OVER-VOLTAGE CURVE TRACER TEST SETU CURVE DUT TRACER Test Both Inputs of Op Amp-Results are ldentical for Voltage Feedback Types, but Not Current Feedback Force a Voltage Using the Collector Output Display Collector Current Versus Voltage Results May Differ Depending on Whether the Other Input is Open or Grounded Once the input current-voltage characteristic has been determined for the device in question, the next step is to determine the minimum level of resistance required to limit fault currents to +5mA. Equation 7.1 illustrates the computation for Rs when the input overvoltage level is known Rs VIN(MAX)-VSUPPLY Eq.7.1 5 mA The worst case condition for overvoltage would be when the power supplies are litially turned off or disconnected. In this case, VSUPPLY is equal to zero. For xample, if the input overvoltage could reach 100V under some type of fault condition then the external resistor should be no smaller than 20kohms Most operational amplifier applications only require protection at one input however there are a few configurations(difference amplifiers, for example)where both inputs can be subjected to overvoltage and both must be protected The need for protection on both inputs is much more common with instrumentation amplifiers5 OVER-VOLTAGE CURVE TRACER TEST SETUP Figure 7.2 Once the input current-voltage characteristic has been determined for the device in question, the next step is to determine the minimum level of resistance required to limit fault currents to ±5mA. Equation 7.1 illustrates the computation for Rs when the input overvoltage level is known: Rs VIN(MAX) VSUPPLY 5 mA = - Eq. 7.1 The worst case condition for overvoltage would be when the power supplies are initially turned off or disconnected. In this case, VSUPPLY is equal to zero. For example, if the input overvoltage could reach 100V under some type of fault condition, then the external resistor should be no smaller than 20kohms. Most operational amplifier applications only require protection at one input; however, there are a few configurations (difference amplifiers, for example) where both inputs can be subjected to overvoltage and both must be protected. The need for protection on both inputs is much more common with instrumentation amplifiers