LMH6574 Datasheet, PDF (19/27 Pages) National Semiconductor (TI) – 4:1 High Speed Video Multiplexer

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LMH6574
SNCS103D – NOVEMBER 2004 – REVISED DECEMBER 2014
Typical Application (continued)
7.2.6 Driving Capacitive Loads
Capacitive output loading applications will benefit from the use of a series output resistor R_OUT. Figure 34 shows
the use of a series output resistor, R_OUT, to stabilize the amplifier output under capacitive loading. Capacitive
loads of 5 to 120 pF are the most critical, causing ringing, frequency response peaking and possible oscillation.
Figure 35 provides a recommended value for selecting a series output resistor for mitigating capacitive loads.
The values suggested in the charts are selected for 0.5 dB or less of peaking in the frequency response. This
gives a good compromise between settling time and bandwidth. For applications where maximum frequency
response is needed and some peaking is tolerable, the value of R_OUT can be reduced slightly from the
recommended values.
R_OUT
45:
V_OUT
LMH6574
C_L
10 pF
R_L
1 k:
Figure 34. Decoupling Capacitive Loads
90
80
70
60
50
40
30
20
10
0
1
V_S = ±5V
LOAD = 1 k:|| C_L
10
100
CAPACTIVE LOAD (pF)
1000
2
C_L = 8.6 pF, R_OUT = 63:
0
C_L = 18 pF, R_OUT = 48:
-2
C_L = 56 pF, R_OUT = 24:
-4
C_L = 100 pF, R_OUT = 19:
-6 _{VOUT = 1 VPP}
C_L || 1 k:
-8 _{VS = ±5V}
A_V = 2 (V/V)
-10
1
10
100
FREQUENCY (MHz)
1000
Figure 35. Suggested R_OUT vs. Capacitive Load
Figure 36. Frequency Response vs. Capacitive Load
7.2.7 ESD Protection
The LMH6574 is protected against electrostatic discharge (ESD) on all pins. The LMH6574 will survive 2000-V
Human Body model and 200-V Machine model events. Under normal operation the ESD diodes have no effect
on circuit performance. There are occasions, however, when the ESD diodes will be evident. If the LMH6574 is
driven by a large signal while the device is powered down the ESD diodes will conduct . The current that flows
through the ESD diodes will either exit the chip through the supply pins or will flow through the device, hence it is
possible to power up a chip with a large signal applied to the input pins. Using the shutdown mode is one way to
conserve power and still prevent unexpected operation.
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