PRELIMINARY
Electrical Characteristics (continued)
APPLICATION SCHEMATIC DRAWINGS USING VICOR CONVERTERS AND THE µRAM
R
SENSE
(2)
5.1
+In
+Out
22µF
PC
+S
+In
SC
SC
C
TRAN
–S
+Out
DC-DC
Converter
PR
–In
µRAM
R
HR
V
REF
C
HR
*
–Out
C
TRAN
*
–In
–Out
*
Optional Component
Figure 1—Typical
Configuration using Remote Sensing
+In
PC
PR
–In
+Out
+In
+Out
DC-DC
Converter
R
SC
SC
SC
C
TRAN
µRAM
R
HR
V
REF
C
HR
*
–Out
–Out
C
TRAN
*
*
Optional Component
–In
Figure 2—Typical
Configuration using SC Control (Oppional C
HR
25µF maximum in SC configuration.)
Functional Description
The MicroRAM has an internal passive filter that
effectively attenuates ripple in the 50kHz to 1MHz range.
An active filter provides attenuation from low frequency
up to the 1MHz range. The user must set the headroom
voltage of the active block with the external R
HR
resistor
to optimize performance. The MicroRAM must be connected
as shown in Figures 1 or 2 depending on the load sensing
method. The transient load current performance can be
increased by the addition of optional C
TRAN
capacitance
to the C
TRAN
pin. The low frequency ripple attenuation
can be increased by addition of optional C
HR
capacitance
to the V
REF
pin as shown in Figures 3a and 3b, on p. 5.
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
Transient load current is supplied by the internal C
TRAN
capacitance, plus optional external capacitance, during the
time it takes the converter loop to respond to the increase
in load. The MicroRAM’s active loop responds in roughly
one microsecond to output voltage perturbations. There
are limitations to the magnitude and the rate of change of
the transient current that the MicroRAM can sustain while
the converter responds. See Figures 8-16, on pp. 6 and 7,
for examples of dynamic performance. A larger headroom
voltage setting will provide increased transient performance,
ripple attenuation and power dissipation while reducing
overall efficiency (see Figures 4a, 4b, 4c and 4d on p. 5).
MicroRAM
Rev. 1.1
Page 3 of 8
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