PRM48BY480X500A00 Datasheet, PDF (33/44 Pages) Vicor Corporation – High Efficiency Converter

PRM48By480x500A00
CCER (uF)
25
CCER 25
CCER + CEL < 47
ESR
(Ohm) 0.1 _{ESR 1}
1
ESR
(Ohm)
22
47 _CEL(uF)
Maxium Capacitance limits
Figure 32 — Output Capacitance Limits
0.1
ESREL
(b) ESR_EL requirements
200 ^{2 ESR 200}
2
ESRCER
(c) ESR_CER requirements
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 1.8 ms independent of the output trim level.
This soft start ramp time is preprogrammed into the microcontroller
and cannot be changed externally.
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.
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 33 — PRM Example 10% to 100% Load Transient Response,
Adaptive Loop Load Line Disabled
PRM^TM Regulator
Page 33 of 44
Rev 1.4
11/2015
Figure 35 — PRM Example 10% to 100% Load Transient Response,
Adaptive Loop Load Line Enabled, V_AL = 0.96 V
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 the next section.
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