National Semiconductor LM6181 Technical data

LM6181 100 mA, 100 MHz Current Feedback Amplifier

May 1998

General Description

The LM6181 current-feedback amplifier offers an unparalleled combination of bandwidth, slew-rate, and output current. The amplifier can directly drive up to 100 pF capacitive loads without oscillating and a 10V signal into a 50Ω or 75Ω back-terminated coax cable system over the full industrial temperature range. This represents a radical enhancement in output drive capability for an 8-pin DIP high-speed amplifier making it ideal for video applications.

™

Built on National’s advanced high-speed VIP Integrated PNP) process, the LM6181 employs currentfeedback providing bandwidth that does not vary dramatically with gain; 100 MHz at A With a slew rate of 2000V/µs, 2nd harmonic distortion of −50 dBc at 10 MHz and settling time of 50 ns (0.1%) the LM6181 dynamic performance makes it ideal for data acquisition, high speed ATE, and precision pulse amplifier applications.

= −1, 60 MHz at AV= −10.

II (Vertically

Typical Application

Features

(Typical unless otherwise noted)

n Slew rate: 2000 V/µs n Settling time (0.1%): 50 ns n Characterized for supply ranges: n Low differential gain and phase error: 0.05%, 0.04˚ n High output drive: n Guaranteed bandwidth and slew rate n Improved performance over EL2020, OP160, AD844,

LT1223 and HA5004

10V into 100Ω

5V and±15V

Applications

n Coax cable driver n Video amplifier n Flash ADC buffer n High frequency filter n Scanner and Imaging systems

Cable Driver

VIP™is a registered trademark of National Semiconductor Corporation.

01132801

01132802

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LM6181

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

Supply Voltage

Differential Input Voltage

Input Voltage

Inverting Input Current 15 mA

Soldering Information

Dual-In-Line Package (N)

Soldering (10 sec) 260˚C

Small Outline Package (M)

Vapor Phase (60 seconds) 215˚C

Infrared (15 seconds) 220˚C

Supply Voltage

18V

Storage Temperature Range −65˚C ≤ T

≤ +150˚C

Maximum Junction Temperature 150˚C

ESD Rating (Note 2)

3000V

Operating Ratings

Supply Voltage Range 7V to 32V

Junction Temperature Range (Note 3)

LM6181AM −55˚C ≤ T

LM6181AI, LM6181I −40˚C ≤ T

Thermal Resistance (θ

, θJC)

8-pin DIP (N) 102˚C/W, 42˚C/W

8-pin SO (M-8) 153˚C/W, 42˚C/W

16-pin SO (M) 70˚C/W, 38˚C/W

≤ +125˚C

≤ +85˚C

Output Short Circuit (Note 7)

15V DC Electrical Characteristics

The following specifications apply for Supply Voltage =±15V, RF= 820Ω, and RL=1kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

Input Offset Voltage 2.0 3.0 2.0 3.0 3.5 5.0 mV

4.0 3.5 5.5 max

TC V

Input Offset Voltage Drift 5.0 5.0 5.0 µV/˚C

Inverting Input Bias Current 2.0 5.0 2.0 5.0 5.0 10 µA

12.0 12.0 17.0

Non-Inverting Input Bias

0.5 1.5 0.5 1.5 2.0 3.0

Current

3.0 3.0 5.0

TC I

Inverting Input Bias Current

30 30 30 nA/˚C

Drift

Non-Inverting Input Bias 10 10 10

Current Drift

Inverting Input Bias Current VS=±4.5V,±16V 0.3 0.5 0.3 0.5 0.3 0.75 µA/V

PSR Power Supply Rejection 3.0 3.0 4.5

Non-Inverting Input Bias

=±4.5V,±16V 0.05 0.5 0.05 0.5 0.05 0.5

Current

Power Supply Rejection 1.5 1.5 3.0

Inverting Input Bias Current −10V ≤ VCM≤ +10V 0.3 0.5 0.3 0.5 0.3 0.75

CMR Common Mode Rejection 0.75 0.75 1.0

Non-Inverting Input Bias

−10V ≤ V

≤ +10V 0.1 0.5 0.1 0.5 0.1 0.5

Current

Common Mode Rejection 0.5 0.5 0.5

CMRR Common Mode Rejection

−10V ≤ V

≤ +10V 60 50 60 50 60 50 dB

Ratio

50 50 50 min

PSRR Power Supply Rejection Ratio V

=±4.5V,±16V 80 70 80 70 80 70 dB

70 70 65 min

Output Resistance AV= −1, f = 300

0.2 0.2 0.2 Ω

kHz

max

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15V DC Electrical Characteristics (Continued)

The following specifications apply for Supply Voltage =±15V, RF= 820Ω, and RL=1kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

Non-Inverting Input

Resistance

10 10 10

MΩ

min

Output Voltage Swing RL=1kΩ 12 11 12 11 12 11 V

11 11 11

= 100Ω 11 10 11 10 11 10

min

7.5 8.0 8.0

Output Short Circuit Current 130 100 130 100 130 100 mA

75 85 85 min

Transimpedance RL=1kΩ 1.8 1.0 1.8 1.0 1.8 0.8

0.5 0.5 0.4 MΩ

= 100Ω 1.4 0.8 1.4 0.8 1.4 0.7 min

0.4 0.4 0.35

Supply Current No Load, VO= 0V 7.5 10 7.5 10 7.5 10 mA

10 10 10 max

Input Common Mode V+−

Voltage Range V−+

1.7V

V+−

1.7V

V−+

1.7V

V+−

1.7V

V−+

1.7V

LM6181

15V AC Electrical Characteristics

The following specifications apply for Supply Voltage =±15V, RF= 820Ω,RL=1kΩ unless otherwise noted. Boldface limits apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

BW Closed Loop Bandwidth A

−3 dB A

PBW Power Bandwidth A

= +2 100 100 100 MHz

= +10 80 80 80

= −1 100 80 100 80 100 80

= −10 60 60 60

= −1, VO=5V

60 60 60

min

SR Slew Rate Overdriven 2000 2000 2000 V/µs

= −1, VO=

10V,

= 150Ω (Note 6)

Settling Time (0.1%) AV= −1, VO=±5V 50 50 50 ns

= 150Ω

Rise and Fall Time VO=1V

r,tf

Propagation Delay Time VO=1V

Non-Inverting Input Noise f=1kHz 3 3 3

n(+)

1400 1000 1400 1000 1400 1000

555

666

min

Current Density

Inverting Input Noise f = 1 kHz 16 16 16

n(−)

Current Density

Input Noise Voltage

f=1kHz 4 4 4

Density

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15V AC Electrical Characteristics (Continued)

The following specifications apply for Supply Voltage =±15V, RF= 820Ω,RL=1kΩ unless otherwise noted. Boldface limits

LM6181

apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

Second Harmonic

, 10 MHz −50 −50 −50 dBc

Distortion

Third Harmonic Distortion 2 V

Differential Gain R

, 10 MHz −55 −55 −50

= 150Ω

= +2 0.05 0.05 0.05 %

NTSC

Differential Phase R

= 150Ω

= +2 0.04 0.04 0.04 Deg

NTSC

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5V DC Electrical Characteristics

The following specifications apply for Supply Voltage =±5V, RF= 820Ω, and RL=1kΩ unless otherwise noted. Boldface lim- its apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

Input Offset Voltage 1.0 2.0 1.0 2.0 1.0 3.0 mV

3.0 2.5 3.5 max

Input Offset Voltage Drift 2.5 2.5 2.5 µV/˚C

Inverting Input 5.0 10 5.0 10 5.0 17.5 µA

Bias Current 22 22 27.0

max

Non-Inverting Input 0.25 1.5 0.25 1.5 0.25 3.0

Bias Current 1.5 1.5 5.0

TC I

Inverting Input Bias 50 50 50 nA/˚C

Current Drift

Non-Inverting Input 3.0 3.0 3.0

Bias Current Drift

Inverting Input Bias Current VS=±4.0V,±6.0V 0.3 0.5 0.3 0.5 0.3 1.0 µA/V

PSR Power Supply Rejection 0.5 0.5 1.0

Non-Inverting Input V

=±4.0V,±6.0V 0.05 0.5 0.05 0.5 0.05 0.5

max

Bias Current

Power Supply Rejection 0.5 0.5 0.5

Inverting Input Bias Current −2.5V ≤ VCM≤ +2.5V 0.3 0.5 0.3 0.5 0.3 1.0

CMR Common Mode Rejection 1.0 1.0 1.5

Non-Inverting Input −2.5V ≤ V

≤ +2.5V 0.12 0.5 0.12 0.5 0.12 0.5

Bias Current

Common Mode Rejection 1.0 0.5 0.5

CMRR Common Mode −2.5V ≤ V

Rejection Ratio 47 47 47

PSRR Power Supply V

=±4.0V,±6.0V 80 70 80 70 80 64

≤ +2.5V 57 50 57 50 57 50 dB

min

Rejection Ratio 70 70 64

Output Resistance AV= −1, f = 300 kHz 0.25 0.25 0.25 Ω

Non-Inverting 8 8 8 MΩ

Input Resistance min

Output Voltage Swing RL=1kΩ 2.6 2.25 2.6 2.25 2.6 2.25 V

2.2 2.25 2.25

= 100Ω 2.2 2.0 2.2 2.0 2.2 2.0

min

2.0 2.0 2.0

Output Short 100 75 100 75 100 75 mA

Circuit Current 70 70 70 min

Transimpedance RL=1kΩ 1.4 0.75 1.4 0.75 1.0 0.6

0.35 0.4 0.3 MΩ

= 100Ω 1.0 0.5 1.0 0.5 1.0 0.4 min

0.25 0.25 0.2

Supply Current No Load, VO= 0V 6.5 8.5 6.5 8.5 6.5 8.5 mA

8.5 8.5 8.5 max

Input Common Mode V+−

Voltage Range V

1.7V

−

1.7V

V+−

1.7V

V−+

1.7V

V+−

1.7V

V−+

1.7V

LM6181

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5V AC Electrical Characteristics

The following specifications apply for Supply Voltage =±5V, RF= 820Ω, and RL=1kΩ unless otherwise noted. Boldface lim-

LM6181

its apply at the temperature extremes; all other limits T

= 25˚C.

Symbol Parameter Conditions LM6181AM LM6181AI LM6181I Units

Typical Limit Typical Limit Typical Limit

(Note 4) (Note 5) (Note 4) (Note 5) (Note 4) (Note 5)

BW Closed Loop Bandwidth −3dBA

PBW Power Bandwidth A

SR Slew Rate A

Settling Time (0.1%) AV= −1, VO=±2V 50 50 50 ns

Rise and Fall Time VO=1V

r,tf

Propagation Delay Time VO=1V

Non-Inverting Input Noise f = 1 kHz 3 3 3

n(+)

= +2 50 50 50 MHz

= +10 40 40 40

=−1 553555355535

= −10 35 35 35

= −1, VO=4

= −1, VO=±2V, 500 375 500 375 500 375 V/µs

= 150Ω (Note 6) min

= 150Ω

40 40 40

8.5 8.5 8.5

888

Current Density

Inverting Input Noise f = 1 kHz 16 16 16

n(−)

Current Density

Input Noise Voltage

f = 1 kHz 4 4 4

Density

Second Harmonic Distortion 2 VPP, 10 MHz −45 −45 −45 dBc

Third Harmonic Distortion 2 V

Differential Gain R

, 10 MHz −55 −55 −55

= 150Ω

= +2 0.063 0.063 0.063 %

NTSC

Differential Phase R

= 150Ω

= +2 0.16 0.16 0.16 Deg

NTSC

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions the device is intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: Human body model 100 pF and 1.5 kΩ.

Note 3: The typical junction-to-ambient thermal resistance of the molded plastic DIP(N) package soldered directly into a PC board is 102˚C/W. The junction-to-

ambient thermal resistance of the S.O. surface mount (M) package mounted flush to the PC board is 70˚C/W when pins 1, 4, 8, 9 and 16 are soldered to a total 2

1 oz. copper trace. The 16-pin S.O. (M) package must have pin 4 and at least one of pins 1, 8, 9, or 16 connected to V−for proper operation. The typical

junction-to-ambient thermal resistance of the S.O. (M-8) package soldered directly into a PC board is 153˚C/W.

Note 4: Typical values represent the most likely parametric norm.

Note 5: All limits guaranteed at room temperature (standard type face) or at operating temperature extremes (bold face type).

Note 6: Measured from +25% to +75% of output waveform.

Note 7: Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150˚C. Output

currents in excess of

Note 8: For guaranteed Military Temperature Range parameters see RETS6181X.

130 mA over a long term basis may adversely affect reliability.

min

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Typical Performance Characteristics

TA= 25˚C unless otherwise noted

LM6181

CLOSED-LOOP

FREQUENCY RESPONSE

=±15V; Rf= 820Ω;

=1kΩ

UNITY GAIN

FREQUENCY RESPONSE

=±15V; AV= +1;

= 820Ω

CLOSED-LOOP

FREQUENCY RESPONSE

=±15V; Rf= 820Ω;

01132834 01132835

= 150Ω

UNIT GAIN

FREQUENCY RESPONSE

=±5V; AV= +1;

= 820Ω

FREQUENCY RESPONSE

vs SUPPLY VOLTAGE

= −1; Rf= 820Ω;

=1kΩ

01132836 01132837

FREQUENCY RESPONSE

vs SUPPLY VOLTAGE

= −1; Rf= 820Ω;

= 150Ω

01132838 01132839

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Typical Performance Characteristics T

LM6181

INVERTING GAIN

FREQUENCY RESPONSE

=±15V; AV= −1;

= 820Ω

01132840 01132841

= 25˚C unless otherwise noted (Continued)

INVERTING GAIN

FREQUENCY RESPONSE

=±5V; AV= −1;

= 820Ω

NON-INVERTING GAIN

FREQUENCY RESPONSE

=±15V; AV= +2;

= 820Ω

INVERTING GAIN

FREQUENCY RESPONSE

=±15V; AV= −10;

= 820Ω

NON-INVERTING GAIN

FREQUENCY RESPONSE

=±5V; AV= +2;

= 820Ω

01132842 01132843

INVERTING GAIN

FREQUENCY RESPONSE

=±5V; AV= −10;

= 820Ω

01132844 01132845

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LM6181

Typical Performance Characteristics T

NON-INVERTING GAIN

FREQUENCY RESPONSE

=±15V; AV= +10;

= 820Ω

01132846 01132847

NON-INVERTING GAIN

FREQUENCY COMPENSATION

=±15V; AV= +2;

= 150Ω

= 25˚C unless otherwise noted (Continued)

NON-INVERTING GAIN

FREQUENCY RESPONSE

=±5V; AV= +10;

= 820Ω

BANDWIDTH vs R

f&RS

AV= −1, RL=1kΩ

OUTPUT SWING vs

PULSED, VS=±15V,

LOAD

=±200 µA, V

IN+

=0V

01132848

01132850

TRANSIMPEDANCE

vs FREQUENCY

=±15V

=1kΩ

01132849

01132851

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Typical Performance Characteristics T

LM6181

TRANSIMPEDANCE

vs FREQUENCY

=±15V

= 100Ω

01132852 01132853

= 25˚C unless otherwise noted (Continued)

TRANSIMPEDANCE

vs FREQUENCY

=±5V

=1kΩ

SETTLING RESPONSE

=±15V; RL= 150Ω;

=±5V; AV=−1

SUGGESTED Rfand RSfor C

AV=−1;RL= 150Ω

SETTLING RESPONSE

=±5V; RL= 150Ω;

=±2V; AV=−1

01132855 01132856

TRANSIMPEDANCE

vs FREQUENCY

=±5V

= 100Ω

01132857

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01132854

LM6181

Typical Performance Characteristics T

SUGGESTED R

and RSFOR C

AV=−1

SUGGESTED R

and RSFOR C

AV=+2

01132858 01132859

= 25˚C unless otherwise noted (Continued)

SUGGESTED R

and RSFOR C

AV= +2; RL= 150Ω

OUTPUT IMPEDANCE

vs FREQ

=±15V; AV=−1

= 820Ω

OUTPUT IMPEDANCE

vs FREQ

=±5V; AV=−1

= 820Ω PSRR (V

01132860

) vs FREQUENCY

01132862 01132863

01132861

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Typical Performance Characteristics T

LM6181

PSRR (V

−

) vs FREQUENCY CMRR vs FREQUENCY

01132864 01132865

= 25˚C unless otherwise noted (Continued)

INPUT VOLTAGE NOISE

vs FREQUENCY

SLEW RATE vs

TEMPERATURE A

= 150Ω,VS=±15V

= −1;

INPUT CURRENT

NOISE vs FREQUENCY

01132866 01132867

SLEW RATE vs

TEMPERATURE A

= 150Ω,VS=±5V

= −1;

01132868 01132869

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LM6181

Typical Performance Characteristics T

−3 dB BANDWIDTH vs TEMPERATURE

=−1

01132870

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+1

=±15V; RL= 100Ω

= 25˚C unless otherwise noted (Continued)

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+1

=±15V; RL=1kΩ

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+1

=±5V; RL=1kΩ

01132871

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+1

=±5V; RL= 100Ω

01132872 01132873

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=−1

=±15V; RL=1kΩ

01132874 01132875

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Typical Performance Characteristics T

LM6181

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=−1

=±15V; RL= 100Ω

01132876 01132877

= 25˚C unless otherwise noted (Continued)

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=−1

=±5V; RL=1kΩ

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=−1

=±5V; RL= 100Ω

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+2

=±15V; RL= 100Ω

01132878

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+2

=±15V; RL=1kΩ

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+2

=±5V; RL=1kΩ

01132879

01132880 01132881

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LM6181

Typical Performance Characteristics T

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

=+2

=±5V; RL= 100Ω

01132882

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= −10

=±15V; RL= 100Ω

= 25˚C unless otherwise noted (Continued)

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= −10

=±15V; RL=1kΩ

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= −10

=±5V; RL=1kΩ

01132883

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= −10

=±5V; RL= 100Ω

01132884 01132885

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= +10

=±15V; RL=1kΩ

01132886

01132887

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Typical Performance Characteristics T

LM6181

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= +10

=±15V; RL= 100Ω

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= +10

=±5V; RL= 100Ω

01132888 01132889

= 25˚C unless otherwise noted (Continued)

SMALL SIGNAL PULSE

RESPONSE vs TEMP,

= +10

=±5V; RL=1kΩ

OFFSET VOLTAGE

vs TEMPERATURE

01132890

OFFSET VOLTAGE

vs TEMPERATURE

01132892

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01132891

TRANSIMPEDANCE

vs TEMPERATURE

01132893

LM6181

Typical Performance Characteristics T

TRANSIMPEDANCE vs

TEMPERATURE

01132894 01132895

PSRR vs TEMPERATURE CMRR vs TEMPERATURE

= 25˚C unless otherwise noted (Continued)

QUIESCENT CURRENT

vs TEMPERATURE

NON-INVERTING BIAS

CURRENT vs TEMPERATURE

01132896 01132897

INVERTING BIAS

CURRENT vs TEMPERATURE

01132898 01132899

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Typical Performance Characteristics T

LM6181

PSR I

B(+)

vs TEMPERATURE PSR I

011328A0 011328A1

= 25˚C unless otherwise noted (Continued)

vs TEMPERATURE

B(−)

CMR I

SC(+)

vs TEMPERATURE CMR I

B(+)

011328A2 011328A3

vs TEMPERATURE I

vs TEMPERATURE

B(−)

vs TEMPERATURE

SC(−)

011328A6 011328A4

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Typical Performance Characteristics

Absolute Maximum Power Derating Curves

LM6181

N-Package

*θJA= Thermal Resistance with 2 square inches of 1 ounce Copper tied to Pins 1, 8, 9 and 16.

M-Package

01132830

01132831

M-8 Package

01132833

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Typical Performance Characteristics (Continued)

LM6181

Simplified Schematic

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01132832

Typical Applications

CURRENT FEEDBACK TOPOLOGY

For a conventional voltage feedback amplifier the resulting small-signal bandwidth is inversely proportional to the desired gain to a first order approximation based on the gainbandwidth concept. In contrast, the current feedback amplifier topology, such as the LM6181, transcends this limitation to offer a signal bandwidth that is relatively independent of the closed-loop gain. Figure 1a and Figure 1b illustrate that for closed loop gains of −1 and −5 the resulting pulse fidelity suggests quite similar bandwidths for both configurations.

01132814

FIGURE 2. RSIs Adjusted to Obtain

the Desired Closed Loop Gain, A

VCL

POWER SUPPLY BYPASSING AND LAYOUT CONSIDERATIONS

A fundamental requirement for high-speed amplifier design is adequate bypassing of the power supply. It is critical to maintain a wideband low-impedance to ground at the amplifiers supply pins to insure the fidelity of high speed amplifier transient signals. 10 µF tantalum and 0.1 µF ceramic bypass capacitors are recommended for each supply pin. The bypass capacitors should be placed as close to the amplifier pins as possible (0.5" or less).

LM6181

01132812

01132813

FIGURE 1. 1a, 1b: Variation of Closed Loop Gain

from −1 to −5 Yields Similar Responses

The closed-loop bandwidth of the LM6181 depends on the feedback resistance, R

. Therefore, RSand not Rf, must be

varied to adjust for the desired closed-loop gain as in Figure

FEEDBACK RESISTOR SELECTION: R

Selecting the feedback resistor, Rf, is a dominant factor in compensating the LM6181. For general applications the LM6181 will maintain specified performance with an 820Ω feedback resistor. Although this value will provide good results for most applications, it may be advantageous to adjust this value slightly. Consider, for instance, the effect on pulse responses with two different configurations where both the closed-loop gains are 2 and the feedback resistors are 820Ω and 1640Ω, respectively. Figure 3a and Figure 3b illustrate the effect of increasing R

while maintaining the same

closed-loop gain —the amplifier bandwidth decreases. Accordingly, larger feedback resistors can be used to slow down the LM6181 (see −3 dB bandwidth vs R

typical curves)

and reduce overshoot in the time domain response. Conversely, smaller feedback resistance values than 820Ω can be used to compensate for the reduction of bandwidth at high closed loop gains, due to 2nd order effects. For example Figure 4 illustrates reducing R

to 500Ω to establish

the desired small signal response in an amplifier configured for a closed loop gain of 25.

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Typical Applications (Continued)

LM6181

3a: Rf= 820Ω

01132815

SLEW RATE CONSIDERATIONS

The slew rate characteristics of current feedback amplifiers are different than traditional voltage feedback amplifiers. In voltage feedback amplifiers slew rate limiting or non-linear amplifier behavior is dominated by the finite availability of the 1st stage tail current charging the compensation capacitor. The slew rate of current feedback amplifiers, in contrast, is not constant. Transient current at the inverting input determines slew rate for both inverting and non-inverting gains. The non-inverting configuration slew rate is also determined by input stage limitations. Accordingly, variations of slew rates occur for different circuit topologies.

DRIVING CAPACITIVE LOADS

The LM6181 can drive significantly larger capacitive loads than many current feedback amplifiers. Although the LM6181 can directly drive as much as 100 pF without oscillating, the resulting response will be a function of the feedback resistor value. Figure 5 illustrates the small-signal pulse response of the LM6181 while driving a 50 pF load. Ringing persists for approximately 70 ns. To achieve pulse responses with less ringing either the feedback resistor can be increased (see typical curves Suggested R

), or resistive isolation can be used (10Ω–51Ω typically

and Rsfor

works well). Either technique, however, results in lowering the system bandwidth.

Figure 6 illustrates the improvement obtained with using a 47Ω isolation resistor.

3b: Rf= 1640Ω

FIGURE 3. Increasing Compensation

with Increasing R

FIGURE 4. Reducing Rffor Large

Closed Loop Gains, R

= 500Ω

01132816

01132817

01132818

FIGURE 5. A

= −1, LM6181 Can Directly

Drive 50 pF of Load Capacitance with 70 ns

of Ringing Resulting in Pulse Response

01132819

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Typical Applications (Continued)

LM6181

01132820

01132821

FIGURE 6. Resistive Isolation of C

Provides Higher Fidelity Pulse Response. R

and RSCould Be Increased to Maintain AV=−1

and Improve Pulse Response Characteristics.

CAPACITIVE FEEDBACK

For voltage feedback amplifiers it is quite common to place a small lead compensation capacitor in parallel with feedback resistance, R

. This compensation serves to reduce the am-

plifier’s peaking in the frequency domain which equivalently tames the transient response. To limit the bandwidth of current feedback amplifiers, do not use a capacitor across

. The dynamic impedance of capacitors in the feedback

loop reduces the amplifier’s stability. Instead, reduced peaking in the frequency response, and bandwidth limiting can be accomplished by adding an RC circuit, as illustrated in Fig- ure 7b.

01132822

01132823

FIGURE 7. RC Limits Amplifier

Bandwidth to 50 MHz, Eliminating

Peaking in the Resulting Pulse Response

Typical Performance Characteristics

OVERDRIVE RECOVERY

When the output or input voltage range of a high speed amplifier is exceeded, the amplifier must recover from an overdrive condition. The typical recovery times for openloop, closed-loop, and input common-mode voltage range overdrive conditions are illustrated in Figures 9, 11, 11, 12 respectively.

The open-loop circuit of Figure 8 generates an overdrive

response by allowing the

0.5V input to exceed the linear input range of the amplifier. Typical positive and negative overdrive recovery times shown in Figure 9 are 5 ns and 25 ns, respectively.

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Typical Performance Characteristics

LM6181

(Continued)

FIGURE 8.

01132824

01132827

FIGURE 11. Closed-Loop Overdrive Recovery

Time of 30 ns from Exceeding Output

Voltage Range from Circuit in Figure 10

The common-mode input of the circuit in Figure 10 is exceeded by a 5V pulse resulting in a typical recovery time of 310 ns shown in Figure 12. The LM6181 supply voltage is

5V.

01132825

FIGURE 9. Open-Loop Overdrive Recovery Time of

5 ns, and 25 ns from Test Circuit in Figure 8

The large closed-loop gain configuration in Figure 10 forces the amplifier output into overdrive. Figure 11 displays the typical 30 ns recovery time to a linear output value.

01132826

FIGURE 10.

01132828

FIGURE 12. Exceptional Output

Recovery from an Input that

Exceeds the Common-Mode Range

www.national.com 24

Connection Diagrams (For Ordering Infor-

mation See Back Page)

8–Pin Dual-In-Line Package (N)/

Small Outline (M-8)

LM6181

Order Number LM6181IN, LM6181AIN,

LM6181AMN, LM6181AIM-8, LM6181IM-8

or LM6181AMJ/883

See NS Package Number J08A, M08A or N08E

16-Pin Small Outline Package (M)

*Heat sinking pins (Note 3)

Order Number LM6181IM or LM6181AIM

See NS Package Number M16A

01132803

01132804

Ordering Information

Package Temperature Range NSC

Military Industrial

−55˚C to +125˚C −40˚C to +85˚C

8-Pin LM6181AMN LM6181AIN N08E

Molded DIP LM6181IN

8-Pin Small Outline LM6181AIM-8 M08A

Molded Package LM6181IM-8

16-Pin LM6181AIM M16A

Small Outline LM6181IM

8-Pin LM6181AMJ/883 J08A

Ceramic DIP

Drawing

www.national.com25

Physical Dimensions inches (millimeters)

unless otherwise noted

LM6181

8-Lead (0.150" Wide) Small Outline Molded Package (M-8)

Order Number LM6181AIM-8 or LM6181IM-8

NS Package Number M08A

8-Pin Ceramic Dual-In-Line Package

Order Number LM6181AMJ/883

NS Package Number J08A

www.national.com 26

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

LM6181

Small Outline Package (M)

Order Number LM6181IM or LM6181AIM

NS Package Number M16A

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

Dual-In-Line-Package (N)

Order Number LM6181AIN, LM6181IN or LM6181AMN

NS Package Number N08E

LM6181 100 mA, 100 MHz Current Feedback Amplifier

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

National Semiconductor Americas Customer Support Center

Email: new.feedback@nsc.com Tel: 1-800-272-9959

www.national.com

National Semiconductor Europe Customer Support Center

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790

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.

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Email: ap.support@nsc.com

National Semiconductor Japan Customer Support Center

Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560

National Semiconductor LM6181 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual

General Description

Typical Application

Features

Applications

Absolute Maximum Ratings (Note 1)

Operating Ratings

15V DC Electrical Characteristics

15V AC Electrical Characteristics

5V DC Electrical Characteristics

5V AC Electrical Characteristics

Typical Performance Characteristics

Typical Performance Characteristics

Typical Applications

CURRENT FEEDBACK TOPOLOGY

POWER SUPPLY BYPASSING AND LAYOUT CONSIDERATIONS

SLEW RATE CONSIDERATIONS

DRIVING CAPACITIVE LOADS

CAPACITIVE FEEDBACK

Typical Performance Characteristics

OVERDRIVE RECOVERY

FIGURE 8.

FIGURE 10.

Connection Diagrams (For Ordering Infor-

Ordering Information

Physical Dimensions inches (millimeters)