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TMUX1308-Q1 bảng dữ liệu(PDF) 23 Page - Texas Instruments |
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TMUX1308-Q1 bảng dữ liệu(HTML) 23 Page - Texas Instruments |
23 / 43 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: S0 Injected curren t into uns elected s witch inpu t S7 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 S1 S2 S3 S4 S5 S6 D ESD n p Log ic D ecode Block n p 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-Q1, TMUX1309-Q1 SCDS414C – DECEMBER 2019 – REVISED AUGUST 2020 Copyright © 2020 Texas Instruments Incorporated Submit Document Feedback 23 Product Folder Links: TMUX1308-Q1 TMUX1309-Q1 |
Số phần tương tự - TMUX1308-Q1_V02 |
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Mô tả tương tự - TMUX1308-Q1_V02 |
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