Datasheet

ADA4860-1
Rev. 0 | Page 15 of 20
DRIVING CAPACITIVE LOADS
If driving loads with a capacitive component is desired, the best
frequency response is obtained by the addition of a small series
resistance, as shown in
Figure 53. Figure 54 shows the optimum
value for R
SERIES
vs. capacitive load. The test was performed with
a 50 MHz, 50% duty cycle pulse, with an amplitude of 200 mV p-p.
The criteria for R
SERIES
selection was based on maintaining
approximately 1 dB of peaking in small signal frequency
response. It is worth noting that the frequency response of the
circuit can be dominated by the passive roll-off of R
SERIES
and C
L
.
05709-052
V
IN
R
L
C
L
R
SERIES
R
F
750Ω
ADA4860-1
Figure 53. Driving Capacitive Loads
14
12
10
8
6
4
2
0
05
040302010
SERIES RESISTANCE (Ω)
CAPACITIVE LOAD (pF)
05709-060
Figure 54. Recommended R
SERIES
vs. Capacitive Load
POWER DOWN PIN
The ADA4860-1 is equipped with a power-down function.
The POWER DOWN pin allows the user to reduce the quiescent
supply current when the amplifier is not being used. The
power-down threshold levels are derived from the voltage
applied to the −V
S
pin. When used in single-supply applications,
this is especially useful with conventional logic levels. The
amplifier is powered down when the voltage applied to the
POWER DOWN pin is greater than (−V
S
+ 0.5 V). The
amplifier is enabled whenever the POWER DOWN pin is left
open, or the voltage on the POWER DOWN pin is less than
(−V
S
+ 0.5 V). If the POWER DOWN pin is not used, it should
be connected to the negative supply.
VIDEO AMPLIFIER
With low differential gain and phase errors and wide 0.1 dB
flatness, the ADA4860-1 is an ideal solution for consumer and
professional video applications.
Figure 55 shows a typical video
driver set for a noninverting gain of +2, where R
F
= R
G
= 499 Ω.
The video amplifier input is terminated into a shunt 75 Ω resistor.
At the output, the amplifier has a series 75 Ω resistor for
impedance matching to the video load.
05709-038
75Ω
CABLE
75Ω
75Ω
V
OU
T
–V
S
+V
S
V
IN
0.1µF
0.1µF
10µF
10µF
75Ω
CABLE
75Ω
ADA4860-1
+
–
R
F
+
+
R
G
Figure 55. Video Driver Schematic
SINGLE-SUPPLY OPERATION
Single-supply operation can present certain challenges for the
designer. For a detailed explanation on op amp single-supply
operation, see Application Note
AN-581.