Vicor Mini MegaPAC AC-DC Switcher - Manual (Page 17)

UG:110 vicorpower.com Applications Engineering: 800 927.9474 Page 17
Interface Connections (Cont.)
Power Good (J3-2)
The optional Power Good signal on J3-3 is referenced to Signal Ground on J3-1, and
indicates the status of the output voltage. This signal is asserted a TTL “1” when the
output voltage is above 95% of nominal. It is a TTL “0” when the output voltage is below
85% of nominal.
If the Trim option is also used, the Power Good trip points DO NOT track with the
trimmed voltage. It is possible to trim the output below the fixed setpoints of the Power
Good circuit and cause a negative Power Good signal.
Power Good Inverted (J3-3)
This is the inverse of the Power Good signal and is referenced to Signal Ground on J3-1.
Signal Ground (J3-1)
Signal Ground on J3-1 is an isolated secondary ground reference for J3 status signals
(see Figure 8). It is used to provide a reference point for the Power Good circuitry and is
not the same as Earth Ground on input power connector J9.
Vcc In (J3-4)
The Vcc In on J3-4 is an input that requires +5 V either from the J10 Auxiliary Vcc, or
from another source. Input current to this pin is limited by an internal resistor to
3 mA. If the J10 Auxiliary Vcc is connected to Vcc In on J3-3, then at least one J10 Signal
Ground must be connected to Signal Ground on J3-1.
+Sense/ –Sense (J2-2 and J2-3) (See Page 10 and 13 for more information on Autosense)
The +Sense on J2-2 should be connected to the +Power Out, and the –Sense on J2-3 to
the –Power Out terminal. Do not reverse or leave the Sense pins open. Sense pins can
be terminated locally at the output of the power supply, in which case the power supply
will provide regulation at the output terminals. The voltage appearing at the load may
drop slightly due to voltage drop in the power cables. If it is necessary to compensate
for voltage drop along the output power cables, this termination should be made close
to the output load. Compensation of up to 0.5 V (0.25 V per lead) can be obtained. Use
twisted pair 22-24 AWG wire for this purpose.
For DualPACs, the +Sense pins are available on connectors designated as J2A-2 and
J2B-2 for outputs A and B, respectively. –Sense pins are on J2A-3 and J2B-3, respectively.
These pins are also duplicated on the power connectors J1A and J1B.
Reminder: Only units with Autosense will automatically operate in Local Sense mode
if no sense connections are made. It will operate in remote sense mode if Remote Sense
connections are made. Units without Autosense MUST have sense connections (Local
or Remote) terminated to their respective output for the unit to operate properly.
Signal Ground
2
Vcc In
4
J3
20K
10K
2N2222
10K
1
Power Good
3
Power Good
Figure 8.
Power Good and Vcc