ADA4858-3 Datasheet, PDF (14/16 Pages) Analog Devices – Single-Supply, High Speed, Triple Op Amp with Charge Pump

ADA4858-3
APPLICATIONS INFORMATION
GAIN CONFIGURATIONS
The ADA4858-3 is a single-supply, high speed, voltage feedback
amplifier. Table 5 provides a convenient reference for quickly
determining the feedback and gain set resistor values and band-
width for common gain configurations.
Table 5. Recommended Values and Frequency Performance¹
Gain
1
RF (Ω)
402
RG (Ω)
N/A
Small Signal
−3 dB BW (MHz)
600
Large Signal 0.1 dB
Flatness (MHz)
88
2
249 249 450
95
5
200 40
160
35
1 _{Conditions: VS = 5 V, TA = 25°C, RL = 150 Ω.}
Figure 38 and Figure 39 show the typical noninverting and
inverting configurations and the recommended bypass
capacitor values.
+V_S ^10µF
V_IN
+
0.1µF
ADA4858-3
–
V_OUT
R_F
R_G
Figure 38. Noninverting Gain Configuration
R_{F +VS 10µF}
V_IN
R_G
0.1µF
–
ADA4858-3
+
V_OUT
Figure 39. Inverting Gain Configuration
DC-COUPLED VIDEO SIGNAL
The ADA4858-3 does not have a rail-to-rail output stage. The
output can be within 1 V of the rails. Having a charge pump
on-board that can provide −3 V on a +5 V supply and −2 V on
+3.3 V supply makes this part excellent for video applications. In
dc-coupled applications, the black color has a 0 V voltage reference.
This means that the output voltage should be able to reach 0 V,
which is feasible with the presence of the charge pump. Figure 40
shows the schematic of a dc-coupled, single-supply application.
It is similar to dual-supply application, where the input is properly
terminated with a 50 Ω resistor to ground. The amplifier itself is
set at a gain of 2 to account for the input termination loss.
The choice of RF and RG should be carefully considered for
maximum flatness vs. power dissipation trade-off. In this case,
the flatness is over 90 MHz, which is more than the high
definition video requirement.
5V
C1
10µF
C2
0.1µF
V_IN
R1
75Ω
+
U1
ADA4858-3
–
R4
75Ω
V_OUT
R5
75Ω
R2
249Ω
R3
249Ω
–V_S
Figure 40. DC-Coupled, Single-Supply Schematic
MULTIPLE VIDEO DRIVER
In applications requiring that multiple video loads be driven
simultaneously, the ADA4858-3 can deliver 5 V supply operation.
Figure 41 shows the ADA4858-3 configured with two video
loads, and Figure 42 shows the two video load performances.
R_F
249Ω
+V_S 10µF
R_G
249Ω
75Ω
CABLE
V_IN
0.1µF
–
ADA4858-3
+
75Ω
75Ω
75Ω ^CABLE
75Ω
75Ω ^CABLE
V_OUT1
75Ω
V_OUT2
75Ω
Figure 41. Video Driver Schematic for Two Video Loads
6.5
R_L = 150Ω
6.0
5.5
R_L = 75Ω
5.0
4.5
4.0
3.5
V_S = 5V
3.0 ^RF ^{= 301Ω}
G=2
V_OUT = 2V p-p
2.5
1
10
100
FREQUENCY (MHz)
1000
Figure 42. Large Signal Frequency Response for Various Loads
Rev. 0 | Page 14 of 16