Vicor VIPAC 28 Vdc MIL-COTS - Manual (Page 9)

8 v i c o r p o w e r . c o m
VIPAC Control
The VIPAC provides the user with choices with respect to how
the unit is operated. It can be controlled locally by applying
the appropriate “digital” signals to the device.
BUS-OK
An internal replica of BUS-OK is wired to the PC pin of all in-
ternal DC-DC converter modules. The modules will be
disabled (no DC output) during initial power up of theVIPAC
until the internal DC input bus voltage to the DC-DC converters
is sufficient to support full load operation. The BUS-OK status
output reflects the status of this inhibit function. This same
logic circuit will shut down the converters when the internal
DC bus voltage is insufficient to support proper operation.
This shut down will occur during normal power down, line
dropouts exceeding the hold up time, or internal faults
causing the internal DC bus voltage at the input of the
converters to collapse. The BUS-OK output provides the user
with an optically isolated status indication of the internal
DC bus. This output, in AC powered system applications, can
provide power supply status, switch in backup (standby)
sources or initiate “power down” sequences to save volatile
memory contents in the event of a power loss. The time from
BUS-OK deassertion to output shut down is dependent upon
the value of hold up capacitors used. The VIPAC online design
tool contains a hold up capacitor calculator which provides ap-
propriate values.
MOD-DIS+, MOD-DIS–
The MOD-DIS input is an optically coupled input and allows for
remote disabling of the output(s) of the VIPAC. Applying current
to the MOD-DIS+, MOD-DIS– input disables the supply.
The minimum input current for disabling the supplies is 3 mA.
The maximum allowable current is 20 mA.
Electrical Connections
Status output pair BUS-OK+, BUS-OK– are the collector (+) and
emitter (–) of an NPN optoisolator output transistor. In a typical
application, the collector terminal BUS-OK+ of the optocoupler
can be connected via current limiting resistors to a source no
greater than 70 Vdc. These resistors should limit the maximum
current to the optocoupler output transistors to 1.5 mA. The
emitter terminal BUS-OK– is connected to the return of the ex-
ternal source. The status OK condition will set the optocoupler
output transistors in saturation and are capable of sinking up to
1.5 mA with a Vce saturation voltage of 0.4 V. Users should be
cautioned that although the output of the VIPAC can be used as
the pull-up source, shortly after BUS-OK changes from OK
(saturated) to NOT OK (high Z), the pull-up voltage will be shut
down. If the pull-up source is one of theVIPACs outputs, it is
advisable to provide a capacitive reservoir in order to maintain
the pull-up potential after loss of DC current output. Use edge
sensing logic to detect assertion of logic outputs, or a separate
source of bias supply voltage (i.e., backup batteries) to provide a
safe pull-up voltage source regardless of the line status.
1.5 mA
max.
V
+
r
BUS-OK
+
–
20 mA max.
Disable
MOD-DIS
V
+
+
–
VIPAC
J3
3
2
7
6
MOD-DIS Input
Apply a current of 3–20 mA
to disable output.
BUS-OK – Status Output
Transistor on when OK.
Vce sat. = < 0.4 V @ 1.5 mA
maximum external pull-up
is 70 Vdc.
BUS–OK signal is isolated
T
ECHNICAL
O
VERVIEW