FNP1500/1800 Front-Ends
& FNR-3 Power Shelf Data Sheet
SUB-D Output Connector Pinout and Signal Specification (Continued)
Output Connector
Description
Pin
Low level
High level
V max
I max
Type
Location
I2C compatible signal
referenced to logic GND
CLOCK, I2C clock line
25
26
27
5 V or 3.3 V logic
Auxiliary power +12 V
(Output 2)
Vo2+ Aux output, insulated from main output
Vo2- Aux output, insulated from main output
Auxiliary power ground
(Output 2)
Internally connected over 10 ꢀ to Vo2-, Auxiliary
GND. Wire separately from auxiliary and main output
GND to minimize noise and avoid voltage drops on
signal- and I2C return. Leave open if not used.
Logic Gnd
28
Open or connected to V sense-
V sense- (+8 % Vo1) or V sense+ (-8 % Vo1)
60V
60V
60V
Output margin PSU 1
Output margin PSU 2
Output margin PSU 3
29
30
31
Open or connected to V sense-
V sense- (+8 % Vo1) or V sense+ (-8 % Vo1)
Open or connected to V sense-
V sense- (+8 % Vo1) or V sense+ (-8 % Vo1)
NC
NC
NC
NC
NC
NC
32
33
34
35
36
37
Synchronized start-up circuit for paralleling operation
Because of hiccup overcurrent protection, when a supply reaches an overcurrent limit, the output voltage will
immediately turn OFF and after a delay turn ON again. In parallel use, all power supplies have to start synchronized
because of the internal hiccup behavior. Otherwise, the supply which has reached overcurrent first will go to hiccup;
this will overload the other supplies, which then will also go to hiccup. When the first supply has recovered from
hiccup (hiccup dead time), the others remain in hiccup. This will immediately drive the first one into hiccup once
again. This means that without a start-up circuit, a system with several power supplies can never recover from an
overload condition or start-up into full load.
The following additional circuit, required to reach synchronized startup, is already implemented inside the
FNR-3-12G and FNR-3-48G shelves.
MCD10074 Rev. 1.2, 15-Apr-10
Page 13 of 17
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