MCD10208 Rev. 1.0, 08-Jul-10
Page 5 of 33
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SQM48T/S20 DC-DC Converter Data Sheet
36-75 VDC Input; 1.2-3.3 VDC @ 20A Outputs
Output Protections
All output circuit protection features are non-latching
and operate in a “hiccup” mode. After an output
protection event occurs, the converter will be turned
off, and held off for approximately 100 ms after
which, the protection circuit will reset and the
converter will attempt to restart. If the fault is still
present, the converter will repeat the above action.
Once the fault is removed, the converter will start
normally.
Output Overcurrent Protection (OCP)
The converter is protected against overcurrent or
short-circuit conditions. Upon sensing an overcurrent
condition, the converter will switch to constant
current operation and thereby begin to reduce output
voltage. When the output voltage drops below
40-50% of the nominal value of output voltage, the
converter will shut down (Fig. x.11).
Once the converter has shut down, it will attempt to
restart nominally every 100 ms with a typical 1-2%
duty cycle (Fig. x.12). The attempted restart will
continue indefinitely until the overload or short circuit
conditions are removed or the output voltage rises
above 40-50% of its nominal value.
Once the output current is brought back into its
specified range, the converter automatically exits the
hiccup mode and continues normal operation.
Output Over-Voltage Protection (OVP)
The converter will shut down if the output voltage
across Vout(+) (Pin 8) and Vout(-) (Pin 4) exceeds
the threshold of the OVP circuitry. The OVP circuitry
contains its own reference, independent of the output
voltage regulation loop. Once the converter has shut
down, it will attempt to restart every 100 ms until the
OVP condition is removed.
Over-Temperature Protection (OTP)
The converter will shut down under an over-
temperature
condition
to
protect
itself
from
overheating caused by operation outside the thermal
derating curves, or operation in abnormal conditions
such as system fan failure. After the converter has
cooled to a safe operating temperature, it will
automatically restart.
Safety Requirements
The
converters
meet
North
American
and
International safety regulatory requirements per
UL60950 and EN60950. Basic Insulation is provided
between input and output.
To comply with safety agencies requirements, an
input line fuse must be used external to the converter.
The Table below provides the recommended fuse
rating for use with this family of products.
Output Voltage
Fuse Rating
3.3V
4A
2.5 -1.8V
3A
1.5 - 1.2V
2A
All SQM converters are UL approved for maximum
fuse rating of 15 A. To protect a group of converters
with a single fuse, the rating can be increased from
the recommended values above.
Electromagnetic Compatibility (EMC)
EMC requirements must be met at the end-product
system level, as no specific standards dedicated to
EMC characteristics of board mounted component dc-
dc converters exist. However, Power-One tests its
converters to several system level standards, primary
of which is the more stringent EN55022, Information
technology
equipment
-
Radio
disturbance
characteristics - Limits and methods of measurement.
Effective internal LC differential filter significantly
reduces input reflected ripple current (Fig. x.9), and
improves EMC.
With the addition of a simple external filter, all
versions of the SQM48 Series converters pass the
requirements of Class B conducted emissions per
EN55022 and FCC requirements. Please contact
Power-One Applications Engineering for details of this
testing.
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) for vertical and horizontal
mounting,
efficiency,
start-up
and
shutdown
parameters, output ripple and noise, transient
response to load step-change, overload and short
circuit.
The figures are numbered as Fig. x.y, where x
indicates the different output voltages, and y
associates with specific plots (y = 1 for the vertical
thermal derating, …). For example, Fig. x.1 will refer
to the vertical thermal derating for all the output
voltages in general.