© 1999 Fairchild Semiconductor Corporation

DS500194

www.fairchildsemi.com

December 1998

Revised December 1999

FSTU6800

10-Bit Bus Switch with Pre-Charged Outputs

and

−2V Undershoot Hardened Circuit (UHC) Protection

General Description

The Fairchild Switch FSTU6800 provides 10-bits of high-

speed CMOS TTL-compatible bus switching. The low on

resistance of the switch allows inputs to be connected to

outputs without adding propagation delay or generating

additional ground bounce noise. Both the A Ports and the B

Ports are “undershoot hardened” with UHC

 protection to

support an extended input range to 2.0V below ground.

Fairchild’s integrated Undershoot Hardened Circuit, UHC

senses undershoot at the I/Os, and responds by preventing

voltage differentials from developing and turning on the

switch. The device also precharges the B Port to a select-

able bias voltage (BiasV) to minimize live insertion noise.

The device is organized as a 10-bit switch with a bus

enable (OE) signal. 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 the B Port is precharged to BiasV

through an equivalent 10-k

Ω resistor.

Features

s 4

Ω switch connection between two ports.

s Undershoot Hardened to -2.0V.

s Soft enable turn-on to minimize bus-to-bus charge

sharing during enable.

s Zero bounce in flow-through mode.

s Output precharge to minimize live insertion noise.

s Control inputs compatible with TTL level.

s See Applications Note AN-5008 for details.

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 Diagram

Truth Table

UHC

 is a trademark of Fairchild Semiconductor Corporation.

Order Number

Package Number

Package Description

FSTU6800WM

M24B

24-Lead Small Outline Integrated Circuit (SOIC), JEDEC MO-153 4.4mm Wide

FSTU6800QSC

MQA24

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

FSTU6800MTC

MTC24

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

Pin Name

Description

OE

Bus Switch Enable

ABus A

BBus B

BiasV

Bus B Voltage Bias

OE

Function

Connect

HBiasV

Precharge