11

FN7198.2

August 2, 2007

Unused Buffers

It is recommended that any unused buffer have the input tied

to the ground plane.

Driving Capacitive Loads

The EL5421 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 10k

Ω with just 1.5dB

of peaking, and 100pF with 6.4dB of peaking. If less peaking

is desired in these applications, a small series resistor

(usually between 5

Ω 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

150

Ω and 10nF are typical. The advantage of a snubber is

that it does not draw any DC load current or reduce the gain.

Power Supply Bypassing and Printed Circuit

Board Layout

The EL5421 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

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.

JEDEC JESD51-3 LOW EFFECTIVE THERMAL

CONDUCTIVITY TEST BOARD

0.6

0.4

0.3

0.2

0.1

0

0

255075

100

125

AMBIENT TEMPERATURE (°C)

85

486mW

θ

20

6°C

/W

M

SO

P1

0

0.5

FIGURE 26. PACKAGE POWER DISSIPATION vs AMBIENT

TEMPERATURE

EL5421