Datasheet AD8051, AD8052, AD8054 (Analog Devices) - 17

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Data Sheet AD8051/ AD8052/ AD8054 APPLICATIONS INFORMATION OVERDRIVE RECOVERY VS = 5V
Overdrive of an amplifier occurs when the output and/or input
G = +1 R
range is exceeded. The amplifier must recover from this over-
L = 2kΩ CL = 50pF
drive condition. As shown in Figure 41, the AD8051/AD8052/
2.60
AD8054 recover within 60 ns from negative overdrive and
2.55 S
within 45 ns from positive overdrive.
T L 2.50 VO 2.45 VS = ±5V 2.40 G = +5 INPUT 1V/DIV RF = 2kΩ RL = 2kΩ OUTPUT 2V/DIV
2
50mV 100ns
-04 62 10
S
0
T L
Figure 43. AD8051/AD8052 200 mV Step Response; CL = 50 pF
VO 10000 VS = 5V ≤ 30% OVERSHOOT
0
RS = 3Ω V/DIV AS SHOWN 100ns
04 2-
) 1000
06
F
01
p
Figure 41. Overdrive Recovery
R D ( S = 0Ω A O DRIVING CAPACITIVE LOADS L E 100 IV T
Consider the AD8051/AD8052 in a closed-loop gain of +1 with
ACI R R G F
+V
P
S = 5 V and a load of 2 kΩ in parallel with 50 pF. Figure 42
CA RS V
and Figure 43 show their frequency and time domain responses,
10 IN VOUT 100mV C
respectively, to a small-signal excitation. The capacitive load
L STEP 50Ω
drive of the AD8051/AD8052/AD8054 can be increased by adding a low value resistor in series with the load. Figure 44
1 1 2 3 4 5 6
43 0 2- and Figure 45 show the effect of a series resistor on the capaci-
ACL (V/V)
06 01 tive drive for varying voltage gains. As the closed-loop gain is Figure 44. AD8051/AD8052 Capacitive Load Drive vs. Closed-Loop Gain increased, the larger phase margin allows for larger capacitive loads with less peaking. Adding a series resistor with lower
1000
closed-loop gains accomplishes the same effect. For large
VS = 5V
capacitive loads, the frequency response of the amplifier is
≤ 30% OVERSHOOT
dominated by the roll-off of the series resistor and the load
)
capacitance.
F RS = 10Ω (p 8 AD R O S = 0Ω L 6 E 100 IV T 4 CI A R R G F 2 CAP R ) S V 0 IN B VOUT d 100mV ( CL –2 STEP IN 50Ω A G –4 10
4
VS = 5V 1 2 3 4 5 6
04
–6
2-
G = +1 ACL (V/V)
06
R
01
–8 L = 2kΩ C
Figure 45. AD8054 Capacitive Load Drive vs. Closed-Loop Gain
L = 50pF –10 VOUT = 200mV p-p –12
41
0.1 1 10 100 500
0 2-
FREQUENCY (MHz)
106 0 Figure 42. AD8051/AD8052 Closed-Loop Frequency Response; CL = 50 pF Rev. K | Page 17 of 24 Document Outline FEATURES APPLICATIONS PIN CONNECTIONS (TOP VIEWS) GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE MAXIMUM POWER DISSIPATION ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION CIRCUIT DESCRIPTION APPLICATION INFORMATION OVERDRIVE RECOVERY DRIVING CAPACITIVE LOADS LAYOUT CONSIDERATIONS ACTIVE FILTERS ANALOG-TO-DIGITAL AND DIGITAL-TO-ANALOG APPLICATIONS SYNC STRIPPER SINGLE-SUPPLY COMPOSITE VIDEO LINE DRIVER OUTLINE DIMENSIONS ORDERING GUIDE