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Tyco Electronics Corp.
9
Data Sheet
November 2001
36 Vdc to 75 Vdc In; 3.3 Vdc and 5 Vdc Out; 16.5 W and 25 W
LUW025-Series Power Modules: dc-dc Converters:
Feature Descriptions (continued)
Output Voltage Set-Point Adjustment
(Trim) (continued)
8-715h
Figure 14. Circuit Configuration to Decrease
Output Voltage
The relationship between the output voltage and the
trim resistor value for a % reduction in output voltage
is:
Connecting an external resistor between the TRIM pin
and VO(+) pin (Radj-up) increases the output voltage set
The relationship between the output voltage and the
trim resistor value for a % increase in output voltage
is:
8-715g
Figure 15. Circuit Configuration to Increase
Output Voltage
Output Overvoltage Protection
The output overvoltage clamp consists of control cir-
cuitry, independent of the primary regulation loop, that
monitors the voltage on the output terminals. This con-
trol loop of the protection circuit has a higher voltage
set point than the primary loop (see Feature Specifica-
tions table). In a fault condition, the overvoltage clamp
ensures that the output voltage does not exceed
VO, clamp, max. This provides a redundant voltage-con-
trol that reduces the risk of output overvoltage.
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 Tref temperature is exceeded. The module
will automatically restart when the Tref temperature
cools sufficiently.
Thermal Considerations
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 is removed by convection and radiation to the sur-
rounding environment.
Considerations include ambient temperature, amount
of airflow, module power dissipation, and need for
increased reliability.
The monitor temperature reference point, Tref, refer-
enced in the specification is T1. Proper cooling can be
verified by measuring the power module’s temperature
at the top center surface of T1 as shown in Figures
17—
18. The temperature at the thermocouple location,
T1, should not exceed 110 °C during the operation of
the module. The output power of the module should not
exceed the rated power.
The thermal data presented is based on measure-
ments taken in a wind tunnel. The test setup shown in
Figure
16 was used to collect data for Figures
17—18.Note that the orientation of the module with respect to
airflow affects thermal performance. Two orientations
TRIM
VO(+)
VI(+)
ON/OFF
VI(–)
Radj-down
RLOAD
VO(–)
CASE
Radj-down
511
%
----------6.11
–
k
=
Radj-up
VO
5.11
() 100 %
+
()
1.225
%
--------------------------------------------------------------
511
%
----------
–
6.11
–
k
=
RLOAD
Radj-up
VI(+)
ON/OFF
CASE
VI(–)
VO(+)
TRIM
VO(–)