74AHC_AHCT257_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 9 May 2008 9 of 16
NXP Semiconductors
74AHC257; 74AHCT257
Quad 2-input multiplexer; 3-state
[1] Typical values are measured at nominal supply voltage (V
CC
= 3.3 V and V
CC
= 5.0 V).
[2] t
pd
is the same as t
PLH
and t
PHL
.
[3] t
en
is the same as t
PZL
and t
PZH
.
[4] t
dis
is the same as t
PLZ
and t
PHZ
.
[5] C
PD
is used to determine the dynamic power dissipation (P
D
in µW).
P
D
=C
PD
× V
CC
2
× f
i
× N+Σ(C
L
× V
CC
2
× f
o
) where:
f
i
= input frequency in MHz;
f
o
= output frequency in MHz;
C
L
= output load capacitance in pF;
V
CC
= supply voltage in V;
N = number of inputs switching;
Σ(C
L
× V
CC
2
× f
o
) = sum of the outputs.
74AHCT257; V
CC
= 4.5 V to 5.5 V
t
pd
propagation
delay
nI0, nI1 to nY; see Figure 6
[2]
C
L
= 15 pF - 3.7 6.5 1.0 8.0 1.0 9.0 ns
C
L
= 50 pF - 4.9 8.5 1.0 10.0 1.0 11.0 ns
S to nY; see
Figure 6
[2]
C
L
= 15 pF - 5.1 9.0 1.0 10.5 1.0 11.5 ns
C
L
= 50 pF - 6.4 10.5 1.0 12.5 1.0 13.5 ns
t
en
enable time OE to nY; see Figure 7
[3]
C
L
= 15 pF - 3.9 8.0 1.0 9.0 1.0 10.0 ns
C
L
= 50 pF - 5.1 10.0 1.0 11.0 1.0 12.0 ns
t
dis
disable time OE to nY; see Figure 7
[4]
C
L
= 15 pF - 4.5 7.5 1.0 8.0 1.0 8.5 ns
C
L
= 50 pF - 6.5 9.5 1.0 10.5 1.0 11.5 ns
C
PD
power
dissipation
capacitance
f
i
= 1 MHz; V
I
= GND to V
CC
[5]
4 outputs switching via
input S
-51- - - - -pF
1 output switching via
input I
-15- - - - -pF
Table 7. Dynamic characteristics
…continued
Voltages are referenced to GND (ground = 0 V); for test circuit see Figure 8.
Symbol Parameter Conditions 25 °C −40 °C to +85 °C −40 °C to +125 °C Unit
Min Typ
[1]
Max Min Max Min Max
