Datasheet LMH6642EP Datasheet (National Semiconductor)

Page 1

查询LMH6643EP供应商

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic Low Power, 130MHz, 75mA Rail-to-Rail Output Amplifiers

General Description

The LMH664XEP family true single supply voltage feedback amplifiers offer high speed (130MHz), low distortion (−62dBc), and exceptionally high output current (approximately 75mA) at low cost and with reduced power consumption when compared against existing devices with similar performance.

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.

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 A minimal peaking (typically 2dB maximum) for any gain setting 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.

This device family offers professional quality video performance 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 throughout the output voltage range. The LMH664XEP family is offered in single (LMH6642EP), dual (LMH6643EP), and quad (LMH6644EP) options. See ordering information for packages offered.

= +2) with

ENHANCED PLASTIC

Extended Temperature Performance of −40˚C to +85˚C

•

Baseline Control - Single Fab & Assembly Site

•

Process Change Notification (PCN)

•

Qualification & Reliability Data

•

Solder (PbSn) Lead Finish is standard

•

Enhanced Diminishing Manufacturing Sources (DMS)

•

−

Support

Features

(VS=±5V, TA= 25˚C, RL=2kΩ,AV= +1. Typical values unless specified).

n −3dB BW (A n Supply voltage range 2.7V to 12.8V n Slew rate (Note 11), (A n Supply current (no load) 2.7mA/amp n Output short circuit current +115mA/−145mA n Linear output current n Input common mode volt. 0.5V beyond V n Output voltage swing 40mV from rails n Input voltage noise (100kHz) 17nV/ n Input current noise (100kHz) 0.9pA/ n THD (5MHz, RL=2kΩ,VO=2VPP,AV= +2) −62dBc n Settling time 68ns n Fully characterized for 3V, 5V, and n Overdrive recovery 100ns n Output short circuit protected (Note 14) n No output phase reversal with CMVR exceeded

= +1) 130MHz

= −1) 130V/µs

Applications

n Selected Military Applications n Selected Avionics Applications

July 2004

75mA

−

, 1V from V

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic Low Power, 130MHz, 75mA Rail-to-Rail

Output Amplifiers

Ordering Information

PART NUMBER VID PART NUMBER NS PACKAGE NUMBER (Note 3)

LMH6642MFXEP V62/04625-01 MF05A

LMH6643MAXEP V62/04625-02 M08A

LMH6644MAXEP V62/04625-03 M14A

(Notes 1, 2) TBD TBD

Note 1: For the following (Enhanced Plastic) versions, check for availability: LMH6642MAEP, LMH6642MAXEP, LMH6642MFEP, LMH6643MAEP, LMH6643MMEP, LMH6643MMXEP, LMH6644MAEP, LMH6644MTEP, LMH6644MTXEP. Parts listed with an "X" are provided in Tape & Reel and parts without an "X" are in Rails.

Note 2: FOR ADDITIONAL ORDERING AND PRODUCT INFORMATION, PLEASE VISIT THE ENHANCED PLASTIC WEB SITE AT: www.national.com/ mil

Note 3: Refer to package details under Physical Dimensions

Page 2

Absolute Maximum Ratings (Note 4)

If Military/Aerospace specified devices are required,

Infrared or Convection Reflow(20 sec) 235˚C

Wave Soldering Lead Temp.(10 sec) 260˚C

please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Operating Ratings (Note 4)

ESD Tolerance 2KV (Note 5)

200V (Note 12)

Differential

2.5V

Output Short Circuit Duration (Note 6), (Note 14)

Supply Voltage (V

Voltage at Input/Output pins V

Input Current

+-V−

) 13.5V

+0.8V, V−−0.8V

10mA

Storage Temperature Range −65˚C to +150˚C

Junction Temperature (Note 7) +150˚C

Soldering Information

Supply Voltage (V

Junction Temperature Range (Note 7) −40˚C to +85˚C

Package Thermal Resistance (Note 7) (θ

SOT23-5 265˚C/W

SOIC-8 190˚C/W

MSOP-8 235˚C/W

SOIC-14 145˚C/W

TSSOP-14 155˚C/W

+–V−

) 2.7V to 12.8V

)

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

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

BW −3dB BW A

0.1dB

0.1dB Gain Flatness AV= +2, RL= 150Ω to V+/2,

PBW Full Power Bandwidth A

Input-Referred Voltage Noise f = 100kHz 17

= +1, V

= +2, −1, V

= 402Ω,V

= +1, −1dB, V

OUT

= 200mV

OUT

= 200mV

OUT

= 200mV

=1V

f = 1kHz 48

Input-Referred Current Noise f = 100kHz 0.90

f = 1kHz 3.3

THD Total Harmonic Distortion f = 5MHz, V

= 100Ω to V+/2

DG Differential Gain V

DP Differential Phase V

= 1V, NTSC, AV=+2

=150Ω to V+/2

=1kΩ to V+/2 0.03

= 1V, NTSC, AV=+2

=150Ω to V+/2

=1kΩ to V+/2 0.03

=2VPP,AV= −1,

CT Rej. Cross-Talk Rejection f = 5MHz, Receiver:

= 510Ω,AV=+2

f=Rg

=5V

= −1, VI=2V

Settling Time VO=2VPP,±0.1%, 8pF Load,

SR Slew Rate (Note 11) A

TC V

Input Offset Voltage

Input Offset Average Drift (Note 15)

Input Bias Current (Note 10) −1.50 −2.60

Input Offset Current 20 800

Common Mode Input

Resistance

Common Mode Input Capacitance

(Note 9)

80 115

90 120 V/µs

Typ

(Note 8)

Max

(Note 9)

19 MHz

40 MHz

−48

0.17

0.05

47 dB

68 ns

5 µV/˚C

−3.25

1000

3MΩ

2pF

Units

MHz

nV/

pA/

dBc

deg

µA

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Page 3

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 9)

CMVR Input Common-Mode Voltage

CMRR ≥ 50dB −0.5 −0.2

Range

CMRR Common Mode Rejection

Stepped from 0V to 1.5V 72 95 dB

Ratio

VOL

OUT

+PSRR Positive Power Supply

Large Signal Voltage Gain VO= 0.5V to 2.5V

=2kΩ to V+/2

= 0.5V to 2.5V

= 150Ω to V+/2

Output Swing High

Output Swing Low

RL=2kΩ to V+/2, VID= 200mV 2.90 2.98

= 150Ω to V+/2, VID= 200mV 2.80 2.93

=2kΩ to V+/2, VID= −200mV 25 75

= 150Ω to V+/2, VID= −200mV 75 150

Output Short Circuit Current Sourcing to V+/2

= 200mV (Note 13)

Output Current V

Sinking to V

= −200mV (Note 13)

OUT +

= 3.0V to 3.5V, VCM= 1.5V 75 85 dB

= 0.5V from either supply

Rejection Ratio

Supply Current (per channel) No Load 2.70 4.00

1.8

1.6

Typ

(Note 8)

Max

(Note 9)

−0.1

2.0

110

65 mA

4.50

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Units

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 9)

BW −3dB BW A

0.1dB

0.1dB Gain Flatness AV= +2, RL= 150Ω to V+/2,

PBW Full Power Bandwidth A

Input-Referred Voltage Noise f = 100kHz 17

= +1, V

= +2, −1, V

= 402Ω,V

= +1, −1dB, V

OUT

= 200mV

OUT

= 200mV

OUT

=2V

90 120

f = 1kHz 48

Input-Referred Current Noise f = 100kHz 0.90

f = 1kHz 3.3

THD Total Harmonic Distortion f = 5MHz, V

DG Differential Gain NTSC, A

=150Ω to V+/2

=1kΩ to V+/2 0.05

DP Differential Phase NTSC, A

=150Ω to V+/2

=1kΩ to V+/2 0.01

=2VPP,AV= +2 −60 dBc

=+2

CT Rej. Cross-Talk Rejection f = 5MHz, Receiver:

Settling Time VO=2VPP,±0.1%, 8pF Load 68 ns

= 510Ω,AV=+2

f=Rg

Typ

(Note 8)

Max

(Note 9)

15 MHz

22 MHz

0.16

0.05

47 dB

nV/

pA/

Units

MHz

deg

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Page 4

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

SR Slew Rate (Note 11) A

TC V

Input Offset Voltage

Input Offset Average Drift (Note 15)

Input Bias Current (Note 10)

Input Offset Current

Common Mode Input

= −1, VI=2V

Resistance

Common Mode Input Capacitance

CMVR Input Common-Mode Voltage

CMRR ≥ 50dB

Range

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

CMRR Common Mode Rejection

Ratio

VOL

Large Signal Voltage Gain VO= 0.5V to 4.50V

Output Swing High

Output Swing Low

OUT

Output Short Circuit Current Sourcing to V+/2

Output Current VO= 0.5V from either supply

+PSRR Positive Power Supply

Rejection Ratio

Supply Current (per channel) No Load

Stepped from 0V to 3.5V

=2kΩ to V+/2

= 0.5V to 4.25V

= 150Ω to V+/2

RL=2kΩ to V+/2, VID= 200mV 4.90 4.98

= 150Ω to V+/2, VID= 200mV 4.65 4.90

=2kΩ to V+/2, VID= −200mV 25 100

= 150Ω to V+/2, VID= −200mV 100 150

= 200mV (Note 13)

Sinking to V

= −200mV (Note 13)

= 4.0V to 6V

(Note 9)

95 125 V/µs

3.8

3.6

72 95

79 90

Typ

(Note 8)

5 µV/˚C

−1.70

Max

(Note 9)

−2.60

−3.25

800

1000

−0.5

−0.2

−0.1

4.0

115

140

70 mA

2.70

4.25

5.00

Units

µA

MΩ

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 9)

BW −3dB BW A

0.1dB

0.1dB Gain Flatness AV= +2, RL= 150Ω to V+/2,

PBW Full Power Bandwidth A

Input-Referred Voltage Noise f = 100kHz 17

= +1, V

= +2, −1, V

= 806Ω,V

= +1, −1dB, V

OUT

= 200mV

OUT

= 200mV

OUT

=2V

95 130

Typ

(Note 8)

Max

(Note 9)

12 MHz

24 MHz

f = 1kHz 48

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Units

MHz

nV/

Page 5

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 9)

Input-Referred Current Noise f = 100kHz 0.90

f = 1kHz 3.3

THD Total Harmonic Distortion f = 5MHz, V

DG Differential Gain NTSC, A

=150Ω to V+/2

=1kΩ to V+/2 0.01

DP Differential Phase NTSC, A

=150Ω to V+/2

=1kΩ to V+/2 0.01

=2VPP,AV= +2 −62 dBc

=+2

CT Rej. Cross-Talk Rejection f = 5MHz, Receiver:

Rf=Rg= 510Ω,AV=+2

SR Slew Rate (Note 11) A

TC V

Settling Time VO=2VPP,±0.1%, 8pF Load,

=5V

= −1, VI=2V

Input Offset Voltage

Input Offset Average Drift (Note 15)

Input Bias Current (Note 10)

Input Offset Current

Common Mode Input

100 135 V/µs

Resistance

Common Mode Input Capacitance

CMVR Input Common-Mode Voltage

CMRR ≥ 50dB

Range

3.8

3.6

CMRR Common Mode Rejection

Ratio

VOL

Large Signal Voltage Gain VO= −4.5V to 4.5V,

Output Swing High

Output Swing Low

OUT

Output Short Circuit Current Sourcing to Ground

Output Current VO= 0.5V from either supply

PSRR Power Supply Rejection Ratio (V

Supply Current (per channel) No Load

Stepped from −5V to 3.5V

74 95

=2kΩ

= −4.0V to 4.0V,

= 150Ω

RL=2kΩ,VID= 200mV 4.90 4.96

= 150Ω,VID= 200mV 4.65 4.80

=2kΩ,VID= −200mV −4.96 −4.90

= 150Ω,VID= −200mV −4.80 −4.65

= 200mV (Note 13)

Sinking to Ground

= −200mV (Note 13)

+,V−

) = (4.5V, −4.5V) to (5.5V,

−5.5V)

75 mA

78 90

Typ

(Note 8)

Max

(Note 9)

0.15

0.04

47 dB

5 µV/˚C

−1.60

−2.60

−3.25

800

1000

−5.5

−5.2

−5.1

4.0

115

145

2.70

4.50

5.50

Units

pA/

deg

MΩ

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

µA

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Page 6

5V Electrical Characteristics (Continued)

Note 4: 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 5: Human body model, 1.5kΩ in series with 100pF.

Note 6: 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 7: The maximum power dissipation is a function of T P

=(T

J(MAX)-TA

Note 8: Typical values represent the most likely parametric norm.

Note 9: All limits are guaranteed by testing or statistical analysis.

Note 10: Positive current corresponds to current flowing into the device.

Note 11: Slew rate is the average of the rising and falling slew rates.

Note 12: Machine Model, 0Ω in series with 200pF.

Note 13: Short circuit test is a momentary test. See Note 14.

Note 14: Output short circuit duration is infinite for V

Note 15: Offset voltage average drift determined by dividing the change in V

)/ θJA. All numbers apply for packages soldered directly onto a PC board.

6V at room temperature and below. For V

, θJA, and TA. The maximum allowable power dissipation at any ambient temperature is

J(MAX)

6V, allowable short circuit duration is 1.5ms.

at temperature extremes by the total temperature change.

Connection Diagrams

SOIC-8 and MSOP-8

(LMH6643)

SOT23-5 (LMH6642) SOIC-8 (LMH6642)

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Top View

20089461

Top View

SOIC-14 and TSSOP-14

(LMH6644)

Top View

20089462

20089463

Top View

20089468

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Page 7

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Typical Performance Characteristics At T

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless oth-

erwise specified.

Closed Loop Frequency Response for Various Supplies Closed Loop Gain vs. Frequency for Various Gain

20089457

20089451

Closed Loop Frequency Response for Various

Closed Loop Gain vs. Frequency for Various Gain

Temperature

20089435

Closed Loop Gain vs. Frequency for Various Supplies

20089448

20089450

Closed Loop Frequency Response for Various

Temperature

20089434

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Page 8

Typical Performance Characteristics At T

otherwise specified. (Continued)

Large Signal Frequency Response

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

Closed Loop Small Signal Frequency Response for

Various Supplies

Closed Loop Frequency Response for Various Supplies

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

OUT(VPP

) for THD<0.5% V

20089447

20089444

0.1dB Gain Flatness for Various Supplies

OUT(VPP

) for THD<0.5%

20089446

20089445

20089409 20089408

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Page 9

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Typical Performance Characteristics At T

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

otherwise specified. (Continued)

OUT(VPP

) for THD<0.5% Open Loop Gain/Phase for Various Temperature

20089410

Open Loop Gain/Phase for Various Temperature HD2 (dBc) vs. Output Swing

20089432

20089433

HD3 (dBc) vs. Output Swing HD2 vs. Output Swing

20089415

20089414

20089404

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Page 10

Typical Performance Characteristics At T

otherwise specified. (Continued)

HD3 vs. Output Swing THD (dBc) vs. Output Swing

20089405 20089406

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Settling Time vs. Input Step Amplitude

(Output Slew and Settle Time) Input Noise vs. Frequency

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

20089413

from V+vs. I

OUT

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SOURCE

20089418 20089419

OUT

from V−vs. I

20089412

SINK

Page 11

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Typical Performance Characteristics At T

otherwise specified. (Continued)

from V+vs. I

OUT

Swing vs. V

SOURCE

20089416 20089417

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

from V−vs. I

OUT

SINK

Short Circuit Current (to VS/2) vs. V

Output Sinking Saturation Voltage vs. I

20089429 20089431

OUT

20089420

Output Sourcing Saturation Voltage vs. I

OUT

20089401

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Page 12

Typical Performance Characteristics At T

otherwise specified. (Continued)

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

Closed Loop Output Impedance vs. Frequency A

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

CMRR vs. Frequency

= +1 PSRR vs. Frequency

20089402 20089403

Crosstalk Rejection vs. Frequency

(Output to Output)

20089407

VOSvs. V

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(Typical Unit) VOSvs. VCM(Typical Unit)

OUT

20089430

20089411

20089427

Page 13

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Typical Performance Characteristics At T

otherwise specified. (Continued)

vs. VS(for 3 Representative Units) VOSvs. VS(for 3 Representative Units)

20089422 20089423

VOSvs. VS(for 3 Representative Units) IBvs. V

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

IOSvs. V

20089424

20089426

ISvs. V

20089425

20089428

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Page 14

Typical Performance Characteristics At T

otherwise specified. (Continued)

vs. V

20089421

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Large Signal Step Response Large Signal Step Response

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

Small Signal Step Response

20089453

20089441 20089439

Small Signal Step Response Small Signal Step Response

20089456 20089436

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Page 15

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Typical Performance Characteristics At T

otherwise specified. (Continued)

Small Signal Step Response Small Signal Step Response

20089452

Large Signal Step Response Large Signal Step Response

= 25˚C, V+= +5, V−= −5V, RF=RL=2kΩ. Unless

20089438

Large Signal Step Response

20089437 20089454

20089460

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Page 16

Application Notes

CIRCUIT DESCRIPTION

The LMH664XEP 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 f

•

(∼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 similar 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 channel. This architecture allows output to reach within millivolts 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, I

Significant power saving (∼40%) compared to competi-

•

tive devices on the market with similar performance.

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

Application Hints

This Op Amp family is a drop-in replacement for the AD805X family of high speed Op Amps in most applications. In addition, the LMH664XEP 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 LMH664XEP guaranteed specifications in order to ensure equal or better level of performance. However, as in most high performance parts, due to subtleties of applications, it is strongly recommended that the performance of the part to be evaluated is tested under actual operating conditions to ensure full compliance to all specifications.

With 3V supplies and a common mode input voltage range that extends 0.5V below V

−

, the LMH664XEP find applica-

tions in low voltage/low power applications. Even with 3V

supplies, 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 frequency response is exceptionally stable confining the typical

-3dB BW over the industrial temperature range to As can be seen from the typical performance plots, the

LMH664XEP output current capability (∼75mA) is enhanced compared to AD805X. This enhancement, increases the output load range, adding to the LMH664XEP’s versatility.

Because of the LMH664XEP’s high output current capability attention should be given to device junction temperature in order not to exceed the Absolute Maximum Rating.

OUT

, etc.)

2.5%.

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:

20089442

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.

Output overdrive recovery time is less than 100ns as can be seen from Figure 2 plot:

20089443

FIGURE 2. Overload Recovery Waveform

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Page 17

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 transimpedance gain setting is kept relatively low. Because of its high slew rate limit and high speed, the LMH664XEP family lends itself well to such an application.

This circuit achieves approximately 1V/mA of transimpedance gain and capable of handling up to 1mA photodiode. Q1, in a common base configuration, isolates the high capacitance of the photodiode (C Amp input in order to maximize speed. Input is AC coupled through C1 to ease biasing and allow single supply operation. With 5V single supply, the device input/output is shifted to near half supply using a voltage divider from V that Q1 collector does not have any voltage swing and the Miller effect is minimized. D1, tied to Q1 base, is for temperature compensation of Q1’s bias point. Q1 collector current 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.

No matter how low an R

is selected, there is a need for Cfin

order to stabilize the circuit. The reason for this is that the Op

from the

) from the Op

. Note

Amp input capacitance and Q1 equivalent collector capacitance together (C signal fed back to the inverting node. C

) will cause additional phase shift to the

will function as a

zero in the feedback path counter-acting the effect of the C and acting to stabilized the circuit. By proper selection of C 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.

(1) where GBWP is the Gain Bandwidth Product of the Op Amp Optimized as such, the I-V converter will have a theoretical

, at:

pole, f

(2) With Op Amp input capacitance of 3pF and an estimate for

Q1 output capacitance of about 3pF as well, C

= 6pF. From

the typical performance plots, LMH6642EP/6643EP family GBWP is approximately 57MHz. Therefore, with R

= 1k,

from Equation 1 and 2 above.

= ∼4.1pF, and fp= 39MHz

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

FIGURE 3. Single Supply Photodiode I-V Converter

20089464

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Page 18

Application Notes (Continued)

For this example, optimum C be around 5pF. This time domain response is shown in Figure 4 below showing about 9ns rise/fall times, corresponding to about 39MHz for f from the +5V supply is around 5mA with no load.

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

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

was empirically determined to

. The overall supply current

20089465

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

LMH6642MF SOT23-5 CLC730068

LMH6642MF 8-Pin SOIC CLC730027

LMH6643MA 8-Pin SOIC CLC730036

LMH6643MA 8-Pin MSOP CLC730123

LMH6644MA 14-Pin SOIC CLC730031

LMH6644MA 14-Pin TSSOP 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 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 byproduct 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 could load down nodes and will contribute to higher overall power dissipation.

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Page 19

Physical Dimensions inches (millimeters) unless otherwise noted

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

5-Pin SOT23

NS Package Number MF05A

8-Pin SOIC

NS Package Number M08A

www.national.com19

Page 20

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic

8-Pin MSOP

NS Package Number MUA08A

14-Pin SOIC

NS Package Number M14A

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Page 21

Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LMH6642EP/LMH6643EP/LMH6644EP Enhanced Plastic Low Power, 130MHz, 75mA Rail-to-Rail

Output Amplifiers

14-Pin TSSOP

NS Package Number MTC14

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