LTC1921 UUUPI FU CTIO SVA (Pin 1): Supply to be Monitored. The voltage at this pin OUT F pin. If VA is outside the specified overvoltage or is compared to the valid supply voltage window and the undervoltage limits, then OUT A is shorted internally to the result is output at OUT A (Pin 5). Supply current is drawn OUT F pin and can shunt enough current to turn off an from VA as well as from VB (Pin 8). optoisolator or LED wired between these pins. OUT A should be clamped externally so that it cannot be driven more than FUSE A (Pin 2): This pin monitors the state of a fuse by 8V below RTN. This is done automatically by the comparing the voltage at this pin to the voltage at VA optoisolator or LED diodes shown in the application circuits. (Pin␣ 1). The result is output at OUT F (Pin 4). OUT B (Pin 6): Indicates the state of V RTN (Pin 3): Supply Return Reference. This pin must be B. If VB is within the specified voltage window (neither undervoltage nor over- at an equal or higher potential than the other pins and voltage), OUT B will exhibit a high internal impedance to the should be wired to the – 48V return. OUT A pin. If VB is outside the specified overvoltage or OUT F (Pin 4): This pin indicates the state of the external undervoltage limits, then OUT B is shorted internally to the fuses by ORing the comparisons made to the FUSE A and OUT A pin and can shunt enough current to turn off an FUSE B pins. If VFUSEA ≅ VA (VFUSEA is within the specified optoisolator or LED wired between these pins. OUT B should window around VA) and VFUSEB ≅ VB, then OUT F will be clamped externally so that it cannot be driven more than exhibit a high internal impedance to the RTN pin. If 8V below RTN. This is done automatically by the VFUSEA ≠ VA or VFUSEB ≠ VB, then OUT F is shorted optoisolator or LED diodes shown in the application circuits. internally to the RTN pin and can shunt enough current to FUSE B (Pin 7): This pin monitors the state of a fuse by turn off an optoisolator or LED wired between these pins. comparing the voltage at this pin to the voltage at V OUT F should be clamped externally so that it cannot be B (Pin␣ 8). The result is output at OUT F (Pin 4). driven more than 8V below RTN. This is done automati- cally by the optoisolator or LED diodes shown in the VB (Pin 8): Supply to be Monitored. The voltage at this pin application circuits. is compared to the valid supply voltage window and the result is output at OUT B (Pin 6). Supply current is drawn OUT A (Pin 5): Indicates the state of VA. If VA is within the from V specified voltage window (neither undervoltage nor over- B as well as from VA (Pin 1). voltage), OUT A will exhibit a high internal impedance to the 1921f 5