© 1999 Fairchild Semiconductor Corporation

DS500043

www.fairchildsemi.com

August 1997

Revised December 1999

FST3125

Quad Bus Switch

General Description

The Fairchild Switch FST3125 provides four high-speed

CMOS TTL-compatible bus switches. The low on resis-

tance of the switch allows inputs to be connected to out-

puts without adding propagation delay or generating

additional ground bounce noise.

The device is organized as four 1-bit switches with sepa-

rate OE inputs. When OE is LOW, the switch is ON and

Port A is connected to Port B. When OE is HIGH, the

switch is OPEN and a high-impedance state exists

between the two ports.

Features

s 4

Ω switch connection between two ports.

s Minimal propagation delay through the switch.

s Zero bounce in flow-through mode.

s Control inputs compatible with TTL level.

Ordering Code:

Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.

Logic Diagram

Pin Descriptions

Connection Diagrams

Pin Assignment for SOIC and TSSOP

Pin Assignment for QSOP

Truth Table

Order Number

Package Number

Package Description

FST3125M

M14A

14-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-120, 0.150 Narrow

FST3125QSC

MQA16

16-Lead Quarter Size Outline Package (QSOP), JEDEC MO-137, 0.150 Wide

FST3125MTC

MTC14

14-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide

Pin Name

Description

Bus Switch Enables

1A, 2A, 3A, 4A

Bus A

1B, 2B, 3B, 4B

Bus B

NC

Not Connected

Inputs

Inputs/Outputs

OE

A,B

LA

= B

HZ