2000 Apr 03
2
Philips Semiconductors
Product specication
Quad 2-input multiplexer; 3-state
74AHC257;
74AHCT257
FEATURES
ESD protection:
HBM EIA/JESD22-A114-A exceeds 2000 V
MM EIA/JESD22-A115-A exceeds 200 V
CDM EIA/JESD22-C101 exceeds 1000 V
Balanced propagation delays
All inputs have Schmitt-trigger actions
Non-inverting data path
Inputs accept voltages higher than VCC
For AHC only: operates with CMOS input levels
For AHCT only: operates with TTL input levels
Specified from 40 to +85 °C and 40 to +125 °C.
DESCRIPTION
The 74AHC/AHCT257 are high-speed Si-gate CMOS
devices and are pin compatible with Low power Schottky
TTL (LSTTL). They are specified in compliance with
JEDEC standard No. 7A.
The 74AHC/AHCT257 has four identical 2-input
multiplexers with 3-state outputs, which select 4 bits of
data from two sources and are controlled by a common
data select input (S).
The data inputs from source 0 (1I0 to 4I0) are selected
when input S is LOW and the data inputs from source 1
(1I1 to 4I1) are selected when S is HIGH. Data appears at
the outputs (1Y to 4Y) in true (non-inverting) form from the
selected inputs.
The 74AHC/AHCT257 is the logic implementation of a
4-pole 2-position switch, where the position of the switch is
determined by the logic levels applied to S. The outputs
are forced to a high impedance OFF-state when OE is
HIGH.
If OE is LOW then the logic equations for the outputs are:
1Y = 1I1 × S+1I0 × S;
2Y = 2I1 × S+2I0 × S;
3Y = 3I1 × S+3I0 × S;
4Y = 4I1 × S+4I0 × S.
The ‘257’ is identical to the ‘258’ but has non-inverting
(true) outputs.
QUICK REFERENCE DATA
GND = 0 V; Tamb =25 °C; tr =tf ≤ 3.0 ns.
Notes
1. CPD is used to determine the dynamic power dissipation (PD in W).
PD =CPD × VCC2 × fi + ∑ (CL × VCC2 × fo) where:
fi = input frequency in MHz;
fo = output frequency in MHz;
∑ (CL × VCC2 × fo) = sum of outputs;
CL = output load capacitance in pF;
VCC = supply voltage in Volts.
2. The condition is VI = GND to VCC.
SYMBOL
PARAMETER
CONDITIONS
TYPICAL
UNIT
AHC
AHCT
tPHL/tPLH
propagation delay
nl0,nI1 to nY
CL = 15 pF; VCC = 5 V
2.9
3.7
ns
StonY
CL = 15 pF; VCC = 5 V
3.5
5.1
ns
CI
input capacitance
VI =VCC or GND
3.0
pF
CO
output capacitance
4.0
pF
CPD
power dissipation
capacitance
CL = 50 pF; fi = 1 MHz; notes 1 and 2
4 outputs switching via input S
45
51
pF
1 output switching via input I
15
pF