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