DCM4623xD2K26E0y7z
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
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
temperature fault is registered, the powertrain immediately stops
switching, the output voltage of the converter falls, and the converter
remains disabled for at least time tFAULT. Then, the converter waits for
the internal temperature to return to below TINT-OTP before
n Current rating (usually greater than the DCM converter’s
maximum current)
n Maximum voltage rating (usually greater than the maximum
possible input voltage)
n Ambient temperature
recovering. Provided the converter is still enabled, the DCM will
n Breaking capacity per application requirements
n Nominal melting I2t
restart after tINIT and tON
.
Output Overvoltage Fault Protection (OVP)
n Recommended fuse: See Agency Approvals for Recommended Fuse
http://www.vicorpower.com/dc-dc/isolated-
regulated/dcm#Documentation
The converter monitors the output voltage during each switching
cycle by a corresponding voltage reflected to the primary side control
circuitry. If the primary sensed output voltage exceeds VOUT-OVP, the
OVP fault protection is triggered. The control logic disables the
powertrain, and the output voltage of the converter falls.
Fault Handling
Input Undervoltage Fault Protection (UVLO)
This type of fault is latched, and the converter will not start again
until the latch is cleared. Clearing the fault latch is achieved by either
disabling the converter via the EN pin, or else by removing the input
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
power such that the input voltage falls below VIN-INIT
.
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.
External Output Capacitance
The DCM converter internal compensation requires a minimum
external output capacitor. An external capacitor in the range of 220
to 2200 µF with ESR of 10 mΩ is required, per DCM for control loop
compensation purposes.
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.
However some DCM models require an increase to the minimum
external output capacitor value in certain loading and trim
condition. In applications where the load can go below 10ꢀ of rated
load but the output trim is held constant, the range of output
capacitor required is given by COUT-EXT-TRANS in the Electrical
Specifications table. If the load can go below 10ꢀ of rated load and
the DCM output trim is also dynamically varied, the range of output
capacitor required is given by COUT-EXT-TRANS-TRIM in the Electrical
Specifications table.
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
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.
Light Load Boosting
Under light load conditions, the DCM converter may operate in light
load boosting depending on the line voltage. Light load boosting
occurs whenever the internal power consumption of the converter
combined with the external output load is less than the minimum
power transfer per switching cycle. In order to maintain regulation,
the error amplifier will switch the powertrain off and on repeatedly,
to effectively lower the average switching frequency, and permit
operation with no external load. During the time when the power
train is off, the module internal consumption is significantly
reduced, and so there is a notable reduction in no-load input power
in light load boosting. When the load is less than 10ꢀ of rated Iout,
the output voltage may rise by a maximum of 2.53 V, above the
output voltage calculated from trim, temperature, and load
line conditions.
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.
Output Undervoltage Fault Protection (UVP)
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
DCM™ DC-DC Converter
Rev 1.0
Page 18 of 23
12/2017
VICOR [ VICOR CORPORATION ]
