PRM48BF480T500A00 Datasheet, PDF (32/45 Pages) Vicor Corporation – PRM™ Regulator

PRM48B x 480 y 500A00
Current Limit (Adaptive Loop operation)
In Adaptive Loop operation, the current limit is controlled by
the internal microcontroller. The current limit approximates a
“brick-wall” limit where the output current is prevented from
crossing the current limit threshold by reducing the output
voltage. The current limit threshold is pre-programmed into the
internal microcontroller and cannot be changed externally.
When the internal sensed current crosses the current limit
threshold, the current limit will be activated after the detection
time t_{LIM_SUPV}. Once activated, the microcontroller will reduce
the error amplifier reference voltage (represented by REF) in
order to maintain the output current at the limit value. Current
limit is able to reduce the output down to V_{OUT_UVP}, below which
the device will shut down do to output under voltage protection.
Soft Start Timing and Start up (Adaptive Loop operation)
In Adaptive Loop operation, the PRM has an internal soft start
sequence which is initiated at every start up. This allows the
PRM to start into fully discharged load capacitance. The soft
start sequence ramps the output by modulating the error
amplifier reference voltage (REF). The result is that the PRM
output will rise at a controlled rate until the final voltage
setpoint is reached. The total ramp time is typically 1.8ms
independent of the output trim level. This soft start ramp time
is preprogrammed into the microcontroller and cannot be
changed externally.
Load Transient Response (Adaptive Loop Operation)
In Adaptive Loop operation, response time is dependent on the
internal compensation. When the Adaptive Loop load line is
disabled, the PRM output voltage will recover to the initial set
value as illustrated in Figure 33 and Figure 34.
Figure 34: PRM Example 100% to 10% Load Transient
Response, Adaptive Loop Load Line Disabled
When the Adaptive Loop load line is enabled, the voltage will
recover to the value determined by the set point and Adaptive
Loop load line settings as illustrated in Figure 35.
Figure 35: PRM Example 10% to 100% Load Transient
Response, Adaptive Loop Load Line Enabled, V_AL = 1.25V
Actual response times are model dependent and will change
based on the load step magnitude, load capacitance and
operating conditions.
Because the compensation is fixed internally the load transient
response cannot be altered for Adaptive Loop operation.
In order to improve the load transient response performance,
the part can be configured for Remote Sense operation with an
external voltage control loop optimized for the specific intended
operating conditions. Remote Sense operation is described in
a later section.
Figure 33: PRM Example 10% to 100% Load Transient
Response, Adaptive Loop Load Line Disabled
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Rev. 1.0
11/2012