HCF4097B
7/10
APPLICATION INFORMATION
In applications where separate power sources are
used to drive V
DD
and the signal inputs, the V
DD
current capability should exceed V
DD
/R
L
(R
L
=
effective external load). This provision avoids
permanent current flow or clamp action on the
V
DD
supply when power is applied or removed
from the HCF4097B.
When switching from one address to another,
some of the ON periods of the channels of the
multiplexers will overlap momentarily, which may
be objectionable in certain applications. Also,
when a channel is turned ON or OFF by an
address input, there is a momentary conductive
path from the channel to V
SS
, which will dump
some charge from any capacitor connected to the
input or output of the channel. The inhibit input
turning on a channel will similarly dump some
charge to V
SS
.
The amount of charge dumped is mostly a
function of the signal level above V
SS
. Typically, at
V
DD
- V
SS
= 10V, a 100 pF capacitor connected to
the input or output of the channel will lose 3-4% of
its voltage at the moment the channel turns ON or
OFF. This loss of voltage is essentially
independent of the address or inhibit signal
transition time, if the transition time is less than 1-
2 ms. When the inhibit signal turns a channel off,
there is no change dumping of V
SS
. Rather, there
is a slight rise in the channel voltage level (65 mV
typ.) due to the capacitance coupling from inhibit
input to channel input or output. Address input
also couple some voltage steps onto the channel
signal levels.
In certain applications, the external load-resistor
current may include both V
DD
and signal line
components. To avoid drawing V
DD
current when
switch current flows into the transmission gate
inputs, the voltage drop across the bidirectional
switch must not exceed 0.8V (calculated from R
ON
values shown in ELECTRICAL
CHARACTERISTICS CHART). No V
DD
current
will flow through R
L
if the switch current flows into
terminal 1 on the HCF4097B.
TEST CIRCUIT
C
L
= 50pF or equivalent (includes jig and probe capacitance)
R
L
= 200K
Ω
R
T
= Z
OUT
of pulse generator (typically 50
Ω
)
Obsolete Product(s) - Obsolete Product(s)
