A CLOSER LOOK AT THE OP-X91 INPUT STAGE REVEALS ADDITIONAL DEVICES AAAI D3-D6: SUBSTRATE PNPs(COLLECTORS TO VNEG) Figure 7.5 An interesting benefit from using substrate PNPs as clamp diodes is that their collectors are connected to the negative supply; thus, when the applied input voltage exceeds either supply rail, the diodes energize, and the fault currents are diverted directly to the supply and not through or into the device's input stage There are al 5kohm resistors in series with each of the inputs to the opX9 1 to limit the fault that these kohm resistors are p-type diffusions placed inside an n-well, which lo current through D1 and D2 when the differential input voltage exceeds 0. 7V. Note then connected to the positive supply. when the applied input voltage exceeds the positive supply, some of the fault current generated is also diverted to Vpos and away from the input stage. As a result of these measures, the input overvoltage characteristic of the oPX91 is well behaved as shown in Figure 7.6. Note that the combination of the kohm resistors and clamp diodes safely limits the input current to less than 2mA, even when the inputs of the device exceed the supply rails by 10v.8 A CLOSER LOOK AT THE OP-X91 INPUT STAGE REVEALS ADDITIONAL DEVICES Figure 7.5 An interesting benefit from using substrate PNPs as clamp diodes is that their collectors are connected to the negative supply; thus, when the applied input voltage exceeds either supply rail, the diodes energize, and the fault currents are diverted directly to the supply and not through or into the device’s input stage. There are also 5kohm resistors in series with each of the inputs to the OPX91 to limit the fault current through D1 and D2 when the differential input voltage exceeds 0.7V. Note that these 5kohm resistors are p-type diffusions placed inside an n-well, which is then connected to the positive supply. When the applied input voltage exceeds the positive supply, some of the fault current generated is also diverted to VPOS and away from the input stage. As a result of these measures, the input overvoltage characteristic of the OPX91 is well behaved as shown in Figure 7.6. Note that the combination of the 5kohm resistors and clamp diodes safely limits the input current to less than 2mA, even when the inputs of the device exceed the supply rails by 10V