AD8051/AD8052/AD8054
APPLICATION INFORMATION
OVERDRIVE RECOVERY
V
= 5V
S
Overdrive of an amplifier occurs when the output and/or input
range is exceeded. The amplifier must recover from this over-
drive condition. As shown in Figure 41, the AD8051/AD8052/
AD8054 recover within 60 ns from negative overdrive and
within 45 ns from positive overdrive.
G = +1
R
= 2kΩ
L
L
C
= 50pF
2.60
2.55
2.50
2.45
V
= ±5V
S
2.40
G = +5
INPUT 1V/DIV
OUTPUT 2V/DIV
R
R
= 2kΩ
= 2kΩ
F
L
100ns
50mV
Figure 43. AD8051/AD8052 200 mV Step Response; CL = 50 pF
10000
1000
100
10
V
= 5V
S
≤ 30%
OVERSHOOT
R
= 3Ω
S
100ns
V/DIV AS SHOWN
R
= 0Ω
S
Figure 41. Overdrive Recovery
DRIVING CAPACITIVE LOADS
Consider the AD8051/AD8052 in a closed-loop gain of +1 with
+VS = 5 V and a load of 2 kΩ in parallel with 50 pF. Figure 42
and Figure 43 show their frequency and time domain responses,
respectively, to a small-signal excitation. The capacitive load
drive of the AD8051/AD8052/AD8054 can be increased by
adding a low value resistor in series with the load. Figure 44
and Figure 45 show the effect of a series resistor on the capaci-
tive drive for varying voltage gains. As the closed-loop gain is
increased, the larger phase margin allows for larger capacitive
loads with less peaking. Adding a series resistor with lower
closed-loop gains accomplishes the same effect. For large
capacitive loads, the frequency response of the amplifier is
dominated by the roll-off of the series resistor and the load
capacitance.
R
R
F
G
R
S
V
IN
V
OUT
100mV
STEP
C
L
50Ω
1
1
2
3
4
5
6
A
(V/V)
CL
Figure 44. AD8051/AD8052 Capacitive Load Drive vs. Closed-Loop Gain
1000
V
= 5V
S
≤ 30%
OVERSHOOT
R
= 10Ω
S
8
R = 0Ω
S
6
4
100
R
R
F
G
2
R
S
V
IN
V
0
OUT
100mV
STEP
C
L
50Ω
–2
–4
10
V
= 5V
1
2
3
4
5
6
S
–6
–8
G = +1
A
(V/V)
CL
R
C
= 2kΩ
= 50pF
L
L
Figure 45. AD8054 Capacitive Load Drive vs. Closed-Loop Gain
V
= 200mV p-p
OUT
–10
–12
0.1
1
10
100
500
FREQUENCY (MHz)
Figure 42. AD8051/AD8052 Closed-Loop Frequency Response; CL = 50 pF
Rev. H | Page 17 of 24
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