PRM48BF480T500A00 Datasheet, PDF (29/45 Pages) Vicor Corporation – PRM™ Regulator

PRM48B x 480 y 500A00
Adaptive Loop Compensation (Adaptive Loop operation)
A factorized power system naturally has a DC load line
associated with it since the regulator stage (PRM) is positioned
before the isolation and voltage transformation stage (VTM.)
Consider for a moment a factorized power system that has the
following parameters:
accordingly increases the output voltage of the PRM in order to
regulate the PRM’s output resistance to a fixed negative
resistance, R_{LL_AL}, settable by way of the AL pin. R_{LL_AL} should
be sized to exactly cancel the R_OUT of the VTM at 25°C. The
AL engine is also able to account for the positive temperature
coefficient of R_OUT by way of its VT pin which will be explained
shortly.
 V_F = 40V
 K_VTM=1/4
 R_{OUT_VTM} =10mohm @ 25°C
At no load the output voltage at the load will be equal to 10V
(V_F • K_VTM). With increasing load current, the output voltage at
the load will drop at a rate proportional to the VTMs R_OUT. It
should be noted that the R_OUT has a positive temperature
coefficient and so the DC load line changes with temperature.
If the presence of this load line is acceptable for your
application, then the PRM can be configured by way of the
TRIM pin alone. Please refer to the Trimming the Output
Voltage section for details. In this case both the AL and VT
pins should be left open.
If the presence of this load line is undesirable, the load line can
be eliminated by way of the PRM’s Adaptive Loop (AL) engine.
The AL engine measures the output current of the PRM and
PRM and VTM Output Voltage
Adaptive Loop Comensation Example
3
2
1
Compensated VTM Output
0
Adaptive Loop compensation brings
‐1
output into regulation
‐2
‐3
0
20
40
60
80
100
Load Current (%)
VTM VOUT (Uncompensated)
PRM VOUT
VTM Vout (Regulated)
Figure 27: Adaptive Loop Compensation Illustration
ON/OFF CONTROL
V_INVIN
38V₃₆to_V5_to5V_75V
SGND
RTRIM
RAL
SGND
CIN
GND
PRM
ENABLE
TRIM
AL
SHARE/
CONTROL NODE
VAUX
REF/
REF_EN
VC
VT
IFB
VTM Startup Pulse
Adaptive Loop Temperature Feedback
VTM
VC
+OUT
TM
PC
+IN
+OUT
LF
VF: 20V to 55V
CF
-IN
SGND
-OUT
+IN
-IN
-OUT
PRIMARY
SECONDARY
ISOLATION BOUNDRY
SGND
Figure 28: PRM-VTM Adaptive Loop Example
VOUT
COUT
SEC_GND
- 29 -
Rev. 1.0
11/2012