LT1210
1.1A, 35MHz Current
Feedback Amplifier
FEATURES
DESCRIPTION
1.1A Minimum Output Drive Current
nn 35MHz Bandwidth, A = 2, R = 10Ω
V
L
nn 900V/µs Slew Rate, A = 2, R = 10Ω
V
L
nn High Input Impedance: 10MΩ
nn Wide Supply Range: ± 5V to ±15V
(TO-220 and DD Packages)
nn Enhanced θ
JA SO-16 Package for ±5V Operation
nn Shutdown Mode: I < 200µA
S
nn Adjustable Supply Current
nn Stable with C = 10,000pF
L
nn Operating Temperature Range: –40°C to 85°C
nn Available in 7-Lead DD, TO-220 and
nn 16-Lead SO Packages
The LT®1210 is a current feedback amplifier with high
output current and excellent large-signal characteristics.
The combination of high slew rate, 1.1A output drive
and ±15V operation enables the device to deliver significant power at frequencies in the 1MHz to 2MHz range.
Short-circuit protection and thermal shutdown ensure
the device’s ruggedness. The LT1210 is stable with large
capacitive loads, and can easily supply the large currents
required by the capacitive loading. A shutdown feature
switches the device into a high impedance and low supply current mode, reducing dissipation when the device
is not in use. For lower bandwidth applications, the supply current can be reduced with a single external resistor.
nn
The LT1210 is available in the TO-220 and DD packages for operation with supplies up to ± 15V. For ±5V
applications the device is also available in a low thermal
resistance SO-16 package.
APPLICATIONS
Cable Drivers
Buffers
nn Test Equipment Amplifiers
nn Video Amplifiers
nn ADSL Drivers
nn
nn
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
Twisted Pair Driver
Total Harmonic Distortion vs Frequency
15V
4.7µF*
–50
100nF
RT
11Ω
2.5W
+
VIN
LT1210
SD
–
T1**
1
4.7µF*
–15V
100nF
RL
100Ω
2.5W
3
845Ω
+
274Ω
TOTAL HARMONIC DISTORTION (dB)
+
–60
–70
RL = 12.5Ω
–80
–90
–100
* TANTALUM
** MIDCOM 671-7783 OR EQUIVALENT
1210 TA01
VS = ±15V
VOUT = 20VP-P
AV = 4
RL = 10Ω
RL = 50Ω
1k
10k
100k
FREQUENCY (Hz)
1M
1210 TA02
Rev C
Document Feedback
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1
LT1210
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Supply Voltage ...................................................... ± 18V
Input Current........................................................ ±15mA
Output Short-Circuit Duration
(Note 2)...........................................Thermally Limited
Operating Temperature Range (Note 3)
LT1210C................................................–40°C to 85°C
LT1210I.................................................–40°C to 85°C
Specified Temperature Range (Note 4)
LT1210C.................................................... 0°C to 70°C
LT1210I.................................................–40°C to 85°C
Junction Temperature ......................................... 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................... 300°C
PIN CONFIGURATION
TOP VIEW
FRONT VIEW
TAB
IS V+
7
6
5
4
3
2
1
OUT
V–
COMP
V+
SHUTDOWN
+IN
–IN
R PACKAGE
7-LEAD PLASTIC D
TJMAX = 150°C, θJA = 25°C/WD
V+ 1
16 V+
V+
2
15 NC
FRONT VIEW
OUT 3
14 V–
7
6
5
4
3
2
1
V+ 4
13 COMP
NC 5
12 SHUTDOWN
–IN 6
11 +IN
NC 7
10 NC
V+ 8
9
TAB
IS V+
V+
OUT
V–
COMP
V+
SHUTDOWN
+IN
–IN
T7 PACKAGE
7-LEAD TO-220
TJMAX = 150°C, θJC = 5°C/W
S PACKAGE
16-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 40°C/W (Note 5)
ORDER INFORMATION
http://www.linear.com/product/LT1210#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1210CR#PBF
LT1210CR#TRPBF
LT1210R
7-Lead Plastic DDPAK
0°C to 70°C
LT1210IR#PBF
LT1210IR#TRPBF
LT1210R
7-Lead Plastic DDPAK
–40°C to 85°C
LT1210CS#PBF
LT1210CS#TRPBF
LT1210CS
16-Lead Plastic SOIC
0°C to 70°C
LT1210CT7#PBF
N/A
LT1210CT7
7-Lead TO-220
0°C to 70°C
Consult ADI Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
2
Rev C
For more information www.analog.com
LT1210
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCM = 0V, ± 5V ≤ VS ≤ ± 15V, pulse tested, VSD = 0V, unless
otherwise noted.
SYMBOL
PARAMETER
VOS
Input Offset Voltage
CONDITIONS
MIN
TYP
MAX
UNITS
±3
±15
±20
mV
mV
l
Input Offset Voltage Drift
IIN+
10
l
Noninverting Input Current
±2
±5
±20
µA
µA
±10
±60
±100
µA
µA
l
IIN–
Inverting Input Current
µV/°C
l
en
Input Noise Voltage Density
f = 10kHz, RF = 1kΩ, RG = 10Ω, RS = 0Ω
3.0
nV/√Hz
+in
Input Noise Current Density
f = 10kHz, RF = 1kΩ, RG = 10Ω, RS = 10kΩ
2.0
pA/√Hz
–in
Input Noise Current Density
f = 10kHz, RF = 1kΩ, RG = 10Ω, RS = 10kΩ
40
pA/√Hz
RIN
Input Resistance
VIN = ±12V, VS = ±15V
VIN = ±2V, VS = ±5V
CIN
Input Capacitance
VS = ±15V
Input Voltage Range
CMRR
PSRR
AV
ROL
VOUT
l
l
1.50
0.25
10
5
MΩ
MΩ
2
pF
VS = ±15V
VS = ± 5V
l
l
±12
±2
±13.5
±3.5
V
V
Common Mode Rejection Ratio
VS = ± 15V, VCM = ±12V
VS = ±5V, VCM = ±2V
l
l
55
50
62
60
dB
dB
Inverting Input Current
Common Mode Rejection
VS = ± 15V, VCM = ±12V
VS = ± 5V, VCM = ±2V
l
l
Power Supply Rejection Ratio
VS = ± 5V to ±15V
l
Noninverting Input Current
Power Supply Rejection
VS = ± 5V to ±15V
l
30
500
nA/V
Inverting Input Current
Power Supply Rejection
VS = ± 5V to ±15V
l
0.7
5
µA/V
Large-Signal Voltage Gain
TA = 25°C, VS = ± 15V, VOUT = ±10V,
RL = 10Ω (Note 5)
Transresistance, ∆VOUT/∆IIN–
Maximum Output Voltage Swing
0.1
0.1
60
55
10
10
77
µA/V
µA/V
dB
71
dB
VS = ± 15V, VOUT = ±8.5V, RL = 10Ω (Note 5)
l
55
68
dB
VS = ±5V, VOUT = ±2V, RL = 10Ω
l
55
68
dB
100
260
kΩ
75
200
kΩ
kΩ
TA = 25°C, VS = ± 15V, VOUT = ±10V,
RL = 10Ω (Note 5)
VS = ± 15V, VOUT = ±8.5V, RL = 10Ω (Note 5)
l
VS = ±5V, VOUT = ±2V, RL = 10Ω
l
75
200
±11.5
l
±10.0
±8.5
V
V
±2.5
±2.0
±3.0
l
V
V
l
1.1
2.0
A
TA = 25°C, VS = ± 15V, RL = 10Ω (Note 5)
TA = 25°C, VS = ± 5V, RL = 10Ω
IOUT
Maximum Output Current (Note 5)
VS = ± 15V, RL = 1Ω
IS
Supply Current (Note 5)
TA = 25°C, VS = ±15V, VSD = 0V
35
50
65
mA
mA
15
30
mA
l
Supply Current, RSD = 51kΩ (Notes 5, 6)
TA = 25°C, VS = ±15V
Positive Supply Current, Shutdown
VS = ± 15V, VSD = 15V
l
200
µA
Output Leakage Current, Shutdown
VS = ± 15V, VSD = 15V
l
10
µA
Rev C
For more information www.analog.com
3
LT1210
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCM = 0V, ± 5V ≤ VS ≤ ± 15V, pulse tested, VSD = 0V, unless
otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
SR
Slew Rate (Note 7)
Slew Rate (Note 5)
TA = 25°C, AV = 2, RL = 400Ω
TA = 25°C, AV = 2, RL = 10Ω
400
900
900
V/µs
V/µs
Differential Gain (Notes 5, 8)
VS = ±15V, RF = 750Ω, RG = 750Ω, RL = 15Ω
0.3
%
Differential Phase (Notes 5, 8)
VS = ±15V, RF = 750Ω, RG = 750Ω, RL = 15Ω
0.1
DEG
Small-Signal Bandwidth
AV = 2, VS = ±15V, Peaking ≤ 1dB,
RF = RG = 680Ω, RL = 100Ω
55
MHz
AV = 2, VS = ± 15V, Peaking ≤ 1dB,
RF = RG = 576Ω, RL = 10Ω
35
MHz
BW
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: A heat sink may be required to keep the junction temperature
below the Absolute Maximum rating. Applies to short circuits to ground
only. A short circuit between the output and either supply may permanently
damage the part when operated on supplies greater than ± 10V.
Note 3: The LT1210C/LT1210I are guaranteed functional over the
temperature range of –40°C to 85°C.
Note 4: The LT1210C is guaranteed to meet specified performance from
0°C to 70°C. The LT1210C is designed, characterized and expected to meet
specified performance from –40°C to 85°C but not tested or QA sampled
at these temperatures. The LT1210I is guaranteed to meet specified
performance from –40°C to 85°C.
4
MAX
UNITS
Note 5: SO package is recommended for ±5V supplies only, as the power
dissipation of the SO package limits performance on higher supplies. For
supply voltages greater than ±5V, use the TO-220 or DD package. See
Thermal Considerations in the Applications Information section for details
on calculating junction temperature. If the maximum dissipation of the
package is exceeded, the device will go into thermal shutdown.
Note 6: RSD is connected between the Shutdown pin and ground.
Note 7: Slew rate is measured at ±5V on a ±10V output signal while
operating on ±15V supplies with RF = 1.5kΩ, RG = 1.5kΩ and RL = 400Ω.
Note 8: NTSC composite video with an output level of 2V.
Rev C
For more information www.analog.com
LT1210
SMALL-SIGNAL BANDWIDTH
RSD = 0Ω, IS = 30mA, VS = ± 5V, Peaking ≤ 1dB
RSD = 0Ω, IS = 35mA, VS = ± 15V, Peaking ≤ 1dB
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
–1
150
30
10
549
590
619
549
590
619
52.5
39.7
26.5
–1
150
30
10
604
649
665
604
649
665
66.2
48.4
46.5
1
150
30
10
604
649
619
–
–
–
53.5
39.7
27.4
1
150
30
10
750
866
845
–
–
–
56.8
35.4
24.7
2
150
30
10
562
590
576
562
590
576
51.8
38.8
27.4
2
150
30
10
665
715
576
665
715
576
52.5
38.9
35.0
10
150
30
10
392
383
215
43.2
42.2
23.7
48.4
40.3
36.0
10
150
30
10
453
432
221
49.9
47.5
24.3
61.5
43.1
45.5
RSD = 7.5kΩ, IS = 15mA, VS = ± 5V, Peaking ≤ 1dB
RSD = 47.5kΩ, IS = 18mA, VS = ± 15V, Peaking ≤ 1dB
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
–1
150
30
10
562
619
604
562
619
604
39.7
28.9
20.5
–1
150
30
10
619
698
698
619
698
698
47.8
32.3
22.2
1
150
30
10
634
681
649
–
–
–
41.9
29.7
20.7
1
150
30
10
732
806
768
–
–
–
51.4
33.9
22.5
2
150
30
10
576
604
576
576
604
576
40.2
29.6
21.6
2
150
30
10
634
698
681
634
698
681
48.4
33.0
22.5
10
150
30
10
324
324
210
35.7
35.7
23.2
39.5
32.3
27.7
10
150
30
10
348
357
205
38.3
39.2
22.6
46.8
36.7
31.3
RSD = 15kΩ, IS = 7.5mA, VS = ± 5V, Peaking ≤ 1dB
RSD = 82.5kΩ, IS = 9mA, VS = ± 15V, Peaking ≤ 1dB
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
AV
RL (Ω)
RF (Ω)
RG (Ω)
– 3dB BW
(MHz)
–1
150
30
10
536
549
464
536
549
464
28.2
20.0
15.0
–1
150
30
10
590
649
576
590
649
576
34.8
22.5
16.3
1
150
30
10
619
634
511
–
–
–
28.6
19.8
14.9
1
150
30
10
715
768
649
–
–
–
35.5
22.5
16.1
2
150
30
10
536
549
412
536
549
412
28.3
19.9
15.7
2
150
30
10
590
665
549
590
665
549
35.3
22.5
16.8
10
150
30
10
150
118
100
16.5
13.0
11.0
31.5
27.1
19.4
10
150
30
10
182
182
100
20.0
20.0
11.0
37.2
28.9
22.5
Rev C
For more information www.analog.com
5
LT1210
TYPICAL PERFORMANCE CHARACTERISTICS
Bandwidth vs Supply Voltage
50
AV = 2
RL = 100Ω
RF = 470Ω
70
60
RF = 560Ω
50
RF = 750Ω
40
RF = 680Ω
30
RF = 1kΩ
20
40
RF = 750Ω
RF = 1kΩ
20
RF = 2kΩ
10
16
0
18
4
16
14
12
10
8
SUPPLY VOLTAGE (±V)
6
–3dB BANDWIDTH (MHz)
–3dB BANDWIDTH (MHz)
70
RF = 330Ω
RF =390Ω
60
50
RF = 470Ω
40
RF = 680Ω
30
20
10
40
30
RF = 680Ω
20
10
14
12
10
8
SUPPLY VOLTAGE (±V)
6
16
0
18
RF = 560Ω
RF = 1.5kΩ
4
14
12
10
8
SUPPLY VOLTAGE (±V)
6
Differential Phase vs
Supply Voltage
0.5
DIFFERENTIAL GAIN (%)
0.4
RF = RG = 750Ω
AV = 2
RL = 15Ω
0.2
RL = 50Ω
0.3
RL = 15Ω
0.2
RL = 50Ω
RL = 30Ω
5
7
11
13
9
SUPPLY VOLTAGE (±V)
15
1210 G07
AV = +2
RL = ∞
VS = ±15V
CCOMP = 0.01µF
1
0
5
7
1
10000
10
100
1000
CAPACITIVE LOAD (pF)
1210 G06
100
RL = 10Ω
0.1
0.1
10
FEEDBACK
RESISTANCE
Spot Noise Voltage and Current
vs Frequency
RF = RG = 750Ω
AV = 2
RL = 10Ω
0.3
0
100
18
Differential Gain vs
Supply Voltage
0.6
0.4
1k
1210 G05
1210 G04
0.5
16
100
BANDWIDTH
RF = 1kΩ
RF = 1.5kΩ
4
10k
–3dB BANDWIDTH (MHz)
80
1
10000
10
100
1000
CAPACITIVE LOAD (pF)
Bandwidth and Feedback Resistance
vs Capacitive Load for Peaking ≤ 5dB
AV = 10
RL = 10Ω
PEAKING ≤ 1dB
AV = 10
RL = 100Ω
PEAKING ≤ 1dB
PEAKING ≤ 5dB
90
1
1210 G03
Bandwidth vs Supply Voltage
50
100
DIFFERENTIAL PHASE (DEG)
AV = 2
RL = ∞
VS = ±15V
CCOMP = 0.01µF
1210 G02
Bandwidth vs Supply Voltage
6
FEEDBACK RESISTANCE
100
18
FEEDBACK RESISTANCE (Ω)
14
12
10
8
SUPPLY VOLTAGE (±V)
6
SPOT NOISE (nV/√Hz OR pA/√Hz)
4
1210 G01
0
10
1k
RF = 1.5kΩ
10
0
BANDWIDTH
RF = 560Ω
30
100
10k
AV = 2
RL = 10Ω
–3dB BANDWIDTH (MHz)
–3dB BANDWIDTH (MHz)
80
PEAKING ≤ 1dB
PEAKING ≤ 5dB
–3dB BANDWIDTH (MHz)
PEAKING ≤ 1dB
PEAKING ≤ 5dB
90
FEEDBACK RESISTANCE (Ω)
100
0
Bandwidth and Feedback Resistance
vs Capacitive Load for Peaking ≤ 1dB
Bandwidth vs Supply Voltage
RL = 30Ω
11
13
9
SUPPLY VOLTAGE (±V)
15
1210 G08
–in
10
en
+in
1
10
100
1k
10k
FREQUENCY (Hz)
100k
1210 G09
Rev C
For more information www.analog.com
LT1210
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage
40
RSD = 0Ω
38
TA = 85°C
34
32
30
28
TA = 125°C
TA = –40°C
26
RSD = 0Ω
25
15
RSD = 15kΩ
10
5
22
4
16
12
14
8
10
SUPPLY VOLTAGE (±V)
6
0
–50
18
50
25
0
75
TEMPERATURE (°C)
–25
100
25
20
15
10
–1.5
–2.0
2.0
1.5
1.0
V–
–50
500
0
25
50
75
TEMPERATURE (°C)
–25
100
RL = 10Ω
–2
–3
–4
RL = 10Ω
4
3
2
RL = 2kΩ
1
V–
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
SOURCING
2.6
SINKING
2.4
2.2
2.0
1.8
1.6
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
60 NEGATIVE
50
125
Supply Current vs Large-Signal
Output Frequency (No Load)
100
RL = 50Ω
VS = ±15V
RF = RG = 1kΩ
POSITIVE
40
30
20
10
0
10k
100
1210 G15
90
SUPPLY CURRENT (mA)
70
RL = 2kΩ
125
100
2.8
Power Supply Rejection Ratio
vs Frequency
POWER SUPPLY REJECTION (dB)
OUTPUT SATURATION VOLTAGE (V)
–1
50
25
0
75
TEMPERATURE (°C)
1210 G14
Output Saturation Voltage vs
Junction Temperature
VS = ±15V
–25
3.0
1210 G13
V+
AV = 1
RL = ∞
Output Short-Circuit Current vs
Junction Temperature
0.5
100
300
400
200
SHUTDOWN PIN CURRENT (µA)
RSD = 82.5kΩ
10
Input Common Mode Limit vs
Junction Temperature
–1.0
5
0
15
1210 G12
OUTPUT SHORT-CIRCUIT CURRENT (A)
30
20
0
–50
125
–0.5
COMMON MODE RANGE (V)
SUPPLY CURRENT (mA)
V+
VS = ±15V
35
RSD = 47.5kΩ
25
1210 G11
Supply Current vs
Shutdown Pin Current
40
RSD = 0Ω
30
5
1210 G10
0
35
RSD = 7.5kΩ
20
24
20
40
AV = 1
RL = ∞
30
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
35
TA = 25°C
36
Supply Current vs
Ambient Temperature, VS = ±15V
SUPPLY CURRENT (mA)
40
Supply Current vs
Ambient Temperature, VS = ± 5V
80
AV = 2
RL = ∞
VS = ±15V
VOUT = 20VP-P
70
60
50
40
30
100k
1M
10M
FREQUENCY (Hz)
100M
1210 G17
1210 G16
20
10k
100k
1M
FREQUENCY (Hz)
10M
1210 G18
Rev C
For more information www.analog.com
7
LT1210
TYPICAL PERFORMANCE CHARACTERISTICS
Output Impedance in Shutdown
vs Frequency
Output Impedance vs Frequency
10k
10
RSD = 82.5kΩ
RSD = 0Ω
1
0.1
0.01
100k
10M
1M
FREQUENCY (Hz)
100M
18
LARGE-SIGNAL VOLTAGE GAIN (dB)
VS = ±15V
IO = 0mA
OUTPUT IMPEDANCE (Ω)
OUTPUT IMPEDANCE (Ω)
100
Large-Signal Voltage Gain vs
Frequency
1k
100
10
1
100k
10M
1M
FREQUENCY (Hz)
VS = ±15V
RL = 10Ω
RF = 680Ω
RG = 220Ω
3RD ORDER INTERCEPT (dBm)
52
9
6
3
0
103
104
105
106
FREQUENCY (Hz)
107
108
1210 G21
+
LT1210
PO
–
50
680Ω
48
46
220Ω
10Ω
MEASURE INTERCEPT AT PO
44
1210 TC01
42
40
12
Test Circuit for 3rd Order Intercept
3rd Order Intercept vs Frequency
54
AV = 4, RL = 10Ω
RF = 680Ω, RG = 220Ω
VS = ±15V, VIN = 5VP-P
1210 G20
1210 G19
56
100M
15
0
2
4
6
FREQUENCY (MHz)
8
10
1210 G22
8
Rev C
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LT1210
APPLICATIONS INFORMATION
Feedback Resistor Selection
The optimum value for the feedback resistors is a function
of the operating conditions of the device, the load impedance and the desired flatness of response. The Typical AC
Performance tables give the values which result in less
than 1dB of peaking for various resistive loads and operating conditions. 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. The curves
stop where the response has more than 5dB of peaking.
14
VS = ±15V
CL = 200pF
12
10
VOLTAGE GAIN (dB)
The LT1210 is a current feedback amplifier with high output current drive capability. The device is stable with large
capacitive loads and can easily supply the high currents
required by capacitive loads. The amplifier will drive low
impedance loads such as cables with excellent linearity
at high frequencies.
8
RF = 3.4kΩ
NO COMPENSATION
RF = 1.5kΩ
COMPENSATION
6
4
2
0
–2
RF = 3.4kΩ
COMPENSATION
–4
–6
1
10
FREQUENCY (MHz)
100
1210 F01
Figure 1.
Also shown is the –3dB bandwidth with the suggested
feedback resistor vs the load capacitance.
For resistive loads, the COMP pin should be left open (see
Capacitive Loads section).
Although the optional compensation works well with
capacitive loads, it simply reduces the bandwidth when
it is connected with resistive loads. For instance, with a
10Ω load, the bandwidth drops from 35MHz to 26MHz
when the compensation is connected. Hence, the compensation was made optional. To disconnect the optional
compensation, leave the COMP pin open.
Capacitive Loads
Shutdown/Current Set
The LT1210 includes an optional compensation network
for driving capacitive loads. This network eliminates most
of the output stage peaking associated with capacitive
loads, allowing the frequency response to be flattened.
Figure 1 shows the effect of the network on a 200pF load.
Without the optional compensation, there is a 6dB peak
at 40MHz caused by the effect of the capacitance on the
output stage. Adding a 0.01µF bypass capacitor between
the output and the COMP pins connects the compensation
and greatly reduces the peaking. A lower value feedback
resistor can now be used, resulting in a response which
is flat to ± 1dB to 40MHz. The network has the greatest
effect for CL in the range of 0pF to 1000pF. The graphs of
Bandwidth and Feedback Resistance vs Capacitive Load
can be used to select the appropriate value of feedback
resistor. The values shown are for 1dB and 5dB peaking at
a gain of 2 with no resistive load. This is a worst-case condition, as the amplifier is more stable at higher gains and
with some resistive load in parallel with the capacitance.
If the shutdown feature is not used, the SHUTDOWN pin
must be connected to ground or V –.
The Shutdown pin can be used to either turn off the biasing for the amplifier, reducing the quiescent current to
less than 200µA, or to control the quiescent current in
normal operation.
The total bias current in the LT1210 is controlled by
the current flowing out of the Shutdown pin. When the
Shutdown pin is open or driven to the positive supply,
the part is shut down. In the shutdown mode, the output
looks like a 70pF capacitor and the supply current is typically less than 100µA. The Shutdown pin is referenced to
the positive supply through an internal bias circuit (see
the Simplified Schematic). An easy way to force shutdown
is to use open-drain (collector) logic. The circuit shown
in Figure 2 uses a 74C906 buffer to interface between 5V
logic and the LT1210. The switching time between the
active and shutdown states is about 1µs. A 24kΩ pull-up
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Rev C
9
LT1210
APPLICATIONS INFORMATION
15V
VIN
+
VOUT
LT1210
– SD
quiescent current can be reduced to 9mA in the inverting
configuration without much change in response. In noninverting mode, however, the slew rate is reduced as the
quiescent current is reduced.
RF
–15V
5V
74C906
ENABLE
24kΩ
15V
RG
1210 F02
Figure 2. Shutdown Interface
resistor speeds up the turn-off time and ensures that
the LT1210 is completely turned off. Because the pin is
referenced to the positive supply, the logic used should
have a breakdown voltage of greater than the positive
supply voltage. No other circuitry is necessary as the
internal circuit limits the Shutdown pin current to about
500µA. Figure 3 shows the resulting waveforms.
RF = 750Ω
RL = 10Ω
IQ = 9mA, 18mA, 36mA
VS = ±15V
1210 F04a
(a) AV = –1
VOUT
RF = 750Ω
RL = 10Ω
ENABLE
IQ = 9mA, 18mA, 36mA
VS = ±15V
1210 F04b
(b) AV = 2
AV = 1
RF = 825Ω
RL = 50Ω
RPULL-UP = 24k
VIN = 1VP-P
VS = ±15V
Slew Rate
Figure 3. Shutdown Operation
For applications where the full bandwidth of the amplifier
is not required, the quiescent current of the device may be
reduced by connecting a resistor from the Shutdown pin
to ground. The quiescent current will be approximately 65
times the current in the Shutdown pin. The voltage across
the resistor in this condition is V + – 3VBE. For example,
a 82kΩ resistor will set the quiescent supply current to
9mA with VS = ±15V.
The photos in Figure 4 show the effect of reducing the quiescent supply current on the large-signal response. The
10
Figure 4. Large-Signal Response vs IQ
1210 F03
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 and will be reduced as
the supply current is reduced. 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
Rev C
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LT1210
APPLICATIONS INFORMATION
the bandwidth is reduced. The photos in Figure 5 show
the large-signal response of the LT1210 for various gain
configurations. The slew rate varies from 770V/µs for a
gain of 1, to 1100V/µs for a gain of – 1.
RF = 825Ω
RL = 10Ω
VS = ±15V
When the LT1210 is used to drive capacitive loads, the
available output current can limit the overall slew rate. In
the fastest configuration, the LT1210 is capable of a slew
rate of over 1V/ns. The current required to slew a capacitor at this rate is 1mA per picofarad of capacitance, so
10,000pF would require 10A! The photo (Figure 6) shows
the large-signal behavior with CL = 10,000pF. The slew
rate is about 150V/µs, determined by the current limit of
1.5A.
1210 F05a
(a) AV = 1
RF = RG = 3kΩ
RL = ∞
VS = ±15V
1210 F06
Figure 6. Large-Signal Response, CL = 10,000pF
Differential Input Signal Swing
RF = RG = 750Ω
RL = 10Ω
VS = ±15V
1210 F05b
(b) AV = –1
The differential input swing is limited to about ± 6V by
an ESD protection device connected between the inputs.
In normal operation, the differential voltage between the
input pins is small, so this clamp has no effect; however,
in the shutdown mode the differential swing can be the
same as the input swing. The clamp voltage will then set
the maximum allowable input voltage. To allow for some
margin, it is recommended that the input signal be less
than ±5V when the device is shut down.
Capacitance on the Inverting Input
RF = RG = 750Ω
RL = 10Ω
VS = ±15V
1210 F05c
(c) AV = 2
Figure 5. Large-Signal Response
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.
Rev C
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11
LT1210
APPLICATIONS INFORMATION
Power Supplies
The LT1210 will operate from single or split supplies
from ± 5V (10V 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 500µV per volt of supply
mismatch. The inverting bias current can change as much
as 5µA per volt of supply mismatch, though typically the
change is less than 0.5µA per volt.
Power Supply Bypassing
To obtain the maximum output and the minimum distortion from the LT1210, the power supply rails should be
well bypassed. For example, with the output stage pouring 1A current peaks into the load, a 1Ω power supply
impedance will cause a droop of 1V, reducing the available
output swing by that amount. Surface mount tantalum
and ceramic capacitors make excellent low ESR bypass
elements when placed close to the chip. For frequencies
above 100kHz, use 1µF and 100nF ceramic capacitors.
If significant power must be delivered below 100kHz,
capacitive reactance becomes the limiting factor. Larger
ceramic or tantalum capacitors, such as 4.7µF, are recommended in place of the 1µF unit mentioned above.
Inadequate bypassing is evidenced by reduced output
swing and “distorted” clipping effects when the output
is driven to the rails. If this is observed, check the supply
pins of the device for ripple directly related to the output
waveform. Significant supply modulation indicates poor
bypassing.
Table 1 and Table 2 list thermal resistance for each package. For the TO-220 package, thermal resistance is given
for junction-to-case only since this package is usually
mounted to a heat sink. Measured values of thermal resistance for several different board sizes and copper areas
are listed for each surface mount package. All measurements were taken in still air on 3/32" FR-4 board with 2
oz 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. R Package, 7-Lead DD
COPPER AREA
TOPSIDE*
BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500 sq. mm 2500 sq. mm 2500 sq. mm
25°C/W
1000 sq. mm 2500 sq. mm 2500 sq. mm
27°C/W
125 sq. mm
35°C/W
2500 sq. mm 2500 sq. mm
*Tab of device attached to topside copper
Thermal Considerations
The LT1210 contains a thermal shutdown feature which
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, which
depends on the power dissipation and the thermal time
constants of the package and heat sinking. Raising the
ambient temperature until the device begins thermal shutdown gives a good indication of how much margin there
is in the thermal design.
12
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 tab of the device. The PCB material
can be very effective at transmitting heat between the pad
area attached to the tab of the device, and a ground or
power plane layer either inside or on the opposite side of
the board. Although the actual thermal resistance of the
PCB material is high, the length/area ratio of the thermal
resistance between the layer is small. Copper board stiffeners and plated through holes can also be used to spread
the heat generated by the device.
Table 2. Fused 16-Lead SO Package
COPPER AREA
TOPSIDE*
BACKSIDE
THERMAL RESISTANCE
BOARD AREA (JUNCTION-TO-AMBIENT)
2500 sq. mm 2500 sq. mm 5000 sq. mm
40°C/W
1000 sq. mm 2500 sq. mm 3500 sq. mm
46°C/W
600 sq. mm
2500 sq. mm 3100 sq. mm
48°C/W
180 sq. mm
2500 sq. mm 2680 sq. mm
49°C/W
180 sq. mm
1000 sq. mm 1180 sq. mm
56°C/W
180 sq. mm
600 sq. mm
780 sq. mm
58°C/W
180 sq. mm
300 sq. mm
480 sq. mm
59°C/W
180 sq. mm
100 sq. mm
280 sq. mm
60°C/W
180 sq. mm
0 sq. mm
180 sq. mm
61°C/W
Rev C
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LT1210
APPLICATIONS INFORMATION
T7 Package, 7-Lead TO-220
Thermal Resistance (Junction-to-Case) = 5°C/W
5V
76mA
A
Calculating Junction Temperature
The junction temperature can be calculated from the
equation:
+
TJ = (PD)(θJA) + TA
–
LT1210
2V
0V
–2V
VO
SD
10Ω
VO = 1.4VRMS
where:
TJ = Junction Temperature
TA = Ambient Temperature
PD = Device Dissipation
θJA = Thermal Resistance (Junction-to-Ambient)
As an example, calculate the junction temperature for the
circuit in Figure 7 for the SO and R packages assuming a
70°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.
PD = (76mA)(10V) – (1.4V)2/ 10 = 0.56W
220Ω
–5V
680Ω
1210 F07
Figure 7.
then:
TJ = (0.56W)(46°C/W) + 70°C = 96°C
for the SO package with 1000 sq. mm topside
heat sinking
TJ = (0.56W)(27°C/W) + 70°C = 85°C
for the R package with 1000 sq. mm topside heat
sinking
Since the maximum junction temperature is 150°C,
both packages are clearly acceptable.
Rev C
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13
LT1210
TYPICAL APPLICATIONS
Precision × 10 High Current Amplifier
CMOS Logic to Shutdown Interface
15V
VIN
+
+
+
LT1097
LT1210
COMP
– SD
–
LT1210
SD
OUT
–
0.01µF
500pF
5V
3kΩ
330Ω
–15V
10kΩ
2N3904
9.09kΩ
OUTPUT OFFSET:
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