Datasheet LT1497 Datasheet (Linear Technology)

FEATURES

■

Minimum Output Current: ±125mA

■

Maximum Supply Current per Amp: 7mA, VS = ±5V

■

Bandwidth: 50MHz, VS = ±15V

■

Slew Rate: 900V/µs, VS = ±15V

■

Wide Supply Range: VS = ±2.5V to ±15V
(Enhanced θJA 16-Pin SO Package)

■

Enhanced θJA SO-8 Package for ±5V Operation

■

0.02% Differential Gain: AV = 2, RL = 150Ω

■

0.015° Differential Phase: AV = 2, RL = 150Ω

■

±13V Output Swing: IL = 100mA, VS = ±15V

■

±3.1V Output Swing: IL = 100mA, VS = ±5V

■

55ns Settling Time to 0.1%, 10V Step

■

Thermal Shutdown Protection

U

APPLICATIONS

■

Twisted-Pair Drivers

■

Video Amplifiers

■

Cable Drivers

■

Test Equipment Amplifiers

■

Buffers

LT1497

Dual 125mA, 50MHz

Current Feedback Amplifier

U

DESCRIPTION

The LT®1497 dual current feedback amplifier features low
power, high output drive, excellent video characteristics
and outstanding distortion performance. From a low 7mA
maximum supply current per amplifier, the LT1497 drives
±100mA with only 1.9V of headroom. Twisted pairs can be
driven differentially with – 70dBc distortion up to 1MHz for
±40mA peak signals.

The LT1497 is available in a low thermal resistance 16-pin
SO package for operation with supplies up to ± 15V. For
±5V operation the device is also available in a low thermal
resistance SO-8 package. The device has thermal and
current limit circuits that protect against fault conditions.

The LT1497 is manufactured on Linear Technology’s
complementary bipolar process. The device has charac­teristics that bridge the performance between the LT1229
and LT1207 dual current feedback amplifiers. The LT1229
has 30mA output drive, 100MHz bandwidth and 12mA
supply current. The LT1207 has 250mA output drive,
60MHz bandwidth and 40mA supply current.

, LTC and LT are registered trademarks of Linear Technology Corporation.

TYPICAL APPLICATION

HDSL2 Single Pair Line Driver

560Ω

560Ω

–

1/2 LT1497

+

V

IN

560Ω

560Ω

–

1/2 LT1497

+

68.1Ω

68.1Ω

1:1*

*MIDCOM 671-7807

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135Ω

1419 TA01

2nd and 3rd Harmonic Distortion of

HDSL2 Single Pair Line Driver

–40

VS = ±5V

= ±1.25V

V

IN

= ±2.5V

V

OUT

–50

–60

–70

2ND

DISTORTION (dBc)

3RD

–80

–90

100k

FREQUENCY (Hz)

1M 2M

1497 TA02

1

LT1497

WW

W

U

ABSOLUTE MAXIMUM RATINGS

Total Supply Voltage (V+ to V–)

LT1497CS8.......................................................... 14V

LT1497CS............................................................ 36V

Noninverting Input Current ................................... ±2mA

Output Short-Circuit Duration (Note 1)..........Continuous

U

W

U

PACKAGE/ORDER INFORMATION

ORDER PART

TOP VIEW

1

OUT A 

–IN A

2

+IN A

T

JMAX

A

3

–

V

4

S8 PACKAGE

8-LEAD PLASTIC SO

= 150°C, θJA = 80°C/ W (NOTE 3)

8

V+
OUT B

7

–IN B

6

B

+IN B

5

NUMBER

LT1497CS8

S8 PART MARKING

1497

Operating Temperature Range (Note 2) ... – 40°C to 85°C

Specified Temperature Range ...................... 0°C to 70°C

Maximum Junction Temperature (See Below) ....... 150°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................... 300°C

TOP VIEW

1

V–

2

NC

3

OUT A

4

–IN A
+IN A

T

JMAX

V
NC
V

A

5

–

6



7

–

8

S PACKAGE

16-LEAD PLASTIC SO

= 150°C, θJA = 40°C/ W (NOTE 3)



16

V–

15

NC 

+

14

V



13

OUT B

12

–IN B

B

11

+IN B

10

NC

–

9

V

ORDER PART

NUMBER

LT1497CS

Consult factory for Industrial and Military grade parts.

ELECTRICAL CHARACTERISTICS

VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

I

I

e
+i
–i
R

C

OS

+

IN

–

IN

n

n

n

IN

IN

Input Offset Voltage TA = 25°C ±3 ±10 mV

● ±15 mV

Input Offset Voltage Matching TA = 25°C ±1 ±3.5 mV

● ±5.0 mV

Input Offset Voltage Drift ● 10 µV/°C
Noninverting Input Current TA = 25°C ±1 ±3 µA

● ±10 µA

Noninverting Input Current Matching TA = 25°C ±0.3 ±1.0 µA

● ±1.5 µA

Inverting Input Current TA = 25°C ±7 ±20 µA

● ±40 µA

Inverting Input Current Matching TA = 25°C ±3 ±10 µA

● ±15 µA

Input Noise Voltage Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 0Ω 3 nV/√Hz
Noninverting Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 10k 2 pA/√Hz
Inverting Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 10k 20 pA/√Hz
Input Resistance VIN = ±13V, VS = ±15V ● 1.5 10 MΩ

VIN = ±3V, VS = ±5V ● 1.5 8 MΩ
VIN = ±0.5V, VS = ±2.5V ● 1.5 8 MΩ

Input Capacitance 3pF

2

LT1497

ELECTRICAL CHARACTERISTICS

VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Voltage Range VS = ±15V ● ±13 ±14 V

VS = ±5V ● ±3.0 ±4.0 V

= ±2.5V ● ±0.5 ±1.5 V

V

S

CMRR Common Mode Rejection Ratio VS = ±15V, VCM = ±13V, TA = 25°C5562 dB

●53 dB

VS = ±5V, VCM = ±3V, TA = 25°C5460dB

●52 dB

VS = ±2.5V, VCM = ±0.5V, TA = 25°C5256 dB

●50 dB

Inverting Input Current VS = ±15V, VCM = ±13V ● 2.0 10 µA/V
Common Mode Rejection V

PSRR Power Supply Rejection Ratio VS = ±2V to ±15V, TA = 25°C6676dB

Noninverting Input Current VS = ±2V to ±15V ● 5 50 nA/V
Power Supply Rejection V

Inverting Input Current VS = ±2V to ±15V ● 0.1 2 µA/V
Power Supply Rejection V

A

R

V

I

I

VOL

OL

OUT

OUT

S

Large-Signal Voltage Gain VS = ±15V, V

Transresistance, ∆V

OUT

/∆I

–

IN

Maximum Output Swing VS = ±15V, RL = 150Ω, TA = 25°C ±12.80 ±13.15 V

Maximum Output Current RL = 1Ω, VS = ±15V ● ±125 ±220 mA

Supply Current per Amplifier VS = ±2.5V to ±5V, TA = 25°C 6.0 7.0 mA

Channel Separation VS = ±15V, V

= ±5V, VCM = ±3V ● 2.5 10 µA/V

S

= ±2.5V, VCM = ±0.5V ● 3.0 10 µA/V

V

S

●63 dB

VS = ±2V to ±5V, TA = 25°C6676dB

●63 dB

= ±2V to ±5V ● 5 50 nA/V

S

= ±2V to ±5V ● 0.1 2 µA/V

S

= ±10V, RL = 150Ω ● 66 80 dB

= ±5V, V

V

S

= ±2.5V, V

V

S

VS = ±15V, V

= ±5V, V

V

S

VS = ±2.5V, V

OUT

= ±2.5V, RL = 50Ω ● 66 80 dB

OUT

= ±0.5V, RL = 50Ω ● 66 80 dB

OUT

= ±10V, RL = 150Ω ● 100 500 kΩ

OUT

= ±2.5V, RL = 50Ω ● 100 500 kΩ

OUT

= ±0.5V, RL = 50Ω ● 100 300 kΩ

OUT

● ±12.60 V

VS = ±15V, IL = ±100mA, TA = 25°C ±12.65 ±13.0 V

● ±12.55 V

VS = ±5V, RL = 50Ω, TA = 25°C ±3.20 ±3.45 V

● ±3.10 V

VS = ±5V, IL = ±100mA, TA = 25°C ±2.75 ±3.10 V

● ±2.65 V

VS = ±2.5V, RL = 50Ω, TA = 25°C ±1.25 ±1.45 V

● ±1.15 V

VS = ±2.5V, IL = ±50mA, TA = 25°C ±1.00 ±1.15 V

● ±0.90 V

= 1Ω, VS = ±5V ● ±125 ±220 mA

R

L

RL = 1Ω, VS = ±2.5V ±140 mA

● 8.0 mA

VS = ±15V, TA = 25°C 7.0 9.0 mA

● 10.5 mA

= ±10V, RL = 150Ω ● 100 120 dB

= ±5V, V

V

S

OUT

= ±2.5V, RL = 50Ω ● 100 115 dB

OUT

3

LT1497

ELECTRICAL CHARACTERISTICS

VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

SR Slew Rate VS = ±15V, TA = 25°C (Note 4) 500 900 V/µs

VS = ±5V, TA = 25°C (Note 4) 200 350 V/µs

BW Small-Signal Bandwidth VS = ±15V, RF = RG = 560Ω, RL = 100Ω 50 MHz

VS = ±5V, RF = RG = 560Ω, RL = 100Ω 35 MHz
VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 30 MHz

t

r

t

s

Small-Signal Rise Time VS = ±15V, RF = RG = 560Ω, RL = 100Ω 7.5 ns

Overshoot VS = ±15V, RF = RG = 560Ω, RL = 100Ω 15 %

Propagation Delay VS = ±15V, RF = RG = 560Ω, RL = 100Ω 6.8 ns

Settling Time VS = ±15V, 10V Step, 0.1%, AV = –1 55 ns

Differential Gain (Note 5) VS = ±15V, RF = RG = 510Ω, RL = 150Ω 0.02 %

Differential Phase (Note 5) VS = ±15V, RF = RG = 510Ω, RL = 150Ω 0.015 Deg

V

= ±5V, RF = RG = 560Ω, RL = 100Ω 9.5 ns

S

VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 11 ns

V

= ±5V, RF = RG = 560Ω, RL = 100Ω 12 %

S

VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 10 %

VS = ±5V, RF = RG = 560Ω, RL = 100Ω 8.4 ns
V

= ±2.5V, RF = RG = 560Ω, RL = 100Ω 9.7 ns

S

VS = ±5V, 5V Step, 0.1%, AV = –1 50 ns

VS = ±15V, RF = RG = 510Ω, RL = 50Ω 0.19 %
VS = ±5V, RF = RG = 510Ω, RL = 150Ω 0.08 %
V

= ±5V, RF = RG = 510Ω, RL = 50Ω 0.41 %

S

VS = ±15V, RF = RG = 510Ω, RL = 50Ω 0.235 Deg
VS = ±5V, RF = RG = 510Ω, RL = 150Ω 0.045 Deg
V

= ±5V, RF = RG = 510Ω, RL = 50Ω 0.310 Deg

S

● 400 V/µs

● 150 V/µs

The ● denotes specifications which apply over the full operating
temperature range.

Note 1: Applies to short circuits to ground only. A short circuit between the
output and either supply may damage the part when operated on supplies
greater than ±10V

Note 2: The LT1497 is designed, characterized and expected to operate
over the temperature range of –40°C to 85°C, but is not tested at –40°C
and 85°C. Guaranteed industrial grade parts are available, consult factory.

Note 3: Thermal resistance varies depending upon the amount of PC board
metal attached to the device. θ
covered with 2oz copper on both sides.

is specified for a 2500mm2 test board

JA

Note 4: Slew rate is measured between ±5V on a ±10V output signal while
operating on ±15V supplies with R
On ±5V supplies slew rate is measured between ±1V on a ±3V output
signal. The slew rate is much higher when the input is overdriven and
when the amplifier is operated inverting. See the Applications Information
section.

Note 5: NTSC composite video with an amplifier output level of 2V peak.

= 453Ω, RG = 49.9Ω and RL = 150Ω.

F

4

LT1497

SUPPLY VOLTAGE (±V)

0

0

–3dB BANDWIDTH (MHz)

10

30

40

50

12

90

1497 G03

20

618

10

416

8

214

60

70

80

PEAKING ≤ 1dB
PEAKING ≤ 5dB

RF = 470Ω

R

F

= 560Ω

RF = 750Ω

RF = 1k

GAIN = 2
R

L

= 100Ω

W

UU

SMALL-SIGNAL BANDWIDTH

VS = ±15V, Peaking ≤ 1dB

A

V

–1 150 560 560 59.2

1 150 560 – 57.0

2 150 510 510 59.1

10 150 270 30 43.4

R

L

R

F

R

G

50 560 560 43.1
20 620 620 30.0

50 560 – 42.7
20 560 – 30.3

50 560 560 41.7
20 620 620 20.7

50 270 30 30.9
20 270 30 19.0

–3dB BW (MHz)

VS = ±5V, Peaking ≤ 1dB

A

V

–1 150 510 510 45.0

1 150 510 – 44.3

2 150 510 510 41.7

10 150 270 30 28.1

UW

TYPICAL PERFORMANCE CHARACTERISTICS

Voltage Gain and Phase
vs Frequency, Gain = 6dB

9
8
7
6
5

4
3

VOLTAGE GAIN (dB)

2
1

RL = 100Ω

0

= RG = 560Ω

R

F

–1

0.1

PHASE

GAIN

1 10 100

FREQUENCY (MHz)

±5V

±5V

±15V

±15V

1497 G01

0
45
90

PHASE SHIFT (DEG)

135
180

225
270

–3dB Bandwidth
vs Supply Voltage

90

80

70

60

50

40

30

–3dB BANDWIDTH (MHz)

20

10

0

PEAKING ≤ 1dB
PEAKING ≤ 5dB

RF = 470Ω

416

214

0

SUPPLY VOLTAGE (±V)

R

= 560Ω

F

RF = 750Ω

RF = 1k

618

10

8

12

R

L

R

F

R

G

–3dB BW (MHz)

50 560 560 32.0
20 560 560 23.2

50 560 – 31.7
20 560 – 22.9

50 560 560 30.4
20 560 560 21.9

50 270 30 21.9
20 270 30 14.6

–3dB Bandwidth
vs Supply Voltage

GAIN = 2

= 1k

R

L

1497 G02

28
26
24
22
20

18
16

VOLTAGE GAIN (dB)

14
12
10

8

0.1

Voltage Gain and Phase
vs Frequency, Gain = 20dB

0

PHASE

RL = 100Ω

= 270Ω

R

F

= 30Ω

R

G

1 10 100

FREQUENCY (MHz)

GAIN

±5V

±5V

±15V

±15V

1497 G04

45
90

PHASE SHIFT (DEG)

135
180

225
270

–3dB Bandwidth
vs Supply Voltage

90

80

70

60

50

40

30

–3dB BANDWIDTH (MHz)

20

10

0

PEAKING ≤ 1dB
PEAKING ≤ 5dB

416

214

0

SUPPLY VOLTAGE (±V)

–3dB Bandwidth
vs Supply Voltage

GAIN = 10

= 1k

R

L

= 270Ω

R

F

RF = 560Ω

618

8

RF = 430Ω

RF = 750Ω

RF = 1k

10

12

1497 G05

90

80

70

60

50

40

30

–3dB BANDWIDTH (MHz)

20

10

0

PEAKING ≤ 1dB
PEAKING ≤ 5dB

RF = 560Ω

618

416

214

0

SUPPLY VOLTAGE (±V)

GAIN = 10

= 100Ω

R

L

RF = 430Ω

RF = 750Ω

8

RF = 270Ω

RF = 1k

10

12

1497 G06

5

LT1497

FEEDBACK RESISTOR (kΩ)

10

CAPACITIVE LOAD (pF)

1000

10000

023

1497 G09

1

1

100

RL = 1k
A

V

= 2

PEAKING ≤ 5dB


VS = ±5V

V

S

= ±15V

TEMPERATURE (°C)

–50



200

250

350

0

25 75

1497 G15

150

100

–25 0

50 100 125

50

300

OUTPUT SHORT-CIRCUIT CURRENT (mA)

VS = ±15V
R

L

= 1Ω

SINKING

SOURCING

UW

TYPICAL PERFORMANCE CHARACTERISTICS

Differential Phase
vs Supply Voltage

0.5
RF = RG = 510Ω

= 2

A

V

AMPLIFIER OUTPUT = 2V PEAK

0.4

0.3

0.2

DIFFERENTIAL PHASE (DEG)

0.1
RL = 150Ω

0

7

5

9

SUPPLY VOLTAGE (±V)

Output Saturation Voltage
vs Junction Temperature, ±15V

+

V

VS = ±15V

= 50mA

I

–1

–2

IL = 125mA

–3



3

IL = 125mA

2

1

OUTPUT SATURATION VOLTAGE (V)

–

V

–50

–25 0

L

IL = 100mA

IL = 100mA

IL = 50mA

25 75

TEMPERATURE (°C)

RL = 50Ω

RL = 1k

11

13

15

1497 G07

IL = 75mA

IL = 75mA

50 100 125

1497 G10

Differential Gain
vs Supply Voltage

0.5

0.4

0.3

0.2

DIFFERENTIAL GAIN (%)

0.1

0

5

RF = RG = 510Ω

= 2

A

V

AMPLIFIER OUTPUT = 2V PEAK

RL = 1k

7

9

SUPPLY VOLTAGE (±V)

Output Saturation Voltage
vs Junction Temperature, ±5V

+

V

VS = ±5V

= 50mA

I

–1

–2

IL = 125mA

–3



3

IL = 125mA

2

1

OUTPUT SATURATION VOLTAGE (V)

–

V

–50

–25 0

L

IL = 100mA

IL = 100mA

IL = 50mA

25 75

TEMPERATURE (°C)

RL = 50Ω

RL = 150Ω

11

13

1497 G08

IL = 75mA

IL = 75mA

50 100 125

1497 G11

Maximum Capacitive Load
vs Feedback Resistor

15

Output Saturation Voltage
vs Junction Temperature, ±2.5V

+

V

VS = ±2.5V

–1

–2

–3



3

2

1

OUTPUT SATURATION VOLTAGE (V)

–

V

–50

–25 0

IL = 25mA

IL = 50mA

IL = 75mA

IL = 25mA

50 100 125

25 75

TEMPERATURE (°C)

IL = 75mA

IL = 50mA

1497 G12

Supply Current
vs Ambient Temperature

8.5

8.0

7.5

7.0



6.5

6.0

5.5

SUPPLY CURRENT PER AMPLIFIER (mA)

5.0

–50

6

VS = ±15V

VS = ±5V

–25 0

TEMPERATURE (°C)

VS = ±2.5V

50 100 125

25 75

1497 G13

Input Common Mode Limit
vs Junction Temperature

+

V

–0.5

–1.0

–1.5



1.5

1.0

COMMON MODE RANGE (V)

0.5

–

V

–50

–25 0

V+ = 2V TO 18V

V– = –2V TO –18V

TEMPERATURE (°C)

50 100 125

25 75

Output Short-Circuit Current
vs Junction Temperature

1497 G14

UW

FREQUENCY (Hz)

–80

OUTPUT TO INPUT CROSSTALK (dB)

–60

–40
–50

–20

–10

–90

–70

–30

10k 1M 10M 100M

1497 G24

–100
–110

100k

VS = ±15V
A

V

= 10

R

L

= 100Ω

R

F

= 560Ω

R

G

= 62Ω

TYPICAL PERFORMANCE CHARACTERISTICS

LT1497

Settling Time to 10mV
vs Output Step

10

8
6
4
2
0

–2

OUTPUT STEP (V)

–4
–6
–8

–10

AV = –1

20

0

AV = 1

SETTLING TIME (ns)

40

A

V

AV = –1

Total Harmonic Distortion
vs Frequency

0.10
VS = ±15V

= 100Ω

R

L

= RG = 560Ω

R

F

0.01

TOTAL HARMONIC DISTORTION (%)

0.001
10 100

V

OUT

V

OUT

1k 10k 100k

FREQUENCY (Hz)

60

= 1

= 7V

= 2V

VS = ±15V

= 560Ω

R

F

80

1497 G16

RMS

RMS

1497 G19

100

Settling Time to 1mV
vs Output Step

10

VS = ±15V

8

= 560Ω

R

F

6

A

= 1

V

4
2
0

–2

OUTPUT STEP (V)

–4

AV = 1

–6
–8

–10

25

0

AV = –1

AV = –1

50

100

75

SETTLING TIME (ns)

125

150

2nd and 3rd Harmonic Distortion
vs Frequency

–20

VS = ±15V

= 5V

= 50Ω
= 560Ω

2ND

3RD



P-P

110

FREQUENCY (MHz)

AV = 1

3RD

V

OUT

–30

R

L

R

F

–40

–50

–60

AV = 1

–70

DISTORTION (dBc)

–80

AV = –1

–90

–100

0.1

175

200

AV = –1
2ND

225

1497 G17

1497 G20

250

Spot Noise Voltage and Current
vs Frequency

100

10

SPOT NOISE (nV/√Hz OR pA/√Hz)

1

10 100

1k 10k 100k

FREQUENCY (Hz)

3rd Order Intercept vs Frequency

40

35

30

25

20

3RD ORDER INTERCEPT (dBm)

15

10

0

10 15 20

5

FREQUENCY (MHz)

VS = ±15V

= 50Ω

R

L

= 270Ω

R

F

= 30Ω

R

G

PO1 = PO2 = 4dBm

–i

n

e

n

+i

n

25 30

1497 G18

1497 G21

Output Impedance vs Frequency

100

VS = ±15V

10

1

RF = RG = 1.5k

0.1

OUTPUT IMPEDANCE (Ω)

RF = RG = 560Ω

0.01
10k 100k

1M 10M 100M

FREQUENCY (Hz)

1497 G22

Power Supply Rejection
vs Frequency

80

70

60

50

40

30

20

POWER SUPPLY REJECTION (dB)

10

0

10k 1M 10M 100M

100k

FREQUENCY (Hz)

VS = ±15V

= 50Ω

R

L

= RG = 560Ω

R

F

POSITIVENEGATIVE

Amplifier Crosstalk vs Frequency

1497 G23

7

LT1497

U

WUU

APPLICATIONS INFORMATION

The LT1497 is a dual current feedback amplifier with high
output current drive capability. Bandwidth is maintained
over a wide range of voltage gains by the appropriate
choice of feedback resistor. These amplifiers will drive low
impedance loads such as cables with excellent linearity at
high frequencies.

Feedback Resistor Selection

The optimum value for the feedback resistor is a function
of the operating conditions of the device, the load imped­ance and the desired flatness of frequency response. The
Small-Signal Bandwidth table gives the values which
result in the highest bandwidth with less than 1dB of
peaking for various gains, loads and supply voltages. If
this level of flatness is not required, a higher bandwidth
can be obtained by use of a lower feedback resistor. The
characteristic curves of Bandwidth vs Supply Voltage
indicate feedback resistors for peaking up to 5dB. These
curves use a solid line when the response has less than
1dB of peaking and a dashed line when the response has
1dB to 5dB of peaking. Note that in a gain of 10 peaking is
always under 1dB for the resistor ranges shown. Reducing
the feedback resistor further than 270Ω in a gain of 10 will
increase the bandwidth, but it also loads the amplifier and
reduces the maximum current available to drive the load.

Capacitive Loads

The LT1497 can drive capacitive loads directly when the
proper value of feedback resistor is used. The graph of
Maximum Capacitive Load vs Feedback Resistor should
be used to select the appropriate value. The graph shows
feedback resistor values for 5dB frequency peaking when
driving a 1k load at a gain of 2. This is a worst-case
condition. The amplifier is more stable at higher gains and
driving heavier loads (smaller load resistors). Alterna­tively, a small resistor (10Ω to 20Ω) can be put in series
with the output to isolate the capacitive load from the
amplifier output. This has the advantage in that the ampli­fier bandwidth is only reduced when the capacitive load is
present, and the disadvantage that the gain is a function of
the load resistance.

Capacitance on the Inverting Input

Current feedback amplifiers require resistive feedback
from the output to the inverting input for stable operation.
Take care to minimize the stray capacitance between the
output and the inverting input. Capacitance on the invert­ing input to ground will cause peaking in the frequency
response (and overshoot in the transient response), but it
does not degrade the stability of the amplifier.

Power Supplies

The LT1497 will operate on single or split supplies from
±2V (4V total) to ±15V (30V total). It is not necessary to
use equal value split supplies, however, the offset voltage
and inverting input bias current will change. The offset
voltage changes about 1mV per volt of supply mismatch.
The inverting bias current can change as much as 10µA
per volt of supply mismatch, though typically the change
is less than 2.5µA per volt.

Thermal Considerations

The LT1497 contains a thermal shutdown feature that
protects against excessive internal (junction) tempera­ture. If the junction temperature of the device exceeds the
protection threshold, the device will begin cycling
between normal operation and an off state. The cycling is
not harmful to the part. The thermal cycling occurs at a
slow rate, typically 10ms to several seconds, depending
upon the power dissipation and the thermal time con­stants of the package and the amount of copper on the
board under the package. Raising the ambient tempera­ture until the device begins thermal shutdown gives a
good indication of how much margin there is in the
thermal design.

For surface mount devices heat sinking is accomplished
by using the heat spreading capabilities of the PC board
and its copper traces. Experiments have shown that the
heat spreading copper layer does not need to be electri­cally connected to the leads of the device. The PCB
material can be very effective at transmitting heat between
the pad area attached to V– pins of the device and a ground

8

LT1497

560Ω

–15V

560Ω

–

+

560Ω

560Ω

86.4mA

15V

200Ω

200Ω

1497 F01

–

+

A

–10V

10V

f = 2MHz

U

WUU

APPLICATIONS INFORMATION

or power plane layer either inside or on the opposite side
of the board. Copper board stiffeners and plated through­holes can also be used to spread the heat generated by the
device. Table 1 lists the thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with 2oz copper.
This data can be used as a rough guideline in estimating
thermal resistance. The thermal resistance for each appli­cation will be affected by thermal interactions with other
components as well as board size and shape.

Table 1. Fused 16-lead and 8-lead SO Packages

COPPER AREA (2oz)

TOPSIDE BACKSIDE COPPER AREA (16-LEAD) (8-LEAD)

600mm
300mm
100mm

0mm

2

2

2

2

2

2

2

2

2

2500mm22500mm
1000mm22500mm

600mm22500mm
180mm22500mm
180mm21000mm

2

180mm

2

180mm

2

180mm

2

180mm

TOTAL θ

780mm
480mm
280mm
180mm

2

2

2

2

2

2

2

2

2

5000mm
3500mm
3100mm
2680mm
1180mm

JA

40°C/W 80°C/W
46°C/W 92°C/W
48°C/W 96°C/W
49°C/W 98°C/W
56°C/W 112°C/W
58°C/W 116°C/W
59°C/W 118°C/W
60°C/W 120°C/W
61°C/W 122°C/W

θ

JA

thermal resistance is 40°C/W. The junction temperature
TJ is:

TJ = (1.24W)(40°C/W) + 85°C = 135°C

The maximum junction temperature for the LT1497 is
150°C, so the heat sinking capability of the board is
adequate for the application.

If the copper area on the PC board is reduced to 180mm

2

the thermal resistance increases to 61°C/W and the junc­tion temperature becomes:

TJ = (1.24W)(61°C/W) + 85°C = 161°C

which is above the maximum junction temperature indi­cating that the heat sinking capability of the board is
inadequate and should be increased.

Calculating Junction Temperature

The junction temperature can be calculated from the
equation:

TJ = (PD)(θJA) + T

A

TJ = Junction Temperature
TA = Ambient Temperature
PD = Power Dissipation

θJA = Thermal Resistance (Junction-to-Ambient)

As an example, calculate the junction temperature for the
circuit in Figure 1 assuming an 85°C ambient temperature.

The device dissipation can be found by measuring the
supply currents, calculating the total dissipation and then
subtracting the dissipation in the load and feedback net­work. Both amplifiers are in a gain of –1.

The dissipation for each amplifier is:

The total dissipation is 1.24W. When a 2500mm2 PC
board with 2oz copper on top and bottom is used, the

PD = (1/2)(86.4mA)(30V) – (10V)2/(200||560) = 0.62W

Figure 1. Thermal Calculation Example

Slew Rate

Unlike a traditional op amp, the slew rate of a current
feedback amplifier is not independent of the amplifier gain
configuration. There are slew rate limitations in both the
input stage and the output stage. In the inverting mode and
for higher gains in the noninverting mode, the signal
amplitude on the input pins is small and the overall slew
rate is that of the output stage. The input stage slew rate
is related to the quiescent current in the input devices.

Referring to the Simplified Schematic, for noninverting
applications the two current sources in the input stage
slew the parasitic internal capacitances at the bases of Q3
and Q4. Consider a positive going input at the base of Q1
and Q2. If the input slew rate exceeds the internal slew rate,

9

LT1497

U

WUU

APPLICATIONS INFORMATION

the normally active emitter of Q2 will turn off as the entire
current available from the current source is used to slew
the base of Q3. The base of Q4 is driven by Q1 without slew
limitation. When the differential input voltage exceeds two
diode drops (about 1.4V) the extra clamp emitter on Q1
turns on and drives the base of Q3 directly. Once the base
of Q3 has been driven within 1.4V of its final value, the
clamp emitter of Q1 turns off and the node must finish
slewing using the current source.

This effect can be seen in Figure 2 which shows the large
signal behavior in a gain of 1 on ±15V supplies. The
clamping action enhances the slew rate beyond the input
limitation, but always leads to slew overshoot after the
clamps turn off. Figure 3 shows that for higher gain

configurations there is much less slew rate enhancement
because the input only moves 2V, barely enough to turn on
the input clamps. In inverting configurations as shown in
Figure 4 the noninverting input does not move so there is
no input slew rate limitation. Slew overshoot is due to
capacitance on the inverting input and can be reduced with
a larger feedback resistor.

The output slew rate is set by the value of the feedback
resistors and the internal capacitance. Larger feedback
resistors will reduce the slew rate as will lower supply
voltages, similar to the way the bandwidth is reduced.
The larger feedback resistors will also cut back on slew
overshoot.

AV = 1
V

= ±15V

S

R

= 560Ω

F

= 100Ω

R

L

1497 F02

Figure 2. Large-Signal Response

WW

SI PLIFIED SCHE ATIC

+IN

= ±15V

S

R

= 560Ω

F

R

= 100Ω

L

RG = 62Ω

AV = 10
V

Figure 3. Large-Signal Response

One Amplifier

Q5

Q3

Q2

–IN

Q1

Q4

Q10

Q6

Q11

Q7

Q8

Q9

Q12

1497 F03

R

AV = –1
V

= ±15V

S

= RG = 560Ω

F

R

= 100Ω

L

Figure 4. Large-Signal Response

+

V

Q13

V

OUT

Q14

–

V

1497 SS

1497 F04

10

U

TYPICAL APPLICATIONS

LT1497

Differential Input/Differential Output Power Amp (AV = 2)

V

IN

+

1/2 LT1497

V

OUT

–

560Ω

1.1k

560Ω

–

–V

1497 TA03

OUT

–V

1/2 LT1497

IN

+

U

PACKAGE DESCRIPTION

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH 


SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD 
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



× 45°

0.016 – 0.050

0.406 – 1.270

0°– 8° TYP

Dimensions in inches (millimeters) unless otherwise noted.

8-Lead Plastic Small Outline (Narrow 0.150)

0.053 – 0.069

(1.346 – 1.752)

0.014 – 0.019

(0.355 – 0.483)

Paralleling Both Amplifiers for Guaranteed 250mA Output Drive

S8 Package

(LTC DWG # 05-08-1610)

0.004 – 0.010

(0.101 – 0.254)

0.050

(1.270)

TYP

V

IN

0.228 – 0.244

(5.791 – 6.197)

560Ω

560Ω

+

1/2 LT1497

–

560Ω

+

1/2 LT1497

–

560Ω

0.189 – 0.197*
(4.801 – 5.004)

7

8

1

2

6

3

3Ω

3Ω

1497 TA04

5

0.150 – 0.157**
(3.810 – 3.988)

4

SO8 0996

V

OUT

0.010 – 0.020

(0.254 – 0.508)

0.008 – 0.010

(0.203 – 0.254)

*

DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH 


SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

**

DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD 
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



× 45°

0.016 – 0.050

0.406 – 1.270

(1.346 – 1.752)

0° – 8° TYP

(0.355 – 0.483)

0.053 – 0.069

0.014 – 0.019

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen­tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

S Package

16-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

16

1

0.050

(1.270)

TYP

0.004 – 0.010

(0.101 – 0.254)

(5.791 – 6.197)

0.228 – 0.244

0.386 – 0.394*
(9.804 – 10.008)

13

14

15

3

2

12

11 10

5

4

6

7

9

0.150 – 0.157**
(3.810 – 3.988)

S16 0695

8

11

LT1497

TYPICAL APPLICATION

±4A Current Boosted Power Amp (AV = 10) Frequency Response of Current Boosted Power Amp

U

15V

3Ω

0.033Ω

Q1
D45VH4

V

OUT

6.2Ω

V

IN

200Ω

+

1/2 LT1497

0.01µF

+

V

–

1.8K

200Ω

+

1/2 LT1497

–

6.2Ω

–

V

1.8k

–15V

3Ω

0.01µF

1497 TA05

Q2
D44VH4

0.033Ω

22
21
20
19
18

17
16

VOLTAGE GAIN (dB)

VS = ±15V

15

= 10

A

V

14

= 1.8k

R

F

= 200Ω

R

G

13

= 6V

V

OUT

12

10k

RL = 50Ω

RL = 2.5Ω

P-P

100k 1M 10M

FREQUENCY (Hz)

1497 TA06

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1206 Single 250mA, 60MHz Current Feedback Amplifier Shutdown Function, Stable with CL = 10,000pF,

900V/µs Slew Rate

LT1207 Dual 250mA, 60MHz Current Feedback Amplifier Dual Version of LT1206
LT1210 Single 1A, 30MHz Current Feedback Amplifier Higher Output Version of LT1206
LT1229/LT1230 Dual/Quad 100MHz Current Feedback Amplifiers 30mA Output Current, 1000V/µs Slew Rate
LT1363/LT1364/LT1365 Single/Dual/Quad 70MHz, 1000V/µs, C-LoadTM Amplifiers 50mA Output Current, 1.5mV Max VOS, 2µA Max I
C-Load is a trademark of Linear Technology Corporation.

B

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● [phone]
FAX: [phone]

●

TELEX: 499-3977 ● www.linear-tech.com

1497f LT/TP 1097 4K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1997