GE Industrial Solutions NaOS NXA025 SMT - Manual (Page 11)

Data Sheet
October 5, 2009 Naos TM NXA025 SMT Non-isolated Power Modules:
10 – 14Vdc Input; 0.8Vdc to 5.5Vdc Output; 25A output current
LINEAGE POWER 11
Feature Descriptions (continued)
Output Voltage Programming (continued)
resistor Rtrim for a particular desired voltage Vo, use the
following equation:
Ω
⎥⎦
⎤
⎢⎣
⎡
− = 1
7887 . 0
* 775
Vo
Rtrim
Where Vo is the desired output voltage
and Rtrim is the external resistor in ohms
For example, to program the output voltage of the
NXA025A0X-S module to 2.5Vdc, Rtrim is calculated as
follows:
⎥⎦
⎤
⎢⎣
⎡
− = 1
7887 . 0
5 . 2
* 775 Rtrim
Ω = 1682 Rtrim
V
O
COM
V
IN
(+)
COM
R
LOAD
R
trim
Sense+
Sense-
1µF ENA Share
Figure 27. Circuit Configuration for Programming
Output voltage
Table 1 provides Rtrim values required for most common
output voltages. To achieve the output voltage tolerance
as specified in the electrical specifications over all
operating input voltage, resistive load and temperature
conditions, use 0.1% thick metal film resistor.
Table 1
Vo,set
(V)
Rtrim
Ω
0.8 11
1.0 208
1.2 404
1.5 699
1.8 994
2.0 1190
2.5 1682
3.3 2468
5.0 4138
Overvoltage Shutdown Open
Forced Load sharing (Parallel Operation)
For additional power requirements, the power module can
be configured for parallel operation with forced load
sharing (See Figure 28). Good layout techniques should
be observed for noise immunity when using multiple units
in parallel. To implement forced load sharing, the
following connections should be made:
• The share pins of all units in parallel must be
connected together. The path of these connections
should be as direct as possible.
• All remote-sense pins should be connected to the
power bus at the same point, i.e., connect all the
SENSE
(+) pins to the (+) side of the bus and all the
SENSE (-) pins to the GROUND of the power bus at
the same point. Close proximity and directness are
necessary for good noise immunity
The share bus is not designed for redundant operation
and the system will be non-functional upon failure of one
of the unit when multiple units are in parallel. The
maximum number of modules tied to share bus is 5.
When not using the parallel feature, leave the share pin
open.
Figure 28. Circuit Configuration for modules in
parallel.