PRM48AY480X400A00 Datasheet, PDF (35/44 Pages) Vicor Corporation – High Efficiency Converter

Design Guidelines (Remote Sense Operation)
In Remote Sense Operation, the PRM48Ay480x400A00 is an
intelligent powertrain module designed to fully exploit external
output voltage feedback and current sensing sub-circuits. These two
external circuits are illustrated in Figure 36, which shows an
example of the PRM in a standalone application with local voltage
feedback and high side current sensing.
In general, these circuits include a precision voltage reference, an
operational amplifier which provides closed loop feedback
compensation, and a high side current sense circuit which includes a
shunt and current sense IC.
The following design procedures refer to the circuit shown
in Figure 36.
Setting the Output Voltage Level (Remote Sense Operation)
The output voltage setpoint is a function of the voltage reference and
the output voltage sense ratio. With reference to Figure 36, R1 and R2
form the output voltage sensing divider which provides the scaled
output voltage to the negative input of the error amplifier; a
dedicated reference IC provides the reference voltage to the positive
input of the error amplifier. Under normal operation, the error
amplifier will keep the voltages at the inverting and non-inverting
inputs equal, and therefore the output voltage is defined by:
V_OUT
 V_REF
u
R1 R2
R2
(5)
Note that the component R1 will also factor into the compensation as
described in a later section.
PRM48Ay480x400A00
It is important to apply proper slew rate to the reference voltage rise
when the control loop is initially enabled. The recommended range
for reference rise time is 1 ms to 9 ms. The lower rise time limit will
ensure optimized modulator timing performance during start up,
and to allow the current limit feature (through IFB pin) to fully
protect the device during power-up. The upper rise time limit is
needed to guarantee a sufficient factorized bus voltage is provided to
any downstream VTM input before the end of the VC pulse.
Setting the Output Current Limit and Overcurrent Protection Level
(Remote Sense Operation)
In Remote Sense Operation, the internal current sensing is disabled,
and an external current sense amplifier must be implemented to
provide feedback to the IFB pin.
The current limit and overcurrent protection set points are linked,
and scale together against the current sense shunt, and the gain of
the current sense amplifier. The output of the current sense IC
provides the IFB voltage which has V_{IFB_IL} and V_{IFB_OC} thresholds for
the two functions respectively. The set points are therefore defined
by:
I _IL

V_{IFB _ IL}
R_S u G_CS
(6)
and
I _OC

V_{IFB _ OC}
R_S u G_CS
(7)
where G_CS is the gain of the current sense amplifier.
ON/OFF
CONTROL
SGND
SGND
V_IN
C_IN
GND
PRM
ENABLE
TRIM
AL
SHARE/
CONTROL NODE
VAUX
REF/
REF_EN
VT
VC
IFB
+IN
+OUT
–IN
SGND
–OUT
SGND
Voltage Sense and Error Amplifier
(Single Ended)
C2
C1 _R3
REF 3312
IN
OUT
GND
R_SS
10 k
V_REF
C_SS
SGND
Voltage Reference with Soft Start
SGND
V_REF
R2
R1
V+
V–
VOUT
SGND
+IN
–IN
RS
External Current Sense
and Feedback
C_OUT
V_OUT
Figure 37 — Remote Sense Example
PRM^TM Regulator
Page 35 of 44
Rev 1.4
11/2015
vicorpower.com
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