Philips Semiconductors

Product specification

74ALS251

8-input multiplexer (3-State)

2

1991 Feb 08

853–1377 01670

FEATURES

DESCRIPTION

The 74ALS251 is a logic implementation of a single 8-position

switch with the switch position controlled by the state of three select

(S0, S1, S2) inputs. True (Y) and complementary (Y) outputs are

both provided.

The output enable (OE) is active Low. When OE is High, both

outputs are in High impedance state, allowing multiple connections

to a common bus without driving nor loading the bus significantly.

When the outputs of more than one device are tied together, the

user must ensure that there is no overlap in the active-Low portion

of the output enable voltages in order to avoid high currents that

could exceed the maximum current rating.

TYPE

TYPICAL

PROPAGATION DELAY

TYPICAL

SUPPLY CURRENT

(TOTAL)

74ALS251

7.0ns

7.5mA

PIN CONFIGURATION

16

15

14

13

12

11

10

7

6

5

4

3

2

1

OE

I7

S0

S1

I6

I4

I5

I3

I2

Y

I1

I0

Y

9

8

GND

S2

SC00066

ORDERING INFORMATION

ORDER CODE

DESCRIPTION

COMMERCIAL RANGE

DRAWING

NUMBER

16-pin plastic DIP

74ALS251N

SOT38-4

16-pin plastic SO

74ALS251D

SOT109-1

INPUT AND OUTPUT LOADING AND FAN-OUT TABLE

PINS

DESCRIPTION

74ALS (U.L.)

HIGH/LOW

LOAD VALUE

HIGH/LOW

I0 – I7

Data inputs

1.0/1.0

20

µA/0.1mA

S0 – S2

Select inputs

1.0/1.0

20

µA/0.1mA

OE

Output Enable input (active-Low)

1.0/1.0

20

µA/0.1mA

Y, Y

Data outputs

130/240

2.5mA/24mA

NOTE:

One (1.0) ALS unit load is defined as: 20

µA in the High state and 0.1mA in the Low state.

LOGIC SYMBOL

GND = Pin 8

SC00067

9

7

S2

OE

4

3

2

1

15

14

13

I0

I1

I2

I3

I4

I5

I6

YY

56

12

I7

10

S1

11

S0

IEC/IEEE SYMBOL

SC00068

MUX

7

11

5

6

0

G

0

7

10

2

9

4

3

2

1

15

14

13

12

EN