Datasheet

September 1993 22
Philips Semiconductors Product specification
Programmable delay timer with oscillator 74HC/HCT5555
Minimum Output Pulse Width
The minimum output pulse width is
determined by the minimum clock
pulse width, plus the maximum
propagation delay of A, B to Q. The
rising edge of Q is dominated by the
A, B to Q propagation delay, while the
falling edge of Q is dominated by RS
to Q propagation delay. These
propagation delays are not equal. The
RS to Q propagation delay is some
what longer, resulting in inaccurate
outputs for extremely short pulses.
The propagation delays are listed in
the section 'AC Characteristics'. With
these numbers it is possible to
calculate the maximum deviation (an
example is shown in Fig.16).
Figure 16 is valid for an external clock
where the trigger is synchronized to
the falling edge of the clock only. The
graph shows that the minimum
programmed pulse width of 100 ns is:
• minimum of 4% too long
• typically 7% too long
• maximum of 10% too long.
SYNCHRONIZATION LIMITS
NUMBER OF STAGES SELECTED CLOCK FREQUENCY (TYPICAL)
1 18 MHz
2 14 MHz
3 11 MHz
4 9.6 MHz
5 8.3 MHz
6 7.3 MHz
7 6.6 MHz
8 6 MHz
..
17 3.2 MHz
18 3.0 MHz
19 2.9 MHz
20 2.8 MHz
21 2.7 MHz
22 2.6 MHz
23 2.5 MHz
24 2.4 MHz