AD8051/AD8052/AD8054
APPLICATION INFORMATION
OVERDRIVE RECOVERY
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.
V
S
= ±5V
G = +5
R
F
= 2kΩ
R
L
= 2kΩ
2.60
VOLTS
V
S
= 5V
G = +1
R
L
= 2kΩ
C
L
= 50pF
2.55
2.50
2.45
2.40
INPUT 1V/DIV
OUTPUT 2V/DIV
VOLTS
50mV
100ns
Figure 43. AD8051/AD8052 200 mV Step Response; C
L
= 50 pF
10000
V
S
= 5V
≤
30%
OVERSHOOT
CAPACITIVE LOAD (pF)
V/DIV AS SHOWN
100ns
01062-040
R
S
= 3Ω
1000
R
S
= 0Ω
Figure 41. Overdrive Recovery
DRIVING CAPACITIVE LOADS
Consider the AD8051/AD8052 in a closed-loop gain of +1 with
+V
S
= 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.
8
6
4
2
100
R
G
R
F
R
S
50Ω
C
L
V
OUT
10
V
IN
100mV
STEP
1
2
3
A
CL
(V/V)
4
5
6
Figure 44. AD8051/AD8052 Capacitive Load Drive vs. Closed-Loop Gain
1000
V
S
= 5V
≤
30%
OVERSHOOT
CAPACITIVE LOAD (pF)
R
S
= 10Ω
R
S
= 0Ω
100
R
G
V
IN
100mV
STEP
R
F
R
S
V
OUT
C
L
GAIN (dB)
0
–2
–4
–6
–8
–10
–12
0.1
50Ω
V
S
= 5V
G = +1
R
L
= 2kΩ
C
L
= 50pF
V
OUT
= 200mV p-p
1
10
FREQUENCY (MHz)
100
500
01062-041
1
2
3
A
CL
(V/V)
4
5
6
Figure 45. AD8054 Capacitive Load Drive vs. Closed-Loop Gain
Figure 42. AD8051/AD8052 Closed-Loop Frequency Response; C
L
= 50 pF
Rev. J | Page 17 of 24
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