DCM300P280x500A40
Output Current Limit
n Maximum voltage rating (usually greater than the maximum
The DCM features a fully operational current limit which effectively
keeps the module operating inside the Safe Operating Area (SOA) for
all valid trim and load profiles. The current limit approximates a
“brick wall” limit, where the output current is prevented from
exceeding the current limit threshold by reducing the output voltage
via the internal error amplifier reference. The current limit threshold
at nominal trim and below is typically 120% of rated output current,
but it can vary between 100% to 130%. In order to preserve the SOA,
when the converter is trimmed above the nominal output voltage,
the current limit threshold is automatically reduced to limit the
available output power.
possible input voltage)
n Ambient temperature
n Breaking capacity per application requirements
n Nominal melting I2t
n Recommended fuse: See Agency Approvals for Recommended Fuse
http://www.vicorpower.com/dc-dc-converter-board-mount/dcm-
dc-dc_converter#Documentation
Fault Handling
Input Undervoltage Fault Protection (UVLO)
When the output current exceeds the current limit threshold, current
limit action is held off by 1ms, which permits the DCM to
momentarily deliver higher peak output currents to the load. Peak
output power during this time is still constrained by the internal
Power Limit of the module. The fast Power Limit and relatively slow
Current Limit work together to keep the module inside the SOA.
Delaying entry into current limit also permits the DCM to minimize
droop voltage for load steps.
The converter’s input voltage is monitored to detect an input under
voltage condition. If the converter is not already running, then it will
ignore enable commands until the input voltage is greater than
VIN-UVLO+. If the converter is running and the input voltage falls
below VIN-UVLO-, the converter recognizes a fault condition, the
powertrain stops switching, and the output voltage of the unit falls.
Input voltage transients which fall below UVLO for less than tUVLO
may not be detected by the fault proection logic, in which case the
converter will continue regular operation. No protection is required
in this case.
Sustained operation in current limit is permitted, and no derating of
output power is required, even in an array configuration.
Some applications may benefit from well matched current
distribution, in which case fine tuning sharing via the trim pins
permits control over sharing. The DCM does not require this for
proper operation, due to the power limit and current limit behaviors
described here.
Once the UVLO fault is detected by the fault protection logic, the
converter shuts down and waits for the input voltage to rise above
VIN-UVLO+. Provided the converter is still enabled, it will then restart.
Input Overvoltage Fault Protection (OVLO)
The converter’s input voltage is monitored to detect an input over
voltage condition. When the input voltage is more than the
Current limit can reduce the output voltage to as little as the UVP
threshold (VOUT-UVP). Below this minimum output voltage
compliance level, further loading will cause the module to shut
down due to the output undervoltage fault protection.
VIN-OVLO+, a fault is detected, the powertrain stops switching, and the
output voltage of the converter falls.
After an OVLO fault occurs, the converter will wait for the input
voltage to fall below VIN-OVLO-. Provided the converter is still enabled,
the powertrain will restart.
Line Impedance, Input Slew rate and Input Stability Requirements
Connect a high-quality, low-noise power supply to the +IN and –IN
terminals. Additional capacitance may have to be added between +IN
and –IN to make up for impedances in the interconnect cables as
well as deficiencies in the source.
The powertrain controller itself also monitors the input voltage.
Transient OVLO events which have not yet been detected by the fault
sequence logic may first be detected by the controller if the input
slew rate is sufficiently large. In this case, powertrain switching will
immediately stop. If the input voltage falls back in range before the
fault sequence logic detects the out of range condition, the
powertrain will resume switching and the fault logic will not
interrupt operation Regardless of whether the powertrain is running
at the time or not, if the input voltage does not recover from OVLO
before tOVLO, the converter fault logic will detect the fault.
Excessive source impedance can bring about system stability issues
for a regulated DC-DC converter, and must either be avoided or
compensated by filtering components. A 100 µF input capacitor is
the minimum recommended in case the source impedance is
insufficient to satisfy stability requirements.
Additional information can be found in the filter design application
note:
www.vicorpower.com/documents/application_notes/vichip_appnote23.pdf
Output Undervoltage Fault Protection (UVP)
Please refer to this input filter design tool to ensure input stability:
http://app2.vicorpower.com/filterDesign/intiFilter.do.
The converter determines that an output overload or short circuit
condition exists by measuring its primary sensed output voltage and
the output of the internal error amplifier. In general, whenever the
powertrain is switching and the primary-sensed output voltage falls
below VOUT-UVP threshold, a short circuit fault will be registered. Once
an output undervoltage condition is detected, the powertrain
immediately stops switching, and the output voltage of the converter
falls. The converter remains disabled for a time tFAULT. Once recovered
and provided the converter is still enabled, the powertrain will again
Ensure that the input voltage slew rate is less than 1V/us, otherwise a
pre-charge circuit is required for the DCM input to control the input
voltage slew rate and prevent overstress to input stage components.
Input Fuse Selection
The DCM is not internally fused in order to provide flexibility in
configuring power systems. Input line fusing is recommended at the
system level, in order to provide thermal protection in case of
catastrophic failure. The fuse shall be selected by closely matching
system requirements with the following characteristics:
enter the soft start sequence after tINIT and tON
.
Temperature Fault Protections (OTP)
The fault logic monitors the internal temperature of the converter. If
the measured temperature exceeds TINT-OTP, a temperature fault is
registered. As with the under voltage fault protection, once a
n Current rating (usually greater than the DCM converter’s
maximum current)
DCM™ DC-DC Converter
Rev 1.1
vicorpower.com
800 927.9474
Page 19 of 25
10/2015
VICOR [ VICOR CORPORATION ]
