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Rev 0.2, 3-Mar-11
www.power-one.com
Page 8 of 14
SQL48T20033 DC-DC Converter
36-75 VDC Input; 3.3 VDC @ 20A Output
Preliminary Data Sheet
Characterization
General Information
The converter has been characterized for many
operational aspects, to include thermal derating
(maximum load current as a function of ambient
temperature and airflow), efficiency, startup and
shutdown parameters, output ripple and noise,
transient response to load step-change, overcurrent,
and short circuit.
The
following
pages
contain
specific
plots
or
waveforms associated with the converter. Additional
comments for specific data are provided below.
Test Conditions
All data presented were taken with the converter
soldered to a test board, specifically a 0.060” thick
printed wiring board (PWB) with four layers. The top
and bottom layers were not metalized. The two inner
layers, comprised of two-ounce copper, were used to
provide traces for connectivity to the converter.
The lack of metallization on the outer layers as well
as the limited thermal connection ensured that heat
transfer from the converter to the PWB was
minimized. This provides a worst-case but consistent
scenario for thermal derating purposes.
All measurements requiring airflow were made in the
vertical
and/or
horizontal
wind
tunnel
using
Infrared(IR) thermography and thermocouples for
thermometry.
Ensuring components on the converter do not
exceed their ratings is important to maintaining high
reliability. If one anticipates operating the converter
at or close to the maximum loads specified in the
derating curves, it is prudent to check actual
operating
temperatures
in
the
application.
Thermographic
imaging
is
preferable;
if
this
capability is not available, then thermocouples may
be used. The use of AWG #36 gauge thermocouples
is recommended to ensure measurement accuracy.
Careful routing of the thermocouple leads will further
minimize measurement error. Refer to Figure H for
the optimum measuring thermocouple location.
Thermal Derating – Air Cooled
Load current vs. ambient temperature and airflow
rates are given in Figures 1 - 3. Ambient temperature
was varied between 25°C and 85°C, with airflow
rates from 30 to 500LFM (0.15 to 2.5m/s).
For each set of conditions, the maximum load
current was defined as the lowest of:
(i) The output current at which any FET junction
temperature
does
not
exceed
a
maximum
temperature of 120°C as indicated by the thermal
measurement, or
(ii) The output current at which the temperature at the
thermocouple locations TC do not exceed 120°C. (Fig.
H)
(iii) The nominal rating of the converter (20A).
Fig. H: Locations of the thermocouples for thermal testing.
Thermal Derating
– Baseplate w/ Coldplate
The maximum load current rating vs. baseplate
temperature is provided in Figure 4. The baseplate
temperature (TB) was maintained ≤ 105°C, with an
airflow rate of
≤ 30LFM (≤ 0.15m/s) and ambient
temperature
≤ 85°C. Thermocouple measurements (in
Fig. H) were recorded with TC ≤ 120°C. The user
should design for TB ≤ 105°C.
Efficiency
Efficiency vs. load current is showing in Figure 5 for
ambient temperature (TA) of 25C, airflow rate of
300LFM (1.5m/s) with vertical mounting and input
voltages of 36V, 48V, 65V and 75V. Also, a plot of
efficiency vs. load current, as a function of ambient
temperature with Vin = 48V, airflow rate of 200 LFM (1
m/s) with vertical mounting is shown in Figure. 6.
Power Dissipation
Power dissipation vs. load current is showing in Figure
7 for TA=25C, airflow rate of 300LFM (1.5m/s) with
vertical mounting and input voltages of 36V, 48V, 65V
and 75V. Also, a plot of power dissipation vs. load
current, as a function of ambient temperature with Vin
= 48V, airflow rate of 200 LFM (1m/s) with vertical
mounting is shown in Figure. 8.
Startup
Output voltage waveforms, during the turn-on transient
using the ON/OFF pin for full rated load currents
(resistive load) are shown with and without external
load
capacitance
in
and
Thermocouple (TB)
Area
Thermocouples (TC)