88 Lineage Power
Data Sheet
April 2008
36 to 75 Vdc Input, 3.3 Vdc Output; 33 W
QHW050F71 Power Modules; dc-dc Converters:
Feature Descriptions
Overcurrent Protection
To provide protection in a fault (output overload) condi-
tion, the unit is equipped with internal current-limiting
circuitry and can endure current limiting for up to one
second. If overcurrent exists for more than one second,
the unit will shut down.
At the point of current-limit inception, the unit shifts
from voltage control to current control. If the output volt-
age is pulled very low during a severe fault, the current-
limit circuit can exhibit either foldback or tailout charac-
teristics (output current decrease or increase).
The module is available in two overcurrent configura-
tions. In one configuration, when the unit shuts down it
will latch off. The overcurrent latch is reset by either
cycling the input power or by toggling the ON/OFF pin
for one second. In the other configuration, the unit will
try to restart after shutdown. If the output overload con-
dition still exists when the unit restarts, it will shut down
again. This operation will continue indefinitely until the
overcurrent condition is corrected.
Remote On/Off
Negative logic remote on/off turns the module off dur-
ing a logic high and on during a logic low. To turn the
power module on and off, the user must supply a
switch to control the voltage between the on/off termi-
nal and the V
I(–) terminal (Von/off). The switch can be an
open collector or equivalent (see Figure 10). A logic
low is V
on/off = 0 V to 1.2 V. The maximum Ion/off during a
logic low is 1 mA. The switch should maintain a logic-
low voltage while sinking 1 mA.
During a logic high, the maximum V
on/off generated by
the power module is 15 V. The maximum allowable
leakage current of the switch at V
on/off = 15 V is 50 µA.
If not using the remote on/off feature, short the ON/OFF
pin to V
I(–).
8-720(F).c
Figure 10. Remote On/Off Implementation
Remote Sense
Remote sense minimizes the effects of distribution
losses by regulating the voltage at the remote-sense
connections. The voltage between the remote-sense
pins and the output terminals must not exceed the out-
put voltage sense range given in the Feature Specifica-
tions table, i.e.:
[V
O(+) – VO(–)] – [SENSE(+) – SENSE(–)] ≤ 0.5 V
The voltage between the V
O(+) and VO(–) terminals
must not exceed the minimum output overvoltage pro-
tection value shown in the Feature Specifications table.
This limit includes any increase in voltage due to
remote-sense compensation and output voltage set-
point adjustment (trim). See Figure 11.
If not using the remote-sense feature to regulate the
output at the point of load, then connect SENSE(+) to
V
O(+) and SENSE(–) to VO(–) at the module.
Although the output voltage can be increased by both
the remote sense and by the trim, the maximum
increase for the output voltage is not the sum of both.
The maximum increase is the larger of either the
remote sense or the trim. Consult the factory if you
need to increase the output voltage more than the
above limitation.
The amount of power delivered by the module is
defined as the voltage at the output terminals multiplied
by the output current. When using remote sense and
trim, the output voltage of the module can be
increased, which at the same output current would
increase the power output of the module. Care should
be taken to ensure that the maximum output power of
the module remains at or below the maximum rated
power.
SENSE(+)
V
O(+)
SENSE(–)
V
O(–)
V
I(–)
+
–
I
on/off
ON/OFF
V
I(+)
LOAD
V
on/off
