A Reliable New Approach to Overvoltage Protection for Sensitive Electronic Signal Inputs

The high demands on the reliability of Electronic systems, especially in industrial environments, continue to present enormous challenges for developers. Overvoltage protection is a key design consideration and challenge because more components are often required to protect the system from overvoltage, but these additional components often impact the system and, in the worst case, even produce error signal. In addition to this, these components add additional cost and further exacerbate space constraints. Therefore, when designing protection Circuits, traditional solutions often require a compromise between system accuracy and protection level.

In general, a common simple design approach is to use an external protection diode, usually a transient voltage suppressor (TVS) diode, installed between the signal line and the power or ground line. TVS diodes are useful because they respond quickly to transient voltage spikes. This type of external overvoltage protection is shown on the left side of Figure 1.

figure 1.Traditional overvoltage protection design with additional discrete components

In the event of a positive transient voltage pulse overvoltage, current will flow through D1 to VDD to clamp the positive transient voltage pulse and the voltage will be limited by the clamping voltage equal to VDD plus the forward voltage on the diode. If the pulse is negative and less than VSS, the same function as above applies, but instead is clamped to VSS via D2. However, if the leakage current caused by overvoltage is not limited, the diode can be damaged. For this reason, a current limiting resistor is added to the path. Bidirectional TVS diodes at the input are often used for enhanced protection under very harsh environmental conditions.

Disadvantages of this type of protection Circuit include increased signal rise and fall times and capacitive effects. Also, no protection is provided when the circuit is powered down.

Actual devices, such as analog-to-digital converters (ADCs), operational amplifiers, etc., usually have built-in protections. As shown on the right side of Figure 1, this protection function consists of a switch architecture. It can also be seen from Figure 1 that the power rails are equipped with input and output protection diodes on both sides. There is a downside to this setup, when the floating signal is present in a powered-down state (the IC is not powered), the switch may act as if it were active (even though it is set to off), with current flowing through the diodes and power rails. This phenomenon will allow current to flow through the signal line, causing the signal line to lose its protection.

Fail-Safe Switch Architecture

One way to address the above problem is to use a fault-protected switch architecture with bidirectional ESD cells, as shown in Figure 2. Instead of using input TVS diodes, ESD cells now clamp transient voltages by constantly comparing the input voltage to the voltage on VDD or VSS. In the event of prolonged overvoltage, the downstream switch will automatically open. This way, the input voltage is no longer limited by the protection diodes clamped on the power rails, but by the maximum voltage rating of the switch. In addition, higher system robustness and reliability can be achieved without affecting the actual signal and its accuracy. In addition, the leakage current is very low when the switch is off, so no additional current limiting resistor is required.

figure 2.Overvoltage protection with integrated bidirectional ESD cell

The ADG5412F, a four-channel single-pole single-throw (SPST) switch from Analog Devices (ADI), uses this input structure. This switch can withstand permanent overvoltages up to ±55 V, regardless of the size of the existing power supply. The ESD cells integrated on each of the four channels can clamp transient voltages up to 5.5 kV. During an overvoltage condition, only the affected channel will turn on, the other channels continue to function normally.

in conclusion

Thanks to this overvoltage protection switch, the circuit can be greatly simplified. This solution offers distinct advantages over traditional discrete solutions, both in ensuring excellent switching performance for precision signal chains, and in optimizing space usage. Therefore, the overvoltage protection provided by the ADG5412F is particularly suitable for high-precision measurement applications in harsh environments.

Edit: muyan Source: EEWORLD

The Links:   NL2432DR22-12B   FP15R12YT3