GE Industrial Solutions NaOS NXA025 SMT - Manual (Page 10)

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 10
Feature Description
Remote On/Off using SEQ/ENA Pin
The NXA025A0X-S SMT power modules feature an
SEQ/ENA pin for remote On/Off operation. If not using
the remote On/Off pin, leave the pin open (module will be
on). The SEQ/ENA signal (V
SEQ/ENA ) is referenced to
ground. Circuit configuration for remote On/Off operation
of the module using SEQ/ENA pin is shown in Figure 25.
During Logic High on the SEQ/ENA pin (transistor Qx is
OFF), the module remains OFF. The external resistor
Rx should be chosen to maintain 3.5V minimum on the
SEQ/ENA pin to insure that the unit is OFF when
transistor Qx is in the OFF state. During Logic-Low
when Qx is turned ON, the module is turned ON. Note
that the external diode is required to make sure the
internal thermal shutdown (THERMAl_SD) and
undervoltage (UVLO) circuits are not disabled when Qx is
turned ON
V
IN
R
2
R
1
Qx
1k
4.99k
Enable
UVLO
THERMAL_SD
SEQ/ENA
Pin
Rx
4.99k
Dx
Figure 25. Remote On/Off Implementation.
The SEQ/ENA pin can also be used to synchronize the
output voltage start-up and shutdown of multiple modules
in parallel. By connecting SEQ/ENA pins of multiple
modules, the output start-up can be synchronized (please
refer to characterization curves). When SEQ/ENA pins
are connected together, all modules will shutdown if any
one of the modules gets disabled due to undervoltage
lockout or overtemperature protection.
Remote Sense
Remote sense feature minimizes the effects of
distribution losses by regulating the voltage at the remote
sense pins. The voltage between the remote sense pins
and the output terminals must not exceed the remote
sense range given in the Feature Specification table, i.e.:
[Vo
(+) – Vo (GND) ] –[SENSE (+) – SENSE (-) ] < 0.5V
Remote sense configuration is shown in Figure 26. If not
using the remote sense feature to regulate the output
voltage at the point of load, connect SENSE (+) to Vo(+)
and Sense (-) to ground. The amount of power delivered
by the module is defined as the voltage at the output
terminals multiplied by the output current. When using
the remote sense, the output voltage of the module can
be increased, which at the same output current would
increase the power output of the module. Ensure that the
maximum output power of the module remains at or
below the maximum rated power (Po,max = Io,max x
Vo,max).
Figure 26. Effective Circuit Configuration for Remote
sense operation
Overcurrent Protection
To provide protection in a fault (output overload)
condition, the unit is equipped with internal
current-limiting circuitry and can endure current limiting
continuously. At the point of current-limit inception, the
unit enters hiccup mode. The unit operates normally once
the output current is brought back into its specified range.
The average output current during hiccup is 10% I
O, max
.
Input Undervoltage Lockout
At input voltages below the input undervoltage lockout
limit, module operation is disabled. The module will begin
to operate at an input voltage above the undervoltage
lockout turn-on threshold.
Overtemperature Protection
To provide protection in a fault condition, the unit is
equipped with a thermal shutdown circuit. The unit will
shutdown if the thermal reference point T
ref
, exceeds
125 o C (typical), but the thermal shutdown is not
intended as a guarantee that the unit will survive
temperatures beyond its rating. The module will
automatically restarts after it cools down.
Output Voltage Programming
The output voltage of the NXA025A0X-S can be
programmed to any voltage from 0.8Vdc to 5.5Vdc by
inserting a series resistor (shown as Rtrim in figure 27) in
the Sense(+) pin of the module. Without an external
resistor in the Sense
(+) pin (Sense (+) pin is shorted to
Vo (+) ), the output voltage of the module will be 0.7887V.
With Sense (+) not connected to Vo (+) , the output of the
module will reach overvoltage shutdown. A 1μF multi-
layer ceramic capacitor is required from Rtrim to Sense
(-)
pin to minimize noise. To calculate the value of the