PRM48BF480T500A00 Datasheet, PDF (26/45 Pages) Vicor Corporation – PRM™ Regulator

PRM48B x 480 y 500A00
REF: Reference (Adaptive Loop operation)
This output pin allows you to monitor the internal reference
voltage in Adaptive Loop operation. During normal operation it
represents the output voltage scaled by a factor of 20.
In Adaptive Loop operation this pin is for monitoring purposes
only and should not be driven or loaded externally.
REF_EN: Reference Enable (Remote Sense operation)
In Remote Sense operation this pin outputs a regulated 3.25V,
4mA voltage source. It is enabled only after successful start up
of the PRM powertrain REF_EN is intended to power the
output current transducer and also the voltage reference for
the external control loop. Powering the reference generator
with REF_EN helps provide a controlled start up, since the
output voltage of the system is able to track the reference level
as it comes up.
SHARE (Adaptive Loop and Slave operation)
This bus sets the output current level for all the PRM modules
when operating in an array (master-slave configuration).
Connect them together among the modules in the shared bus.
One PRM should be configured as a master by connecting
TRIM for Adaptive Loop operation. All other PRMs should be
configured as slaves by pulling their respective TRIM pins low.
This pin can be used to monitor the error voltage externally.
0 to 100% load is represented by a voltage between
0.79 V and 7.40.
CONTROL NODE (Remote Sense operation)
In Remote Sense operation, this is the input to the modulator
which determines the powertrain timing and ultimately the
module output power. An internal 0.5 mA current sink is
always active. The bi-directional buffer between CONTROL
NODE and the modulator has two states. In normal operation,
CONTROL NODE will be above the 0.79 V switching
threshold, and will drive the modulator through the buffer. An
internal 7.4V clamp determines the maximum output power
that can be requested of the modulator.
When CONTROL NODE falls below 0.79 V, the converter will
stop switching. An internal circuit clamps the modulator input
to 0.79 V, and a buffer will source up to 2.5 mA out of the pin
at that clamp level. For this reason, the output impedance of
the amplifier driving CONTROL NODE must be taken into
account. A rail-to-rail operational amplifier with low output
impedance is always recommended.
The powertrain small signal (plant) response consists of a
single pole determined by the load resistance, the powertrain
equivalent output resistance, and the total output capacitance
(internal and external to the module). Both the modulator gain
and the equivalent output resistance vary as a function of line,
load and output voltage. As the load increases, the powertrain
pole moves to higher frequency. As a result, the closed loop
crossover frequency will be the highest at full load and lowest
at minimum load. Figure 24 shows a reference AC small-signal
model.
+
CIN_INT
V_IN
rEQ_IN
-
+
+
RCN
I_{CN_Low}
VCN · GCN
rEQ_OUT
COUT_INT
-
-
Figure 24 – PRM48B[x]480[y]500A00 AC small signal
model
IFB: Current Feedback (Remote Sense operation)
In Remote Sense operation, IFB is the input for the module
output overcurrent protection and current limit features. A
voltage proportional to the powertrain output current must be
applied to IFB in order for overcurrent protection to operate
properly.
If the IFB voltage exceeds the IFB pin’s overcurrent protection
threshold, the powertrain will stop switching. If the IFB voltage
falls below the overcurrent protection threshold within t_BLANK
time, then the powertrain will immediately resume switching.
Otherwise a fault is detected.
The current limit threshold for the IFB pin is set lower than the
protection threshold. When the IFB pin average voltage
exceeds the current limit threshold, an internal integrator will
activate a clamp amplifier which overrides the modulator input
maximum level. This causes the powertrain to maintain a
constant output current.
The bandwidth of this current limit integrator is significantly
slower than that of the CONTROL NODE input. Therefore this
current limit cannot be used in lieu of properly compensating
the (external) control loop to avoid exceeding maximum
current or power ratings for the device.
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Rev. 1.0
11/2012