PRM48BF480T500A00 Datasheet, PDF (31/45 Pages) Vicor Corporation – PRM™ Regulator

PRM48B x 480 y 500A00
MICRO
CONTROLLER
60.4k
2.18V to 3.98V
20K
VT
(-55C to 125C)
VTM TM
SGND
Figure 30: VT Connections
PRM and VTM Output Voltage
Adaptive Loop With Temperature Compensation
3
2
Compensation slope
1
increases with
temperature based on VT
feedback
Compensated VTM Output
0
VTM ROUT increases with
‐1
temperature
‐2
‐3
0
20
40
60
80
100
Load Current (%)
VTM VOUT: 25C (Uncompensated)
VTM Vout (Regulated)
VTM VOUT: ‐55C (Uncompensated)
VTM VOUT: 100C (Uncompensated)
PRM VOU: 25C (VT = 2.98V)
PRM VOUT: ‐55C (VT = 2.18V)
PRM VOUT: 100C (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 of
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 1.0 Ω;
the ESR value of ceramic capacitors needs to be between
2 mΩ and 200 mΩ.
C_CER (uF)
25
C_CER ≤ 25
C_CER + C_EL < 47
ESR
(Ohm) _{0.1 ≤ ESR ≤ 1}
1
ESR
(Ohm)
0.02 ≤ ESR ≤ 0.2
0.1
0.2
0.02
22
47 _{CEL( uF)}
ESR_EL
ESR_CER
(a) Maxium Capacitance limits
(b) ESR_EL requirements
(c) ESR_CER requirements
Figure 32: Output Capacitance Limits
- 31 -
Rev. 1.0
11/2012