AD811JR-REEL7 Analog Devices Inc, AD811JR-REEL7 Datasheet - Page 13

• Manufacturer Part Number: AD811JR-REEL7
• Description: IC OPAMP VIDEO HP 8-SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD811JR-REEL7

• Rohs Status: RoHS non-compliant
• Applications: Current Feedback
• Number Of Circuits: 1
• -3db Bandwidth: 140MHz
• Slew Rate: 2500 V/µs
• Current - Supply: 16.5mA
• Current - Output / Channel: 100mA
• Voltage - Supply, Single/dual (±): ±4.5 V ~ 18 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)

Driving Capacitive Loads
The feedback and gain resistor values in Table 3 result in very
flat closed-loop responses in applications where the load capaci-
tances are below 10 pF. Capacitances greater than this result in
increased peaking and overshoot, although not necessarily in a
sustained oscillation.
There are at least two very effective ways to compensate for this
effect. One way is to increase the magnitude of the feedback
resistor, which lowers the 3 dB frequency. The other method is
to include a small resistor in series with the output of the ampli-
fier to isolate it from the load capacitance. The results of these
two techniques are illustrated in Figure 39. Using a 1.5 kΩ
feedback resistor, the output ripple is less than 0.5 dB when
driving 100 pF. The main disadvantage of this method is that it
sacrifices a little bit of gain flatness for increased capacitive load
drive capability. With the second method, using a series resistor,
the loss of flatness does not occur.
V
Figure 38. Recommended Connection for Driving a Large Capacitive Load
IN
12
–3
–6
9
6
3
0
1
R
R
V
C
R
GAIN = +2
Figure 39. Performance Comparison of Two Methods
G
T
S
L
L
= ±15V
= 100pF
= 10kΩ
0.1µF
2
3
for Driving a Capacitive Load
–
+
AD811
FREQUENCY (MHz)
–V
+V
R
4
7
S
FB
S
10
R
R
0.1µF
FB
S
6
= 30Ω
= 649Ω
R
R
R
FB
S
S
C
= 0
(OPTIONAL)
L
= 1.5kΩ
100
R
L
V
OUT
Rev. E | Page 13 of 20
Figure 40 shows recommended resistor values for different load
capacitances. Refer again to Figure 39 for an example of the
results of this method. Note that it may be necessary to adjust
the gain setting resistor, R
results due to the divider formed by the series resistor, R
the load resistance.
Applications that require driving a large load capacitance at a
high slew rate are often limited by the output current available
from the driving amplifier. For example, an amplifier limited to
25 mA output current cannot drive a 500 pF load at a slew rate
greater than 50 V/µs. However, because of the AD811’s 100 mA
output current, a slew rate of 200 V/µs is achievable when driv-
ing the same 500 pF capacitor, as shown in Figure 41.
V
V
OUT
100
IN
Figure 41. Output Waveform of an AD811 Driving a 500 pF Load.
90
80
70
60
50
40
30
20
10
0
10
100
90
10
0%
Figure 40. Recommended Value of Series Resistor vs.
Gain = +2, R
2V
5V
the Amount of Capacitive Load
LOAD CAPACITANCE (pF)
FB
G
= 649 Ω, R
, to correct for the attenuation which
100
S
GAIN = +2
V
R
IS FOR FLATTEST
FREQUENCY RESPONSE
= 15 Ω, R
S
S
= ±15V
VALUE SPECIFIED
100ns
S
= 10 kΩ
1000
AD811
S
, and