5

Application Information

Often it is desirable to buffer the Hl-524 output, to avoid

loading errors due to the channel “ON” resistance:

The buffer amplifier should offer sufficient bandwidth and

slew rate to avoid degradation of the anticipated signals. For

video switching, the HA-5033 and HA-2542 offer good

performance plus

±100mA output current for driving coaxial

cables. For general wideband applications, the HA-2541

offers the convenience of unity gain stability plus 90ns

settling (to

±0.1%) and ±10V output swing. Also, the Hl-524

includes a feedback resistance for use with the HA-2541.

This resistance matches and tracks the channel “ON”

resistance, to minimize offset voltage due to the buffer's bias

currents.

Note that the on-chip feedback element between pins 16

and 18 includes two switches in series, to simulate a channel

two or more Hl-524s to operate into one HA-2541, with their

feedback elements connected in parallel. Thus, only the

selected multiplexer provides feedback, and the amplifier

remains stable.

All Hl-524 pins labeled ‘SlG GND’ (pins 3, 4, 6, 13, 15)

should be externally connected to signal ground for best

crosstalk performance.

Bypass capacitors (0.1

µF to 1µF) are recommended from

each HI-524 supply pin to power ground (pins 1 and 17 to

pin 8). Locate the buffer amplifier near the Hl-524 so the two

capacitors may bypass both devices.

If an analog input 1V or greater is present when supplies are

off, a low resistance is seen from that input to a supply line.

(For example, the resistance is approximately 160

Ω for an

input of -3V.) Current flow may be blocked by a diode in

each supply line, or limited by a resistor in series with each

channel. The best solution, of course, is to arrange that no

digital or analog inputs are present when the power supplies

are off.

FIGURE 4. ACCESS TIME WAVEFORMS

50ns/DIV.

1V/DIV.

5V/DIV.

OUTPUT

+

-

HA-2541

14

BUFFERED

CH2

75

Ω

7

CH3

75

Ω

5

75

Ω

CH4

12

CH1

75

Ω

2

18

16

20pF(NOTE)

OUTPUT

HA-524

NOTE: Capacitor value may be selected to optimize AC performance.

FIGURE 5.

HI-524