To protect an op amp from unexpected failures

Pay attention to overvoltage and supply sequence

Figure 1 : Sensor Input and Op Amp Connection Diagram

The power supply of the operational amplifier must be established at or before the input signal is entered. Otherwise, overvoltage or latch problems may occur.

When an operational amplifier is used as an input circuit for an external sensor (Figure 1).

The power on state of the op amplifier is in the correct order before the sensor signal is fed into the op amplifier. But is it guaranteed that this procedure is always followed correctly?

In this case, the channel protector product makes it easy to protect the op amplifier from accidental input signals.

4 channel protector (ADG5462F) product description

ADG5462F is a 4-channel protector that provides ±55V overvoltage protection.

Easy to use, the signal path is inserted in series to protect sensitive components from overvoltage.

Without serialization, the input line can be cut off when the power is not on, providing strong protection for sensitive input circuits.10 Ω after electrify, low on resistance (Ron) does not affect the input line.

Not only before switching on the power supply, after switching on the power supply can also be set as the upper limit and lower limit of the over-voltage cut off. The set voltage can be directly connected to the operational amplifier power supply, or can be set by resistor divider.

Through the high-pressure process to achieve bearing capacity. Even if the components increase, the worry does not increase.

The main features

Input pin is protected by -55V ~ +55V voltage when the input is not connected.
Isolated by grooves to prevent latches.
Optimized for low on-resistance and flatness of on-resistance
Through overvoltage detection, digital output channel action state.
ADG5462F can work with ±5V ~ ±22V dual power supply or 8V ~ 44V single power supply.

Terminal function

Figure 2 : Functional Block Diagram of the ADG5462F

SX: Input (source) terminal

DX: Output (drain) terminal

VDD: power supply (+)

VSS: power supply (-)

POSFV: fault detection voltage level (+)

NegFV: fault detection voltage level (-)

DR: Output setting input in case of fault (Hi-Z/ fault detection level)

FF: Fault status output

GND: reference potential

Sample protection circuit

Here are three examples of protection circuits using ADG5462F:

Usage 1: Cut off the input of the sensor before starting

Figure 3 : Connection Diagram to Block Input from the Sensor before Power Up

Using optical system components and so on as sensors,

the input signal will anyway have to input the sensor output to the op amplifier before the power input of the op amplifier.

In this case, as shown in Figure 3, by using the ADG5462F, the sensor and op amplifier can be isolated, thus avoiding the problem.

The ADG5462F also has a withstand voltage of ±55V in the absence of power, so there will be no failure even if the sensor signal is input to the ADG5462F before the power is switched on.

Usage 2: Cut off excessive input

Figure 4 : Connection Diagram to Cut Off Excessive Input

The signal range of the operational amplifier that can be input is within the power range of the operational amplifier, so in the case of Figure 4, it is within ±5V.

Even when calculated and designed not to apply overvoltage above ±5V to the operational amplifier, the sensor may suddenly output signals above the threshold level because it monitors information from the natural world.

The solution in this case is the connection example shown in Figure 4.

As shown in Figure 4, when the input signal reaches above the threshold voltage of ±5V set by POSFV and NOGFV pins, the protector detects overvoltage and the output is turned off to protect the operational amplifier.

Usage 3: Adjust the break condition according to the circuit of the rear segment

Figure 5 : Connection Diagram with Cutoff Condition Adjusted to Subsequent Circuit

Application of method 2.

Even if the power supply voltage of the front and rear circuits is different, if it reaches above the threshold voltage of ±5V set by the POSFV and NOGFV pins, the protector will detect the overvoltage and turn off the output to protect the operational amplifier.

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