a theoretical 45˚ phase margin.
Application Notes (Continued)
SINGLE SUPPLY, LOW POWER PHOTODIODE
AMPLIFIER:
The circuit shown in Figure 3 is used to amplify the current
from a photo-diode into a voltage output. In this circuit, the
emphasis is on achieving high bandwidth and the transim-
pedance gain setting is kept relatively low. Because of its
high slew rate limit and high speed, the LMH664X family
lends itself well to such an application.
This circuit achieves approximately 1V/mA of transimped-
ance gain and capable of handling up to 1mApp from the
photodiode. Q1, in a common base configuration, isolates
the high capacitance of the photodiode (Cd) from the Op
Amp input in order to maximize speed. Input is AC coupled
through C1 to ease biasing and allow single supply opera-
tion. With 5V single supply, the device input/output is shifted
to near half supply using a voltage divider from VCC. Note
that Q1 collector does not have any voltage swing and the
Miller effect is minimized. D1, tied to Q1 base, is for tem-
perature compensation of Q1’s bias point. Q1 collector cur-
rent was set to be large enough to handle the peak-to-peak
photodiode excitation and not too large to shift the U1 output
too far from mid-supply.
(1)
where GBWP is the Gain Bandwidth Product of the Op Amp
Optimized as such, the I-V converter will have a theoretical
pole, fp, at:
(2)
With Op Amp input capacitance of 3pF and an estimate for
Q1 output capacitance of about 3pF as well, CIN = 6pF. From
the typical performance plots, LMH6642/6643 family GBWP
is approximately 57MHz. Therefore, with Rf = 1k, from Equa-
tion 1 and 2 above.
Cf = ∼4.1pF, and fp = 39MHz
No matter how low an Rf is selected, there is a need for Cf in
order to stabilize the circuit. The reason for this is that the Op
20018564
FIGURE 3. Single Supply Photodiode I-V Converter
17
www.national.com
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:
Application Notes (Continued)
For this example, optimum Cf was empirically determined to
be around 5pF. This time domain response is shown in
Figure 4 below showing about 9ns rise/fall times, corre-
sponding to about 39MHz for fp. The overall supply current
from the +5V supply is around 5mA with no load.
Device
Package
Evaluation
Board PN
LMH6642MF
LMH6642MA
LMH6643MA
LMH6643MM
LMH6644MA
LMH6644MT
SOT23-5
8-Pin SOIC
8-Pin SOIC
8-Pin MSOP
14-Pin SOIC
14-Pin TSSOP
CLC730068
CLC730027
CLC730036
CLC730123
CLC730031
CLC730131
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 selec-
tion. 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. Ei-
ther way, keeping the resistor values lower, will diminish this
interaction to a large extent. On the other hand, choosing
very low value resistors could load down nodes and will
contribute to higher overall power dissipation.
20018565
FIGURE 4. Converter Step Response (1VPP, 20 ns/DIV)
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
Ordering Information
Package
Part Number
LMH6642MF
LMH6642MFX
LMH6642MA
LMH6642MAX
LMH6643MA
LMH6643MAX
LMH6643MM
LMH6643MMX
LMH6644MA
LNH6644MAX
LMH6644MT
LMH6644MTX
Package Marking
Transport Media
1k Units Tape and Reel
3k Units Tape and Reel
Rails
NSC Drawing
5-Pin SOT-23
A64A
MF05A
SOIC-8
LMH6642MA
LMH6643MA
A65A
M08A
2.5k Units Tape and Reel
Rails
2.5k Units Tape and Reel
1k Units Tape and Reel
3.5k Units Tape and Reel
Rails
MSOP-8
SOIC-14
MUA08A
M14A
LMH6644MA
LMH6644MT
2.5k Units Tape and Reel
Rails
TSSOP-14
MTC14
2.5k Units Tape and Reel
www.national.com
18
Physical Dimensions inches (millimeters) unless otherwise noted
5-Pin SOT23
NS Package Number MF05A
8-Pin SOIC
NS Package Number M08A
19
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Pin MSOP
NS Package Number MUA08A
www.national.com
20
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
14-Pin SOIC
NS Package Number M14A
21
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
14-Pin TSSOP
NS Package Number MTC14
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.
National Semiconductor
Americas Customer
Support Center
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
National Semiconductor
Asia Pacific Customer
Support Center
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
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
Email: ap.support@nsc.com
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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