1010 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 (continued)
Output Overvoltage Protection
The output overvoltage protection consists of circuitry
that monitors the voltage on the output terminals. If the
voltage on the output terminals exceeds the overvolt-
age protection threshold, then the module will shut
down and latch off. The overvoltage latch is reset by
either cycling the input power for one second or by tog-
gling the on/off signal for one second. If the auto-restart
option is chosen, the unit will “hiccup” until the tempera-
ture is within specification.
Overtemperature Protection
These modules feature an overtemperature protection
circuit to safeguard against thermal damage. The cir-
cuit shuts down and latches off the module when the
maximum case 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. If the auto-restart option is cho-
sen, the unit will “hiccup” until the temperature is within
specification.
Thermal Considerations
Introduction
The power modules operate in a variety of thermal
environments; however, sufficient cooling should be
provided to help ensure reliable operation of the unit.
Heat-dissipating components inside the unit are ther-
mally coupled to the case. Heat is removed by conduc-
tion, convection, and radiation to the surrounding
environment. Proper cooling can be verified by mea-
suring the case temperature. Peak temperature (T
C)
occurs at the position indicated in Figure 14.
8-2104(F)
Note: Top view, pin locations are for reference only.
Measurements shown in millimeters and (inches).
Figure 14. Case Temperature Measurement
Location
The temperature at this location should not exceed
100 °C. The output power of the module should not
exceed the rated power for the module as listed in the
Ordering Information table.
Although the maximum case temperature of the power
modules is 100 °C, you can limit this temperature to a
lower value for extremely high reliability.
Heat Transfer Without Heat Sinks
Increasing airflow over the module enhances the heat
transfer via convection. Figures 15 and 16 show the
maximum power that can be dissipated by the module
without exceeding the maximum case temperature ver-
sus local ambient temperature (T
A) for natural convec-
tion through 3 m/s (600 ft./min.).
Note that the natural convection condition was mea-
sured at 0.05 m/s to 0.1 m/s (10 ft./min. to 20 ft./min.);
however, systems in which these power modules may
be used typically generate natural convection airflow
rates of 0.3 m/s (60 ft./min.) due to other heat dissipat-
ing components in the system.
8-2321(F).a
Figure 15. Forced Convection Power Derating with
No Heat Sink; Transverse Orientation
14
(0.55)
ON/OFF TRIM
(+)SENSE
(–)SENSE
33 (1.30)
VI(+)
V
I(–) VO(–)
V
O(+)
20
0
LOCAL AMBIENT TEMPERATURE, TA (°C)
POWER DISSIPATION, PD (W)
10 20 30 40 50 60 70 80 90 100
3.0 m/s (600 ft./min.)
2.0 m/s (400 ft./min.)
1.0 m/s (200 ft./min.)
15
10
5
0
0.1 m/s (20 ft./min.)
NATURAL
CONVECTION
