DCD24AP480T320A50 Datasheet, PDF (18/25 Pages) Vicor Corporation – DCM™ DC-DC Converter

Design Guidelines
Building Blocks and System Design
The DCM™ converter input accepts the full 18.0 to 36.0 V range, and
it generates an isolated trimmable 48.0 Vdc output. Multiple DCMs
may be paralleled for higher power capacity via wireless load
sharing, even when they are operating off of different input voltage
supplies.
The DCM converter provides a regulated output voltage around
defined nominal load line and temperature coefficients. The load line
and temperature coefficients enable configuration of an array of
DCM converters which manage the output load with no share bus
among modules. Downstream regulators may be used to provide
tighter voltage regulation, if required.
The DCM24AP480x320A50 may be used in standalone applications
where the output power requirements are up to 320 W. However, it is
easily deployed as arrays of modules to increase power handling
capacity. Arrays of up to eight units have been qualified for 2560 W
capacity. Application of DCM converters in an array requires no
derating of the maximum available power versus what is specified
for a single module.
Soft Start
When the DCM starts, it will go through a soft start. The soft start
routine ramps the output voltage by modulating the internal error
amplifier reference. This causes the output voltage to approximate a
piecewise linear ramp. The output ramp finishes when the voltage
reaches either the nominal output voltage, or the trimmed output
voltage in cases where trim mode is active.
During soft-start, the maximum load current capability is reduced.
Until Vout achieves at least V_{OUT-FL-THRESH}, the output current must be
less than I_OUT-START in order to guarantee startup. Note that this is
current available to the load, above that which is required to charge
the output capacitor.
Nominal Output Voltage Load Line
Throughout this document, the programmed output voltage, (either
the specified nominal output voltage if trim is inactive or the
trimmed output voltage if trim is active), is specified at full load, and
at room temperature. The actual output voltage of the DCM is given
by the programmed trimmed output voltage, with modification
based on load and temperature. The nominal output voltage is 48.0
V, and the actual output voltage will match this at full load and room
temperature with trim inactive.
The largest modification to the actual output voltage compared to
the programmed output is due to the 5.263% V_OUT-NOM load line,
which for this model corresponds to ΔV_OUT-LOAD of 2.5262V. As the
load is reduced, the internal error amplifier reference, and by
extension the output voltage, rises in response. This load line is the
primary enabler of the wireless current sharing amongst an array of
DCMs.
The load line impact on the output voltage is absolute, and does not
scale with programmed trim voltage.
For a given programmed output voltage, the actual output voltage
versus load current at for nominal trim and room temperature is
given by the following equation:
V_OUT @ 25° = 48.0 + 2.5262 • (1 - I_OUT / 6.67)
(1)
DCM™ DC-DC Converter
Page 18 of 25
Rev 1.1
07/2015
DCM24AP480x320A50
Nominal Output Voltage Temperature Coefficient
A second additive term to the programmed output voltage is based
on the temperature of the module. This term permits improved
thermal balancing among modules in an array, especially when the
factory nominal trim point is utilized (trim mode inactive). This term
is much smaller than the load line described above, representing
only a -6.40 mV/°C change. Regulation coefficient is relative to 25°C.
For nominal trim and full load, the output voltage relates to the
temperature according to the following equation:
V_OUT-FL = 48.0 -6.400 • 0.001 • (T_INT - 25)
(2)
where T_INT is in °C.
The impact of temperature coefficient on the output voltage is
absolute, and does not scale with trim or load.
Trim Mode and Output Trim Control
When the input voltage is initially applied to a DCM, and after t_INIT
elapses, the trim pin voltage V_TR is sampled. The TR pin has an
internal pull up resistor to V_CC, so unless external circuitry pulls the
pin voltage lower, it will pull up to V_CC. If the initially sampled trim
pin voltage is higher than V_TRIM-DIS, then the DCM will disable
trimming as long as the V_IN remains applied. In this case, for all
subsequent operation the output voltage will be programmed to the
nominal. This minimizes the support components required for
applications that only require the nominal rated Vout, and also
provides the best output setpoint accuracy, as there are no additional
errors from external trim components
If at initial application of V_IN, the TR pin voltage is prevented from
exceeding V_TRIM-EN, then the DCM will activate trim mode, and it will
remain active for as long as V_IN is applied.
V_OUT set point under full load and room temperature can be
calculated using the equation below:
V_OUT-FL @ 25°C = 19.95 + (37.560 • V_TR/V_CC) (3)
Note that the trim mode is not changed when a DCM recovers from
any fault condition or being disabled.
Module performance is guaranteed through output voltage trim
range V_OUT-TRIMMING. If V_OUT is trimmed above this range, then certain
combinations of line and load transient conditions may trigger the
output OVP.
Overall Output Voltage Transfer Function
Taking load line (equation 1), temperature coefficient (equation 2)
and trim (equation 3) into account, the general equation relating the
DC V_OUT to programmed trim (when active), load, and temperature is
given by:
V_OUT = 19.95 + (37.560 • Vtr/Vcc)
+ 2.5262 • (1 - I_OUT / 6.67)
-6.400 • 0.001 • (T_INT -25) + ∆V_OUT-LL
(4)
Finally, note that when the load current is below 10% of the rated
capacity, there is an additional ∆V which may add to the output
voltage, depending on the line voltage which is related to Burst
Mode. Please see the section on Burst Mode below for details.
Use 0 V for ∆V_OUT-LL when load is above 10% of rated load. See
section on Burst Mode operation for light load effects on output
voltage.
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