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LT1497 Dual 125mA, 50MHz Current Feedback Amplifier
FEATURES
s s s s s
DESCRIPTION
The LT(R)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.
s s s s s s s
Minimum Output Current: 125mA Maximum Supply Current per Amp: 7mA, VS = 5V Bandwidth: 50MHz, VS = 15V Slew Rate: 900V/s, VS = 15V Wide Supply Range: VS = 2.5V to 15V (Enhanced JA 16-Pin SO Package) Enhanced JA SO-8 Package for 5V Operation 0.02% Differential Gain: AV = 2, RL = 150 0.015 Differential Phase: AV = 2, RL = 150 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
APPLICATIONS
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Twisted-Pair Drivers Video Amplifiers Cable Drivers Test Equipment Amplifiers Buffers
TYPICAL APPLICATION
HDSL2 Single Pair Line Driver
560 560
- 40
2nd and 3rd Harmonic Distortion of HDSL2 Single Pair Line Driver
VS = 5V VIN = 1.25V VOUT = 2.5V
- 50
68.1
DISTORTION (dBc)
1/2 LT1497 VIN
1:1* 560 560 135
- 60
- 70
2ND 3RD
- 80
68.1
*MIDCOM 671-7807
- 90 100k FREQUENCY (Hz)
1419 TA01
1497 TA02
1/2 LT1497
U
U
U
+ + -
-
1M
2M
1
LT1497
ABSOLUTE MAXIMUM RATINGS
Total Supply Voltage (V + to V -) LT1497CS8.......................................................... 14V LT1497CS............................................................ 36V Noninverting Input Current ................................... 2mA Output Short-Circuit Duration (Note 1) .......... Continuous Operating Temperature Range (Note 2) ... - 40C to 85C Specified Temperature Range ...................... 0C to 70C Maximum Junction Temperature (See Below) ....... 150C Storage Temperature Range .................. - 65C to 150C Lead Temperature (Soldering, 10 sec)................... 300C
PACKAGE/ORDER INFORMATION
ORDER PART NUMBER
TOP VIEW OUT A 1 A +IN A 3 V- 4 B 6 -IN B 5 +IN B 8 V+ 7 OUT B
LT1497CS8
-IN A 2
S8 PACKAGE 8-LEAD PLASTIC SO
S8 PART MARKING 1497
TJMAX = 150C, JA = 80C/ W (NOTE 3)
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 VOS PARAMETER Input Offset Voltage Input Offset Voltage Matching Input Offset Voltage Drift IIN+ Noninverting Input Current Noninverting Input Current Matching IIN- Inverting Input Current Inverting Input Current Matching en + in - in RIN Input Noise Voltage Density Noninverting Input Noise Current Density Inverting Input Noise Current Density Input Resistance TA = 25C
q
CONDITIONS TA = 25C
q
TA = 25C
q q
TA = 25C
q
TA = 25C
q
TA = 25C
q
f = 1kHz, RF = 1k, RG = 10, RS = 0 f = 1kHz, RF = 1k, RG = 10, RS = 10k f = 1kHz, RF = 1k, RG = 10, RS = 10k VIN = 13V, VS = 15V VIN = 3V, VS = 5V VIN = 0.5V, VS = 2.5V
q q q
CIN
Input Capacitance
2
U
U
W
WW U
W
TOP VIEW V- 1 16 V - 15 NC 14 V + A B 13 OUT B 12 -IN B 11 +IN B 10 NC 9 V-
ORDER PART NUMBER LT1497CS
NC 2 OUT A 3 -IN A 4 +IN A 5 V- 6 NC 7 V- 8
S PACKAGE 16-LEAD PLASTIC SO
TJMAX = 150C, JA = 40C/ W (NOTE 3)
MIN
TYP 3 1 10 1 0.3 7 3 3 2 20
MAX 10 15 3.5 5.0 3 10 1.0 1.5 20 40 10 15
UNITS mV mV mV mV V/C A A A A A A A A nV/Hz pA/Hz pA/Hz M M M pF
1.5 1.5 1.5
10 8 8 3
LT1497
ELECTRICAL CHARACTERISTICS
VCM = 0V, 2.5V VS 15V (LT1497CS), 2.5V VS 5V (LT1497CS8), pulse tested unless otherwise noted.
SYMBOL PARAMETER Input Voltage Range CONDITIONS VS = 15V VS = 5V VS = 2.5V VS = 15V, VCM = 13V, TA = 25C
q q q q
MIN 13 3.0 0.5 55 53 54 52 52 50
TYP 14 4.0 1.5 62 60 56 2.0 2.5 3.0
MAX
UNITS V V V dB dB dB dB dB dB
CMRR
Common Mode Rejection Ratio
VS = 5V, VCM = 3V, TA = 25C
q
VS = 2.5V, VCM = 0.5V, TA = 25C
q
Inverting Input Current Common Mode Rejection PSRR Power Supply Rejection Ratio
VS = 15V, VCM = 13V VS = 5V, VCM = 3V VS = 2.5V, VCM = 0.5V VS = 2V to 15V, TA = 25C
q q q q
10 10 10
A/V A/V A/V dB dB dB dB
66 63 66 63
76 76 5 5 0.1 0.1 50 50 2 2
VS = 2V to 5V, TA = 25C
q
Noninverting Input Current Power Supply Rejection Inverting Input Current Power Supply Rejection AVOL Large-Signal Voltage Gain
VS = 2V to 15V VS = 2V to 5V VS = 2V to 15V VS = 2V to 5V VS = 15V, VOUT = 10V, RL = 150 VS = 5V, VOUT = 2.5V, RL = 50 VS = 2.5V, VOUT = 0.5V, RL = 50 VS = 15V, VOUT = 10V, RL = 150 VS = 5V, VOUT = 2.5V, RL = 50 VS = 2.5V, VOUT = 0.5V, RL = 50 VS = 15V, RL = 150, TA = 25C
q q q q q q q q q q q
nA/V nA/V A/V A/V dB dB dB k k k V V V V V V V V V V V V mA mA mA
66 66 66 100 100 100 12.80 12.60 12.65 12.55 3.20 3.10 2.75 2.65 1.25 1.15 1.00 0.90 125 125
80 80 80 500 500 300 13.15 13.0 3.45 3.10 1.45 1.15 220 220 140 6.0 7.0 8.0 9.0 10.5
ROL
Transresistance, VOUT/IIN-
VOUT
Maximum Output Swing
VS = 15V, IL = 100mA, TA = 25C
q
VS = 5V, RL = 50, TA = 25C
q
VS = 5V, IL = 100mA, TA = 25C
q
VS = 2.5V, RL = 50, TA = 25C
q
VS = 2.5V, IL = 50mA, TA = 25C
q
IOUT
Maximum Output Current
RL = 1, VS = 15V RL = 1, VS = 5V RL = 1, VS = 2.5V VS = 2.5V to 5V, TA = 25C
q q
IS
Supply Current per Amplifier
q
mA mA mA mA dB dB
VS = 15V, TA = 25C
q
7.0
q q
Channel Separation
VS = 15V, VOUT = 10V, RL = 150 VS = 5V, VOUT = 2.5V, RL = 50
100 100
120 115
3
LT1497
ELECTRICAL CHARACTERISTICS
VCM = 0V, 2.5V VS 15V (LT1497CS), 2.5V VS 5V (LT1497CS8), pulse tested unless otherwise noted.
SYMBOL SR PARAMETER Slew Rate CONDITIONS VS = 15V, TA = 25C (Note 4)
q
MIN 500 400 200 150
TYP 900 350 50 35 30 7.5 9.5 11 15 12 10 6.8 8.4 9.7 55 50 0.02 0.19 0.08 0.41 0.015 0.235 0.045 0.310
MAX
UNITS V/s V/s V/s V/s MHz MHz MHz ns ns ns % % % ns ns ns ns ns % % % % Deg Deg Deg Deg
VS = 5V, TA = 25C (Note 4)
q
BW
Small-Signal Bandwidth
VS = 15V, RF = RG = 560, RL = 100 VS = 5V, RF = RG = 560, RL = 100 VS = 2.5V, RF = RG = 560, RL = 100 VS = 15V, RF = RG = 560, RL = 100 VS = 5V, RF = RG = 560, RL = 100 VS = 2.5V, RF = RG = 560, RL = 100 VS = 15V, RF = RG = 560, RL = 100 VS = 5V, RF = RG = 560, RL = 100 VS = 2.5V, RF = RG = 560, RL = 100 VS = 15V, RF = RG = 560, RL = 100 VS = 5V, RF = RG = 560, RL = 100 VS = 2.5V, RF = RG = 560, RL = 100 VS = 15V, 10V Step, 0.1%, AV = - 1 VS = 5V, 5V Step, 0.1%, AV = - 1 VS = 15V, RF = RG = 510, RL = 150 VS = 15V, RF = RG = 510, RL = 50 VS = 5V, RF = RG = 510, RL = 150 VS = 5V, RF = RG = 510, RL = 50 VS = 15V, RF = RG = 510, RL = 150 VS = 15V, RF = RG = 510, RL = 50 VS = 5V, RF = RG = 510, RL = 150 VS = 5V, RF = RG = 510, RL = 50
tr
Small-Signal Rise Time
Overshoot
Propagation Delay
ts
Settling Time Differential Gain (Note 5)
Differential Phase (Note 5)
The q 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 - 40C to 85C, but is not tested at - 40C and 85C. 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. JA is specified for a 2500mm2 test board covered with 2oz copper on both sides.
Note 4: Slew rate is measured between 5V on a 10V output signal while operating on 15V supplies with RF = 453, RG = 49.9 and RL = 150. 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.
4
LT1497
SMALL-SIGNAL BANDWIDTH
VS = 15V, Peaking 1dB
AV -1 RL 150 50 20 150 50 20 150 50 20 150 50 20 RF 560 560 620 560 560 560 510 560 620 270 270 270 RG 560 560 620 - - - 510 560 620 30 30 30 - 3dB BW (MHz) 59.2 43.1 30.0 57.0 42.7 30.3 59.1 41.7 20.7 43.4 30.9 19.0
1
2
10
TYPICAL PERFORMANCE CHARACTERISTICS
Voltage Gain and Phase vs Frequency, Gain = 6dB
9 8 7 PHASE GAIN 5V 15V 0 45 90
- 3dB BANDWIDTH (MHz)
VOLTAGE GAIN (dB)
6 5 4 3 2 1 0
135 180 5V 15V 225 270
60 50 40 30 20 10
RF = 470 RF = 560 RF = 750 RF = 1k
- 3dB BANDWIDTH (MHz)
-1 0.1
RL = 100 RF = RG = 560 1 10 FREQUENCY (MHz) 100
1497 G01
Voltage Gain and Phase vs Frequency, Gain = 20dB
28 26 24
VOLTAGE GAIN (dB)
PHASE
5V
- 3dB BANDWIDTH (MHz)
22 20 18 16 14 12 10 8 0.1 RL = 100 RF = 270 RG = 30 1 10 FREQUENCY (MHz) 5V 15V GAIN
135 180 225 270
60 50 40 30 20 10 RF = 560
- 3dB BANDWIDTH (MHz)
UW
15V
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U
W
VS = 5V, Peaking 1dB
AV -1 RL 150 50 20 150 50 20 150 50 20 150 50 20 RF 510 560 560 510 560 560 510 560 560 270 270 270 RG 510 560 560 - - - 510 560 560 30 30 30 - 3dB BW (MHz) 45.0 32.0 23.2 44.3 31.7 22.9 41.7 30.4 21.9 28.1 21.9 14.6
1
2
10
- 3dB Bandwidth vs Supply Voltage
90 80 70 PEAKING 1dB PEAKING 5dB
90
- 3dB Bandwidth vs Supply Voltage
GAIN = 2 RL = 1k
80 70 60 50 40 30 20 10 0 RF = 560 RF = 750 RF = 1k RF = 470 PEAKING 1dB PEAKING 5dB GAIN = 2 RL = 100
PHASE SHIFT (DEG)
PHASE SHIFT (DEG)
0 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE ( V) 16 18
0
2
4
6 8 10 12 14 SUPPLY VOLTAGE ( V)
16
18
1497 G02
1497 G03
- 3dB Bandwidth vs Supply Voltage
0 45 90
90 80 70 RF = 270 RF = 430 PEAKING 1dB PEAKING 5dB 90 GAIN = 10 RL = 1k 80 70 60 50 40
- 3dB Bandwidth vs Supply Voltage
PEAKING 1dB PEAKING 5dB GAIN = 10 RL = 100
RF = 430 RF = 560
RF = 270
RF = 750 RF = 1k
30 20 10 0 RF = 750 0 2 4 RF = 1k 16 18
100
1497 G04
0 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE ( V) 16 18
6 8 10 12 14 SUPPLY VOLTAGE ( V)
1497 G05
1497 G06
5
LT1497 TYPICAL PERFORMANCE CHARACTERISTICS
Differential Phase vs Supply Voltage
0.5 RF = RG = 510 AV = 2 AMPLIFIER OUTPUT = 2V PEAK 0.5 RF = RG = 510 AV = 2 AMPLIFIER OUTPUT = 2V PEAK
DIFFERENTIAL PHASE (DEG)
0.4
DIFFERENTIAL GAIN (%)
0.3
RL = 50
0.3
CAPACITIVE LOAD (pF)
0.2
0.1 RL = 150 0 5 7 RL = 1k 15
1497 G07
11 13 9 SUPPLY VOLTAGE ( V)
Output Saturation Voltage vs Junction Temperature, 15V
V+ VS = 15V V+
OUTPUT SATURATION VOLTAGE (V)
OUTPUT SATURATION VOLTAGE (V)
-1 -2 IL = 125mA -3 3 2 1 V- - 50 - 25 IL = 125mA
-1 -2 IL = 125mA -3 3 2 1 V- - 50 - 25 IL = 125mA
OUTPUT SATURATION VOLTAGE (V)
IL = 50mA
IL = 75mA
IL = 100mA
IL = 100mA
IL = 50mA
IL = 75mA 100 125
50 25 75 0 TEMPERATURE (C)
Supply Current vs Ambient Temperature
8.5 V+ - 0.5
8.0
OUTPUT SHORT-CIRCUIT CURRENT (mA)
SUPPLY CURRENT PER AMPLIFIER (mA)
COMMON MODE RANGE (V)
7.5 VS = 15V 7.0 6.5 6.0 5.5 5.0 - 50 - 25 VS = 5V VS = 2.5V
50 25 75 0 TEMPERATURE (C)
6
UW
1497 G10
Differential Gain vs Supply Voltage
10000
Maximum Capacitive Load vs Feedback Resistor
RL = 1k AV = 2 PEAKING 5dB 1000
0.4
VS = 5V
RL = 50
100
VS = 15V
0.2
10
0.1
RL = 1k
RL = 150
0
1
5 7 11 13 9 SUPPLY VOLTAGE ( V) 15
1497 G08
0
1 2 FEEDBACK RESISTOR (k)
3
1497 G09
Output Saturation Voltage vs Junction Temperature, 5V
VS = 5V IL = 50mA IL = 75mA V+ -1 -2 -3 3 2 1
Output Saturation Voltage vs Junction Temperature, 2.5V
VS = 2.5V IL = 25mA IL = 75mA
IL = 50mA
IL = 100mA
IL = 100mA
IL = 75mA IL = 25mA IL = 50mA 100 125
IL = 50mA
IL = 75mA 100 125
50 25 75 0 TEMPERATURE (C)
V- - 50 - 25
50 25 75 0 TEMPERATURE (C)
1497 G11
1497 G12
Input Common Mode Limit vs Junction Temperature
350 300 250
Output Short-Circuit Current vs Junction Temperature
VS = 15V RL = 1
V + = 2V TO 18V -1.0 -1.5 1.5 1.0 0.5 V- - 50 - 25 V - = - 2V TO -18V
SINKING 200 SOURCING 150 100 50 0 - 50 - 25
100
125
50 25 75 0 TEMPERATURE (C)
100
125
50 25 75 0 TEMPERATURE (C)
100
125
1497 G13
1497 G14
1497 G15
LT1497 TYPICAL PERFORMANCE CHARACTERISTICS
Settling Time to 10mV vs Output Step
10 8 6
OUTPUT STEP (V)
6
OUTPUT STEP (V)
4 2 0 -2 -4 -6 -8 -10 0 20 AV = 1 AV = -1
4 2 0 -2 -4 -6 -8
AV = 1
AV = -1
SPOT NOISE (nV/Hz OR pA/Hz)
AV = -1
AV = 1
VS = 15V RF = 560
60 40 SETTLING TIME (ns)
Total Harmonic Distortion vs Frequency
0.10
TOTAL HARMONIC DISTORTION (%)
- 40
DISTORTION (dBc)
3RD ORDER INTERCEPT (dBm)
VS = 15V RL = 100 RF = RG = 560
0.01
VOUT = 7VRMS VOUT = 2VRMS
0.001 10
100
1k 10k FREQUENCY (Hz)
Output Impedance vs Frequency
100 VS = 15V
OUTPUT TO INPUT CROSSTALK (dB)
POWER SUPPLY REJECTION (dB)
OUTPUT IMPEDANCE ()
10
1 RF = RG = 1.5k 0.1 RF = RG = 560 0.01 10k
100k
1M 10M FREQUENCY (Hz)
UW
80
1497 G16
1497 G19 1497 G22
Settling Time to 1mV vs Output Step
10 8
100
Spot Noise Voltage and Current vs Frequency
VS = 15V RF = 560
- in
10
AV = 1
AV = -1
en + in
100
-10
0
25 50 75 100 125 150 175 200 225 250 SETTLING TIME (ns)
1497 G17
1 10
100
1k 10k FREQUENCY (Hz)
100k
1497 G18
2nd and 3rd Harmonic Distortion vs Frequency
- 20 - 30 VS = 15V VOUT = 5VP-P RL = 50 RF = 560 40 35 30 25 20 15 10
3rd Order Intercept vs Frequency
VS = 15V RL = 50 RF = 270 RG = 30 PO1 = PO2 = 4dBm
- 50 - 60 - 70 - 80 - 90 AV = -1 3RD AV = 1 2ND AV = 1 3RD AV = -1 2ND
-100 100k 0.1 1 FREQUENCY (MHz) 10
1497 G20
0
5
10 15 20 FREQUENCY (MHz)
25
30
1497 G21
Power Supply Rejection vs Frequency
80 70 60 50 NEGATIVE 40 30 20 10 0 10k 100k 1M 10M FREQUENCY (Hz) 100M
1497 G23
Amplifier Crosstalk vs Frequency
- 10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 VS = 15V AV = 10 RL = 100 RF = 560 RG = 62
VS = 15V RL = 50 RF = RG = 560
POSITIVE
-100 -110 10k 100k 1M 10M FREQUENCY (Hz) 100M
1497 G24
100M
7
LT1497
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 270 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 (10 to 20) 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 10A per volt of supply mismatch, though typically the change is less than 2.5A 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
U
W
U
U
LT1497
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 2500mm2 1000mm2 600mm2 180mm2 180mm2 180mm2 180mm2 180mm2 180mm2 2500mm2 2500mm2 2500mm2 2500mm2 1000mm2 600mm2 300mm2 100mm2 0mm2 TOTAL COPPER AREA 5000mm2 3500mm2 3100mm2 2680mm2 1180mm2 780mm2 480mm2 280mm2 180mm2 JA (16-LEAD) 40C/W 46C/W 48C/W 49C/W 56C/W 58C/W 59C/W 60C/W 61C/W JA (8-LEAD) 80C/W 92C/W 96C/W 98C/W 116C/W 120C/W 122C/W
560 560 560 A 15V
Calculating Junction Temperature The junction temperature can be calculated from the equation: TJ = (PD)(JA) + TA TJ = Junction Temperature TA = Ambient Temperature PD = Power Dissipation JA = Thermal Resistance (Junction-to-Ambient) As an example, calculate the junction temperature for the circuit in Figure 1 assuming an 85C 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: PD = (1/2)(86.4mA)(30V) - (10V)2/(200||560) = 0.62W The total dissipation is 1.24W. When a 2500mm2 PC board with 2oz copper on top and bottom is used, the Slew Rate
Figure 1. Thermal Calculation Example
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,
+
118C/W
+
-
-
U
W
U
U
thermal resistance is 40C/W. The junction temperature TJ is: TJ = (1.24W)(40C/W) + 85C = 135C The maximum junction temperature for the LT1497 is 150C, so the heat sinking capability of the board is adequate for the application. If the copper area on the PC board is reduced to 180mm2 the thermal resistance increases to 61C/W and the junction temperature becomes: TJ = (1.24W)(61C/W) + 85C = 161C which is above the maximum junction temperature indicating that the heat sinking capability of the board is inadequate and should be increased.
112C/W
86.4mA 200 560 f = 2MHz 10V -10V
200 - 15V
1497 F01
9
LT1497
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.
RF = 560 AV = 1 VS = 15V RL = 100
1497 F02
RF = 560 AV = 10 VS = 15V RL = 100
Figure 2. Large-Signal Response
Figure 3. Large-Signal Response
SI PLIFIED SCHE ATIC
One Amplifier
V+ Q5 Q6 Q7 Q13 Q3 Q8 Q2 +IN Q1 Q9 Q4 Q14 Q10 Q11 Q12 V-
1497 SS
10
U
W
W
U
U
RG = 62
1497 F03
RF = RG = 560 AV = - 1 VS = 15V RL = 100
1497 F04
Figure 4. Large-Signal Response
W
- IN
VOUT
LT1497
TYPICAL APPLICATIONS
Differential Input/Differential Output Power Amp (AV = 2)
VIN
+
1/2 LT1497 VOUT
-
560
1.1k 560
-
1/2 LT1497 - VIN - VOUT
+
1497 TA03
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.014 - 0.019 (0.355 - 0.483) *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
0.016 - 0.050 0.406 - 1.270
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254)
0.053 - 0.069 (1.346 - 1.752) 0 - 8 TYP
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
*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
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.
U
U
Paralleling Both Amplifiers for Guaranteed 250mA Output Drive
+
1/2 LT1497
VIN
3 VOUT
-
560 560
+
1/2 LT1497
3
-
560
560
1497 TA04
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 0.053 - 0.069 (1.346 - 1.752) 0.004 - 0.010 (0.101 - 0.254) 8 7 6 5
0.050 (1.270) TYP
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
SO8 0996
1
2
3
4
S Package 16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.386 - 0.394* (9.804 - 10.008) 0.004 - 0.010 (0.101 - 0.254) 16 15 14 13 12 11 10 9
0.050 (1.270) TYP
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
S16 0695
1
2
3
4
5
6
7
8
11
LT1497
TYPICAL APPLICATION
4A Current Boosted Power Amp (AV = 10)
15V
6.2
VIN 200
+ -
V+ 3
Q1 D45VH4 VOUT
VOLTAGE GAIN (dB)
1/2 LT1497
1.8K
+
200 1/2 LT1497
-
V- 1.8k Q2 D44VH4
6.2
- 15V
RELATED PARTS
PART NUMBER LT1206 LT1207 LT1210 LT1229/LT1230 LT1363/LT1364/LT1365 DESCRIPTION Single 250mA, 60MHz Current Feedback Amplifier Dual 250mA, 60MHz Current Feedback Amplifier Single 1A, 30MHz Current Feedback Amplifier Dual/Quad 100MHz Current Feedback Amplifiers Single/Dual/Quad 70MHz, 1000V/s, C-LoadTM Amplifiers COMMENTS Shutdown Function, Stable with CL = 10,000pF, 900V/s Slew Rate Dual Version of LT1206 Higher Output Version of LT1206 30mA Output Current, 1000V/s Slew Rate 50mA Output Current, 1.5mV Max VOS, 2A Max IB
C-Load is a trademark of Linear Technology Corporation.
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
U
Frequency Response of Current Boosted Power Amp
22 21
0.01F
0.033
20 19 18 17 16 15 14 13 VS = 15V AV = 10 RF = 1.8k RG = 200 VOUT = 6VP-P 100k 1M FREQUENCY (Hz) RL = 2.5
RL = 50
3
12 10k
10M
1497 TA06
0.01F
1497 TA05
0.033
1497f LT/TP 1097 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1997

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