February 16, 2009
QSW025A0B Series Power Modules; DC-DC Converters
36 – 75Vdc Input; 12Vdc Output; 25A Output Current
To provide protection in a fault output overload condition,
the module is equipped with internal current-limiting
circuitry and can endure current limiting for a few mili-
seconds. If the overcurrent condition persists beyond a
few milliseconds, the module will shut down and remain
latched off. The overcurrent latch is reset by either
cycling the input power or by toggling the on/off pin for
one second. If the output overload condition still exists
when the module restarts, it will shut down again. This
operation will continue indefinitely until the overcurrent
condition is corrected.
An auto-restart option is also available. An auto-restart
feature continually attempts to restore the operation until
fault condition is cleared.
Two remote on/off options are available. Positive logic
remote on/off turns the module on during a logic-high
voltage on the ON/OFF pin, and off during a logic low.
Negative logic remote on/off turns the module off during
a logic high and on during a logic low. Negative logic,
device code suffix "1," is the factory-preferred
configuration. The on/off circuit is powered from an
internal bias supply. To turn the power module on and
off, the user must supply a switch to control the voltage
between the on/off terminal and the Vi (-) terminal
(Von/off). The switch can be an open collector or
equivalent (see Figure 12). A logic low is Von/off = -0.3V
to 0.8V. The typical Ion/off during a logic low is 10 µA.
The switch should maintain a logic-low voltage while
sinking 10µA. During a logic high, the maximum Von/off
generated by the power module is 3.5V. The maximum
allowable leakage current of the switch at Von/off = 2.0V
is 4µA. If using an external voltage source, the maximum
voltage V on/off on the pin is 13.5V with respect to the
Vi (-) terminal.
If not using the remote on/off feature, perform one of the
following to turn the unit on:
For negative logic, short ON/OFF pin to VI(-).
For positive logic: leave ON/OFF pin open.
Figure 12. Remote On/Off Implementation.
Output Overvoltage Clamp
The output overvoltage clamp consists of a control
circuit, independent of the primary regulation loop, that
monitors the voltage on the output terminals and clamps
the voltage when it exceeds the overvoltage set point.
The control loop of the clamp has a higher voltage set
point than the primary loop. This provides a redundant
voltage control that reduces the risk of output
These modules feature an overtemperature protection
circuit to safeguard against thermal damage. The circuit
shuts down and latches off the module when the
maximum device reference temperature is exceeded.
The module can be restarted by cycling the dc input
power for at least one second or by toggling the remote
on/off signal for at least one second.
Input Under/Over voltage Lockout
At input voltages above or below the input under/over
voltage lockout limits, module operation is disabled. The
module will begin to operate when the input voltage level
changes to within the under and overvoltage lockout
Active Load Sharing (Parallel Operation with
For additional power requirements, the power module
can be configured for parallel operation with active load
sharing. Good layout techniques should be observed
for noise immunity when using multiple units in parallel.
To implement active load sharing, the following
requirements should be followed:
The share pins of all units in parallel must be
connected together. The path of these connections
should be as direct as possible. Vin(-) is the return
for the active share signal for each module;
therefore, all modules in parallel must use the same
Vin source. The share signal trace should be placed
as close to the Vin(-) power plane as possible.
These modules contain circuitry to block reverse
current flow upon start-up, when output voltage is
present from other parallel modules, eliminating the
requirement for external output ORing devices.
However, output ORing devices should be used, if
fault tolerance is desired in parallel applications.
When using modules in parallel without output
ORing devices, the On/Off signal for one module
shall be 40mS ahead of the other modules, to allow
output voltage to be established, before the
remaining modules startup. If using output ORing
devices, the 40mS delay is not required.
When not using the parallel feature, leave the share