EL5221C
Dual 12MHz Rail-to-Rail Input-Output Buffer
Driving Capacitive Loads
Power Supply Bypassing and Printed Circuit
Board Layout
The EL5221C can drive a wide range of capacitive
loads. As load capacitance increases, however, the -3dB
bandwidth of the device will decrease and the peaking
increase. The buffers drive 10pF loads in parallel with
10kΩ with just 1.5dB of peaking, and 100pF with 6.4dB
of peaking. If less peaking is desired in these applica-
tions, a small series resistor (usually between 5Ω and
50Ω) can be placed in series with the output. However,
this will obviously reduce the gain slightly. Another
method of reducing peaking is to add a "snubber" circuit
at the output. A snubber is a shunt load consisting of a
resistor in series with a capacitor. Values of 150Ω and
10nF are typical. The advantage of a snubber is that it
does not draw any DC load current or reduce the gain
The EL5221C can provide gain at high frequency. As
with any high frequency device, good printed circuit
board layout is necessary for optimum performance.
Ground plane construction is highly recommended, lead
lengths should be as short as possible, and the power
supply pins must be well bypassed to reduce the risk of
oscillation. For normal single supply operation, where
the VS- pin is connected to ground, a 0.1µF ceramic
capacitor should be placed from VS+ to pin to VS- pin. A
4.7µF tantalum capacitor should then be connected in
parallel, placed in the region of the buffer. One 4.7µF
capacitor may be used for multiple devices. This same
capacitor combination should be placed at each supply
pin to ground if split supplies are to be used.
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ELANTEC [ ELANTEC SEMICONDUCTOR ]
