
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
resistance. These switches open for VEN = Low. This allows
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
F to 1F) 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
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
Test Circuits and Waveforms TA = 25oC, VSUPPLY = ±15V, VAH = 2.4V, VAL = 0.8V, Unless Otherwise Specified
50ns/DIV.
1V/DIV.
5V/DIV.
S4 ON
S1 ON
VA INPUT
OUTPUT
+
-
HA-2541
14
BUFFERED
CH2
75
7
CH3
75
5
75
CH4
12
CH1
75
2
18
16
20pF(NOTE)
OUTPUT
HA-524
NOTE: Capacitor value may be selected to optimize AC performance.
FIGURE 5.
HI-524