Transcript
LT1357 25MHz, 600V/µs Op Amp
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DESCRIPTION
FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■
The LT ®1357 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 500Ω load to ±12V with ±15V supplies and a 150Ω load to ±2.5V on ±5V supplies. The amplifier is also stable with any capacitive load which makes it useful in buffer or cable driver applications.
25MHz Gain Bandwidth 600V/µs Slew Rate 2.5mA Maximum Supply Current Unity-Gain Stable C-LoadTM Op Amp Drives All Capacitive Loads 8nV/√Hz Input Noise Voltage 600µV 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 ±12V Minimum Output Swing into 500Ω ±2.5V Minimum Output Swing into 150Ω Specified at ±2.5V, ±5V, and ±15V
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.
U APPLICATIONS ■ ■ ■ ■ ■
Wideband Amplifiers Buffers Active Filters Data Acquisition Systems Photodiode Amplifiers
, LTC and LT are registered trademarks of Linear Technology Corporation. C-Load is a trademark of Linear Technology Corporation
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TYPICAL APPLICATION AV = –1 Large-Signal Response
DAC I-to-V Converter
6pF DAC INPUTS
12
5k
– 565A-TYPE
LT1357
VOUT
+ 0.1µF
5k
( )
V VOS + IOS 5kΩ + OUT < 1LSB A VOL 1357 TA01
1357 TA02
1
LT1357
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ABSOLUTE MAXIMUM RATINGS Total Supply Voltage (V + to V –) ............................... 36V Differential Input Voltage (Transient Only, Note 1) ... ±10V Input Voltage ............................................................ ±VS Output Short-Circuit Duration (Note 2) ............ Indefinite Operating Temperature Range ................ –40°C to 85°C
Specified Temperature Range (Note 6) ... –40°C to 85°C Maximum Junction Temperature (See Below) Plastic Package ................................................ 150°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C
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PACKAGE/ORDER INFORMATION TOP VIEW NULL
1
8
NULL
–IN
2
7
V+
+IN
3
6
VOUT
V–
4
5
NC
ORDER PART NUMBER LT1357CN8
ORDER PART NUMBER
TOP VIEW NULL
1
8
NULL
–IN
2
7
V+
+IN
3
6
VOUT
V–
4
5
NC
N8 PACKAGE, 8-LEAD PLASTIC DIP
S8 PACKAGE, 8-LEAD PLASTIC SOIC
TJMAX = 150°C, θJA = 130°C/ W
TJMAX = 150°C, θJA = 190°C/ W
LT1357CS8 S8 PART MARKING 1357
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
TA = 25°C, VCM = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VOS
Input Offset Voltage
±15V ±5V ±2.5V
IOS
Input Offset Current
IB
Input Bias Current
en
Input Noise Voltage
f = 10kHz
±2.5V to ±15V
8
nV/√Hz
in
Input Noise Current
f = 10kHz
±2.5V to ±15V
0.8
pA/√Hz
RIN
Input Resistance
VCM = ±12V Differential
±15V ±15V
35
80 6
MΩ MΩ
CIN
Input Capacitance
±15V
3
pF
Input Voltage Range +
±15V ±5V ±2.5V
12.0 2.5 0.5
13.4 3.5 1.1
V V V
Input Voltage Range –
±15V ±5V ±2.5V
CMRR
Common Mode Rejection Ratio
VCM = ±12V VCM = ±2.5V VCM = ±0.5V
PSRR
Power Supply Rejection Ratio
VS = ±2.5V to ±15V
AVOL
Large-Signal Voltage Gain
VOUT = ±12V, RL = 1k VOUT = ±10V, RL = 500Ω VOUT = ±2.5V, RL = 1k VOUT = ±2.5V, RL = 500Ω VOUT = ±2.5V, RL = 150Ω VOUT = ±1V, RL = 500Ω
2
VSUPPLY
TYP
MAX
UNITS
0.2 0.2 0.3
0.6 0.6 0.8
mV mV mV
±2.5V to ±15V
40
120
nA
±2.5V to ±15V
120
500
nA
±15V ±5V ±2.5V ±15V ±15V ±5V ±5V ±5V ±2.5V
MIN
–13.2 –12.0 – 3.3 – 2.5 – 0.9 – 0.5
V V V
80 78 68
97 84 75
dB dB dB
92
106
dB
20.0 7.0 20.0 7.0 1.5 7.0
65 25 45 25 6 30
V/mV V/mV V/mV V/mV V/mV V/mV
LT1357
ELECTRICAL CHARACTERISTICS
TA = 25°C, VCM = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VSUPPLY
MIN
TYP
MAX
UNITS
VOUT
Output Swing
RL = 1k, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 150Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV
±15V ±15V ±5V ±5V ±2.5V
13.3 12.0 3.5 2.5 1.3
13.8 12.8 4.0 3.3 1.7
±V ±V ±V ±V ±V
IOUT
Output Current
VOUT = ±12V VOUT = ±2.5V
±15V ±5V
24.0 16.7
30 25
mA mA
ISC
Short-Circuit Current
VOUT = 0V, VIN = ±3V
±15V
30
42
mA
SR
Slew Rate
AV = –2, (Note 3)
±15V ±5V
300 150
600 220
V/µs V/µs
Full Power Bandwidth
10V Peak, (Note 4) 3V Peak, (Note 4)
±15V ±5V
9.6 11.7
MHz MHz
GBW
Gain Bandwidth
f = 200kHz, RL = 2k
±15V ±5V ±2.5V
25 22 20
MHz MHz MHz
tr , tf
Rise Time, Fall Time
AV = 1, 10%-90%, 0.1V
±15V ±5V
8 9
ns ns
Overshoot
AV = 1, 0.1V
±15V ±5V
27 27
% %
Propagation Delay
50% VIN to 50% VOUT, 0.1V
±15V ±5V
9 11
ns ns
Settling Time
10V Step, 0.1%, AV = –1 10V Step, 0.01%, AV = –1 5V Step, 0.1%, AV = –1 5V Step, 0.01%, AV = –1
±15V ±15V ±5V ±5V
115 220 110 380
ns ns ns ns
Differential Gain
f = 3.58MHz, AV = 2, RL = 1k
±15V ±5V
0.1 0.1
% %
Differential Phase
f = 3.58MHz, AV = 2, RL = 1k
±15V ±5V
0.50 0.35
RO
Output Resistance
AV = 1, f = 100kHz
±15V
0.3
IS
Supply Current
±15V ±5V
2.0 1.9
2.5 2.4
mA mA
TYP
MAX
UNITS
0.8 0.8 1.0
mV mV mV
ts
18 15
Deg Deg Ω
0°C ≤ TA ≤ 70°C, VCM = 0V unless otherwise noted. SYMBOL
PARAMETER
VOS
Input Offset Voltage
Input VOS Drift IOS
CONDITIONS
(Note 5)
Input Offset Current
IB
Input Bias Current
CMRR
Common Mode Rejection Ratio
VCM = ±12V VCM = ±2.5V VCM = ±0.5V
PSRR
Power Supply Rejection Ratio
VS = ±2.5V to ±15V
AVOL
Large-Signal Voltage Gain
VOUT = ±12V, RL = 1k VOUT = ±10V, RL = 500Ω VOUT = ±2.5V, RL = 1k VOUT = ±2.5V, RL = 500Ω VOUT = ±2.5V, RL = 150Ω VOUT = ±1V, RL = 500Ω
VSUPPLY
MIN
±15V ±5V ±2.5V
● ● ●
±2.5V to ±15V
●
±2.5V to ±15V
●
±2.5V to ±15V
●
±15V ±5V ±2.5V
● ● ●
79 77 67
dB dB dB
●
90
dB
● ● ● ● ● ●
15 5 15 5 1 5
V/mV V/mV V/mV V/mV V/mV V/mV
±15V ±15V ±5V ±5V ±5V ±2.5V
5
8
µV/°C
180
nA
750
nA
3
LT1357
ELECTRICAL CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VCM = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
VSUPPLY
MIN
TYP
MAX
UNITS
VOUT
Output Swing
RL = 1k, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 150Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV
±15V ±15V ±5V ±5V ±2.5V
● ● ● ● ●
13.2 11.5 3.4 2.3 1.2
±V ±V ±V ±V ±V
IOUT
Output Current
VOUT = ±11.5V VOUT = ±2.3V
±15V ±5V
● ●
23.0 15.3
mA mA
ISC
Short-Circuit Current
VOUT = 0V, VIN = ±3V
±15V
●
25
mA
SR
Slew Rate
AV = –2, (Note 3)
±15V ±5V
● ●
225 125
V/µs V/µs
GBW
Gain-Bandwidth
f = 200kHz,RL = 2k
±15V ±5V
● ●
15 12
MHz MHz
IS
Supply Current
±15V ±5V
● ●
VSUPPLY ±15V ±5V ±2.5V
● ● ●
±2.5V to ±15V
●
2.9 2.8
mA mA
TYP
MAX 1.3 1.3 1.5
UNITS mV mV mV
5
8
µV/°C
–40°C ≤ TA ≤ 85°C, VCM = 0V unless otherwise noted. (Note 6) SYMBOL VOS
PARAMETER Input Offset Voltage
CONDITIONS
Input VOS Drift
(Note 5)
MIN
IOS
Input Offset Current
±2.5V to ±15V
●
300
nA
IB
Input Bias Current
±2.5V to ±15V
●
900
nA
CMRR
Common Mode Rejection Ratio
VCM = ±12V VCM = ±2.5V VCM = ±0.5V
±15V ±5V ±2.5V
● ● ●
PSRR
Power Supply Rejection Ratio
VS = ±2.5V to ±15V
●
90
dB
AVOL
Large-Signal Voltage Gain
VOUT = ±12V, RL = 1k VOUT = ±10V, RL = 500Ω VOUT = ±2.5V, RL = 1k VOUT = ±2.5V, RL = 500Ω VOUT = ±2.5V, RL = 150Ω VOUT = ±1V, RL = 500Ω
±15V ±15V ±5V ±5V ±5V ±2.5V
● ● ● ● ● ●
10.0 2.5 10.0 2.5 0.6 2.5
V/mV V/mV V/mV V/mV V/mV V/mV
VOUT
Output Swing
RL = 1k, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV RL = 150Ω, VIN = ±40mV RL = 500Ω, VIN = ±40mV
±15V ±15V ±5V ±5V ±2.5V
● ● ● ● ●
13.0 11.0 3.4 2.1 1.2
±V ±V ±V ±V ±V
IOUT
Output Current
VOUT = ±11V VOUT = ±2.1V
±15V ±5V
● ●
22 14
mA mA
ISC
Short-Circuit Current
VOUT = 0V, VIN = ±3V
±15V
●
24
mA
SR
Slew Rate
AV = –2, (Note 3)
±15V ±5V
● ●
180 100
V/µs V/µs
GBW
Gain-Bandwith
f = 200kHz, RL = 2k
±15V ±5V
● ●
14 11
MHz MHz
IS
Supply Current
±15V ±5V
● ●
4
78 76 66
dB dB dB
3.0 2.9
mA mA
LT1357
ELECTRICAL CHARACTERISTICS The ● denotes specifications that apply over the full specified temperature range. Note 1: Differential inputs of ±10V are appropriate for transient operation only, such as during slewing. Large, sustained differential inputs will cause excessive power dissipation and may damage the part. See Input Considerations in the Applications Information section of this data sheet for more details. Note 2: A heat sink may be required to keep the junction temperature below absolute maximum when the output is shorted indefinitely.
Note 3: 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 4: Full power bandwidth is calculated from the slew rate measurement: FPBW = SR/2πVP. Note 5: This parameter is not 100% tested. Note 6: The LT1357 is designed, characterized and expected to meet these extended temperature limits, but is not tested at – 40°C and at 85°C. Guaranteed I grade parts are available; consult factory.
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TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage and Temperature V+
3.0
400
TA = 25°C ∆VOS < 1mV
–0.5 125°C 2.0
25°C –55°C
1.5
1.0
VS = ±15V TA = 25°C IB+ + IB– IB = ———— 2
300
–1.0
INPUT BIAS CURRENT (nA)
COMMON-MODE RANGE (V)
2.5 SUPPLY CURRENT (mA)
Input Bias Current vs Input Common-Mode Voltage
Input Common-Mode Range vs Supply Voltage
–1.5 –2.0
2.0 1.5 1.0
200 100 0
–100
0.5 0
5 10 15 SUPPLY VOLTAGE (±V)
V–
20
0
5 10 15 SUPPLY VOLTAGE (±V)
1357 G01
100
300 250 200 150 100
INPUT VOLTAGE NOISE (nV/√Hz)
350
Open-Loop Gain vs Resistive Load 100
10 VS = ±15V TA = 25°C AV = 101 RS = 100k
TA = 25°C
en 10
1 in
INPUT CURRENT NOISE (pA/√Hz)
INPUT BIAS CURRENT (nA)
400
15
1357 G03
Input Noise Spectral Density
VS = ±15V IB+ + IB– IB = ———— 2
–10 –5 0 5 10 INPUT COMMON-MODE VOLTAGE (V)
1357 G02
Input Bias Current vs Temperature 450
–200 –15
20
VS = ±15V VS = ±5V
90
OPEN-LOOP GAIN (dB)
0.5
80
70
60
50 0 –50
–25
0 25 50 75 TEMPERATURE (°C)
100
125
1358/1359 G04
1
10
100
1k 10k FREQUENCY (Hz)
0.1 100k 1357 G05
50
10
100 1k LOAD RESISTANCE (Ω)
10k 1357 G06
5
LT1357 U W
TYPICAL PERFORMANCE CHARACTERISTICS Output Voltage Swing vs Supply Voltage
Open-Loop Gain vs Temperature
TA = 25°C
OUTPUT VOLTAGE SWING (V)
–1
99 98 97 96 95
–2
RL = 500Ω
–3 3
RL = 500Ω
2 1
94 93 –50
–25
0 25 50 75 TEMPERATURE (°C)
100
V
125
1.5
20
Settling Time vs Output Step (Inverting) 10 8
50 SINK
40 SOURCE 35
1mV
4 2 0 –2 –4 –6
30 125
50
100 150 200 SETTLING TIME (ns)
60
PHASE
GAIN (dB)
40 30
VS = ±15V GAIN
60
VS = ±5V
40
VS = ±5V
20 0
10 0
1M 10M FREQUENCY (Hz)
100M 1357 G13
6
–10 10k
AV = –1 RF = RG = 2k TA = 25°C 100k
1M 10M FREQUENCY (Hz)
250
38
50
36
100 80
20
0.1
100k
100 150 200 SETTLING TIME (ns)
48
TA = 25°C
34
46 PHASE MARGIN
32
44
30
42
28
40
26
38
24
36
22
34
GAIN-BANDWIDTH
20 100M 1357 G14
18
32 0
5 10 15 SUPPLY VOLTAGE (±V)
30 20 1357 G15
PHASE MARGIN (DEG)
50
VS = ±15V
PHASE (DEG)
AV = 100
1
50
1357 G12
120
AV = 10
0.01 10k
250
Gain-Bandwidth and Phase Margin vs Supply Voltage
70
VS = ±15V TA = 25°C
AV = 1
1mV
–8 –10
Gain and Phase vs Frequency
10
10mV
–4
1357 G11
Output Impedance vs Frequency
100
VS = ±15V AV = –1
0 –2
10mV
1357 G10
1k
2
–6
GAIN-BANDWIDTH (MHz)
100
1mV
4
1mV
–8 –10
10mV
6
OUTPUT SWING (V)
55
0 25 50 75 TEMPERATURE (°C)
–40°C
1357 G09
6
–25
85°C
V – +0.5 –50 –40 –30 –20 –10 0 10 20 30 40 50 OUTPUT CURRENT (mA)
VS = ±15V AV = 1
10mV
8
OUTPUT SWING (V)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
2.5 2.0
10
60
45
25°C
25°C
Settling Time vs Output Step (Noninverting)
VS = ±5V
25 –50
OUTPUT IMPEDANCE (Ω)
–2.5
1357 G08
Output Short-Circuit Current vs Temperature 65
–2.0
1.0
5 10 15 SUPPLY VOLTAGE (±V)
1357 G07
–40°C
–1.5
RL = 1k
+
0
85°C
VS = ±5V VIN = 100mV
–1.0
RL = 1k
OUTPUT VOLTAGE SWING (V)
RL = 1k VO = ±12V VS = ±15V
100 OPEN-LOOP GAIN (dB)
V + –0.5
V+
101
Output Voltage Swing vs Load Current
LT1357 U W
TYPICAL PERFORMANCE CHARACTERISTICS Gain-Bandwidth and Phase Margin vs Temperature
PHASE MARGIN VS = ±5V
4
46
3
44 42
30
40
28 GAIN-BANDWIDTH VS = ±15V
26 24 22 GAIN-BANDWIDTH VS = ±5V
20
18 –50
–25
0 25 50 75 TEMPERATURE (°C)
100
38 36
5 TA = 25°C AV = 1 RL = 2k
2
2
0 –1
±5V
–2 –3
32
–4
30 125
3
±15V
1
34
±2.5V
C = 100pF
2 0
C = 50pF
–2 –4 C=0
–6 –8 –10 100k
1M 10M FREQUENCY (Hz)
VS = ±15V TA = 25°C
– PSRR 80
60
40
20
1k
10k 100k 1M FREQUENCY (Hz)
1358/1359 G19
Slew Rate vs Supply Voltage
100 80 60 40 20 0
100M
1000
200
100k 1M FREQUENCY (Hz)
400
10M
100M
VS = ±15V AV = –1 RF = RG = 2k SR+ + SR – SR = ————— 2 TA = 25°C
900
VS = ±15V
500
400
10k
Slew Rate vs Input Level
Slew Rate vs Temperature
600
1k
1357 G21
600
SLEW RATE (V/µs)
SLEW RATE (V/µs)
10M
VS = ±15V TA = 25°C
1357 G20
1000
800
100M
Common-Mode Rejection Ratio vs Frequency 120
+PSRR
0 100
100M
AV = –1 RF = RG = 2k SR+ + SR– SR = ————— 2 TA = 25°C
10M 1M FREQUENCY (Hz)
1357 G18
800
SR+ + SR– SR = ————— 2 AV = –2
SLEW RATE (V/µs)
VOLTAGE MAGNITUDE (dB)
C = 500pF
POWER SUPPLY REJECTION RATIO (dB)
100
4
–5 100k
100M
Power Supply Rejection Ratio vs Frequency
C = 1000pF
±2.5V
–4
10M 1M FREQUENCY (Hz)
±15V
±5V
1357 G17
10
6
0 –1
–3
–5 100k
Frequency Response vs Capacitive Load 8
1
–2
1357 G16
VS = ±15V TA = 25°C AV = –1
TA = 25°C AV = –1 RF = RG = 2k
4
COMMON-MODE REJECTION RATIO (dB)
32
5
48 PHASE MARGIN (DEG)
GAIN-BANDWIDTH (MHz)
34
50
GAIN (dB)
PHASE MARGIN VS = ±15V
GAIN (dB)
38 36
Frequency Response vs Supply Voltage (AV = –1)
Frequency Response vs Supply Voltage (AV = 1)
300 200 VS = ±5V
700 600 500 400 300 200
100
100 0
0
5 10 SUPPLY VOLTAGE (±V)
15 1357 G22
0 –50
–25
0 25 50 75 TEMPERATURE (°C)
100
125
1357 G23
0
0
2
4
6 8 10 12 14 16 18 20 INPUT LEVEL (VP-P) 1357 G24
7
LT1357 U W
TYPICAL PERFORMANCE CHARACTERISTICS
0.01
30
0.001 AV = 1
AV = 1 20 15 10 5
1k 10k FREQUENCY (Hz)
VS = ±15V RL = 2k AV = 1, 1% MAX DISTORTION AV = –1, 2% MAX DISTORTION
0 100k
100k
1M FREQUENCY (Hz)
DIFFERENTIAL PHASE (DEGREES)
HARMONIC DISTORTION (dB)
–60 –70 2ND HARMONIC –80 –90 100k 200k
400k 1M 2M FREQUENCY (Hz)
4M
10M
DIFFERENTIAL GAIN 0.10
0.05
0.50 DIFFERENTIAL PHASE 0.45
0.40
0.35
AV = 2 RL = 1k TA = 25°C ±5
±10 SUPPLY VOLTAGE (V)
1357 G28
1357 TA31
10M
VS = ±15V TA = 25°C AV = 1
50 AV = –1
0 10p
100p
1000p 0.01µ 0.1µ CAPACITIVE LOAD (F)
1µ 1357 G30
1354 G29
Small-Signal Transient (AV = –1)
Small-Signal Transient (AV = 1)
8
±15
DIFFERENTIAL GAIN (PERCENT)
–50
1M FREQUENCY (Hz)
Capacitive Load Handling 100
0.15
3RD HARMONIC
VS = ±5V RL = 2k 2% MAX DISTORTION
1357 G27
Differential Gain and Phase vs Supply Voltage
–30 –40
4
1357 G26
2nd and 3rd Harmonic Distortion vs Frequency VS = ±15V VO = 2VP-P RL = 2k AV = 2
AV = 1 6
0 100k
10M
1357 G25
AV = –1
8
2
OVERSHOOT (%)
100
OUTPUT VOLTAGE (VP-P)
25
AV = –1
0.0001 10
10 AV = –1
TA = 25°C VO = 3VRMS RL = 2k
OUTPUT VOLTAGE (VP-P)
TOTAL HARMONIC DISTORTION (%)
Undistorted Output Swing vs Frequency (±5V)
Undistorted Output Swing vs Frequency (±15V)
Total Harmonic Distortion vs Frequency
Small-Signal Transient (AV = –1, CL = 1000pF)
1357 TA32
1357 TA33
LT1357 U W
TYPICAL PERFORMANCE CHARACTERISTICS Large-Signal Transient (AV = 1)
Large-Signal Transient (AV = 1, CL = 10,000pF)
Large-Signal Transient (AV = –1)
1357 TA34
1357 TA35
1357 TA36
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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
LT1357 2
–
CF > (RG • CIN)/RF
+
7
+
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 5kΩ, a parallel capacitor of value
6 4
8 1 10k
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
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 (0.01µF to 0.1µF). For high drive current applications use low ESR bypass capacitors (1µF to 10µF 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.
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/µs 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., 75Ω) should be placed in
9
LT1357
U
W
U
U
APPLICATIONS INFORMATION series with the output. The other end of the cable should be terminated with the same value resistor to ground. 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 NPN/PNP 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 transient differential input voltages up to 10V without damage and need no clamping or source resistance for protection. Differential inputs, however, generate large supply currents (tens of mA) as required for high slew rates. If the device is used with sustained differential inputs, the average supply current will increase, excessive power dissipation will result and the part may be damaged. The part should not be used as a comparator, peak detector or other open-loop application with large, sustained differential inputs. Under normal, closed-loop operation, an increase of power dissipation is only noticeable in applications with large slewing outputs and is proportional to the magnitude of the differential input voltage and the percent of the time that the inputs are apart. Measure the average supply current for the application in order to calculate the power dissipation. 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 • 130°C/W) LT1357CS8: TJ = TA + (PD • 190°C/W)
10
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 70°C, VS = ±15V, RL = 120Ω (Note: the minimum short-circuit current at 70°C is 25mA, so the output swing is guaranteed only to 3V with 120Ω.) PDMAX = (30V • 2.9mA) + (15V–3V)(25mA) = 387mW TJMAX = 70°C + (387mW • 190°C/W) = 144°C 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 500Ω 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 ten 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
LT1357 U
U
W
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APPLICATIONS INFORMATION 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.
W
SI PLIFIED SCHE ATIC W
V+
R1 500Ω
+IN
RC
OUT
–IN C
CC
V–
1357 SS01
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510)
0.300 – 0.325 (7.620 – 8.255)
0.009 – 0.015 (0.229 – 0.381)
(
+0.035 0.325 –0.015 8.255
+0.889 –0.381
)
0.045 – 0.065 (1.143 – 1.651)
0.130 ± 0.005 (3.302 ± 0.127)
0.065 (1.651) TYP
0.100 ± 0.010 (2.540 ± 0.254)
0.400* (10.160) MAX 8
7
6
5
1
2
3
4
0.255 ± 0.015* (6.477 ± 0.381) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076)
N8 1197
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
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.
11
LT1357
U
PACKAGE DESCRIPTION
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) 0.010 – 0.020 × 45° (0.254 – 0.508)
8
0.053 – 0.069 (1.346 – 1.752)
0.008 – 0.010 (0.203 – 0.254)
5
6
0.004 – 0.010 (0.101 – 0.254)
0°– 8° TYP
0.016 – 0.050 0.406 – 1.270
7
0.014 – 0.019 (0.355 – 0.483)
0.150 – 0.157** (3.810 – 3.988)
0.228 – 0.244 (5.791 – 6.197)
0.050 (1.270) TYP
*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
1
2
3
4 SO8 0996
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TYPICAL APPLICATIONS Instrumentation Amplifier R5 432Ω R1 20k
R4 20k
3.4k
R2 2k
2.61k 100pF
R3 2k
– LT1357
–
200kHz, 4th Order Butterworth Filter
+
3.4k
5.62k
VIN
– LT1357
330pF VOUT
–
2.61k
5.11k
LT1357
+
1000pF
+
VIN
47pF
– VOUT
LT1357
+
+
1357 TA04
R4 1 R2 R3 R2 + R3 1 + = 104 + AV = + R3 2 R1 R4 R5 TRIM R5 FOR GAIN TRIM R1 FOR COMMON MODE REJECTION BW = 250kHz
1357 TA03
RELATED PARTS PART NUMBER
DESCRIPTION
COMMENTS
LT1358/LT1359
Dual/Quad 2mA, 25MHz, 600V/µs Op Amp
Good DC Precision, Stable with All Capacitive Loads
LT1360
4mA, 50MHz, 800V/µs Op Amp
Good DC Precision, Stable with All Capacitive Loads
LT1361/LT1362
Dual/Quad 4mA, 50MHz, 800V/µs Op Amp
Good DC Precision, Stable with All Capacitive Loads
12
Linear Technology Corporation
1357fa LT/TP 0598 REV A 2K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
LINEAR TECHNOLOGY CORPORATION 1994
