PRM48AF480T400A00 Datasheet, PDF (37/45 Pages) Vicor Corporation – PRM™ Regulator

PRM48A x 480 y 400A00
Midband Gain Design: R1,R3 (Remote Sense operation)
With reference to Figure 37: curve ABC is the:
 minimum output voltage in the application
 maximum input voltage expected in the application
 maximum load
PRM open loop response, and is where the maximum
crossover frequency occurs. In order for the maximum
crossover frequency to occur at the design choice F_CMAX, the
compensation gain must be equal and opposite of the
powertrain gain at this frequency. For stability purposes, the
compensation should be in the Mid-band (J-K) at the
crossover. Using Equation (8), the mid-band gain can be
selected appropriately.
Compensation Zero Design :C1 (Remote Sense operation):
With reference to Figure 37: curve EFG is the:
 maximum output voltage in the application
 minimum input voltage expected in the application
 minimum load in the application
PRM open loop response, and is where the minimum
crossover frequency F_CMIN occurs. Based on stability criteria,
the compensation must be in the mid-band at the minimum
crossover frequency, therefore F_CMIN will occur where EFG is
equal and opposite of G_MB. C1 can be selected using Equation
(9) so that F_Z1 occurs prior to F_CMIN.
High Frequency Pole Design: C2 (Remote Sense
operation):
Using Equation (10), C2 should be selected so that F_P2 is at
least one decade above F_CMAX and prior to the gain bandwidth
product of the operational amplifier (10MHz for this example).
For applications with a higher desired crossover frequency the
use of a high gain bandwidth product amplifier may be
necessary to ensure that the real pole can be set at least one
decade above the maximum crossover frequency.
80
60 ^I _{Compensation Gain}
Open Loop Gain vs. Frequency
Application's op-amp G·BW
40
E
F
PRM Open Loop Min Load
A
B
20
PRM Open Loop Max Load
0
J
F_CMIN F_CMAX
K
L
-20
C
-40
G
Frequency, Log scale
(y-intercept is application specific)
Figure 37 – Reference asymptotic Bode plot for the considered system
- 37 -
Rev. 1.0
11/2012