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LT1357 25MHz, 600V/s Op Amp
FEATURES
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DESCRIPTION
The LT1357 is a high speed, very high slew rate operational amplifier with outstanding AC and DC performance. The LT1357 has much lower supply current, lower input offset voltage, lower input bias current, and higher DC gain than devices with comparable bandwidth. The circuit topology is a voltage feedback amplifier with the slewing characteristics of a current feedback amplifier. The amplifier is a single gain stage with outstanding settling characteristics which makes the circuit an ideal choice for data acquisition systems. The output drives a 500 load to 12.5V with 15V supplies and a 150 load to 3V on 5V supplies. The amplifier is also stable with any capacitive load which makes it useful in buffer or cable driver applications. The LT1357 is a member of a family of fast, high performance amplifiers using this unique topology and employing Linear Technology Corporation's advanced bipolar complementary processing. For dual and quad amplifier versions of the LT1357 see the LT1358/LT1359 data sheet. For higher bandwidth devices with higher supply current see the LT1360 through LT1365 data sheets. For lower supply current amplifiers see the LT1354 and LT1355/ LT1356 data sheets. Singles, duals, and quads of each amplifier are available.
C-Load is a trademark of Linear Technology Corporation
25MHz Gain-Bandwidth 600V/s Slew Rate 2.5mA Maximum Supply Current Unity Gain Stable C-LoadTM Op Amp Drives All Capacitive Loads 8nV/Hz Input Noise Voltage 600V Maximum Input Offset Voltage 500nA Maximum Input Bias Current 120nA Maximum Input Offset Current 20V/mV Minimum DC Gain, RL=1k 115ns Settling Time to 0.1%, 10V Step 220ns Settling Time to 0.01%, 10V Step 12.5V Minimum Output Swing into 500 3V Minimum Output Swing into 150 Specified at 2.5V, 5V, and 15V
APPLICATIONS
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Wideband Amplifiers Buffers Active Filters Data Acquisition Systems Photodiode Amplifiers
TYPICAL APPLICATION
DAC I-to-V Converter AV = -1 Large-Signal Response
6pF DAC INPUTS 12 5k
-
565A-TYPE LT1357 VOUT
+
0.1F 5k V V OS + IOS 5k + OUT < 1LSB A VOL
1358/1359 TA01
()
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1357 TA02
1
LT1357
ABSOLUTE MAXIMUM RATINGS
Total Supply Voltage (V + to V -) ............................... 36V Differential Input Voltage ....................................... 10V Input Voltage ............................................................VS Output Short-Circuit Duration (Note 1) ............ Indefinite Operating Temperature Range ................ -40C to 85C Specified Temperature Range ................. -40C to 85C Maximum Junction Temperature (See Below) Plastic Package ................................................ 150C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW NULL -IN +IN V- 1 2 3 4 8 7 6 5 NULL V+ VOUT NC
ORDER PART NUMBER LT1357CN8
N8 PACKAGE, 8-LEAD PLASTIC DIP
TJMAX = 150C, JA = 130C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VOS PARAMETER Input Offset Voltage CONDITIONS
TA = 25C, VCM = 0V unless otherwise noted.
VSUPPLY 15V 5V 2.5V 2.5V to 15V 2.5V to 15V MIN TYP 0.2 0.2 0.3 40 120 8 0.8 35 80 6 3 12.0 2.5 0.5 13.4 3.5 1.1 -13.2 -12.0 - 3.3 - 2.5 - 0.9 - 0.5 83 78 68 92 15V 15V 5V 5V 5V 2.5V 15V 15V 5V 5V 2.5V 20.0 7.0 20.0 7.0 1.5 7.0 13.3 12.5 3.5 3.0 1.3 97 84 75 106 65 25 45 25 6 30 13.8 13.0 4.0 3.3 1.7 MAX 0.6 0.6 0.8 120 500 UNITS mV mV mV nA nA nV/Hz pA/Hz M M pF V V V V V V dB dB dB dB V/mV V/mV V/mV V/mV V/mV V/mV V V V V V
IOS IB en in RIN CIN
Input Offset Current Input Bias Current Input Noise Voltage Input Noise Current Input Resistance Input Capacitance Input Voltage Range + f = 10kHz f = 10kHz VCM = 12V Differential
Input Voltage Range -
CMRR
Common-Mode Rejection Ratio
VCM = 12V VCM = 2.5V VCM = 0.5V VS = 2.5V to 15V VOUT = 12V, RL = 1k VOUT = 10V, RL = 500 VOUT = 2.5V, RL = 1k VOUT = 2.5V, RL = 500 VOUT = 2.5V, RL = 150 VOUT = 1V, RL = 500 RL = 1k, VIN = 40mV RL = 500, VIN = 40mV RL = 500, VIN = 40mV RL = 150, VIN = 40mV RL = 500, VIN = 40mV
PSRR AVOL
Power Supply Rejection Ratio Large-Signal Voltage Gain
VOUT
Output Swing
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TOP VIEW NULL -IN +IN V- 1 2 3 4 8 7 6 5 NULL V+ VOUT NC
ORDER PART NUMBER LT1357CS8 S8 PART MARKING 1357
S8 PACKAGE, 8-LEAD PLASTIC SOIC
TJMAX = 150C, JA = 190C/ W
2.5V to 15V 2.5V to 15V 15V 15V 15V 15V 5V 2.5V 15V 5V 2.5V 15V 5V 2.5V
LT1357
ELECTRICAL CHARACTERISTICS
SYMBOL IOUT ISC SR PARAMETER Output Current Short-Circuit Current Slew Rate Full Power Bandwidth GBW Gain-Bandwidth CONDITIONS VOUT = 12.5V VOUT = 3V VOUT = 0V, V IN = 3V AV = -2, (Note 2) 10V Peak, (Note 3) 3V Peak, (Note 3) f = 200kHz, RL = 2k
TA = 25C, VCM = 0V unless otherwise noted.
VSUPPLY 15V 5V 15V 15V 5V 15V 5V 15V 5V 2.5V 15V 5V 15V 5V 15V 5V 15V 15V 5V 5V 15V 5V 15V 5V 15V 15V 5V 18 15 MIN 25 20 30 300 150 TYP 30 25 42 600 220 9.6 11.7 25 22 20 8 9 27 27 9 11 115 220 110 380 0.1 0.1 0.50 0.35 0.3 2.0 1.9 2.5 2.4 MAX UNITS mA mA mA V/s V/s MHz MHz MHz MHz MHz ns ns % % ns ns ns ns ns ns % % Deg Deg mA mA
tr , tf
Rise Time, Fall Time Overshoot Propagation Delay
AV = 1, 10%-90%, 0.1V AV = 1, 0.1V 50% VIN to 50% VOUT, 0.1V 10V Step, 0.1%, AV = -1 10V Step, 0.01%, AV = -1 5V Step, 0.1%, AV = -1 5V Step, 0.01%, AV = -1 f = 3.58MHz, AV = 2, RL = 1k f = 3.58MHz, AV = 2, RL = 1k AV = 1, f = 100kHz
ts
Settling Time
Differential Gain Differential Phase RO IS Output Resistance Supply Current
ELECTRICAL CHARACTERISTICS
SYMBOL VOS PARAMETER Input Offset Voltage CONDITIONS
0C TA 70C, VCM = 0V unless otherwise noted.
VSUPPLY 15V 5V 2.5V
q q q q q q q q q q
MIN
TYP
MAX 0.8 0.8 1.0
UNITS mV mV mV V/C nA nA dB dB dB dB V/mV V/mV V/mV V/mV V/mV V/mV
Input VOS Drift IOS IB CMRR Input Offset Current Input Bias Current Common-Mode Rejection Ratio
(Note 4)
2.5V to 15V 2.5V to 15V 2.5V to 15V
5
8 180 750
VCM = 12V VCM = 2.5V VCM = 0.5V VS = 2.5V to 15V VOUT = 12V, RL = 1k VOUT = 10V, RL = 500 VOUT = 2.5V, RL = 1k VOUT = 2.5V, RL = 500 VOUT = 2.5V, RL = 150 VOUT = 1V, RL = 500
15V 5V 2.5V 15V 15V 5V 5V 5V 2.5V
81 77 67 90 15 5 15 5 1 5
PSRR AVOL
Power Supply Rejection Ratio Large-Signal Voltage Gain
q q q q q q
3
LT1357
ELECTRICAL CHARACTERISTICS
SYMBOL VOUT PARAMETER Output Swing CONDITIONS RL = 1k, VIN = 40mV RL = 500, VIN = 40mV RL = 500, VIN = 40mV RL = 150, VIN = 40mV RL = 500, VIN = 40mV VOUT = 12.2V VOUT = 2.8V VOUT = 0V, V IN = 3V AV = -2, (Note 2) f = 200kHz,RL = 2k
0C TA 70C, VCM = 0V unless otherwise noted.
VSUPPLY 15V 15V 5V 5V 2.5V 15V 5V 15V 15V 5V 15V 5V 15V 5V
q q q q q q q q q q q q q q
MIN 13.2 12.2 3.4 2.8 1.2 24.4 18.7 25 225 125 15 12
TYP
MAX
UNITS V V V V V mA mA mA V/s V/s MHz MHz
IOUT ISC SR GBW IS
Output Current Short-Circuit Current Slew Rate Gain-Bandwidth Supply Current
2.9 2.8
mA mA
ELECTRICAL CHARACTERISTICS
SYMBOL VOS PARAMETER Input Offset Voltage CONDITIONS
-40C TA 85C, VCM = 0V unless otherwise noted. (Note 5)
VSUPPLY 15V 5V 2.5V
q q q q q q q q q q
MIN
TYP
MAX 1.3 1.3 1.5
UNITS mV mV mV V/C nA nA dB dB dB dB V/mV V/mV V/mV V/mV V/mV V/mV V V V V V mA mA mA V/s V/s
Input VOS Drift IOS IB CMRR Input Offset Current Input Bias Current Common-Mode Rejection Ratio
(Note 4)
2.5V to 15V 2.5V to 15V 2.5V to 15V
5
8 300 900
VCM = 12V VCM = 2.5V VCM = 0.5V VS = 2.5V to 15V VOUT = 12V, RL = 1k VOUT = 10V, RL = 500 VOUT = 2.5V, RL = 1k VOUT = 2.5V, RL = 500 VOUT = 2.5V, RL = 150 VOUT = 1V, RL = 500 RL = 1k, VIN = 40mV RL = 500, VIN = 40mV RL = 500, VIN = 40mV RL = 150, VIN = 40mV RL = 500, VIN = 40mV VOUT = 12V VOUT = 2.6V VOUT = 0V, V IN = 3V AV = -2, (Note 2)
15V 5V 2.5V 15V 15V 5V 5V 5V 2.5V 15V 15V 5V 5V 2.5V 15V 5V 15V 15V 5V
80 76 66 90 10.0 2.5 10.0 2.5 0.6 2.5 13.0 12.0 3.4 2.6 1.2 24.0 17.3 24 180 100
PSRR AVOL
Power Supply Rejection Ratio Large-Signal Voltage Gain
q q q q q q q q q q q q q q q q
VOUT
Output Swing
IOUT ISC SR
Output Current Short-Circuit Current Slew Rate
4
LT1357
ELECTRICAL CHARACTERISTICS
SYMBOL GBW IS PARAMETER Gain-Bandwith Supply Current CONDITIONS f = 200kHz, RL = 2k
-40C TA 85C, VCM = 0V unless otherwise noted. (Note 5)
VSUPPLY 15V 5V 15V 5V
q q q q
MIN 14 11
TYP
MAX
UNITS MHz MHz
3.0 2.9
mA mA
The q denotes specifications that apply over the full operating temperature range. Note 1: A heat sink may be required to keep the junction temperature below absolute maximum when the output is shorted indefinitely. Note 2: Slew rate is measured between 10V on the output with 6V input for 15V supplies and 1V on the output with 1.75V input for 5V supplies.
Note 3: Full power bandwidth is calculated from the slew rate measurement: FPBW = SR/2VP. Note 4: This parameter is not 100% tested. Note 5: The LT1357 is not tested and is not quality-assurance sampled at -40C and at 85C. These specifications are guaranteed by design, correlation, and/or inference from 0C, 25C, and/or 70C tests.
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage and Temperature
3.0
V+ -0.5 TA = 25C VOS < 1mV
125C 2.0 25C - 55C 1.5
COMMON-MODE RANGE (V)
-1.5 -2.0
INPUT BIAS CURRENT (nA)
2.5
SUPPLY CURRENT (mA)
1.0
0.5 0 5 10 15 SUPPLY VOLTAGE (V) 20
1357 G01
Input Bias Current vs Temperature
450 400 VS = 15V IB+ + IB- IB = -------- 2 100
INPUT VOLTAGE NOISE (nV/Hz)
INPUT BIAS CURRENT (nA)
350 300 250 200 150 100 50 0 - 50
OPEN-LOOP GAIN (dB)
-25
0 25 50 75 TEMPERATURE (C)
UW
100
1358/1359 G04
Input Common-Mode Range vs Supply Voltage
400 300 200 100 0
Input Bias Current vs Input Common-Mode Voltage
VS = 15V TA = 25C IB+ + IB- IB = -------- 2
-1.0
2.0 1.5 1.0 0.5 V- 0 5 10 15 SUPPLY VOLTAGE (V) 20
1357 G02
-100 -200 -15
-10 -5 0 5 10 INPUT COMMON-MODE VOLTAGE (V)
15
1357 G03
Input Noise Spectral Density
10 VS = 15V TA = 25C AV = 101 RS = 100k en 10 in 1 100
Open-Loop Gain vs Resistive Load
TA = 25C VS = 15V VS = 5V
INPUT CURRENT NOISE (pA/Hz)
90
80
70
60
1 125 10 100 1k 10k FREQUENCY (Hz)
0.1 100k
1357 G05
50 10 100 1k LOAD RESISTANCE () 10k
1357 G06
5
LT1357
TYPICAL PERFORMANCE CHARACTERISTICS
Open-Loop Gain vs Temperature
101 100
OPEN-LOOP GAIN (dB)
OUTPUT VOLTAGE SWING (V)
99 98 97 96 95 94 93 -50
OUTPUT VOLTAGE SWING (V)
RL = 1k VO = 12V VS = 15V
-25
0 25 50 75 TEMPERATURE (C)
Output Short-Circuit Current vs Temperature
65
OUTPUT SHORT-CIRCUIT CURRENT (mA)
VS = 5V
60
OUTPUT SWING (V)
55 50 45 SINK 40 SOURCE 35 30 25 -50 -25 0 25 50 75 TEMPERATURE (C) 100 125
2 0 -2 -4 -6 -8 -10 50 10mV 100 150 200 SETTLING TIME (ns) 250
1357 G11
OUTPUT SWING (V)
Output Impedance vs Frequency
1k VS = 15V TA = 25C AV = 100 AV = 10 70 60 50
OUTPUT IMPEDANCE ()
100
GAIN-BANDWIDTH (MHz)
GAIN (dB)
10 AV = 1 1
0.1 0 0.01 10k -10 10k
100k
1M 10M FREQUENCY (Hz)
6
UW
100
1357 G07 1357 G10 1357 G13
Output Voltage Swing vs Supply Voltage
V+ TA = 25C -1 -2 -3 3 2 1 V
125
+
Output Voltage Swing vs Load Current
V + -0.5
RL = 1k
-1.0 -1.5 -2.0 -2.5
VS = 5V VIN = 100mV -40C
85C
RL = 500
25C 2.5 2.0 -40C 1.5 1.0
25C
RL = 500
85C
RL = 1k 0 5 10 15 SUPPLY VOLTAGE (V) 20
1357 G08
V - +0.5 -50 -40 -30 -20 -10 0 10 20 30 40 50 OUTPUT CURRENT (mA)
1357 G09
Settling Time vs Output Step (Noninverting)
10 8 6 4 1mV 10mV VS = 15V AV = 1
10 8 6 4 2 0 -2 -4 -6 -8 -10
Settling Time vs Output Step (Inverting)
10mV 1mV
VS = 15V AV = -1 10mV 1mV
1mV
50
100 150 200 SETTLING TIME (ns)
250
1357 G12
Gain and Phase vs Frequency
120 PHASE VS = 15V GAIN VS = 5V VS = 5V VS = 15V 100 80 60 40 20 0 AV = -1 RF = RG = 2k TA = 25C 100k 1M 10M FREQUENCY (Hz) 100M
1357 G14
Gain-Bandwidth and Phase Margin vs Supply Voltage
38 36 34 TA = 25C PHASE MARGIN 50 48 46
PHASE (DEG)
PHASE MARGIN (DEG)
32 30 28 26 24 22 20 18 0
44 42 40 38 36
40 30 20 10
GAIN-BANDWIDTH
34 32 30
100M
5 10 15 SUPPLY VOLTAGE (V)
20
1357 G15
LT1357
TYPICAL PERFORMANCE CHARACTERISTICS
Gain-Bandwidth and Phase Margin vs Temperature
38 36 GAIN-BANDWIDTH (MHz) 34 32 30 28 26 24 22 20 GAIN-BANDWIDTH VS = 5V -25 0 25 50 75 TEMPERATURE (C) 100 GAIN-BANDWIDTH VS = 15V PHASE MARGIN VS = 5V PHASE MARGIN VS = 15V 50 48 46 PHASE MARGIN (DEG) 44 42 40 38 36 34 32 30 125 5 4 3 2
GAIN (dB)
GAIN (dB)
18 -50
Frequency Response vs Capacitive Load
10 8
POWER SUPPLY REJECTION RATIO (dB)
-PSRR 80
COMMON-MODE REJECTION RATIO (dB)
VOLTAGE MAGNITUDE (dB)
6 4 2 0 -2 -4 -6 -8 -10 100k
VS = 15V TA = 25C AV = -1
C = 1000pF C = 500pF C = 100pF C = 50pF
1M 10M FREQUENCY (Hz)
Slew Rate vs Supply Voltage
1000 AV = -1 RF = RG = 2k SR+ + SR- SR = ---------- 2 TA = 25C 600 500
800
SLEW RATE (V/s)
SLEW RATE (V/s)
400 300 200
600
SLEW RATE (V/s)
400
200
0 0 5 10 SUPPLY VOLTAGE (V) 15
1357 G22
UW
1357 G16
Frequency Response vs Supply Voltage (AV = 1)
5 TA = 25C AV = 1 RL = 2k 4 15V 3 2 1 0 -1 -2 -3 2.5V 10M 1M FREQUENCY (Hz) 100M
1357 G17
Frequency Response vs Supply Voltage (AV = -1)
TA = 25C AV = -1 RF = RG = 2k
1 0 -1 -2 -3 -4 -5 100k 5V
5V 2.5V
15V
-4 -5 100k
10M 1M FREQUENCY (Hz)
100M
1357 G18
Power Supply Rejection Ratio vs Frequency
100 +PSRR 120 VS = 15V TA = 25C 100 80 60 40 20 0 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M
Common-Mode Rejection Ratio vs Frequency
VS = 15V TA = 25C
60
40
C=0
20
100M
1358/1359 G19
0 100
1k
10k
100k 1M FREQUENCY (Hz)
10M
100M
1357 G21
1357 G20
Slew Rate vs Temperature
1000 VS = 15V SR+ + SR- SR = ---------- 2 AV = -2 900 800 700 600 500 400 300 200 100 0 - 50 0 -25 0 25 50 75 TEMPERATURE (C) 100 125
Slew Rate vs Input Level
VS = 15V AV = -1 RF = RG = 2k SR+ + SR - SR = ---------- 2 TA = 25C
VS = 5V 100
0
2
4
6 8 10 12 14 16 18 20 INPUT LEVEL (VP-P)
1357 G24
1357 G23
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LT1357
TYPICAL PERFORMANCE CHARACTERISTICS
Total Harmonic Distortion vs Frequency
0.01 30 TA = 25C VO = 3VRMS RL = 2k AV = -1 25
TOTAL HARMONIC DISTORTION (%)
OUTPUT VOLTAGE (VP-P)
AV = 1 20 15 10 5 VS = 15V RL = 2k AV = 1, 1% MAX DISTORTION AV = -1, 2% MAX DISTORTION 1M FREQUENCY (Hz) 10M
1357 G26
OUTPUT VOLTAGE (VP-P)
AV = -1 0.001 AV = 1
0.0001 10
100
1k 10k FREQUENCY (Hz)
2nd and 3rd Harmonic Distortion vs Frequency
-30 -40 -50 -60 -70 2ND HARMONIC -80 -90 100k 200k 3RD HARMONIC
DIFFERENTIAL PHASE (DEGREES)
HARMONIC DISTORTION (dB)
VS = 15V VO = 2VP-P RL = 2k AV = 2
0.50 DIFFERENTIAL PHASE 0.45
0.05
OVERSHOOT (%)
400k 1M 2M FREQUENCY (Hz)
Small-Signal Transient (AV = 1)
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UW
1357 G25
Undistorted Output Swing vs Frequency (15V)
10
Undistorted Output Swing vs Frequency (5V)
8
AV = -1 AV = 1
6
4
2
VS = 5V RL = 2k 2% MAX DISTORTION 1M FREQUENCY (Hz) 10M
1357 G27
100k
0 100k
0 100k
Differential Gain and Phase vs Supply Voltage
0.15 DIFFERENTIAL GAIN 0.10
DIFFERENTIAL GAIN (PERCENT)
Capacitive Load Handling
100 VS = 15V TA = 25C AV = 1
50 AV = -1
0.40
AV = 2 RL = 1k TA = 25C 5 10 SUPPLY VOLTAGE (V) 15
1354 G29
4M
10M
1357 G28
0.35
0 10p
100p
1000p 0.01 0.1 CAPACITIVE LOAD (F)
1
1357 G30
Small-Signal Transient (AV = -1)
Small-Signal Transient (AV = -1, CL = 1000pF)
1357 TA31
1357 TA32
1357 TA33
LT1357
TYPICAL PERFORMANCE CHARACTERISTICS
Large-Signal Transient (AV = 1) Large-Signal Transient (AV = -1) Large-Signal Transient (AV = 1, CL = 10,000pF)
APPLICATIONS INFORMATION
The LT1357 may be inserted directly into many high speed amplifier applications improving both DC and AC performance, provided that the nulling circuitry is removed. The suggested nulling circuit for the LT1357 is shown below.
Offset Nulling
V+ 3
+ -
1 10k
7 LT1357 6 4 8
2
V-
1357 AI01
Layout and Passive Components The LT1357 amplifier is easy to apply and tolerant of less than ideal layouts. For maximum performance (for example fast settling time) use a ground plane, short lead lengths, and RF-quality bypass capacitors (0.01F to 0.1F). For high drive current applications use low ESR bypass capacitors (1F to 10F tantalum). Sockets should be avoided when maximum frequency performance is required, although low profile sockets can provide reasonable performance up to 50MHz. For more details see Design Note 50.
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1357 TA34
1357 TA35
1357 TA36
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The parallel combination of the feedback resistor and gain setting resistor on the inverting input can combine with the input capacitance to form a pole which can cause peaking or oscillations. For feedback resistors greater than 5k, a parallel capacitor of value CF > RG x CIN/RF should be used to cancel the input pole and optimize dynamic performance. For unity-gain applications where a large feedback resistor is used, CF should be greater than or equal to CIN. Capacitive Loading The LT1357 is stable with any capacitive load. This is accomplished by sensing the load induced output pole and adding compensation at the amplifier gain node. As the capacitive load increases, both the bandwidth and phase margin decrease so there will be peaking in the frequency domain and in the transient response as shown in the typical performance curves.The photo of the small-signal response with 1000pF load shows 50% peaking. The large signal response with a 10,000pF load shows the output slew rate being limited to 5V/s by the short-circuit current. Coaxial cable can be driven directly, but for best pulse fidelity a resistor of value equal to the characteristic impedance of the cable (i.e., 75) should be placed in series with the output. The other end of the cable should be terminated with the same value resistor to ground.
9
LT1357
APPLICATIONS INFORMATION
Input Considerations Each of the LT1357 inputs is the base of an NPN and a PNP transistor whose base currents are of opposite polarity and provide first-order bias current cancellation. Because of variation in the matching of NPN and PNP beta, the polarity of the input bias current can be positive or negative. The offset current does not depend on beta matching and is well controlled. The use of balanced source resistance at each input is recommended for applications where DC accuracy must be maximized. The inputs can withstand differential input voltages of up to 10V without damage and need no clamping or source resistance for protection. Power Dissipation The LT1357 combines high speed and large output drive in a small package. Because of the wide supply voltage range, it is possible to exceed the maximum junction temperature under certain conditions. Maximum junction temperature (TJ) is calculated from the ambient temperature (TA) and power dissipation (PD) as follows: LT1357CN8: TJ = TA + (PD x 130C/W) LT1357CS8: TJ = TA + (PD x 190C/W) Worst case power dissipation occurs at the maximum supply current and when the output voltage is at 1/2 of either supply voltage (or the maximum swing if less than 1/2 supply voltage). Therefore PDMAX is: PDMAX = (V+ - V -)(ISMAX) + (V+/2)2/RL Example: LT1357CS8 at 70C, VS = 15V, RL = 120 (Note: the minimum short-circuit current at 70C is 25mA, so the output swing is guaranteed only to 3V with 120.) PDMAX = (30V)(2.9mA) + (15V-3V)(25mA) = 387mW TJMAX = 70C + (387mW)(190C/W) = 144C Circuit Operation The LT1357 circuit topology is a true voltage feedback amplifier that has the slewing behavior of a current feedback amplifier. The operation of the circuit can be understood by referring to the simplified schematic. The inputs are buffered by complementary NPN and PNP emitter followers which drive a 500 resistor. The input voltage appears across the resistor generating currents which are mirrored into the high impedance node. Complementary followers form an output stage which buffers the gain node from the load. The bandwidth is set by the input resistor and the capacitance on the high impedance node. The slew rate is determined by the current available to charge the gain node capacitance. This current is the differential input voltage divided by R1, so the slew rate is proportional to the input. Highest slew rates are therefore seen in the lowest gain configurations. For example, a 10V output step in a gain of 10 has only a 1V input step, whereas the same output step in unity gain has a 10 times greater input step. The curve of Slew Rate vs Input Level illustrates this relationship. The LT1357 is tested for slew rate in a gain of -2 so higher slew rates can be expected in gains of 1 and -1, and lower slew rates in higher gain configurations. The RC network across the output stage is bootstrapped when the amplifier is driving a light or moderate load and has no effect under normal operation. When driving a capacitive load (or a low value resistive load) the network is incompletely bootstrapped and adds to the compensation at the high impedance node. The added capacitance slows down the amplifier which improves the phase margin by moving the unity gain frequency away from the pole formed by the output impedance and the capacitive load. The zero created by the RC combination adds phase to ensure that even for very large load capacitances, the total phase lag can never exceed 180 degrees (zero phase margin) and the amplifier remains stable.
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LT1357
TYPICAL APPLICATIONS
Instrumentation Amplifier
R5 432 R1 20k R2 2k R4 20k
VIN
3.4k VIN
SI PLIFIED SCHE ATIC
V+
-IN C CC
V-
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.
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LT1357
R3 2k
-
LT1357 VOUT
- +
+
+
R4 1 R2 R3 R2 + R3 1 + = 104 + + R3 2 R1 R4 R5 TRIM R5 FOR GAIN TRIM R1 FOR COMMON-MODE REJECTION BW = 250kHz AV =
1357 TA03
200kHz, 4th Order Butterworth Filter
3.4k 100pF 47pF 5.62k 330pF 2.61k
-
LT1357
2.61k
5.11k 1000pF
-
LT1357 VOUT
+
+
1357 TA04
W
W
R1 500
+IN
RC OUT
1357 SS01
11
LT1357
PACKAGE DESCRIPTION U
Dimension in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP
0.400 (10.160) MAX 8 7 6 5
0.250 0.010 (6.350 0.254)
1
2
3
4
0.300 - 0.320 (7.620 - 8.128)
0.045 - 0.065 (1.143 - 1.651)
0.130 0.005 (3.302 0.127)
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.020 (0.508) MIN
(
+0.025 0.325 -0.015 +0.635 8.255 -0.381
)
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
N8 0392
S8 Package 8-Lead Plastic SOIC
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157* (3.810 - 3.988)
1 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0294
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0494 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

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