PRM48AY480X400A00 Datasheet, PDF (29/44 Pages) Vicor Corporation – High Efficiency Converter

When CONTROL NODE falls below 0.79 V, the converter will stop
switching. An internal circuit clamps the modulator input to 7.40 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.
+
VIN
-
CONTROL NODE
+
VCN
-
rEQ_IN
CIN_INT
RCN
ICN_LOW
VCN · GCN
rEQ_OUT
+
COUT_INT
-
Figure 24 — PRM48Ay480x400A00 AC small signal model
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.
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.
PRM48Ay480x400A00
Design Guidelines
The PRM48Ay480x400A00 regulator is specifically designed to
provide a controlled Factorized Bus distribution voltage for powering
downstream VTM Transformer — fast, efficient, isolated, low noise
Point-of-Load (POL) converters.
The PRM48Ay480x400A00 can be configured for two operating
modes depending on the type of regulation required.
In Adaptive Loop Operation the regulation circuitry is enabled
within the device and regulates the voltage at the output terminals.
The PRM48Ay480x400A00 has a programmable Adaptive Loop load
line which can be used to compensate for downstream VTM output
resistance allowing for precise point of load regulation without the
need for remote sensing.
In Remote Sense Operation, the internal regulation circuitry is
disabled and the voltage regulation circuitry is provided externally
allowing for remote sensing directly at the point of load. In certain
applications Remote Sense Operation can improve regulation
accuracy, and allow for operating with high amounts of load
capacitance and optimizing load transient response.
Operating Mode Selection
The operating mode is selected through use of the TRIM pin.
When the part is first enabled after V_IN is applied, the TRIM voltage is
sampled. The TRIM pin has an internal pull up resistor to V_{CC_INT}, so
unless external circuitry pulls the pin voltage lower,
it will float up to V_{CC_INT}.
If TRIM is pulled lower than 0.45 V during the first startup after
V_IN is applied, the part will be configured for Remote Sense / Slave
Operation, where the internal voltage regulation circuitry is disabled.
In this case, for all subsequent operation the part will output a
voltage dependent on the SHARE / CONTROL NODE voltage
provided externally (either from an external regulation circuit or
master PRM).
To configure the part for Remote Sense or Slave Operation, connect
the TRIM pin to SGND. It is recommended to make this connection
through a 0 Ω jumper for troubleshooting purposes.
If the sampled TRIM voltage is higher than 0.55 V during the first
startup after V_IN is applied, then the part will be configured for
Adaptive Loop Operation, and the internal voltage regulation
circuitry is enabled. The PRM will output a voltage dependent on the
TRIM voltage, and will remain in this mode for as long as
V_IN is applied.
To configure the part for Adaptive Loop Operation, leave the TRIM
pin disconnected, or apply a voltage/resistance within the specified
range.
The operating mode is detected during the first start up after V_IN is
applied. This selection persists until V_IN is removed from the part,
and is not changed by fault or disable events. Changing the operating
mode can only be done by removing V_IN.
PRM^TM Regulator
Page 29 of 44
Rev 1.4
11/2015
vicorpower.com
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