UG:108
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Applications Engineering: 800 927.9474
Page 21
Interface Connections (Cont.)
Power Good (P2-3)
The optional Power Good signal on P2-3 is referenced to Signal Ground on P2-1, 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. In addition to the electrical Power Good signal, the QPAC (XQ) comes
with a DC OK LED as a standard feature.
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. Good circuit and cause a negative
Power Good signal.
Power Good Inverted (P2-2)
This is the inverse of the Power Good signal and is referenced to Signal Ground on P2-1.
Signal Ground (P2-1)
Signal Ground on P2-1 is an isolated secondary ground reference for P2 status signals. 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 J1.
Vcc In (P2-4)
The Vcc In on P2-4 is an input that re5 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 P2-4, then at least one J10 Signal
Ground must be connected to Signal Ground on P2-1.
+Sense/ –Sense (P2-7 and P2-6)
The +Sense on P2-7 should be connected to the +Power Out, and the –Sense on P2-6 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.
Figure 9.
Power Good and Vcc
Signal Ground
2
Vcc In
4
P2
10K
2.49K
2N2222
2.49K
1
Power Good
3
Power Good Inverted
