TMUX13 datasheet(23/42 Pages) TI

23 / 42 page

• Harsh environments and applications with long cabling, such as in factory automation and automotive

systems, may be susceptible to injected currents from switching or transient events

• Other self-contained systems can also be subject to injected current if the input signal is coming from various

sensors or current sources

Injected Current Impact: Typical CMOS switches have ESD protection diodes on the inputs and outputs. These

diodes not only serve as ESD protection but also provide a voltage clamp to prevent the inputs or outputs going

above VDD or below GND/VSS. When current is injected into the pin of a disabled signal path, a small amount of

current goes thorough the ESD diode but most of the current goes through conduction to the Drain. If forward

diode voltage of the ESD diode (VF) is greater than the PMOS threshold voltage (VT), the PMOS of all OFF

switches turns ON and there would be undesirable subthreshold leakage between the source and the drain that

can lift the OFF source pins up also. Figure 8-13 shows a simplified diagram of typical CMOS switch and

associated injected current path:

Injected curren t into

uns elected s witch inpu t

Som e c urre nt goe s

throug h ES D

Drain voltage

VDD + VF (ESD)

M ost c urre nt goe s throug h

a s conduc ti on

VDD (PMOS gate voltage)

Selected switch inp ut

ESD

Log ic D ecode

Block

ESD

Log ic D ecode

Block

Figure 8-13. Simplified diagram of typical CMOS switch and Associated Injected Current Path

It is quite difficult to cut off these current paths. The drain pin can never be allowed to exceed the voltage above

VDD by more than a VT. Analog pins can be protected against current injection by adding external components

like Schottky diode from Drain pin to ground to clamp the drain voltage at < VDD + VT to cut off the current path.

Change in RON due to Current Injection: Because the ON resistance of the enabled FET switch is impacted by

the change in the supply rail, when the drain pin voltage exceeds the supply voltage by more than a VT, an error

in the output signal voltage can be expected. This undesired change in the output can cause issues related to

false trigger events and incorrect measurement readings, potentially compromising the accuracy and reliability of

the system. As shown in Figure 8-14, S2 is the enabled signal path that is conducting a signal from S2 pin to D

pin. Because there is an injected current at the disabled S1 pin, the voltage at that pin increases above the

supply voltage and the ESD protection diode is forward biased, shifting the power supply rail. This shift in supply

voltage alters the RON of the internal FET switches, causing a ∆V error on the output at the D pin.

www.ti.com

TMUX1308, TMUX1309

SCDS426C – MARCH 2020 – REVISED AUGUST 2020

Submit Document Feedback

Product Folder Links: TMUX1308 TMUX1309

TMUX13 датащи(PDF) 23 Page - Texas Instruments

TMUX13 датащи(HTML) 23 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

датащи скачать

ссылки URL