LM6172
Dual High Speed, Low Power, Low Distortion, Voltage
Feedback Amplifiers

General Description

The LM6172 is a dual high speed voltage feedback amplifier.
It is unity-gain stable and provides excellent DC and AC per-
formance. With 100 MHz unity-gain bandwidth, 3000V/µs
slew rate and 50 mA of output current per channel, the
LM6172 offers high performance in dual amplifiers; yet it
only consumes 2.3 mA of supply current each channel.

The LM6172 operates on

15V power supply for systems

requiring large voltage swings, such as ADSL, scanners and
ultrasound equipment. It is also specified at

5V power sup-

ply for low voltage applications such as portable video sys-
tems.

The LM6172 is built with National's advanced VIP

III (Ver-

tically Integrated PNP) complementary bipolar process. See
the LM6171 datasheet for a single amplifier with these same
features.

Features

(Typical Unless Otherwise Noted)

Easy to Use Voltage Feedback Topology

High Slew Rate

3000V/µs

Wide Unity-Gain Bandwidth

100 MHz

Low Supply Current

2.3 mA/Channel

High Output Current

50 mA/channel

Specified for

15V and

5V Operation

Applications

Scanner I-to-V Converters

ADSL/HDSL Drivers

Multimedia Broadcast Systems

Video Amplifiers

NTSC, PAL

and SECAM Systems

ADC/DAC Buffers

Pulse Amplifiers and Peak Detectors

LM6172 Driving Capacitive Load

Connection Diagram

VIP

is a trademark of National Semiconductor Corporation.

PAL

is a registered trademark of and used under license from Advanced Micro Devices, Inc.

DS012581-50

DS012581-44

8-Pin DIP/SO

DS012581-1

Top View

May 1999

LM6172

Dual

High

Speed,

Low

Power

Low

Distortion,

oltage

Feedback

Amplifiers

DS012581

www.national.com

Absolute Maximum Ratings

(Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

ESD Tolerance (Note 2)

Human Body Model

3 kV

Machine Model

300V

Supply Voltage (V

- V

)

36V

Differential Input Voltage (Note 9)

10V

Output Short Circuit to Ground

(Note 3)

Continuous

Storage Temp. Range

-65°C to +150°C

Maximum Junction Temperature

(Note 4)

150°C

Operating Ratings

(Note 1)

Supply Voltage

5.5V

36V

Junction Temperature Range

LM6172I

-40°C

+85°C

Thermal Resistance (

)

N Package, 8-Pin Molded DIP

95°C/W

M Package, 8-Pin Surface Mount

160°C/W

15V DC Electrical Characteristics

Unless otherwise specified, all limits guaranteed for T

= 25°C,V

= +15V, V

= -15V, V

= 0V, and R

= 1 k

. Boldface

limits apply at the temperature extremes

Typ

(Note 5)

LM6172I

Symbol

Parameter

Conditions

Limit

Units

(Note 5)

Input Offset Voltage

0.4

max

TC V

Input Offset Voltage

µV/°C

Average Drift

Input Bias Current

1.2

µA

max

Input Offset Current

0.02

µA

max

Input Resistance

Common Mode

Differential Mode

4.9

Open Loop Output Resistance

CMRR

Common Mode Rejection Ratio

10V

110

min

PSRR

Power Supply Rejection Ratio

15V to

min

Large Signal Voltage

= 1 k

Gain (Note 6)

min

= 100

min

Output Swing

= 1 k

13.2

12.5

min

-13.1

-12.5

-12

max

= 100

min

-8.5

-6

-5

max

Continuous Output Current

Sourcing, R

= 100

(Open Loop) (Note 7)

min

Sinking, R

= 100

-85

-60

-50

max

Output Short Circuit

Sourcing

107

Current

Sinking

-105

Supply Current

Both Amplifiers

4.6

www.national.com

15V DC Electrical Characteristics

(Continued)

Unless otherwise specified, all limits guaranteed for T

= 25°C,V

= +15V, V

= -15V, V

= 0V, and R

= 1 k

. Boldface

limits apply at the temperature extremes

Typ

(Note 5)

LM6172I

Symbol

Parameter

Conditions

Limit

Units

(Note 5)

max

15V AC Electrical Characteristics

Unless otherwise specified, T

= 25°C, V

= +15V, V

= -15V, V

= 0V, and R

= 1 k

LM6172I

Symbol

Parameter

Conditions

Typ

Units

(Note 5)

Slew Rate

= +2, V

= 13 V

3000

V/µs

= +2, V

= 10 V

2500

V/µs

Unity-Gain Bandwidth

100

MHz

-3 dB Frequency

= +1

160

MHz

= +2

MHz

Bandwidth Matching between Channels

MHz

Phase Margin

Deg

Settling Time (0.1%)

= -1, V

OUT

5V,

= 500

Differential Gain (Note 8)

0.28

Differential Phase (Note 8)

0.6

Deg

Input-Referred

f = 1 kHz

Voltage Noise

Input-Referred

f = 1 kHz

Current Noise

Second Harmonic

f = 10 kHz

-110

Distortion (Note 10)

f = 5 MHz

-50

Third Harmonic

f = 10 kHz

-105

Distortion (Note 10)

f = 5 MHz

-50

5V DC Electrical Characteristics

Unless otherwise specified, all limits guaranteed for T

= 25°C, V

= +5V, V

= -5V, V

= 0V, and R

= 1 k

. Boldface

limits apply at the temperature extremes

Typ

(Note 5)

LM6172I

Symbol

Parameter

Conditions

Limit

Units

(Note 5)

Input Offset Voltage

0.1

max

TC V

Input Offset Voltage

µV/°C

Average Drift

Input Bias Current

1.4

2.5

µA

3.5

max

Input Offset Current

0.02

1.5

µA

2.2

max

Input Resistance

Common Mode

Differential Mode

4.9

Output Resistance

CMRR

Common Mode Rejection Ratio

2.5V

105

www.national.com

5V DC Electrical Characteristics

(Continued)

Unless otherwise specified, all limits guaranteed for T

= 25°C, V

= +5V, V

= -5V, V

= 0V, and R

= 1 k

. Boldface

limits apply at the temperature extremes

Typ

(Note 5)

LM6172I

Symbol

Parameter

Conditions

Limit

Units

(Note 5)

min

PSRR

Power Supply Rejection Ratio

15V to

min

Large Signal Voltage

= 1 k

Gain (Note 6)

min

= 100

min

Output Swing

= 1 k

3.4

3.1

min

-3.3

-3.1

-3

max

= 100

2.9

2.5

2.4

min

-2.7

-2.4

-2.3

max

Continuous Output Current

Sourcing, R

= 100

(Open Loop) (Note 7)

min

Sinking, R

= 100

-27

-24

-23

max

Output Short Circuit

Sourcing

Current

Sinking

-72

Supply Current

Both Amplifiers

4.4

max

5V AC Electrical Characteristics

Unless otherwise specified, T

= 25°C, V

= +5V, V

= -5V, V

= 0V, and R

= 1 k

LM61722

Typ

(Note 5)

Symbol

Parameter

Conditions

Units

Slew Rate

= +2, V

= 3.5 V

750

V/µs

Unity-Gain Bandwidth

MHz

-3 dB Frequency

= +1

130

MHz

= +2

MHz

Phase Margin

Deg

Settling Time (0.1%)

= -1, V

OUT

1V,

= 500

Differential Gain (Note 8)

0.4

Differential Phase (Note 8)

0.7

Deg

Input-Referred

f = 1 kHz

Voltage Noise

Input-Referred

f = 1 kHz

Current Noise

Second Harmonic

f = 10 kHz

-110

Distortion (Note 10)

f = 5 MHz

-48

Third Harmonic

f = 10 kHz

-105

www.national.com

5V AC Electrical Characteristics

(Continued)

Unless otherwise specified, T

= 25°C, V

= +5V, V

= -5V, V

= 0V, and R

= 1 k

LM61722

Typ

(Note 5)

Symbol

Parameter

Conditions

Units

Distortion (Note 10)

f = 5 MHz

-50

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended 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, 1.5 k

in series with 100 pF. Machine Model, 200

in series with 100 pF.

Note 3: Continuous short circuit operation can result in exceeding the maximum allowed junction temperature of 150°C.

Note 4: The maximum power dissipation is a function of T

J(max)

, and T

. The maximum allowable power dissipation at any ambient temperature is

= (T

J(max)

- T

. All numbers apply for packages soldered directly into a PC board.

Note 5: Typical Values represent the most likely parametric norm.

Note 6: All limits are guaranteed by testing or statistical analysis.

Note 7: Large signal voltage gain is the total output swing divided by the input signal required to produce that swing. For V

15V, V

OUT

5V. For V

5V,

OUT

1V.

Note 8: The open loop output current is the output swing with the 100

load resistor divided by that resistor.

Note 9: Differential gain and phase are measured with A

= +2, V

= 1 V

at 3.58 MHz and both input and output 75

terminated.

Note 10: Differential input voltage is applied at V

15V.

Note 11: Harmonics are measured with A

= +2, V

= 1 V

and R

= 100

Typical Performance Characteristics

unless otherwise noted, T

= 25°C

Supply Voltage vs
Supply Current

DS012581-14

Supply Current vs
Temperature

DS012581-15

Input Offset Voltage
vs Temperature

DS012581-16

Input Bias Current vs
Temperature

DS012581-17

Short Circuit Current vs
Temperature (Sourcing)

DS012581-18

Short Circuit Current vs
Temperature (Sinking)

DS012581-35

www.national.com

Typical Performance Characteristics

unless otherwise noted, T

= 25°C (Continued)

Large Signal Voltage
Gain vs Load

DS012581-39

Input Voltage Noise
vs Frequency

DS012581-40

Input Voltage Noise
vs Frequency

DS012581-41

Input Current Noise
vs Frequency

DS012581-42

Input Current Noise
vs Frequency

DS012581-43

Slew Rate vs
Supply Voltage

DS012581-25

Slew Rate vs
Input Voltage

DS012581-26

Large Signal Pulse Response
A

= +1, V

15V

DS012581-2

Small Signal Pulse Response
A

= +1, V

15V

DS012581-3

Large Signal Pulse Response
A

= +1, V

DS012581-4

Small Signal Pulse Response
A

= +1, V

DS012581-5

www.national.com

Typical Performance Characteristics

unless otherwise noted, T

= 25°C (Continued)

Large Signal Pulse Response
A

= +2, V

15V

DS012581-6

Small Signal Pulse Response
A

= +2, V

15V

DS012581-7

Large Signal Pulse Response
A

= +2, V

DS012581-8

Small Signal Pulse Response
A

= +2, V

DS012581-9

Large Signal Pulse Response
A

= -1, V

15V

DS012581-10

Small Signal Pulse Response
A

= -1, V

15V

DS012581-11

Large Signal Pulse Response
A

= -1, V

DS012581-12

Small Signal Pulse Response
A

= -1, V

DS012581-13

Closed Loop Frequency
Response vs Supply Voltage
(A

= +1)

DS012581-28

www.national.com

LM6172 Simplified Schematic

Application Notes
LM6172 Performance Discussion

The LM6172 is a dual high-speed, low power, voltage feed-
back amplifier. It is unity-gain stable and offers outstanding
performance with only 2.3 mA of supply current per channel.
The

combination

100

MHz

unity-gain

bandwidth,

3000V/µs slew rate, 50 mA per channel output current and
other attractive features makes it easy to implement the
LM6172 in various applications. Quiescent power of the
LM6172 is 138 mW operating at

15V supply and 46 mW at

5V supply.

LM6172 Circuit Operation

The class AB input stage in LM6172 is fully symmetrical and
has a similar slewing characteristic to the current feedback
amplifiers. In the LM6172 Simplified Schematic, Q1 through
Q4 form the equivalent of the current feedback input buffer,
R

the equivalent of the feedback resistor, and stage A buff-

ers the inverting input. The triple-buffered output stage iso-
lates the gain stage from the load to provide low output im-
pedance.

LM6172 Slew Rate Characteristic

The slew rate of LM6172 is determined by the current avail-
able to charge and discharge an internal high impedance
node capacitor. This current is the differential input voltage
divided by the total degeneration resistor R

. Therefore, the

slew rate is proportional to the input voltage level, and the
higher slew rates are achievable in the lower gain configura-
tions.

When a very fast large signal pulse is applied to the input of
an amplifier, some overshoot or undershoot occurs. By plac-
ing an external series resistor such as 1 k

to the input of

LM6172, the slew rate is reduced to help lower the over-
shoot, which reduces settling time.

Reducing Settling Time

The LM6172 has a very fast slew rate that causes overshoot
and undershoot. To reduce settling time on LM6172, a 1 k

resistor can be placed in series with the input signal to de-
crease slew rate. A feedback capacitor can also be used to
reduce overshoot and undershoot. This feedback capacitor
serves as a zero to increase the stability of the amplifier cir-
cuit. A 2 pF feedback capacitor is recommended for initial
evaluation. When the LM6172 is configured as a buffer, a
feedback resistor of 1 k

must be added in parallel to the

feedback capacitor.

Another possible source of overshoot and undershoot
comes from capacitive load at the output. Please see the
section "Driving Capacitive Loads" for more detail.

Driving Capacitive Loads

Amplifiers driving capacitive loads can oscillate or have ring-
ing at the output. To eliminate oscillation or reduce ringing,
an isolation resistor can be placed as shown in

Figure 1. The

combination of the isolation resistor and the load capacitor
forms a pole to increase stability by adding more phase mar-
gin to the overall system. The desired performance depends
on the value of the isolation resistor; the bigger the isolation
resistor, the more damped (slow) the pulse response be-
comes. For LM6172, a 50

isolation resistor is recom-

mended for initial evaluation.

DS012581-55

www.national.com

Driving Capacitive Loads

(Continued)

Layout Consideration

PRINTED CIRCUIT BOARDS AND HIGH SPEED OP
AMPS

There are many things to consider when designing PC
boards for high speed op amps. Without proper caution, it is
very easy to have excessive ringing, oscillation and other de-
graded AC performance in high speed circuits. As a rule, the
signal traces should be short and wide to provide low induc-
tance and low impedance paths. Any unused board space
needs to be grounded to reduce stray signal pickup. Critical
components should also be grounded at a common point to
eliminate voltage drop. Sockets add capacitance to the

board and can affect frequency performance. It is better to
solder the amplifier directly into the PC board without using
any socket.

USING PROBES

Active (FET) probes are ideal for taking high frequency mea-
surements because they have wide bandwidth, high input
impedance and low input capacitance. However, the probe
ground leads provide a long ground loop that will produce er-
rors in measurement. Instead, the probes can be grounded
directly by removing the ground leads and probe jackets and
using scope probe jacks.

COMPONENTS SELECTION AND FEEDBACK
RESISTOR

It is important in high speed applications to keep all compo-
nent leads short because wires are inductive at high fre-
quency.

For

discrete

components,

choose

carbon

composition-type resistors and mica-type capacitors. Sur-
face mount components are preferred over discrete compo-
nents for minimum inductive effect.

Large values of feedback resistors can couple with parasitic
capacitance and cause undesirable effects such as ringing
or oscillation in high speed amplifiers. For LM6172, a feed-
back resistor less than 1 k

gives optimal performance.

Compensation for Input
Capacitance

The combination of an amplifier's input capacitance with the
gain setting resistors adds a pole that can cause peaking or
oscillation. To solve this problem, a feedback capacitor with
a value

x C

)/R

can be used to cancel that pole. For LM6172, a feedback ca-
pacitor of 2 pF is recommended.

Figure 4 illustrates the com-

pensation circuit.

Power Supply Bypassing

Bypassing the power supply is necessary to maintain low
power supply impedance across frequency. Both positive
and negative power supplies should be bypassed individu-
ally by placing 0.01 µF ceramic capacitors directly to power
supply pins and 2.2 µF tantalum capacitors close to the
power supply pins.

DS012581-45

FIGURE 1. Isolation Resistor Used

to Drive Capacitive Load

DS012581-51

FIGURE 2. The LM6172 Driving a 510 pF Load

with a 30

Isolation Resistor

DS012581-52

FIGURE 3. The LM6172 Driving a 220 pF Load

with a 50

Isolation Resistor

DS012581-46

FIGURE 4. Compensating for Input Capacitance

www.national.com

Power Supply Bypassing

(Continued)

Termination

In high frequency applications, reflections occur if signals
are not properly terminated.

Figure 6 shows a properly termi-

nated signal while

Figure 7 shows an improperly terminated

signal.

To minimize reflection, coaxial cable with matching charac-
teristic impedance to the signal source should be used. The
other end of the cable should be terminated with the same
value terminator or resistor. For the commonly used cables,
RG59 has 75

characteristic impedance, and RG58 has

characteristic impedance.

Power Dissipation

The maximum power allowed to dissipate in a device is de-
fined as:

= (T

J(max)

- T

Where P

is the power dissipation in a device

J(max)

is the maximum junction temperature

is the ambient temperature

is the thermal resistance of a particular package

For example, for the LM6172 in a SO-8 package, the maxi-
mum power dissipation at 25°C ambient temperature is
780 mW.

Thermal resistance,

, depends on parameters such as

die size, package size and package material. The smaller
the die size and package, the higher

becomes. The 8-pin

DIP package has a lower thermal resistance (95°C/W) than
that of 8-pin SO (160°C/W). Therefore, for higher dissipation
capability, use an 8-pin DIP package.

The total power dissipated in a device can be calculated as:

= P

+ P

is the quiescent power dissipated in a device with no load

connected at the output. P

is the power dissipated in the de-

vice with a load connected at the output; it is not the power
dissipated by the load.

Furthermore,

supply current x total supply voltage with no load

output current x (voltage difference between sup-
ply voltage and output voltage of the same supply)

For example, the total power dissipated by the LM6172 with
V

15V and both channels swinging output voltage of

10V into 1 k

+ P

2[(2.3 mA)(30V)] + 2[(10 mA)(15V - 10V)]

138 mW + 100 mW

238 mW

DS012581-47

FIGURE 5. Power Supply Bypassing

DS012581-53

FIGURE 6. Properly Terminated Signal

DS012581-54

FIGURE 7. Improperly Terminated Signal

www.national.com

Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

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
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com

National Semiconductor
Europe

Fax: +49 (0) 1 80-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 1 80-530 85 85
English

Tel: +49 (0) 1 80-532 78 32

Français Tel: +49 (0) 1 80-532 93 58
Italiano

Tel: +49 (0) 1 80-534 16 80

National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: sea.support@nsc.com

National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507

www.national.com

8-Lead (0.300" Wide) Molded Dual-In-Line Package

Order Number LM6172IN

NS Package Number N08E

LM6172

Dual

High

Speed,

Low

Power

Low

Distortion,

oltage

Feedback

Amplifiers

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.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM6172

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LM6172