TMUX1308 datasheet(26/46 Pages) TI2

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9.3.5.1 TMUX13xx is Powered, Channel is Unselected, and the Input Signal is Greater Than VDD (VDD = 5

V, VINPUT = 5.5 V)

A typical CMOS switch would have an internal ESD diode to the supply pin rated for

≅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; the current path, however, is now to GND which does not have the same issues as the

current injected into the supply rail.

9.3.5.2 TMUX13xx is Powered, Channel is Selected, and the Input Signal is Greater Than VDD (VDD = 5 V,

VINPUT = 5.5 V)

The injection current control circuitry is fully active when the channel is unselected and an overvoltage event is

present (overvoltage being defined as 0.5 V above the supply rail). However, in situations where the channel

is selected and an overvoltage event occurs, this protection circuitry will still be partially active. In this instance,

a portion of the injected current will be redirected through the protection circuitry to GND, but will not be a

full shunt. So, some current will also flow through the source to drain path. This allows the device to tolerate

overvoltage conditions in the event of the channel being selected, but precautions are still necessary to protect

the device from overcurrent events such as implementing a current limiting resistor to keep the device below the

maximum continuous source and drain current specification.

9.3.5.3 TMUX13xx is Unpowered and the Input Signal has a Voltage Present (VDD = 0 V, VINPUT = 3 V)

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.

9.4 Device Functional Modes

When the EN pin of the TMUX1308 is pulled low, one of the switches is closed based on the state of the address

lines. Similarly, when the EN pin of the TMUX1309 is pulled low, two of the switches are closed based on the

state of the address lines. When the EN pin is pulled high, all the switches are in an open state regardless of the

state of the address lines.

Unused logic control pins must be tied to GND or VDD to ensure the device does not consume additional current

as highlighted in Implications of Slow or Floating CMOS Inputs. Unused signal path inputs (Sx and Dx) should be

connected to GND.

9.5 Truth Tables

Table 9-1 and Table 9-2 provides the truth tables for the TMUX1308 and TMUX1309 respectively.

Table 9-1. TMUX1308 Truth Table

EN A2

Selected Signal Path Connected To Drain

(D) Pin

X(1) X(1) X(1)

All channels are off

(1)

X denotes do not care.

TMUX1308, TMUX1309

SCDS426E – MARCH 2020 – REVISED OCTOBER 2022

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