DCM290Y138X600A40 Datasheet, PDF (19/25 Pages) Vicor Corporation – Regulated DC Converter

Overall Output Voltage Transfer Function
Taking trim (equation 1), load line (equation 2) and temperature
coefficient (equation 3) into account, the general equation relating
the DC V_OUT at nominal line to programmed trim (when active), load,
and temperature is given by:
V_OUT = 10.00 + (6.48 • Vtr/Vcc) + 0.73 +ΔV – 0.73
• I_OUT /43.5 - 0.138 • (T_INT -25)/75
(4)
Use 0 V for ΔV when load is from 5% to 100% load, and up to 2.3 V
when operating at <5% load. See section on Burst Mode operation for
light load effects on output voltage.
Output Current Limit
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 105% of maximum output
current, but can vary from 100% to 117% of maximum output
current. In order to preserve the SOA, in cases where the converter is
trimmed above the nominal output voltage, the current limit
threshold is automatically reduced to limit the available output
power.
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.
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.
Current limit can reduce the output voltage to as little as the UVP
threshold (V_OUT-UVP). Below this minimum output voltage
compliance level, further loading will cause the module to shut
down due to the output undervoltage fault protection.
Line Impedance, Input Slew rate and Output Stability Requirements
Connect a high-quality, low-noise power supply to the +IN and –IN
terminals. An external capacitance of 0.68uF is required. 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.
Significant source impedance can bring system stability issue for a
regulated DC-DC converter and needs to be avoided or compensated.
Additional information can be found in the filter design application
note: www.vicorpower.com/documents/application_notes/
vichip_appnote23.pdf
Please refer to this input filter design tool to ensure input stability:
http://app2.vicorpower.com/filterDesign/intiFilter.do.
Ensure that the input voltage slew rate is less than 1V/us, otherwise a
DCM™ DC-DC Converter
Page 19 of 25
Rev 1.3
04/2015
DCM290P138T600A40
pre-charge circuit is required for the DCM input to control the input
voltage slew rate and prevent overstress to input stage components.
For the DCM, output voltage stability is guaranteed as long as hold
up capacitance C_OUT-EXE falls within the specified ranges.
Input Fuse Selection
DCM is not internally fused in order to provide flexibility in
configuring power systems. Input line fusing is recommended at
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:
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
n Breaking capacity per application requirements
n Nominal melting I²t
n Recommended fuse: 5A Bussmann PC-Tron
(see agency approval for additional fuses)
Fault Handling
Input Undervoltage Fault Protection (UVLO)
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
V_IN-UVLO+. If the converter is running and the input voltage falls
below V_IN-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 t_UVLO
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.
Once the UVLO fault is detected by the fault protection logic, the
converter shuts down and waits for the input voltage to rise above
V_IN-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
V_IN-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 V_IN-OVLO-. Provided the converter is still enabled,
the powertrain will restart.
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 t_OVLO, 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
vicorpower.com
800 927.9474