S1

S2

I

I/O

D

-ûV error

ON

OFF

+ûV error

V

S2

V

D

V

S2

To avoid the complications of added external protection to your system, the TMUX1308 and TMUX1309 devices

have an internal injection current control feature which eliminates the need for external diode/resistor networks

typically used to protect the switch and keep the input signals within the supply voltage. The internal injection

current control circuitry allows signals on disabled signal paths to exceed the supply voltage without affecting the

signal of the enabled signal path. The injection current control circuitry also protects the TMUX13xx from

currents injected into disabled signal paths without impacting the enabled signal path, which typical CMOS

switches do not support. Additionally, the TMUX1308 and TMUX1309 do not have any internal diode paths to the

supply pin, which eliminates the risk of damaging components connected to the supply pin, or providing

unintended power to the system supply rail. Figure 8-12 shows a simplified diagram of one signal path for the

TMUX13xx devices and the associated injection current circuit.

ESD

n

p

Control

Circuitry

Simplified injection curr ent circuitry

Log ic D ecode

Block

ESD

Control

Circuitry

Simplified injection curr ent circuitry

Figure 8-15. Simplified Diagram of Injection Current Control

The injection current control circuitry is independently controlled for each source or drain pin (Sx, D). The control

circuitry for a particular pin is enabled when that input is disabled by the logic pins and the injected current

causes the voltage at the pin to be above VDD or below GND. The injection current circuit includes a FET to

shunt undesired current to GND in the case of overvoltage or injected current events. Each injection current

circuit is rated to handle up to 50 mA, however the device can support a maximum current of 100 mA at any

given time. Depending on the system application, a series limiting resistor may be needed and must be sized

appropriately. Figure 8-15 shows the TMUX13xx protection circuitry with an injected current at an input pin.

TMUX1308, TMUX1309

SCDS426C – MARCH 2020 – REVISED AUGUST 2020

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