What are Overvoltage & Fault events?
An overvoltage or fault event is when a signal with a voltage greater than the maximum rating of the analog switch or multiplexer is fed into the device. These events can occur for many reasons such as EMI from a switching power source or rotating electrical device, miswiring, incorrect grounding, or lightning strikes. The excess voltage and current can cause damage to the multiplexer and downstream components as seen in Figure 1. In this situation a 20V sensor line in plugged into a 5V system, representing a miswiring event.
Figure 1
How TI Overvoltage & Fault Protected switches and multiplexers function
TI offers a portfolio of switches and multiplexers with integrated overvoltage/fault protection. TI’s overvoltage protection devices have an internal sensing block that detects when a signal violates the voltage threshold. When this occurs, the switch is opened and the signal path enters a high impedance state. In addition, some devices have a fault flag pin (FLT or FF) that will indicate when a fault event has happened. An example of this can be seen in Figure 2.
Figure 2
Certain overvoltage protected devices also include integrated diodes on the drain pins that will clamp the voltage to help prevent damage. In dual rail switches, the output voltage is clamped to either VDD or VSS depending on the polarity of the fault. This can be seen in Figure 3 below.
Figure 3
Fault supply pins (VFP in Figure 4) are offered on some parts which allow for configurable voltage clamp thresholds. This enables the multiplexer to isolate two subsystems with different voltage levels. In Figure 4 below, the 12V set on the VFP pin is the clamp threshold level.
Figure 4
How can this affect your system?
TI’s portfolio of switches and multiplexers with overvoltage protection add a range of benefits to your system over non-protected alternatives. They protect themselves and downstream components in the system from being damaged by overvoltage events. They can also indicate when a fault condition exists in the system through the fault flag pin. Additionally, they allow non-fault channels to continue to operate normally with little impact on performance.
Which TI switches and multiplexers have this feature?
Devices that offer this feature will have “Overvoltage protection” listed in the “Features” section on ti.com. Many devices have an F suffix in their part number (ex. TMUX7308F). The table below shows a selection of the overvoltage/fault protected portfolio. Both the low voltage selection guide and mid voltage selection guide have protection devices highlighted as well (note: some low voltage parts are not overvoltage protected, only powered off protected, check the features list to confirm)
|
Overvoltage Analog Switch/Multiplexer Selection Guide |
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| Device |
Configuration / Channels |
Power Supply Voltage(V) |
Features | Package (Dimensions) |
| TMUX1072 |
2:1 SPDT / 2 channels |
Single: 2.5, 3.3, 5 | 18V Fault Protection, supports input voltage beyond the supply | UQFN (1.7mm x 2mm) VSSOP (3mm x 3mm) |
| TMUX7308F | 8:1 / 1 channel | Single: 12, 16, 20, 36, 44 Dual: +/-5, +/-10, +/-15, +/-18, +/-22 |
+/- 60V Fault Protection | WQFN (4mm x 4mm) TSSOP (4.4mm x 5mm) |
| TMUX7309F | 4:1 / 2 channels | Single: 12, 16, 20, 36, 44 Dual: +/-5, +/-10, +/-15, +/-18, +/-22 |
+/- 60V Fault Protection | WQFN (4mm x 4mm) |
| TMUX7348F | 8:1 / 1 channels | Single: 12, 16, 20, 36, 44 Dual: +/-5, +/-10, +/-15, +/-18, +/-22 |
+/- 60V Fault Protection, Adjustable Fault Threshold | QFN (4mm x 4mm) |
| TMUX7412F | 1:1 SPST / 4 channels | Single: 12, 16, 20, 36, 44 Dual: +/-5, +/-10, +/-15, +/-18, +/-22 |
+/- 60V Fault Protection | WQFN (4mm x 4mm) |
| TMUX7462F | 1:1 SPST / 4 channels | Single: 12, 16, 20, 36, 44 Dual: +/-5, +/-10, +/-15, +/-18, +/-22 |
+/- 60V Fault Protection, Adjustable Fault Threshold | WQFN (4mm x 4mm) |
For more information on this topic, please watch these TI Precision Labs video TI Precision Labs Video