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ADA4862-3YRZ-RL

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
ADA4862-3
Rev. A | Page 12 of 16
Option 2
Another option exists for running the ADA4862-3 as a unity-
gain 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. Frequency and transient response are
shown in
Figure 35 and Figure 36.
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
G
G
F
i
G
F
i
O
R
RR
V
R
R
VV
(1)
which simplifies to V
O
= V
i
.
0.01μF
0.01μF
V
IN
R
T
V
OUT
+V
S
–V
S
GAIN OF +1
05600-030
10μF
10μF
R
F
R
G
Figure 34. Unity Gain of Option 2
1
–7
0.1
1000
FREQUENCY (MHz)
GAIN (dB)
1 10 100
0
–1
–2
–3
–4
–5
–6
G = +1
R
L
= 150Ω
05600-027
Figure 35. Frequency Response of Option 2
05600-039
G = +1
V
S
= ±5V
R
L
= 150Ω
TIME = 2ns/DIV
200
OUTPUT VOLTAGE (mV)
150
100
50
0
–50
–100
–150
–200
Figure 36. Small Signals Transient Response of Option 2
0.01μF
0.01μF
V
IN
R
T
V
OUT
+V
S
–V
S
GAIN OF –1
05600-031
10μF
10μF
Figure 37. Inverting Configuration (G = −1)
2.0
–2.0
OUTPUT VOLTAGE (V)
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
C
L
= 9pF
C
L
= 6pF
C
L
= 4pF
G = –1
R
L
= 150Ω
V
OUT
= 2V p-p
V
S
= ±5V
TIME = 5ns/DIV
05600-017
Figure 38. Large Signal Transient Response for Various Capacitor Loads
ADA4862-3
Rev. A | Page 13 of 16
VIDEO LINE DRIVER
The ADA4862-3 was designed to excel in video driver
applications.
Figure 39 shows a typical schematic for a video
driver operating on a bipolar supplies.
75Ω
CABLE
75Ω
75Ω
V
OUT
–V
S
+V
S
V
IN
0.1μF
0.1μF
10μF
10μF
75Ω
CABLE
75Ω
05600-033
ADA4862-3
+
–
Figure 39. Video Driver Schematic
In applications that require two video loads be driven
simultaneously, the ADA4862-3 can deliver.
Figure 40 shows
the ADA4862-3 configured with dual video loads.
Figure 41
shows the dual video load performance.
75Ω
CABLE
75Ω
CABLE
75Ω
75Ω
75Ω
75Ω
V
OUT
2
V
OUT
1
–V
S
+V
S
V
IN
0.1μF
0.1μF
10μF
10μF
75Ω
CABLE
75Ω
05600-034
+
2
1
8
7
6
–
Figure 40. Video Driver Schematic for Two Video Loads
8
0
0.1
1000
FREQUENCY (MHz)
CLOSED-LOOP GAIN (dB)
1 10 100
7
6
5
4
3
2
1
G = +2
R
L
= 75Ω
C
L
= 4pF
V
OUT
= 2V p-p
V
S
= ±5V
V
S
= +5V
05600-008
Figure 41. Large Signal Frequency Response for Various Supplies, R
L
= 75 Ω
SINGLE-SUPPLY OPERATION
The ADA4862-3 can also operate in single-supply applications.
Figure 42 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 circuits ac input impedance.
For more information on single-supply operation of op amps,
see
www.analog.com/library/analogDialogue/archives/35-
02/avoiding/
.
C2
1μF
R2
50kΩ
R4
50kΩ
R3
1kΩ
C1
22μF
R1
50Ω
C6
220μF
R5
75Ω
R6
75Ω
C5
22μF
ADA4862-3
+5V
05600-035
V
OUT
V
IN
–V
S
C3
2.2μF
C4
0.01μF
+5V
Figure 42. Single-Supply Video Driver Schematic
POWER DOWN
The ADA4862-3 is equipped with an independent Power Down
pin for each amplifier allowing the user to reduce the supply
current when an amplifier is inactive. The voltage applied to the
−V
S
pin is the logic reference, making single-supply applications
useful with conventional logic levels. In a typical 5 V single-
supply application, the −V
S
pin is connected to analog ground.
The amplifiers are powered down when applied logic levels are
greater than −V
S
+ 1 V. The amplifiers are enabled whenever the
disable pins are left either floating (disconnected) or the
applied logic levels are lower than 1 V above −V
S
.
ADA4862-3
Rev. A | Page 14 of 16
LAYOUT CONSIDERATIONS
As is the case with all high speed applications, careful attention
to printed circuit board 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. Termination resistors and
loads should be located as close as possible to their respective
inputs and outputs. Input and output traces should be kept 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 ADA4862-3. High quality capacitors with low
equivalent series resistance (ESR), such as multilayer ceramic
capacitors (MLCCs), should be used to minimize supply voltage
ripple and power dissipation. A large, usually tantalum, 10 μF to
47 μF capacitor located in proximity to the ADA4862-3 is
required to provide good decoupling for lower frequency
signals. In addition, 0.1 μF MLCC decoupling capacitors should
be located 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.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

ADA4862-3YRZ-RL

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Buy ADA4862-3YRZ-RL
Manufacturer:
Analog Devices Inc.
Description:
High Speed Operational Amplifiers LC Current Feedback RR Triple
Lifecycle:
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