LT1187M [Linear]
Low Power Video Difference Amplifier; 低功耗视频差分放大器器型号: | LT1187M |
厂家: | Linear |
描述: | Low Power Video Difference Amplifier |
文件: | 总12页 (文件大小:386K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LT1187
Low Power
Video Difference Amplifier
U
DESCRIPTIO
EATURE
S
F
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The LT1187 is a difference amplifier optimized for opera-
tion on ±5V, or a single 5V supply, and gain ≥2. This
versatile amplifier features uncommitted high input im-
pedance (+) and (–) inputs, and can be used in differential
or single-ended configurations. Additionally, a second set
of inputs give gain adjustment and DC control to the
difference amplifier.
Differential or Single-Ended Gain Block (Adjustable)
–3dB Bandwidth, AV = ±2
Slew Rate
Low Supply Current
Output Current
CMRR at 10MHz
LT1193 Pin Compatible
Low Cost
Single 5V Operation
Drives Cables Directly
Output Shutdown
50MHz
165V/µs
13mA
±20mA
40dB
The LT1187’s high slew rate, 165V/µs, wide bandwidth,
50MHz, and ±20mA output current require only 13mA of
supply current. The shutdown feature reduces the power
dissipation to a mere 15mW, and allows multiple amplifi-
ers to drive the same cable.
O U
PPLICATI
S
A
The LT1187 is a low power version of the popular LT1193,
and is available in 8-pin miniDIPs and SO packages. For
applications with gains of 10 or more, see the LT1189
data sheet.
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Line Receivers
Video Signal Processing
Cable Drivers
Tape and Disc Drive Systems
U
O
TYPICAL APPLICATI
Cable Sense Amplifier for Loop Through Connections
with DC Adjust
Closed-Loop Gain vs Frequency
40
V
IN
V
= ±5V
= 1k
S
L
R
30
20
5V
3
2
+
–
7
CABLE
6
V
LT1187
OUT
1
8
V
+
–
DC
4
10
–5V
1k
0
1k
–10
0.1
1
10
100
FREQUENCY (MHz)
LT1187 • TA01
LT1187 • TA02
1
LT1187
W W W
U
/O
ABSOLUTE AXI U RATI GS
PACKAGE RDER I FOR ATIO
Total Supply Voltage (V + to V –) ............................. 18V
Differential Input Voltage ........................................ ±6V
Input Voltage .......................................................... ±VS
Output Short Circuit Duration (Note 1) ........ Continuous
Operating Temperature Range
LT1187M..................................... – 55°C to 150°C
LT1187C............................................. 0°C to 70°C
Junction Temperature (Note 2)
Plastic Package (CN8,CS8) ......................... 150°C
Ceramic Package (CJ8,MJ8) ....................... 175°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
TOP VIEW
ORDER PART
+/REF
–IN
1
2
3
4
8
7
6
5
–/FB
NUMBER
+
V
LT1187MJ8
LT1187CJ8
LT1187CN8
LT1187CS8
+IN
OUT
S/D
–
V
J8 PACKAGE
N8 PACKAGE
8-LEAD HERMETIC DIP 8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SOIC
LT1187 • POI01
S8 PART MARKING
1187
TJMAX = 175°C, θJA = 100°C/W (J8)
TJMAX = 150°C, θJA = 100°C/W (N8)
JMAX = 150°C, θJA = 150°C/W (S8)
T
Consult factory for Industrial grade parts.
+
5V LECTR AL CHARACTERIST
E
IC
ICS TA = 25°C, (Note 3)
–
VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open.
LT1187M/C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OS
Input Offset Voltage
Either Input, (Note 4)
SOIC Package
2.0
2.0
10
11
mV
mV
I
I
Input Offset Current
Input Bias Current
Either Input
Either Input
0.2
1.0
µA
µA
OS
±0.5 ±2.0
65
B
e
Input Noise Voltage
Input Noise Current
Input Resistance
f = 10kHz
O
nV/√Hz
pA/√Hz
kΩ
n
i
f = 10kHz
O
1.5
n
R
Differential
Either Input
(Note 5)
100
IN
C
V
Input Capacitance
2.0
pF
IN
Input Voltage Limit
±380
3.5
mV
IN LIM
Input Voltage Range
Common-Mode Rejection Ratio
Power Supply Rejection Ratio
Output Voltage Swing
–2.5
70
V
CMRR
PSRR
V
CM
= –2.5V to 3.5V
100
dB
V = ±2.375V to ±8V
S
70
85
dB
V
V = ±5V, R = 1k, A = 50
S
±3.8
±6.7
±6.4
±4.0
±7.0
±6.8
V
OUT
L
V
V = ±8V, R = 1k, A = 50
S
L
V
V = ±8V, R = 300Ω, A = 50, (Note 3)
S
L
V
G
Gain Error
V = ±1V, A = 10, R = 1k
0.2
165
53
1.0
%
V/µs
MHz
MHz
ns
E
O
V
L
SR
Slew Rate
(Note 6, 10)
V = 1V , (Note 7)
100
150
FPBW
BW
Full Power Bandwidth
Small Signal Bandwidth
Rise Time, Fall Time
Propagation Delay
Overshoot
O
P-P
A = 10
V
5.7
230
26
t , t
r
A = 50, V = ±1.5V, 20% to 80% (Note 10)
325
f
V
O
t
R = 1k, V = ±125mV, 50% to 50%
ns
PD
L
O
V = ±50mV
O
0
%
t
Settling Time
3V Step, 0.1%, (Note 8)
100
0.6
0.8
13
ns
s
Diff A
Differential Gain
Differential Phase
Supply Current
R = 1k, A = 4, (Note 9)
%
V
L
V
Diff Ph
R = 1k, A = 4, (Note 9)
DEG
P-P
L
V
I
16
mA
mA
S
–
Shutdown Supply Current
Pin 5 at V
0.8
1.5
2
LT1187
+
5V LECTR AL CHARACTERIST
E
IC
ICS TA = 25°C, (Note 3)
–
VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open.
LT1187M/C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
µA
–
I
t
t
Shutdown Pin Current
Turn On Time
Pin 5 at V
5
25
S/D
ON
–
Pin 5 from V to Ground, R = 1k
500
600
ns
L
–
Turn Off Time
Pin 5 from Ground to V , R = 1k
ns
OFF
L
5V LECTR AL CHARACTERIST
ICS
open.
TA = 25°C, (Note 3)
E
IC
–
VS+ = 5V, VS = 0V, VREF = 2.5V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to VREF, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5
LT1187M/C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OS
Input Offset Voltage
Either Input, (Note 4)
SOIC Package
2.0
2.0
10
12
mV
mV
I
I
Input Offset Current
Either Input
Either Input
0.2
1.0
±2.0
3.5
µA
µA
V
OS
Input Bias Current
±0.5
B
Input Voltage Range
Common-Mode Rejection Ratio
Output Voltage Swing
2.0
70
CMRR
V
CM
= 2.0V to 3.5V
100
4.0
0.15
130
5.3
12
dB
V
V
R = 300Ω to Ground
V
V
High
Low
3.6
OUT
L
OUT
OUT
(Note 3)
0.4
SR
Slew Rate
V = 1.5V to 3.5V
O
V/µs
MHz
mA
BW
Small-Signal Bandwidth
Supply Current
A = 10
V
I
I
15
1.5
25
S
–
–
Shutdown Supply Current
Shutdown Pin Current
Pin 5 at V
Pin 5 at V
0.8
5
mA
µA
S/D
+
5V LECTR AL CHARACTERIST
E
IC
ICS –55°C ≤ TA ≤ 125°C, (Note 3)
–
VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open.
LT1187M
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
mV
µV/°C
µA
V
OS
Input Offset Voltage
Either Input, (Note 4)
2.0
15
∆V /∆T
OS
Input V Drift
8.0
OS
I
I
Input Offset Current
Either Input
Either Input
0.2
1.5
±3.5
3.5
OS
B
Input Bias Current
±0.5
µA
Input Voltage Range
–2.5
70
V
CMRR
PSRR
Common-Mode Rejection Ratio
Power Supply Rejection Ratio
Output Voltage Swing
V
CM
= –2.5V to 3.5V
100
85
dB
V = ±2.375V to ±8V
S
60
dB
V
OUT
V = ±5V, R = 1k, A = 50
±3.7
±6.6
±6.4
±4.0
±7.0
±6.8
0.2
13
V
S
L
V
V = ±8V, R = 1k, A = 50
S
L
V
V = ±8V, R = 300Ω, A = 50, (Note 3)
S
L
V
G
E
Gain Error
V = ±1V, A = 10, R = 1k
1.2
17
%
mA
mA
µA
O
V
L
I
Supply Current
S
–
Shutdown Supply Current
Shutdown Pin Current
Pin 5 at V , (Note 11)
0.8
1.5
25
–
I
Pin 5 at V
5
S/D
3
LT1187
+
5V LECTR AL CHARACTERIST
E
IC
ICS 0°C ≤ TA ≤ 70°C, (Note 3)
–
VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open.
LT1187C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
mV
µV/°C
µA
V
OS
Input Offset Voltage
Either Input, (Note 4)
2.0
12
∆V /∆T
OS
Input V Drift
9.0
OS
I
I
Input Offset Current
Either Input
Either Input
0.2
1.5
±3.5
3.5
OS
B
Input Bias Current
±0.5
µA
Input Voltage Range
–2.5
70
V
CMRR
PSRR
Common-Mode Rejection Ratio
Power Supply Rejection Ratio
Output Voltage Swing
V
CM
= –2.5V to 3.5V
100
85
dB
V = ±2.375V to ±8V
S
65
dB
V
OUT
V = ±5V, R = 1k, A = 50
±3.7
±6.6
±6.4
±4.0
±7.0
±6.8
0.2
13
V
S
L
V
V = ±8V, R = 1k, A = 50
S
L
V
V = ±8V, R = 300Ω, A = 50, (Note 3)
S
L
V
G
E
Gain Error
V = ±1V, A = 10, R = 1k
1.0
17
%
mA
mA
µA
O
V
L
I
Supply Current
S
–
Shutdown Supply Current
Shutdown Pin Current
Pin 5 at V , (Note 11)
0.8
5
1.5
25
–
I
Pin 5 at V
S/D
ELECTRICAL CHARACTERISTICS
5V
0°C ≤ TA ≤ 70°C, (Note 3)
VS+ = 5V, VS– = 0V, VREF = 2.5V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to VREF, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open.
LT1187C
TYP
SYMBOL
PARAMETER
CONDITIONS
MIN
MAX
UNITS
V
OS
Input Offset Voltage
Either Input, (Note 4)
SOIC Package
2.0
2.0
12.0
13.0
mV
mV
∆V /∆T
Input V Drift
9.0
0.2
µV/°C
µA
µA
V
OS
OS
I
I
Input Offset Current
Either Input
Either Input
1.5
±3.5
3.5
OS
B
Input Bias Current
±0.5
Input Voltage Range
Common-Mode Rejection Ratio
Output Voltage Swing
2.0
70
CMRR
V
CM
= 2.0V to 3.5V
100
4.0
0.15
12
dB
V
V
OUT
R = 300Ω to Ground
L
V
V
High
Low
3.5
OUT
OUT
(Note 3)
0.4
16
I
I
Supply Current
mA
mA
µA
S
–
Shutdown Supply Current
Shutdown Pin Current
Pin 5 at V , (Note 11)
0.8
5
1.5
25
–
Pin 5 at V
S/D
Note 1: A heat sink may be required to keep the junction temperature below
absolute maximum when the output is shorted continuously.
Note 6: Slew rate is measured between ±0.5V on the output, with a V step
IN
of ±0.75V, A = 3 and R = 1k.
V L
Note 2: T is calculated from the ambient temperature T and power dissipation
Note 7: Full power bandwidth is calculated from the slew rate measurement:
FPBW = SR/2πVp.
Note 8: Settling time measurement techniques are shown in “Take the
Guesswork Out of Settling Time Measurements,” EDN, September 19, 1985.
J
A
P
D
according to the following formulas:
LT1187MJ8,LT1187CJ8: T = T + (P × 100°C/W)
J
A
D
LT1187CN8:
LT1187CS8:
T = T + (P × 100°C/W)
J A D
T = T + (P × 150°C/W)
J
A
D
Note 9: NTSC (3.58MHz).
Note 3: When R = 1k is specified, the load resistor is R + R , but when
L
FB1
FB2
Note 10: AC parameters are 100% tested on the ceramic and plastic DIP
packaged parts (J8 and N8 suffix) and are sample tested on every lot of the SO
packaged parts (S8 suffix).
R = 300Ω is specified, then an additional 430Ω is added to the output such
L
that (R + R ) in parallel with 430Ω is R = 300Ω.
FB1
FB2
L
Note 4: V measured at the output (pin 6) is the contribution from both input
OS
Note 11: See Application section for shutdown at elevated temperatures. Do
pair, and is input referred.
not operate shutdown above T > 125°C.
J
Note 5: V
is the maximum voltage between –V and +V (pin 2 and
IN LIM
IN IN
pin 3) for which the output can respond.
4
LT1187
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Input Bias Current vs
Common-Mode Voltage vs
Temperature
Common-Mode Voltage
Input Bias Current vs Temperature
+
100
0
V
3.0
2.5
V
= ±5V
S
+
–0.5
–1.0
–1.5
–2.0
V
= 1.8V TO 9V
+I
B
2.0
1.5
1.0
0.5
–100
–200
–300
–400
–I
B
I
OS
–55°C
2.0
1.5
1.0
0.5
25°C
+
V
= –1.8V TO –9V
0
125°C
–
–0.5
V
–5 –4 –3 –2 –1
0
1
2
3
4
5
–50 –25
0
25
50
75
100 125
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
COMMON-MODE VOLTAGE (V)
LT1187 • TPC02
LT1187 • TPC03
LT1187 • TPC01
Equivalent Input Noise Voltage vs
Frequency
Equivalent Input Noise Current vs
Frequency
Supply Current vs Supply Voltage
600
500
400
300
200
100
0
12
10
8
16
14
12
10
8
V
= ±5V
= 25°C
= 0Ω
V
= ±5V
= 25°C
= 100k
S
A
S
S
A
S
T
T
R
R
–55°C
25°C
6
125°C
4
2
0
10
100
1k
10k
100k
10
100
1k
10k
100k
0
2
4
6
8
10
FREQUENCY (Hz)
FREQUENCY (Hz)
±SUPPLY VOLTAGE (V)
LT1187 • TPC04
LT1187 • TPC05
LT1187 • TPC06
Shutdown Supply Current vs
Temperature
Gain Error vs Temperature
Open-Loop Gain vs Temperature
8
6
4
2
0
6
5
4
3
2
1
0
0
–0.05
–0.10
–0.15
V
S
= ±5V
= ±2V
= 10
= 1k
V
= ±5V
V
S
V
O
= ±5V
= ±3V
S
V
OUT
V
R
R
L
= 1k
A
L
V
= –V + 0.6V
EE
S/D
V
S/D
= –V + 0.4V
EE
R
L
= 500Ω
V
S/D
= –V + 0.2V
EE
V
S/D
= –V
EE
–0.20
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LT1187 • TPC09
LT1187 • TPC07
LT1187 • TPC08
5
LT1187
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Open-Loop Voltage Gain vs
Gain Bandwidth Product vs
Supply Voltage
Gain, Phase vs Frequency
Load Resistance
100
80
60
40
20
0
100
80
16k
12k
8k
60
50
V
T
= ±5V
= 25°C
= 1k
S
T
= –55°C
A
= 20dB
A
T
V
V
V
= ±5V
= ±3V
= +25˚C
S
O
A
A
PHASE
R
L
= 25°C
A
T
60
T
A
= 125˚C
40
20
0
GAIN
40
30
4k
–20
–20
0
100k
1M
10M
100M
100
1k
LOAD RESISTANCE (Ω)
10k
0
2
4
6
8
10
FREQUENCY (Hz)
±SUPPLY VOLTAGE (V)
LT1187 • TPC11
LT1187 • TPC12
Gain Bandwidth Product and
Unity Gain Phase Margin vs
Temperature
Common-Mode Rejection Ratio
vs Frequency
Output Impedance vs Frequency
65
55
45
35
100
10
80
70
60
60
50
40
30
V
T
= ±5V
= 25°C
V
= ±5V
= 1k
S
A
S
L
V
= ±5V
= 25°C
= 1k
S
A
L
R
T
R
GAIN BANDWIDTH
PRODUCT
50
40
30
A
= 10
= 2
V
UNITY GAIN
PHASE MARGIN
1.0
0.1
A
V
1k
10k
100k
1M
10M
100M
–50 –25
0
25
50
75 100 125
100k
1M
10M
100M
TEMPERATURE (°C)
FREQUENCY (Hz)
FREQUENCY (Hz)
LT1187 • TPC13
LT1187 • TPC14
LT1187 • TPC15
Power Supply Rejection Ratio vs
Frequency
Output Short Circuit Current vs
Temperature
+
± Output Swing vs Supply Voltage
V
36
35
–0.7
–0.8
–0.9
–1.0
–1.1
80
60
40
20
0
V
= ±5V
V
= ±5V
S
A
S
T
= 25°C
125°C
V
= ±300mV
RIPPLE
25°C
34
33
32
31
30
+PSRR
–PSRR
–55°C
R
L
= 1k
±1.8V ≤ V ≤ ±9V
S
125°C
25°C
0.5
0.4
0.3
–55°C
0.2
0.1
–20
–
–50 –25
0
25
50
75
100 125
0
2
4
6
8
10
1k
10k
100k
1M
10M
100M
V
TEMPERATURE (°C)
FREQUENCY (Hz)
±SUPPLY VOLTAGE (V)
LT1187 • TPC17
LT1187 • TPC18
LT1187 • TPC16
6
LT1187
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Swing vs
Load Resistance
Output Voltage Step vs
Settling Time, AV = 2
Slew Rate vs Temperature
250
200
150
5
3
4
2
V
S
L
= ±5V
= 1k
= ±0.5V
= 2
V
= ±5V
= 25°C
= 1k
V
= ±5V
S
A
L
S
R
V
T
R
T
A
= –55°C
O
V
10mV
A
T
= 25°C
= 25°C
A
–SLEW RATE
+SLEW RATE
T
= 125°C
A
1
0
–1
–3
–5
T
A
–2
–4
10mV
T
= –55°C
A
T
A
= 125°C
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
10
100
LOAD RESISTANCE (Ω)
1000
40
50
60
70
80
90
100
SETTLING TIME (ns)
LT1187 • TPC20
LT1187 • TPC19
LT1187 • TPC21
Harmonic Distortion vs
Output Voltage
Large-Signal Transient Response
–30
–35
–40
–45
–50
–55
–60
V
= ±5V
= 25°C
= 1k
S
A
L
T
R
f = 1MHz
= 10
HD
3
A
V
HD
2
4
6
7
0
1
2
3
5
OUTPUT VOLTAGE (V
)
P-P
INPUT IN LIMITING, AV = 3, SR = 180V/µs
LT1187 • TPC22
LT1187 • TPC23
Small-Signal Transient Response
Small-Signal Transient Response
AV = 2, RFB = 1k, OVERSHOOT = 25%
AV = 2, RFB = 1k, OVERSHOOT = 25%
LT1187 • TPC24
LT1187 • TPC25
7
LT1187
APPLICATIO S I FOR ATIO
U
U U
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The primary use of the LT1187 is in converting high speed
differential signals to a single-ended output. The LT1187
videodifferenceamplifierhastwouncommittedhighinput
impedance (+) and (–) inputs. The amplifier has another
set of inputs which can be used for reference and feed-
back. Additionally, this set of inputs give gain adjust and
DC control to the difference amplifier. The voltage gain of
the LT1187issetlikeaconventionaloperationalamplifier.
Feedback is applied to pin 8, and it is optimized for gains
of2orgreater. Theamplifiercanbeoperatedsingle-ended
by connecting either the (+) or (–) inputs to the +/REF (pin
1). The voltage gain is set by the resistors: (RFB + RG)/RG.
Power Supply Bypassing
The LT1187 is quite tolerant of power supply bypassing.
In some applications a 0.1µF ceramic disc capacitor
placed 1/2 inch from the amplifier is all that is required. In
applications requiringgood settling time, it isimportant to
use multiple bypass capacitors. A 0.1µF ceramic disc in
parallel with a 4.7µF tantalum is recommended.
Calculating the Output Offset Voltage
Both input stages contribute to the output offset voltage at
pin 6. The feedback correction forces balance in the input
stages by introducing an Input VOS at pin 8. The complete
expression for the output offset voltage is:
Like the single-ended case, the differential voltage gain is
setbytheexternalresistors:(RFB +RG)/RG. Themaximum
input differential signal for which the output will respond
is approximately ±0.38V.
VOUT =(VOS +IOS(RS)+IB(RREF)) ×(RFB+RG)/RG +IB(RFB)
RS represents the input source resistance, typically 75Ω,
and RREF represents the finite source impedance from the
DC reference voltage, for VREF grounded, RREF = 0Ω. The
IOS is normally a small contributor and the expression
simplifies to:
S/D
S/D
+
+
V
V
5
5
3
2
3
2
7
7
V
+
+
IN
V
–
–
IN
6
6
LT1187
LT1187
V
V
OUT
1
8
1
8
OUT
+/REF
–/FB
+/REF
–/FB
VOUT = VOS(RFB+RG)/RG + IB(RFB)
4
4
–
–
V
V
If RFB is limited to 1k the last term of the equation
contributes only 2mV, since IB is less than 2µA.
R
R
FB
FB
R
+
+
R
G
FB
R
R
G
FB
A
= +
V
R
G
A
V
= –
R
G
+
7
V
R
G
R
G
6
S/D
S/D
+
+
V
V
5
5
3
2
3
2
7
7
+
–
+
R
FB
V
V
IN DIFF
IN DIFF
–
8
Q1
Q2
Q3
Q4
6
6
LT1187
+/REF
–/FB
LT1187
V
V
OUT
1
8
1
8
OUT
V
+/REF
–/FB
IN
R
G
R
G
V
+
3
2
1
REF
+
IN
R
–
+
4
4
–
R
R
E
1.1k
E
1.1k
–
V
R
V
R
R
S
R
S
R
REF
FB
FB
345µA
350µA
R
FB
R
+R
G
R
G
FB
FB
–
4
V
V
= (V
IN DIFF
+ V
)
V
O
=
V
–
V
IN
O
IN
IN DIFF
(
(
(
(
R
ILT1187 • AI02
G
R
R
R
G
G
G
LT1187 • AI01
Figure 1. Simplified Input Stage Schematic
8
LT1187
U
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APPLICATIO S I FOR ATIO
Operating with Low Closed-Loop Gains
Small-Signal Transient Response
The LT1187 has been optimized for closed-loop gains of
2 or greater. For a closed-loop gain of 2 the response
peaks about 2dB. Peaking can be eliminated by placing a
capacitor across the feedback resistor, (feedback zero).
This peaking shows up as time domain overshoot of
about 25%.
Closed-Loop Voltage Gain vs Frequency
9
8
C
= 0pF
FB
7
6
5
AV = 2, WITH 8pF FEEDBACK CAPACITOR
LT1187 • AI05
C
= 5pF
FB
4
3
2
Extending the Input Range
C
= 10pF
FB
V
= ±5V
= 25°C
= 2
= 900Ω
= 900Ω
S
A
V
FB
G
T
Figure 1 shows a simplified schematic of the LT1187. In
normal operation the REF pin 1 is grounded or taken to a
DC offset control voltage and differential signals are ap-
plied between pins 2 and 3. The input responds linearly
until all of the 345µA current flows through the 1.1k
resistor and Q1 (or Q2) turns off. Therefore the maximum
inputswingis380mVP or760mVP-P. Theseconddifferen-
tial pair, Q3 and Q4, is running at slightly larger current so
that when the first input stage limits, the second stage
remains biased to maintain the feedback.
A
R
R
1
0
–1
100k
1M
10M
100M
FREQUENCY (Hz)
LT1187 • AI03
Small-Signal Transient Response
Occasionally it is necessary to handle signals larger than
760mVP-P at the input. The LT1187 input stage can be
tricked to handle up to 1.5VP-P. To do this, it is necessary
to ground pin 3 and apply the differential input signal
between pin 1 and 2. The input signal is now applied
across two 1.1k resistors in series. Since the input signal
is applied to both input pairs, the first pair will run out of
bias current before the second pair, causing the amplifier
to go open-loop. The results of this technique are shown
in the following scope photo.
AV = 2, OVERSHOOT = 25%, RFB = RG = 1k
LT1187 • AI04
9
LT1187
U
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APPLICATIO S I FOR ATIO
LT1187 in Unity Gain
Performance Characteristics section. At very high el-
evated temperature it is important to hold the shutdown
pin close to the negative supply to keep the supply current
from increasing.
A
B
Send Color Video Over Twisted-Pair
With an LT1187 it is possible to send and receive color
compositevideosignalsmorethan1000feetonalowcost
twisted-pair. A bidirectional “video bus” consists of the
LT1195opampandtheLT1187videodifferenceamplifier.
A pair of LT1195s at TRANSMIT 1, is used to generate
differential signals to drive the line which is back-termi-
natedinitscharacteristicimpedance.TheLT1187,twisted-
pair receiver, converts signals from differential to single-
ended. Topology of the LT1187 provides for cable com-
pensation at the amplifier’s feedback node as shown. In
this case, 1000 feet of twisted-pair is compensated with
1000pF and 50Ω to boost the 3dB bandwidth of the
systemfrom750kHzto4MHz. Thisbandwidthisadequate
to pass a 3.58MHz chroma subcarrier, and the 4.5MHz
soundsubcarrier.Attenuationinthecablecanbecompen-
sated by lowering the gain set resistor RG. At TRANSMIT
2, another pair of LT1195s serve the dual function to
provide cable termination via low output impedance, and
generatedifferentialsignalsforTRANSMIT2. Cabletermi-
nation is made up of a 15Ω and 33Ω attenuator to reduce
the differentialinput signalto the LT1187. Maximuminput
C
(A) STANDARD INPUTS, PINS 2 TO 3, VIN = 1.0VP-P
(B) EXTENDED INPUTS, PINS 2 TO 2, VIN = 1.0VP-P
(C) EXTENDED INPUTS, PINS 1 TO 2, VIN = 2.0VP-P
LT1187 • AI06
Using the Shutdown Feature
The LT1187 has a unique feature that allows the amplifier
to be shutdown for conserving power, or for multiplexing
severalamplifiersontoa commoncable. The amplifierwill
shutdown by taking pin 5 to V–. In shutdown, the amplifier
dissipates15mWwhilemaintainingatruehighimpedance
output state of 20k in parallel with the feedback resistors.
For MUX applications, the amplifiers may be configured
inverting, noninverting, or differential. When the output is
loaded with as little 1k from the amplifier’s feedback
resistors, theamplifiershutsoffin600ns. Thisshutoffcan
be under the control of HC CMOS operating between 0V
and –5V.
signal for the LT1187 is 760mVP-P
.
The ability to maintain shutoff is shown on the curve
Shutdown Supply Current vs Temperature in the Typical
1.5MHz Square Wave Input and Unequalized Response Through
1000 Feet of Twisted-Pair
1MHz Sine Wave Gated Off with Shutdown Pin
SHUTDOWN
VOUT
AV = 2, RFB = RG = 1k
LT1187 • AI08
LT1187 • AI07
10
LT1187
U
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APPLICATIO S I FOR ATIO
1.5MHz Square Wave Input and Equalized Response
Through 1000 Feet of Twisted-Pair
Multiburst Pattern Passed Through
1000 Feet of Twisted-Pair
LT1187 • AI10
LT1187 • AI09
Bidirectional Video Bus
TRANSMIT 1
TRANSMIT 2
3
3
+
+
6
6
1k
1k
LT1195
1k
LT1195
75Ω
75Ω
2
2
–
–
1k
1k
1k
1k
1k
2
3
2
3
–
+
–
+
6
6
LT1195
LT1195
33Ω
15Ω
33Ω
15Ω
33Ω
15Ω
33Ω
S/D
5
S/D
5
3
2
1
8
3
+
–
+
–
+
–
+
15Ω
2
1
8
75Ω
75Ω
6
6
LT1187
LT1187
1000 FEET
TWISTED-PAIR
–
R
R
FB
300Ω
FB
300Ω
1000pF
1000pF
50Ω
R
R
300Ω
G
G
50Ω
300Ω
LT1187 • AI11
RECEIVE 2
RECEIVE 1
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LT1187
W
W
SI PLIFIED SCHE ATIC
+
V
7
V
BIAS
V
BIAS
C
M
+
–
3
2
C
FF
V
6
+V
+V
OUT
*
–
V
4
5
S/D
1
+/REF
8
–/FB
* SUBSTRATE DIODE, DO NOT FORWARD BIAS
LT1187 • SS
U
PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.
0.405
(10.287)
MAX
0.005
(0.127)
MIN
0.200
(5.080)
MAX
0.290 – 0.320
(7.366 – 8.128)
CORNER LEADS OPTION
(4 PLCS)
6
5
8
7
0.015 – 0.060
(0.381 – 1.524)
0.023 – 0.045
0.025
0.220 – 0.310
(0.58 – 1.14)
HALF LEAD
OPTION
J8 Package
8-Lead Hermetic DIP
(0.635)
RAD TYP
(5.588 – 7.874)
0.008 – 0.018
(0.203 – 0.460)
0° – 15°
0.045 – 0.065
(1.14 – 1.65)
FULL LEAD
OPTION
1
2
3
4
0.045 – 0.065
(1.14 – 1.65)
0.385 ± 0.025
(9.779 ± 0.635)
0.125
3.175
MIN
0.100 ± 0.010
0.014 – 0.026
(2.540 ± 0.254)
(0.360 – 0.660)
0.400
(10.160)
MAX
0.130 ± 0.005
(3.302 ± 0.127)
0.300 – 0.320
(7.620 – 8.128)
0.045 – 0.065
(1.143 – 1.651)
8
7
6
5
4
0.065
(1.651)
TYP
0.250 ± 0.010
(6.350 ± 0.254)
N8 Package
8-Lead Plastic DIP
0.009 – 0.015
(0.229 – 0.381)
0.125
(3.175)
MIN
0.020
(0.508)
MIN
+0.025
–0.015
1
2
3
0.045 ± 0.015
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
0.325
+0.635
8.255
(
)
–0.381
0.018 ± 0.003
(0.457 ± 0.076)
0.189 – 0.197
(4.801 – 5.004)
0.010 – 0.020
(0.254 – 0.508)
7
5
8
6
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
S8 Package
8-Lead Plastic SOIC
0.228 – 0.244
(5.791 – 6.197)
0.150 – 0.157
(3.810 – 3.988)
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
BSC
0.014 – 0.019
(0.355 – 0.483)
0°– 8° TYP
1
2
3
4
BA/LT/GP 0293 10K REV0
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
12
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1993
相关型号:
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