ESD

n

p

Control

Circuitry

Simplified injection curr ent circuitry

Log ic D ecode

Block

ESD

Control

Circuitry

Simplified injection curr ent circuitry

Injected current into

unselected switch input

Figure 8-16. Injected Current at Input Pin

Figure 8-17 shows an example of using a series limiting resistor in the case of an overvoltage event.

ESD

n

p

Control

Circuitry

Simplified injection curr ent circuitry

Log ic D ecode

Block

ESD

Control

Circuitry

Simplified injection curr ent circuitry

Figure 8-17. Over-voltage Event with Series Resistor

If the voltage at the source or drain pins is greater than VDD, or less than GND, the protection FET will be turned

on for any disabled signal path and shunt the pin the GND. In this event, a series resistor is needed to limit the

total current injected into the device to be less than 100 mA. Two example scenarios are:

A typical CMOS switch would have an internal ESD diode to the supply pin rated for about ≈30 mA that would be

turned on and a series limited resistor would be needed. However, any conducted current would be injected into

the supply rail potentially damaging the system, unexpectedly turning on other devices on the same supply rail,

or requiring additional components for protection. The TMUX13xx implementation also handles this scenario with

a series limiting resistor, however, the current path is now to GND which doesn’t have the same issues as the

current injected into the supply rail.

Many CMOS switches are unable to support a voltage at the input without a valid supply voltage present

otherwise the voltage will be coupled from input to output and could damage downstream devices or impact

power-sequencing. The TMUX13xx circuitry can handle an input signal present without a supply voltage while

minimizing power transfer from the input to output of the switch. By limiting the output voltage coupling to 400

mV the TMUX1308 and TMUX1309 help reduce the chance of conduction through any downstream ESD diodes.

www.ti.com

TMUX1308, TMUX1309

SCDS426C – MARCH 2020 – REVISED AUGUST 2020

Copyright © 2020 Texas Instruments Incorporated

Submit Document Feedback

25

Product Folder Links: TMUX1308 TMUX1309