V

+

or NO

NC

IN

COM

VOUT

GND

VIL to VIH

VIN

+

V

+

0.047PF

Protection

Diode

Motor or

inductive

load

LMS4684

SNOSAL0C – DECEMBER 2004 – REVISED APRIL 2013

www.ti.com

FUNCTIONAL DESCRIPTION

The LMS4684 is a low voltage dual, extremely low On-Resistance analog switch that can operate over a supply

voltage range of 1.8V to 5.5V. The LMS4684 has been fully characterized to operate in applications with 3V

nominal supply voltage and features very low on resistance and fast Turn-Off and Turn-On times with break-

before-make switching.

The switch operates asymmetrically; one terminal is normally closed (NC) and the other terminal normally open

(NO).

Both NC and NO terminals are connected to a common terminal (COM). This configuration is ideal for

applications with asymmetric loads such as speaker handsets and internal speakers.

Applications Information

ANALOG INPUT SIGNAL

Analog input signals can range from GND to V+ and are passed through the switch with very little change. Each

switch is bidirectional so any pin can be an input or output.

Exercise care when making connection to an inductive load, such as a motor. As is true with any analog switch

used with an inductive load, the back emf produced when the switch is turned off can damage the LMS4684 by

electrical overstress. For such applications, a diode should be connected across the motor to prevent damage to

the switch, as indicated in Figure 16. Be sure the diode has adequate current carrying capabilities.

Figure 16. Inductive Load Over-Voltage Protection

DIGITAL CONTROL INPUTS

The IN pin can be driven to 5.5V regardless of the voltage level of the supply pin V+. For example, if the

LMS4684 is operated with a supply of 2V, the digital control input could still be driven to 5V. Power consumption

is increased when the control pin is driven rail-to-rail.

SUPPLY VOLTAGE

It is good general practice to first apply the supply voltage to a CMOS device before sriving any other pins. This

is also true for the LMS4684 analog switch, which is a CMOS device.

However, if it is necessary to have an analog signal applied before the supply voltage is applied and the analog

signal source is not limited to 20 mA max, a diode connected between the supply voltage and the V+ pin as

shown in Figure 17 will provide input protection. This will limit the max analog voltage to a diode drop below V+.

This diode, D1, will also provide protection against some over voltage situations.

8

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