PDU138
APPLICATION NOTES
ADDRESS UPDATE
The PDU138 is a memory device. As such,
special precautions must be taken when
changing the delay address in order to prevent
spurious output signals. The timing restrictions
are shown in Figure 1.
After the last signal edge to be delayed has
appeared on the OUT pin, a minimum time, T
OAX
,
is required before the address lines can change.
This time is given by the following relation:
T
OAX
= max { (A
i
- A
i-1
) * T
INC
, 0 }
where A
i-1
and A
i
are the old and new address
codes, respectively. Violation of this constraint
may, depending on the history of the input signal,
cause spurious signals to appear on the OUT pin.
The possibility of spurious signals persists until
the required T
OAX
has elapsed.
A similar situation occurs when using the EN/
signal to disable the output while IN is active. In
this case, the unit must be held in the disabled
state until the device is able to “clear” itself. This
is achieved by holding the EN/ signal high and the
IN signal low for a time given by:
T
DISH
= A
i
* T
INC
Violation of this constraint may, depending on the
history of the input signal, cause spurious signals
to appear on the OUT pin. The possibility of
spurious signals persists until the required T
DISH
has elapsed.
INPUT RESTRICTIONS
There are three types of restrictions on input
pulse width and period listed in the
AC
Characteristics
table. The
recommended
conditions are those for which the delay tolerance
specifications and monotonicity are guaranteed.
The
suggested
conditions are those for which
signals will propagate through the unit without
significant distortion. The
absolute
conditions
are those for which the unit will produce some
type of output for a given input.
When operating the unit between the
recommended and absolute conditions, the
delays may deviate from their values at low
frequency. However, these deviations will remain
constant from pulse to pulse if the input pulse
width and period remain fixed. In other words,
the delay of the unit exhibits frequency and pulse
width dependence when operated beyond the
recommended conditions. Please consult the
technical staff at Data Delay Devices if your
application has specific high-frequency
requirements.
Please note that the increment tolerances listed
represent a design goal. Although most delay
increments will fall within tolerance, they are not
guaranteed throughout the address range of the
unit. Monotonicity is, however, guaranteed over
all addresses.
A2-A0
T
AENS
EN/
T
ENIS
IN
TD
A
OUT
A
i-1
T
OAX
T
AIS
A
i
PW
IN
T
DISH
PW
OU
T
DISO
Figure 1: Timing Diagram
Doc #02004
5/6/02
DATA DELAY DEVICES, INC.
Tel: 973-773-2299
Fax: 973-773-9672
http://www.datadelay.com
2
DATADELAY [ DATA DELAY DEVICES, INC. ]
