MCD10085 Rev. 1.1, 08-Jul-10 Page 5 of 30 www.power-one.com
SQM48 Series Data Sheet
SemiQ
TM
Family 25A DC-DC Converters
Protection Features
Input Undervoltage Lockout
Input undervoltage lockout is standard with this converter.
The converter will shut down when the input voltage drops
below a pre-determined voltage.
The input voltage must be at least 35 V for the converter to
turn on. Once the converter has been turned on, it will shut
off when the input voltage drops below 31 V. This feature is
beneficial in preventing deep discharging of batteries used in
telecom applications.
Output Overcurrent Protection (OCP)
The converter is protected against overcurrent or short cir-
cuit conditions. Upon sensing an overcurrent condition, the
converter will switch to constant current operation and there-
by 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.
Output Overvoltage 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 refer-
ence, 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.
Overtemperature Protection (OTP)
The converter will shut down under an overtemperature con-
dition to protect itself from overheating caused by operation
outside the thermal derating curves, or operation in abnor-
mal conditions such as system fan failure. After the conver-
ter has cooled to a safe operating temperature, it will auto-
matically restart.
Safety Requirements
The converters meet North American and International safe-
ty regulatory requirements per UL60950 and EN60950
(pending). 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 be-
low provides the recommended fuse rating for use with this
family of products.
Output Voltage Fuse Rating
2.5 V 4-
2.0 - 1.5 V 3-
1.2 V 2.5-
Modules are UL approved for maximum fuse rating of 15-A.
To protect a group of modules 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 characte-
ristics 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 distur-
bance 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 of converters pass the requirements of Class
B conducted emissions per EN55022 and FCC, and meet at
a minimum, Class A radiated emissions per EN 55022 and
Class B per FCC Title 47CFR, Part 15-J. Please contact
di/dt 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.
