TI offers a broad range of protection multiplexers and switches in different configurations to protect upstream and downstream components from and during fault conditions while maximizing signal integrity. The key differentiating features of these protection switches are:

• Powered Off Protection: Protects switch and isolates signal path when signals are present at the I/O pins and VDD = 0 V. See the Eliminate Power Sequencing With Powered-off Protection Signal Switched Tech Note and Simplify power sequencing with powered-off protection for more information. TI switches with powered-off protection will protect downstream components when input signals are present in the I/O pins while the switch is not powered. The switch maintains a high-impedance state on the I/O pins which prevents back-powering V_DD and the Select (SEL) pin with the following features.
  • Provides electrical isolation between subsystems.
  • Prevents data from being transmitted unintentionally.
  • Eliminates need for power sequencing solutions.
  • Reduces BOM count and cost Simplifies system design.
  • Improves system reliability.
    Figure 5-1 Powered-off Protection

• Over Voltage Protection / Fault Detection : Fault-protect multiplexers have built in fault-protected features such as overvoltage detection and protection. These can easily be identified with an 'F' appended to the multiplexer name, such as TMUX7412F, TMUX7308F and TMUX7462F. These devices detect overvoltage inputs by comparing the voltage on a source pin with the supplies. A signal is considered overvoltage if it exceeds the supply voltage by the threshold voltage (V_T or V_TH), listed in the data sheet. Upon detection of an overvoltage event, the switch enters a high impedance state, isolates the signal path and protects downstream components.

  Depending on the device the overvoltage threshold can be determined 1 of 3 ways; A fixed threshold, a threshold that is equal to the VDD supply, or a configurable threshold via an extra supply provided through the IC.

  Figure 5-2 Overvoltage Protection Threshold

The TMUX1072 is a unique low voltage device that supports overvoltage detection as well. This devices has a fixed threshold for fault events. When the voltage at the COM pin exceeds the overvoltage threshold, VOVP_TH, the open drain output FLT pin pulls the pin low to indicate an overvoltage event has been detected and the I/O path goes HI-Z. The open drain output will release the FLT pin when the voltage on the COM pin returns below the VOVP_TH.

• Undervoltage Protection - Devices with undervotlage protection detect undervoltage inputs on the I/O's by comparing the voltage on a source pin with the supplies. A signal is considered undervoltage if it falls below the supply voltage by the threshold voltage (V_TH), listed in the data sheet. Upon detection of an undervoltage event, the switch enters a high impedance state, isolates the signal path and protects downstream components.

  Depending on the device, the overvoltage threshold can be determined 1 of 2 ways; A threshold that is equal to the VSS supply, or a configurable threshold via an extra supply provided through the IC.

  Figure 5-4 Undervoltage Protection Threshold
• Input voltage tolerance : This is defined as a specific protection referencing the maximum voltage that can be applied to any source pin. The voltage can be referenced from source pin to supply or between the source pins and one or more drain pins. Below is an example of a device with a maximum voltage that can be applied to any source input pin of +60 V or -60 V. It shall be cautioned that the device is rated to handle maximum stress of 85 V across different pins as well. The device has different maximum stress ratings across different pin combinations and are defined as the following :

1. Between the source pins and supply rails

   For example, if the device is powered by VDD supply of 20 V, the maximum negative signal level on any source pin is –60 V to maintain the 60 V maximum rating on any source pin. If the device is powered by VDD supply of 40 V, the maximum negative signal level on any source pin is reduced to –45 V to maintain the 85 V maximum rating across the source pin and the supply.

2. Between the source pins and one or more drain pins

   For example, if channel S1 is ON and the voltage on S1(A) pin is 40 V. In this case, the drain voltage is also 40 V. The maximum negative voltage on any of the other source pins is –45 V to maintain the 85 V maximum rating across the source pin and the drain pin.

Table 5-2 shows performance specification of analog protection switches: