PRM48BY480X500A00 Datasheet, PDF (32/44 Pages) Vicor Corporation – High Efficiency Converter

PRM48By480x500A00
V_CCINT
10 KΩ
AL
V_AL
R_AL
SGND
Figure 29 — AL Connections
SGND
Micro
Controller
SGND
Similar to TRIM, AL is sampled during every start up to determine if
the Adaptive Loop load line is enabled or disabled. If the AL pin is
allowed to pull up to 3.20 V or higher during start up, then the PRM
will disable the Adaptive Loop load line as long as the PRM remains
operating. In this case, for all subsequent operation the output
voltage will be remain at the set voltage, and the AL pin will be
ignored.
This selection persists until the PRM is restarted with the ENABLE
pin, or due to fault auto-recovery. When AL is enabled, the voltage at
this pin is sampled at 120 µs intervals to determine the load line. The
load line can be adjusted during normal operation, however it is not
recommended to use this pin in an external analog feedback loop.
Adaptive Loop Temperature Compensation
(Adaptive Loop Operation)
By connecting the VT pin of the PRM to the VTM’s TM pin, the PRM is
able to monitor the internal temperature of the VTM. Knowing the
VTM’s internal temperature and the temperature coefficient of the
VTM’s R_OUT, which is preprogrammed into the PRMs microcontroller,
the AL engine is able to scale the nominal value of R_{LL_AL} (set by the
AL pin) to track the VTM’s R_OUT over temperature. In this way the
output resistance of the PRM can be tuned to cancel the output
resistance of the VTM with the addition of a single resistor across the
AL pin and a connection of the VTM’s TM pin to the PRMs VT pin.
The VTM TM voltage is equal to the VTM internal sensed temperature
in Kelvin divided by 100. For a temperature range of -55°C to 125°C
the TM voltage will range from 2.18 V to 3.98 V. The Adaptive Loop
temperature compensation is pre-programed into the internal
microcontroller and is 0.3%/°C assuming the VT pin is connected to
the TM pin of a compatible VTM.
The TM pin has an internal pull down to SGND, and temperature
compensation is disabled for VT voltages less than 1.9 V. To disable
temperature compensation, leave the VT pin unconnected and open
circuit. When disabled, the temperature defaults 25°C.
PRM^TM Regulator
Page 32 of 44
Rev 1.4
11/2015
V_CCINT
Micro
Controller
60.4k
20 KΩ
2.18 V to 3.98 V
VT ^{(-55°C to 125°C)}
VTM TM
SGND
SGND
Figure 30 — VT Connections
PRM and VTM Output Voltage
Adaptive Loop With Temperature Compensation
3
2
PRM
Output
HOT
PRM
Output
AMBIENT
PRM ^{Output COLD}
1
Compensation slope
increases with
temperature based
on VT feedback
0
Compensated VTM Output
-1
VTM ROUT increases
with temperature
-2
-3
0
20
VTM V_OUT: -55°C (Uncompensated)
PRM V_OUT: -55°C (VT = 2.18 V)
40
60
Load Current (%)
VTM V_OUT: 25°C (Uncompensated)
PRM V_OUT: 25°C (VT = 2.98 V)
VTM V_OUT (Regulated)
80
100
VTM V_OUT: 100°C (Uncompensated)
PRM V_OUT: 100°C (VT = 3.73V)
Figure 31 — Adaptive Loop Temperature Compensation Illustration
The discussion thus far only considered the case where the AL
engine is used to compensate for the R_OUT of the VTM. The AL engine
can be more generally used to account for distribution resistances in
both the factorized bus and the VTM’s output distribution bus. For
more information on how to apply the AL engine towards this end
please contact Vicor’s Applications Engineering department.
Stability Considerations and External Capacitance
(Adaptive Loop Operation)
In Adaptive Loop Operation, the internal voltage regulation is
enabled which has a pre-determined, fixed compensation network.
The compensation is designed to be stable over a fixed set of
operating and load conditions including load capacitance.
Besides internal output capacitors, external output capacitors also
contribute to the closed loop frequency response, thus should be
identified and understood, in order to maintain the control loop
stability. This includes capacitance placed directly on the PRM
output, as well as capacitance on the output of any downstream VTM
(if used) reflected to its input.
Figure 32 illustrates the requirements for external capacitors for both
the capacitance and ESR value. As shown in Figure 32 (a), the
maximum capacitance value of ceramic capacitor is 25 µF, and the
capacitance of a combination of ceramic and electrotype capacitors
needs to be less than 47 µF. As shown in Figure 32 (b) and (c), the
ESR value of electrotype capacitors needs to be between
0.1 Ω and 1 Ω; the ESR value of ceramic capacitors needs to be
between 2 mΩ and 200 mΩ.
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