ADA4855-3 Analog Devices, ADA4855-3 Datasheet - Page 16

• Manufacturer Part Number: ADA4855-3
• Description: Single Supply, High Speed, Rail-to-Rail Output, Triple Op Amp
• Manufacturer: Analog Devices

Specifications of ADA4855-3

• Vcc-vee: 3V to 5.5V
• Packages: CSP
• -3db Bandwidth: 400MHz
• Slew Rate: 800V/µs
• Vos: 1mV
• Ib: 4.5µA
• # Opamps Per Pkg: 3
• Input Noise (nv/rthz): 6.5nV/rtHz

ADA4855-3
RGB VIDEO DRIVER
Figure 51 shows a typical RGB driver application using dual
supplies. The gain of the amplifier is set at +2, where R
1 kΩ. The amplifier inputs are terminated with shunt 75 Ω
resistors, and the outputs have series 75 Ω resistors for proper
video matching. In Figure 51, the PD pin is not shown connected
to any signal source for simplicity. If the power-down function
is not used, it is recommended that the PD pin be tied to the
positive supply or be left floating (not connected).
DRIVING MULTIPLE VIDEO LOADS
Each amplifier in the ADA4855-3 can drive up to three video
loads simultaneously, as shown in Figure 52. When driving
three video loads, the ADA4855-3 maintains its excellent
performance for 0.1 dB flatness and 3 dB bandwidth. Figure 53
shows the large signal frequency response of the ADA4855-3
with three different load configurations: 150 Ω, 75 Ω and 50 Ω.
V
IN
V
V
V
IN
IN
IN
(R)
(G)
(B)
CABLE
75Ω
75Ω
Figure 52. Video Driver Schematic for Triple Video Loads
1kΩ
R
G
PD
75Ω
1
2
3
4
75Ω
ADA4855-3
75Ω
ADA4855-3
+
–
16
5
Figure 51. RGB Video Driver
15
6
+V
–V
1kΩ
1kΩ
1kΩ
1kΩ
S
S
14
7
75Ω
75Ω
10µF
0.1µF
0.1µF
10µF
–V
–V
13
8
1kΩ
R
S
S
F
0.1µF
12
11
10
V
V
9
OUT
OUT
0.1µF
0.1µF
0.1µF
(B)
(R)
75Ω
75Ω
75Ω
1kΩ 1kΩ
+V
+V
0.1µF
CABLE
CABLE
CABLE
S
S
0.1µF
0.1µF
75Ω
75Ω
75Ω
75Ω
+
+
10µF
10µF
V
75Ω
75Ω
75Ω
F
OUT
= R
V
V
V
(G)
OUT
OUT
OUT
G
Rev. 0 | Page 16 of 20
=
1
2
3
PD (POWER-DOWN) PIN
The ADA4855-3 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 +V
this is especially useful with conventional logic levels. The
amplifier is enabled when the voltage applied to the PD pin is
greater than +V
voltage threshold is typically +3.75 V, and in a ±2.5 V dual-
supply application, the voltage threshold is typically +1.25 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 +V
pin is not used, it is best to connect it to the positive supply.
Table 7. Power-Down Voltage Control
PD Pin
Not Active
Active
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
1
Figure 53. Large Signal Frequency Response vs. Loads
V
G = 2
OUT
S
S
− 1.25 V. In a single-supply application, the
= 2V p-p
pin. When used in single-supply applications,
<2 V
5 V
>3.75 V
FREQUENCY (MHz)
10
±2.5 V
<0 V
R
R
R
>1.25 V
L
L
L
= 150Ω
= 75Ω
= 50Ω
100
S
. If the PD
3 V
<1 V
>1.75 V
200