AD ADA4856-3YCPZ-RL

Single-Supply, High Speed, Fixed G = +2,
Rail-to-Rail Output Video Amplifier
ADA4856-3
NC
3
PD
4
OUT1
–VS
13
12 +VS
11 OUT2
ADA4856-3
10 –IN2
9
+IN3
5
6
7
+VS
8
NOTES
1. NC = NO CONNECT.
2. EXPOSED PAD CONNECTED TO –VS.
07686-001
2
14
–VS
+IN2
15
OUT3
1
16
–IN3
NC
–IN1
CONNECTION DIAGRAM
Voltage feedback architecture
Rail-to-rail output swing: 0.1 V to 4.9 V
High speed amplifier
−3 dB bandwidth: 225 MHz
0.1 dB flatness at 2 V p-p: 74 MHz
Slew rate: 800 V/μs
Settling time to 0.1% with 2 V step: 5 ns
High input common-mode voltage range
−VS − 0.2 V to +VS − 1 V
Supply range: 3 V to 5.5 V
Differential gain error: 0.01%
Differential phase error: 0.01°
Low power
7.8 mA/amplifier typical supply current
Power-down feature
Available in 16-lead LFCSP
+IN1
FEATURES
Figure 1.
APPLICATIONS
Professional video
Consumer video
Imaging
Instrumentation
Base stations
Active filters
Buffers
7
The ADA4856-3 (triple) is a fixed gain of +2, single-supply, railto-rail output video amplifier. It provides excellent video
performance with 225 MHz, −3 dB bandwidth, 800 V/μs slew rate,
and 74 MHz, 0.1 dB flatness into a 150 Ω load. It has a wide
input common-mode voltage range that extends 0.2 V below
ground and 1 V below the positive rail. In addition, the output
voltage swings within 200 mV of either supply, making this video
amplifier easy to use on single-supply voltages as low as 3.3 V.
6
The ADA4856-3 is available in a 16-lead LFCSP and is designed
to work over the extended industrial temperature range of
−40°C to +105°C.
VS = 5V, VOUT = 1.4V p-p
VS = 3.3V, VOUT = 1.4V p-p
VS = 3.3V, VOUT = 2V p-p
5
VS = 5V, VOUT = 2V p-p
4
3
2
1
07686-058
The ADA4856-3 offers a typical low power of 7.8 mA per amplifier,
while being capable of delivering up to 52 mA of load current.
It also features a power-down function for power sensitive
applications that reduces the supply current to 1 mA.
CLOSED-LOOP GAIN (dB)
GENERAL DESCRIPTION
RL = 150Ω
0
1
10
100
FREQUENCY (MHz)
1000
Figure 2. Large Signal Frequency Response
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2008 Analog Devices, Inc. All rights reserved.
ADA4856-3
TABLE OF CONTENTS
Features .............................................................................................. 1 Theory of Operation ...................................................................... 12 Applications ....................................................................................... 1 Applications Information .............................................................. 13 Connection Diagram ....................................................................... 1 Using the ADA4856-3 in Gains Equal to +1, −1........................ 13 General Description ......................................................................... 1 Using the ADA4856-3 in Gains Equal to +3, +4, and +5 ..... 14 Revision History ............................................................................... 2 20 MHz Active Low-Pass Filter ................................................ 15 Specifications..................................................................................... 3 Video Line Driver ....................................................................... 15 5 V Operation ............................................................................... 3 Single-Supply Operation ........................................................... 16 3.3 V Operation ............................................................................ 4 Power Down ................................................................................ 16 Absolute Maximum Ratings............................................................ 5 Layout Considerations ............................................................... 16 Thermal Resistance ...................................................................... 5 Power Supply Bypassing ............................................................ 16 Maximum Power Dissipation ..................................................... 5 Outline Dimensions ....................................................................... 17 ESD Caution .................................................................................. 5 Ordering Guide .......................................................................... 17 Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 REVISION HISTORY
10/08—Revision 0: Initial Version
Rev. 0 | Page 2 of 20
ADA4856-3
SPECIFICATIONS
5 V OPERATION
TA = 25°C, +VS = 5 V, −VS = 0 V, G = +2, RL = 150 Ω to midsupply, unless otherwise noted.
Table 1.
Parameter
DYNAMIC PERFORMANCE
−3 dB Bandwidth
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1% (Rise/Fall)
NOISE/DISTORTION PERFORMANCE
Harmonic Distortion (HD2/HD3)
Crosstalk, Output to Output
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
DC PERFORMANCE
Input Offset Voltage
Input Offset Voltage Drift
Input Bias Current
Input Offset Current
Closed-Loop Gain
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
OUTPUT CHARACTERISTICS
Output Voltage Swing
Linear Output Current Per Amplifier
POWER-DOWN
Turn-On Time
Turn-Off Time
Input Bias Current
Turn-On Voltage
POWER SUPPLY
Operating Range
Quiescent Current per Amplifier
Supply Current When Disabled
Power Supply Rejection Ratio
Test Conditions
Min
Typ
Max
Unit
VO = 0.1 V p-p
VO = 1.4 V p-p
VO = 2 V p-p
VO = 1.4 V p-p
VO = 2 V p-p
VO = 2 V step
VO = 2 V step
370
225
200
90
74
800
4.8/5.2
MHz
MHz
MHz
MHz
MHz
V/μs
ns
fC = 5 MHz, VO = 2 V p-p, RL = 1 kΩ
fC = 20 MHz, VO = 2 V p-p, RL = 1 kΩ
f = 5 MHz, G = +2
f = 100 kHz
f = 100 kHz
−92/−110
−68/−71
−80
14
2
0.01
0.01
dBc
dBc
dBc
nV/√Hz
pA/√Hz
%
Degrees
1.95
1.3
5.5
−3.8
±0.05
2
90
3.4
2.05
3.2
0.5
mV
μV/°C
μA
μA
V/V
dB
VCM = −0.2 V to +4 V
94
MΩ
pF
V
dB
HD2 ≤ −60 dBc, RL = 10 Ω
0.1 to 4.9
52
V
mA
78
950
0.2
−125
3.75
ns
ns
μA
μA
V
−VS − 0.2
Enabled
Powered down
+VS − 1
3
∆VS = 4.5 V to 5.5 V
Rev. 0 | Page 3 of 20
5.5
7.8
1.1
96
V
mA
mA
dB
ADA4856-3
3.3 V OPERATION
TA = 25°C, +VS = 3.3 V, −VS = 0 V, G = +2, RL = 150 Ω to midsupply, unless otherwise noted.
Table 2.
Parameter
DYNAMIC PERFORMANCE
−3 dB Bandwidth
Bandwidth for 0.1 dB Flatness
Slew Rate
Settling Time to 0.1% (Rise/Fall)
NOISE/DISTORTION PERFORMANCE
Harmonic Distortion (HD2/HD3)
Crosstalk, Output to Output
Input Voltage Noise
Input Current Noise
Differential Gain Error
Differential Phase Error
DC PERFORMANCE
Input Offset Voltage
Input Offset Voltage Drift
Input Bias Current
Input Offset Current
Closed-Loop Gain
Open-Loop Gain
INPUT CHARACTERISTICS
Input Resistance
Input Capacitance
Input Common-Mode Voltage Range
Common-Mode Rejection Ratio
OUTPUT CHARACTERISTICS
Output Voltage Swing, Load Resistance
Linear Output Current Per Amplifier
POWER-DOWN
Turn-On Time
Turn-Off Time
Turn-On Voltage
POWER SUPPLY
Operating Range
Quiescent Current per Amplifier
Quiescent Current When Powered Down
Power Supply Rejection Ratio
Test Conditions
Min
Typ
Max
Unit
VO = 0.1 V p-p
VO = 2 V p-p
VO = 2 V p-p
VO = 2 V step
VO = 2 V step
370
225
77
800
4.8/7
MHz
MHz
MHz
V/μs
ns
fC = 5 MHz, VO = 2 V p-p, RL = 1 kΩ
fC = 20 MHz, VO = 2 V p-p, RL = 1 kΩ
f = 5 MHz, G = +2
f = 100 kHz
f = 100 kHz
−95/−128
−74/−101
−78
14
2
0.01
0.01
dBc
dBc
dBc
nV/√Hz
pA/√Hz
%
Degrees
1.95
1.2
5.5
−3.8
±0.05
2
90
3
2.05
3.2
0.5
mV
μV/°C
μA
μA
V/V
dB
VCM = −0.2 V to +2.3 V
94
MΩ
pF
V
dB
HD2 ≤ −60 dBc, RL = 10 Ω
0.1 to 3.22
49
V
mA
78
950
2.05
ns
ns
V
−VS − 0.2
+VS − 1
3
∆VS = 2.97 V to 3.63 V
Rev. 0 | Page 4 of 20
5.5
7.5
0.98
94
V
mA
mA
dB
ADA4856-3
ABSOLUTE MAXIMUM RATINGS
MAXIMUM POWER DISSIPATION
1
Rating
6V
See Figure 3
(−VS − 0.2 V) to (+VS − 1 V)
±VS
Observe power curves
−65°C to +125°C
−40°C to +105°C
300°C
Specification is for device in free air.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
The maximum power that can be safely dissipated by the
ADA4856-3 is limited by the associated rise in junction
temperature. The maximum safe junction temperature for
plastic encapsulated devices is determined by the glass transition
temperature of the plastic, approximately 150°C. Temporarily
exceeding this limit may cause a shift in parametric performance
due to a change in the stresses exerted on the die by the package.
Exceeding a junction temperature of 175°C for an extended
period can result in device failure.
To ensure proper operation, it is necessary to observe the
maximum power derating curves.
3.0
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, θJA is specified
for a device soldered in a circuit board for surface-mount packages.
2.5
2.0
1.5
1.0
0.5
07686-103
Parameter
Supply Voltage
Internal Power Dissipation1
Common-Mode Input Voltage
Differential Input Voltage
Output Short-Circuit Duration
Storage Temperature Range
Operating Temperature Range
Lead Temperature (Soldering, 10 sec)
MAXIMUM POWER DISSIPATION (W)
Table 3.
90
100
80
70
60
50
40
30
20
0
10
0
Unit
°C/W
–10
θJC
17.5
–20
θJA
67
–40
Package Type
16-Lead LFCSP
–30
Table 4.
AMBIENT TEMPERATURE (°C)
Figure 3. Maximum Power Dissipation vs. Ambient Temperature
ESD CAUTION
Rev. 0 | Page 5 of 20
ADA4856-3
+IN1
–IN1
OUT1
–VS
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
16
15
14
13
12 +VS
NC
1
+IN2
2
ADA4856-3
11 OUT2
NC
3
TOP VIEW
(Not to Scale)
10 –IN2
PD
4
6
7
8
–IN3
OUT3
–VS
NOTES
1. NC = NO CONNECT.
2. EXPOSED PAD CONNECTED TO –VS.
Figure 4. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17 (EPAD)
Mnemonic
NC
+IN2
NC
PD
+IN3
−IN3
OUT3
−VS
+VS
−IN2
OUT2
+VS
−VS
OUT1
−IN1
+IN1
Exposed Pad (EPAD)
Description
No Connect.
Noninverting Input 2.
No Connect.
Power Down.
Noninverting Input 3.
Inverting Input 3.
Output 3.
Negative Supply.
Positive Supply.
Inverting Input 2.
Output 2.
Positive Supply.
Negative Supply.
Output 1.
Inverting Input 1.
Noninverting Input 1.
The exposed pad must be connected to −VS.
Rev. 0 | Page 6 of 20
+VS
07686-003
5
+IN3
9
ADA4856-3
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, +VS = 5 V, G = +2, RL = 150 Ω, large signal VOUT = 2 V p-p, small signal VOUT = 100 mV p-p, unless otherwise noted.
7
7
VS = 5V, VOUT = 1.4V p-p
VS = 3.3V
CLOSED-LOOP GAIN (dB)
4
3
2
1
10
100
FREQUENCY (MHz)
VS = 5V, VOUT = 2V p-p
4
3
2
1
07686-005
1
VS = 3.3V, VOUT = 2V p-p
5
07686-008
CLOSED-LOOP GAIN (dB)
VS = 5V
5
0
VS = 3.3V, VOUT = 1.4V p-p
6
6
0
1
1000
Figure 5. Small Signal Frequency Response vs. Supply Voltage
10
100
FREQUENCY (MHz)
1000
Figure 8. Large Signal Frequency Response vs. Supply Voltage
2
6.2
TA = +105°C
TA = +25°C
0
CLOSED-LOOP GAIN (dB)
CLOSED-LOOP GAIN (dB)
6.1
VS = 3.3V, VOUT = 1.4V p-p
VS = 5V, VOUT = 1.4V p-p
6.0
VS = 3.3V, VOUT = 2V p-p
VS = 5V, VOUT = 2V p-p
5.9
TA = –40°C
TA = +25°C
TA = +85°C
TA = +105°C
TA = –40°C
–2
TA = +85°C
–4
1
10
100
FREQUENCY (MHz)
–8
1000
Figure 6. Large Signal 0.1 dB Flatness vs. Supply Voltage
07686-009
5.8
07686-006
–6
1M
10M
100M
FREQUENCY (Hz)
Figure 9. Small Signal Frequency Response vs. Temperature
7
CL = 4.4pF
6
RL = 150Ω
5
4
3
2
0
1
10
100
FREQUENCY (MHz)
CL = 2.2pF
4
2
0
–2
–4
07686-007
1
CL = 6.6pF
07686-010
CLOSED-LOOP GAIN (dB)
CLOSED-LOOP GAIN (dB)
RL = 1kΩ
6
1G
–6
1
1000
10
100
1000
FREQUENCY (MHz)
Figure 7. Small Signal Frequency Response vs. Load Resistance
Figure 10. Small Signal Frequency Response vs. Capacitive Load
Rev. 0 | Page 7 of 20
ADA4856-3
–50
–50
RL = 1kΩ
VOUT = 2V p-p
–60
–70
–70
DISTORTION (dBc)
DISTORTION (dBc)
RL = 1kΩ
VOUT = 1V p-p
VS = 3.3V
–60
–80
–90
HD3
–100
HD2
–110
–80
–90
–100
HD3
–110
–130
–130
07686-011
–120
–140
0.1
–140
100
1
10
FREQUENCY (MHz)
07686-014
HD2
–120
0.1
Figure 11. Harmonic Distortion vs. Frequency
1
10
FREQUENCY (MHz)
100
Figure 14. Harmonic Distortion vs. Frequency
0
–10
–20
–40
OUT3
–60
OUT1
–80
OUT2
07686-012
–100
–120
0.1
1
10
100
–30
–40
–60
–70
–100
–110
–120
1M
1000
10M
FREQUENCY (Hz)
100M
Figure 15. Crosstalk vs. Frequency
0.5
–10
0.4
–20
0.3
–30
0.2
SETTLING TIME (%)
0
–40
–50
+PSRR
–PSRR
–70
–80
0.1
0
–0.1
–0.2
–90
0.1
1
10
07685-024
–0.3
07686-013
PSRR (dB)
IN2, IN3, OUT1
–90
Figure 12. Forward Isolation vs. Frequency
–100
0.01
IN1, IN2, OUT3
–80
FREQUENCY (MHz)
–60
IN1, IN3, OUT2
–50
07686-015
ALL HOSTILE CROSSTALK (dB)
FORWARD ISOLATION (dB)
–20
–0.4
–0.5
100
TIME (2ns/DIV)
FREQUENCY (MHz)
Figure 13. Power Supply Rejection Ratio (PSRR) vs. Frequency
Figure 16. Settling Time
Rev. 0 | Page 8 of 20
ADA4856-3
25.0
24.5
VS = 5V
QUIESCENT CURRENT (mA)
VOLTAGE NOISE (nV/√Hz)
1k
100
24.0
23.5
23.0
1k
10k
FREQUENCY (Hz)
100k
2.7
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
Figure 20. Quiescent Current vs. Supply Voltage
0.06
1.5
VS = 5V
VS = 3.3V
VS = 5V
VS = 3.3V
1.0
OUTPUT VOLTAGE (V)
0.04
0.02
0
–0.02
–0.04
0.5
0
–0.5
07686-018
–1.0
–0.06
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 18. Small Signal Transient Response vs. Supply Voltage
Figure 21. Large Signal Transient Response vs. Supply Voltage
0.08
1.5
0.06
1.0
OUTPUT VOLTAGE (V)
0.04
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.02
0
–0.02
–0.04
0.5
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0
–0.5
–1.0
07686-019
–0.06
–0.08
07686-022
OUTPUT VOLTAGE (V)
3.0
SUPPLY VOLTAGE (V)
Figure 17. Output Voltage Noise vs. Frequency
OUTPUT VOLTAGE (V)
07686-057
22.0
1M
07686-021
10
100
07686-017
22.5
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 19. Small Signal Transient Response vs. Capacitive Load
Figure 22. Large Signal Transient Response vs. Capacitive Load
Rev. 0 | Page 9 of 20
ADA4856-3
0.08
1.5
1.0
0.04
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0.06
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.02
0
–0.02
–0.04
CL = 2.2pF
CL = 4.4pF
CL = 6.6pF
0.5
0
–0.5
07686-023
VS = 3.3V
–0.08
07686-026
–1.0
–0.06
VS = 3.3V
–1.5
TIME (10ns/DIV)
TIME (10ns/DIV)
Figure 23. Small Signal Transient Response vs. Capacitive Load
Figure 26. Large Signal Transient Response vs. Capacitive Load
4
2.5
2 × VIN
3
2 × VIN
2.0
1.5
VOUT
VOUT
1.0
1
VOLTAGE (V)
VOLTAGE (V)
2
0
–1
0.5
0
–0.5
–1.0
–2
07686-025
–4
VS = 3.3V
–2.0
–2.5
TIME (50ns/DIV)
TIME (50ns/DIV)
Figure 24. Output Overdrive Recovery
Figure 27. Output Overdrive Recovery
3.0
23.6
VPD
QUIESCENT CURRENT (mA)
2.0
VOUT
0.5
0
–0.5
–1.0
07686-056
VOLTAGE (V)
1.5
1.0
VS = 5V
23.4
–1.5
TIME (1us/DIV)
23.2
23.0
22.8
22.6
VS = 3.3V
22.4
22.2
22.0
21.8
–40
–25
–10
5
20
35
50
65
80
95
TEMPERATURE (°C)
Figure 25. Turn-On/Turn-Off Time
Figure 28. Quiescent Current vs. Temperature
Rev. 0 | Page 10 of 20
110
125
07686-132
2.5
07686-028
–1.5
–3
ADA4856-3
1.8
5.00
1.7
4.95
1.5
1.4
1.3
1.2
1.1
07686-034
1.0
0.9
0.8
–40
–20
0
20
40
60
80
100
120
TEMPERATURE (°C)
1
0.1
07686-135
OUTPUT IMPEDENCE (Ω)
10
10M
100M
FREQUENCY (Hz)
4.80
4.75
4.70
4.65
4.60
0.01
0.1
1
10
Figure 31. Output Saturation Voltage vs. Load Current
100
1M
4.85
LOAD CURRENT (mA)
Figure 29. Offset Drift vs. Temperature
0.01
100k
4.90
07686-038
SATURATION VOLTAGE (mV)
OFFSET VOLTAGE (mV)
1.6
1G
Figure 30. Output Impedance vs. Frequency
Rev. 0 | Page 11 of 20
100
ADA4856-3
THEORY OF OPERATION
Besides a novel input stage, the ADA4856-3 employs the Analog
Devices, Inc., patented rail-to-rail output stage. This output
stage makes an efficient use of the power supplies, allowing the
op amp to drive up to three video loads to within 300 mV from
both rails. In addition, this output stage provides the amplifier
with very fast overdrive characteristics, an important property
in video applications.
The ADA4856-3 comes in a 16-lead LFCSP that has an exposed
thermal pad for lower operating temperature. This pad is connected
internally to the negative rail. To avoid printed circuit board (PCB)
layout problems, the ADA4856-3 features a new pinout flow that
is optimized for video applications. As shown in Figure 4, the
feedback and gain resistors are on-chip, which minimizes the
number of components needed and improves the design layout.
The ADA4856-3 is fabricated in Analog Devices dielectrically
isolated eXtra Fast Complementary Bipolar 3 (XFCB3) process,
which results in the outstanding speed and dynamic range
displayed by the amplifier.
+VS
C1
Gm2
+IN
R
–IN
C
–VS
Figure 32. High Level Design Schematic
Rev. 0 | Page 12 of 20
OUT
Gm1
07686-147
The ADA4856-3 is a voltage feedback op amp that employs a
new input stage that achieves a high slew rate while maintaining
a wide common-mode input range. The input common-mode
range of the ADA4856-3 extends from 200 mV below the negative
rail to about 1 V from the positive rail. This feature makes the
ADA4856-3 ideal for low voltage single-supply applications. In
addition, this new input stage does not sacrifice noise performance
for slew rate. At 14 nV/√Hz, the ADA4856-3 is one of the
lowest noise rail-to-rail output video amplifiers in the market.
ADA4856-3
APPLICATIONS INFORMATION
+VS
USING THE ADA4856-3 IN GAINS EQUAL TO +1, −1
10µF
The ADA4856-3 was designed to offer outstanding video
performance, simplify applications, and minimize board area.
0.1µF
The ADA4856-3 is a triple amplifier with on-chip feedback
and gain set resistors. The gain is fixed internally at G = +2. The
inclusion of the on-chip resistors not only simplifies the design of
the application but also eliminates six surface-mount resistors,
saving valuable board space and lowering assembly costs.
Whereas the ADA4856-3 has a fixed gain of G = +2, it can be
used in other gain configurations, such as G = −1 and G = +1.
RF
RG
VOUT
VIN
RT
0.1µF
07686-030
10µF
–VS
Unity-Gain Operation
Option 1
GAIN OF +1
Figure 34. Unity Gain of Option 2
There are two options for obtaining unity gain (G = +1). The
first is shown in Figure 33. In this configuration, the –IN input
pin is tied to the output (feedback is now provided with the two
internal 402 Ω resistors in parallel), and the input is applied to
the noninverting input. The noise gain for this configuration is 1.
Inverting Unity-Gain Operation
In this configuration, the noninverting input is tied to ground
and the input signal is applied to the inverting input. The noise
gain for this configuration is +2, see Figure 35.
+VS
+VS
10µF
10µF
0.1µF
0.1µF
VIN
VIN
RT
VOUT
RT
VOUT
0.1µF
10µF
–VS
–VS
GAIN OF –1
GAIN OF +1
Figure 35. Inverting Configuration (G = −1)
Figure 33. Unity Gain of Option 1
Another option exists for running the ADA4856-3 as a unitygain amplifier. In this configuration, the noise gain is +2, see
Figure 34. The frequency response and transient response for
this configuration closely match the gain of +2 plots because the
noise gains are equal. This method does have twice the noise gain
of Option 1; however, in applications that do not require low noise,
Option 2 offers less peaking and ringing. By tying the inputs
together, the net gain of the amplifier becomes 1. Equation 1 shows
the transfer characteristic for the schematic shown in Figure 34.
⎞
⎟
⎟
⎠
(1)
6
3
which simplifies to VOUT = VIN.
OPTION 1
G = +1
VS = 5V
RL = 100Ω
VOUT = 100mV p-p
G = –1
0
OPTION 2
G = +1
–3
–6
–9
07686-044
⎛ R + RG
⎞
⎟ + V IN ⎜ F
⎜ R
⎟
G
⎝
⎠
Figure 36 shows the small signal frequency response for both
gain of +1 (Option 1 and Option 2) and gain of −1 configurations.
It is clear that G = +1, Option 2 has better flatness and no peaking
compared to Option 1.
MAGNITUDE (dB)
Option 2
⎛ − RF
VOUT = V IN ⎜⎜
⎝ RG
10µF
07686-031
07686-032
0.1µF
–12
1
10
100
FREQUENCY (MHz)
Figure 36. G = +1 and G = −1
Rev. 0 | Page 13 of 20
1000
ADA4856-3
USING THE ADA4856-3 IN GAINS EQUAL TO +3,
+4, AND +5
Depending on certain applications, it might be useful to have a
fixed gain amplifier that can provide various gains. The advantage
of having a fixed gain amplifier is the ease of layout, the reduced
number of components needed, and the matching of the gain
and feedback resistors.
As shown in Figure 40, the large signal frequency response
for G = +4 is also flat out to 65 MHz, and it has a bandwidth
of 180 MHz.
Gain of+ 5 Configuration
The gain of +5 is very similar to the G = +3 configuration but with
U2 set to a gain of −1, which ends up being added to twice the
output of U1 to generate VOUT with G = +5.
Gain of +3 Configuration
–VS
Figure 37 shows the ADA4856-3 used as an amplifier with a
fixed gain of +3. No external resistors are required, just a simple
trace connecting certain inputs and outputs. Connect VIN to U1,
which is set to a gain of +2, and U2, which is set to unity. U3 then
takes the output of U1 and gains it up by +2 and subtracts the
output of U2 to produce VOUT. As shown in Figure 40, the large
signal frequency response for G = +3 is flat out to 65 MHz, with a
bandwidth of 165 MHz, a 2 V p-p output voltage, and a 100 Ω load.
0.1µF
15
14
0.1µF
VIN
1
12
2
11
3
ADA4856-3
+VS
VOUT
10
PD 4
+VS
9
5
+
14
6
7
10µF
0.1µF
13
–VS
2
3
Figure 39. Gain of +5
12
+VS
10
PD 4
+VS
9
5
6
7
Figure 40 shows the large signal frequency response of the three
closed-loop gain sets (+3, +4, and +5) with flatness that extends
to 65 MHz and a −3 dB bandwidth of 150 MHz.
VOUT
11
ADA4856-3
+
8
15
G = +4
12
10µF
0.1µF
G = +3
07686-045
–VS
Figure 37. Gain of +3
Gain of +4 Configuration
To get a gain of +4, set one amplifier to a gain of +1 and set the
other two amplifiers to a gain of +2. Figure 38 shows VIN going in
U2 at unity, then U1 takes the output of U2 and gains it by +2, and
then feeds it to U3, which also gains it by +2 to produce VOUT.
–VS
CLOSED-LOOP GAIN (dB)
9
0.1µF
6
3
0
–3
–6
–9
RL = 100Ω
VS = 5V
VOUT = 2V p-p
–12
–15
–18
1
0.1µF
15
14
+
16
13
1
12
2
11
ADA4856-3
+VS
VOUT
+VS
9
5
6
7
+
8
10µF
0.1µF
–VS
07686-046
0.1µF
VIN
100
1000
Figure 40. Large Signal Frequency Response for All Three Gains
10
PD 4
10
FREQUENCY (MHz)
10µF
0.1µF
3
G = +5
07686-048
1
10µF
0.1µF
0.1µF
VIN
+
8
07686-047
0.1µF
15
10µF
13
–VS
16
+
16
Figure 38. Gain of +4
Rev. 0 | Page 14 of 20
ADA4856-3
20 MHz ACTIVE LOW-PASS FILTER
VIDEO LINE DRIVER
The ADA4856-3 triple amplifier lends itself to higher order
active filters. Figure 41 shows a 20 MHz, 6-pole, Sallen-Key
low-pass filter.
The ADA4856-3 was designed to excel in video driver applications.
Figure 43 shows a typical schematic for a video driver operating
on bipolar supplies.
75Ω
VIN (R)
R1
93.1Ω
VIN
C1
33pF
OUT1
U1
OP AMP
+
R2
604Ω
VOUT (R)
–VS
75Ω
16
15
14
C2
22pF
VIN (G)
2
75Ω
–
+VS
11
ADA4856-3
3
10
PD 4
9
75Ω
VOUT (G)
+VS
OUT2
U2
OP AMP
+
R4
732Ω
C3
33pF
10µF
0.1µF
12
1
R3
113Ω
0.1µF
0.1µF
13
+
–
5
6
7
0.1µF
8
VIN (B)
C4
15pF
+
10µF
0.1µF
0.1µF
75Ω
75Ω
07686-051
–VS
VOUT (B)
Figure 43. Video Driver Schematic
U3
OP AMP
+
R6
475Ω
C5
47pF
OUT3
VOUT
C6
15pF
07686-049
R5
121Ω
In applications that require multiple video loads be driven
simultaneously, the ADA4856-3 can deliver. Figure 44 shows
the ADA4856-3 configured with triple video loads. Figure 45
shows the triple video load performance.
+VS
Figure 41. 20 MHz, 6-Pole Low-Pass Filter
75Ω
CABLE
0.1µF
75Ω
FOUR POLES
–VS
VOUT2
75Ω
0.1µF
+
TWO POLES
0
VOUT1
75Ω
75Ω CABLE
ADA4856-3
SIX POLES
10
75Ω
CABLE
75Ω
–
VIN
20
75Ω
0.1µF
The filter has a gain of approximately 18 dB, which is set by
three fixed gain of 2 stages, and a flat frequency response out to
14 MHz. This type of filter is commonly used at the output of a
video DAC as a reconstruction filter. The frequency response of
the filter is shown in Figure 42.
75Ω
75Ω
CABLE
VOUT3
10µF
75Ω
Figure 44. Video Driver Schematic for Triple Video Loads
6.5
–10
6.0
–20
RL = 150Ω
RL = 75Ω
RL = 50Ω
5.5
–40
–50
–60
1
10
100
200
5.0
4.5
4.0
3.5
FREQUENCY (MHz)
Figure 42. 20 MHz, Low-Pass Filter Frequency Response
VS = 5V
VOUT = 1V p-p
3.0
07686-053
MAGNITUDE (dB)
–30
07686-050
MAGNITUDE (dB)
10µF
07686-052
–
2.5
1
10
100
200
FREQUENCY (MHz)
Figure 45. Large Signal Frequency Response for Various Loads
Rev. 0 | Page 15 of 20
ADA4856-3
SINGLE-SUPPLY OPERATION
POWER DOWN
The ADA4856-3 can operate in single-supply applications.
Figure 46 shows the schematic for a single 5 V supply video
driver. Resistors R2 and R4 establish the midsupply reference.
Capacitor C2 is the bypass capacitor for the midsupply reference.
Capacitor C1 is the input coupling capacitor, and C6 is the output
coupling capacitor. Capacitor C5 prevents constant current from
being drawn through the internal gain set resistor. Resistor R3
sets the ac input impedance of the circuit.
The ADA4856-3 is equipped with a PD (power-down) pin for
all three amplifiers. This allows the user to reduce the quiescent
supply current when an amplifier is inactive. The power-down
threshold levels are derived from the voltage applied to the +VS
pin. When used in single-supply applications, this is especially
useful with conventional logic levels. The amplifier is enabled
when the voltage applied to the PD pin is greater than +VS − 1.25 V.
In a 5 V single-supply application, the typical threshold voltage
is +3.75 V, and in a 3.3 V dual-supply application, the typical
threshold voltage is +2 V. The amplifier is also enabled when the
PD pin is left floating (not connected). However, the amplifier is
powered down when the voltage on the PD pin is lower than 2.5 V
from +VS. If the PD pin is not used, it is best to connect it to the
positive supply
For more information on single-supply operation of op amps,
see “Avoiding Op-Amp Instability Problems In Single-Supply
Applications”, Analog Dialogue, Volume 35, Number 2, MarchMay, 2001, at www.analog.com.
+5V
R2
50kΩ
+5V
C2
1µF
C3
2.2µF
R4
50kΩ
C4
0.01µF
R3
1kΩ
Table 6. Power-Down Voltage Control
C6
220µF
VIN
C1
22µF
R1
50Ω
R5
75Ω
07686-035
Figure 46. AC-Coupled, Single-Supply Video Driver Schematic
In addition, the ADA4856-3 can be configured in dc-coupled,
single-supply operation. The common-mode input voltage
can go about 200 mV below ground, which makes it a true singlesupply part. However, in video applications, the black level is set
at 0 V, which means that the output of the amplifier must go to
the ground level as well. This part has a rail-to-rail output stage;
it can go as close as 100 mV from either rail. Figure 47 shows
the schematic for adding 50 mV dc offset to the input signal so
that the output is not clipped while still properly terminating
the input with 75 Ω.
5V
5V
C2
0.1µF
R1
3.74kΩ
VIN
U1
R3
75Ω
–VS
VOUT
R4
75Ω
ADA4856-3
07686-156
R2
76.8Ω
±2.5 V
3.3 V
>3.75 V
<2 V
>1.25 V
<0 V
>2.05 V
<1.3 V
LAYOUT CONSIDERATIONS
–VS
C1
10µF
5V
Not Active
Active
VOUT
R6
75Ω
ADA4856-3
C5
22µF
PD Pin
As is the case with all high speed applications, careful attention
to printed circuit board (PCB) layout details prevents associated
board parasitics from becoming problematic. Proper RF design
technique is mandatory. The PCB should have a ground plane
covering all unused portions of the component side of the
board to provide a low impedance return path. Removing the
ground plane on all layers from the area near the input and output
pins reduces stray capacitance. Locate termination resistors and
loads as close as possible to their respective inputs and outputs.
Keep input and output traces as far apart as possible to minimize
coupling (crosstalk) though the board. Adherence to microstrip
or stripline design techniques for long signal traces (greater than
about 1 inch) is recommended.
POWER SUPPLY BYPASSING
Careful attention must be paid to bypassing the power supply pins
of the ADA4856-3. Use high quality capacitors with low equivalent
series resistance (ESR), such as multilayer ceramic capacitors
(MLCCs), to minimize supply voltage ripple and power dissipation.
A large, usually tantalum, 10 μF to 47 μF capacitor located in
proximity to the ADA4856-3 is required to provide good
decoupling for lower frequency signals. In addition, locate 0.1 μF
MLCC decoupling capacitors as close to each of the power supply
pins as is physically possible, no more than 1/8 inch away. The
ground returns should terminate immediately into the ground
plane. Locating the bypass capacitor return close to the load
return minimizes ground loops and improves performance.
Figure 47. DC-Coupled Single Supply Video Driver Schematic
Rev. 0 | Page 16 of 20
ADA4856-3
OUTLINE DIMENSIONS
4.00
BSC SQ
12° MAX
1.00
0.85
0.80
0.65 BSC
TOP
VIEW
3.75
BSC SQ
0.75
0.60
0.50
(BOTTOM VIEW)
9
0.80 MAX
0.65 TYP
SEATING
PLANE
PIN 1
INDICATOR
1
2.25
2.10 SQ
1.95
8
5
4
0.25 MIN
1.95 BSC
0.05 MAX
0.02 NOM
0.35
0.30
0.25
16
13
12
0.20 REF
COPLANARITY
0.08
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
072808-A
PIN 1
INDICATOR
0.60 MAX
0.60 MAX
COMPLIANT TO JEDEC STANDARDS MO-220-VGGC
Figure 48.16-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
4 mm × 4 mm Body, Very Thin Quad
(CP-16-4)
Dimensions shown in millimeters
ORDERING GUIDE
Model
ADA4856-3YCPZ-R2 1
ADA4856-3YCPZ-R71
ADA4856-3YCPZ-RL1
1
Temperature Range
–40°C to +105°C
–40°C to +105°C
–40°C to +105°C
Package Description
16-Lead LFCSP_VQ
16-Lead LFCSP_VQ
16-Lead LFCSP_VQ
Z = RoHS Compliant Part.
Rev. 0 | Page 17 of 20
Package Option
CP-16-4
CP-16-4
CP-16-4
Ordering Quantity
250
1,500
5,000
ADA4856-3
NOTES
Rev. 0 | Page 18 of 20
ADA4856-3
NOTES
Rev. 0 | Page 19 of 20
ADA4856-3
NOTES
©2008 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D07686-0-10/08(0)
Rev. 0 | Page 20 of 20