Data Sheet
MicroRAM
Features
•
RoHS Compliant (with F or G pin option)
•
>40 dB ripple attenuation from
60 Hz to 1 MHz
•
Integrated OR’ing diode supports
N+1 redundancy
•
Significantly improves load
transient response
•
Efficiency up to 98%
•
User selectable performance optimization
•
Combined active and passive filtering
•
3 – 30 Vdc input range
•
20 and 30 Ampere ratings
TM
Output Ripple Attenuation Module
Actual size:
2.28 x 1.45 x 0.5 in
57,9 x 36,8 x 12,7 mm
Product Highlights
Vicor’s MicroRAM output ripple attenuation
module combines both active and passive
filtering to achieve greater than 40 dB of
noise attenuation from 60 Hz to 1 Mhz. The
MicroRAM operates over a range of 3 to
30 Vdc, is available in either 20 or 30 A
models and is compatible with most
manufacturers switching converters
including all Vicor DC-DC converter
models.
The MicroRAM’s closed loop architecture
greatly improves load transient response and
with dual mode control, insures precise point
of load voltage regulation, The MicroRAM
supports redundant and parallel operation
with its integrated OR’ing diode function.
It is available in Vicor’s standard Micro
package (quarter brick) with a variety of
terminations for through hole, socket or
surface mount applications.
Absolute Maximum Ratings
Parameter
+In to –In
Load current
Ripple Input (Vp-p)
Mounting torque
Pin soldering temperature
Rating
30
40
40
100
500
4–6
(0.45 – 0.68)
500 (260)
750 (390)
Unit
Vdc
Vdc
Adc
mV
mV
In. lbs
(Nm)
°F (°C)
°F (°C)
Notes
Continuous
100ms
Continuous
60 Hzc 100 kHz
100 kHz – 2 MHz
6 each, 4-40 screw
<5 sec; wave solder
<7 sec; wave solder
Thermal Resistance
Parameter
Baseplate to sink
flat, greased surface
with thermal pad (P/N 20265)
Baseplate to ambient
free convection
1000 LFM
Typ
0.16
0.14
8.0
1.9
Unit
°C/Watt
°C/Watt
°C/Watt
°C/Watt
Part Numbering
uRAM 2
Product
Type
2
= 20 A
3
= 30 A
C
Product Grade Temperatures (°C)
Grade Operating
Storage
C
= – 20 to +100
– 40 to +125
T
= – 40 to +100
– 40 to +125
H
= – 40 to +100
– 55 to +125
M
= – 55 to +100
– 65 to +125
1
2
S
N
F
G
=
=
=
=
=
=
2
Pin Style*
Short Pin
Long Pin
Short ModuMate
Long ModuMate
Short RoHS
Long RoHS
1
Baseplate
1
= Slotted
2
= Threaded
3
= Thru-hole
*Pin styles S & N are compatible with the ModuMate interconnect system for socketing and surface mounting.
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
MicroRAM Data Sheet
Rev. 1.4
Page 1 of 10
Set your site on VICOR at www.vicorpower.com
ELECTRICAL CHARACTERISTICS
Electrical characteristics apply over the full operating range of input voltage, output power and baseplate temperature, unless otherwise
specified. All temperatures refer to the operating temperature at the center of the baseplate.
µRAM MODULE SPECIFICATIONS
(-20°C to +100°C baseplate temperature)
Parameter
Operating current range
µRAM2xxx
µRAM3xxx
Operating input voltage
Transient output response
Load current step <1A/µsec
Transient output response
Load current step <1A/µsec
(CTRAN = 820 µF)
VHR headroom voltage range
@ 1A load
Output ripple
Input Vp-p = 100 mV
1
Min
0.02
0.02
3.0
Typ
Max
20
30
30
50
Unit
A
A
Vdc
mVp-p
Notes
No internal current limiting. Converter input must be
properly fused such that the µRAM output current
does not exceed the maximum operating current
rating by more than 30% under a steady state condition.
Continuous
Step load change;
see Figures 9, 12, & 15, pp. 6-7
Optional capacitance CTRAN can be used
to increase transient current capability; See Figures
1 & 2 on p. 3 and Figures 10, 13, & 16 on pp. 6-7
See Figures 5, 6 & 7
See Table 1 for headroom setting resistor values
Ripple frequency 60 Hz to 100 kHz; optional capacitor
CHR = 100 µF required to increase low frequency
attenuation as shown in Figures 3a and 3b
see Figures 8, 11, & 14, pp. 6 – 7
Ripple frequency 100 kHz to 2 MHz;
see Figures 8, 11, & 14, pp. 6-7
See Table 1 RSC value
Vin – Vout
50
mVp-p
325
425
10
5
mV
mVp-p
mVrms
Output ripple
Input Vp-p = 500 mV
SC output voltage
OR’ing threshold
µRAM bias current
Power dissipation
µRAM2xxx VHR = 380 mV@1 A
µRAM3xxx VHR = 380 mV@1 A
1
2
10
5
1.23
10
60
7.5
11.5
mVp-p
mVrms
Vdc
mV
mA
W
W
Vin = 28 V; Iout = 20 A
Vin = 28 V; Iout = 30 A
Headroom is the voltage difference between the +Input and +Output pins.
R
HR
= (µRAM +Out/V
HR
) x 2.3 k (see Table 1 for example values)
SC resistor is required to trim the converter output up to accommodate the headroom of the µRAM module when remote sense
is not used. This feature can only be used when the trim reference of the converter is in the 1.21 to 1.25 Volt range.
(see Table 1 with calculated R
SC
resistor values)
R
SC
= ((µRAM +Out)/1.23 V x 1k) – 2 k
2
µRAM Out
3.0 V
5.0 V
12.0 V
15.0 V
24.0 V
28.0 V
V
HR
@ 1A
375 mV
375 mV
375 mV
375 mV
375 mV
375 mV
R
HR
Value (ohms)
18.4 k
30.6 k
73.6 k
92.0 k
147.2 k
171.7 k
R
SC
Value (ohms)
0.439 k
2.07 k
7.76 k
10.20 k
17.50 k
20.76 k
Table 1
– RHR and RSC are computed values for a 375 mV case. To compute different headroom voltages, or for standard resistor
values and tolerances, use Notes 1 and 2.
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
MicroRAM Data Sheet
Rev. 1.4
Page 2 of 10
Set your site on VICOR at www.vicorpower.com
ELECTRICAL CHARACTERISTICS (CONT.)
APPLICATION SCHEMATIC DRAWINGS USING VICOR CONVERTERS AND THE µRAM
R
SENSE
5.1
+IN
+OUT
22
μF
PC
+S
+IN
SC
+OUT
DC-DC
Converter
PR
–IN
R
HR
Vref
SC
LOAD
C
HR
*
C
TRAN
–S
C
TRAN
*
–IN
–OUT
–OUT
*
Optional Component
Figure 1
—
Typical Configuration using Remote Sensing
20 kΩ
IRML6401
+IN
PC
PR
–IN
+OUT
+IN
+OUT
DC-DC
Converter
R
SC
SC
SC
C
TRAN
μRAM
R
HR
Vref
LOAD
C
HR
*
1
µF
–OUT
C
TRAN
*
–IN
–OUT
*
Optional Component
Figure 2
—
Typical Configuration using SC Control (Oppional CHR 25µF maximum in SC configuration.)
FUNCTIONAL DESCRIPTION
The MicroRAM has an internal passive filter that
effectively attenuates ripple in the 50 kHz to 1 MHz
range. An active filter provides attenuation from low
frequency up to the 1 MHz 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.
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).
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
MicroRAM Data Sheet
Rev. 1.4
Page 3 of 10
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FUNCTIONAL DESCRIPTION (CONT.)
The active loop senses the output current and reduces the
headroom voltage in a linear fashion to approximate constant
power dissipation of MicroRAM with increasing loads (see
Figures 5, 6 & 7, p. 6). The headroom setting can be reduced
to decrease power dissipation where the transient requirement
is low and efficient ripple attenuation is the primary
performance concern.
The active dynamic headroom range is limited on the low end
by the initial headroom setting and the maximum expected
load. If the maximum load in the application is 10 Amps, for
example, the 1 Amp headroom can be set 75mV lower to
conserve power and still have active headroom at the
maximum load current of 10 Amps. The high end or
maximum headroom range is limited by the internal OR’ing
diode function.
The SC or trim-up function can be used when remote sensing
is not available on the source converter or is not desirable. It
is specifically designed for converters with a 1.23 Volt
reference and a 1k ohm input impedance like Vicor Maxi,
Mini, Micro converters. In comparison to remote sensing, the
SC configuration will have an error in the load voltage versus
load current. It will be proportional to the output current and
the resistance of the load path from the output of the
MicroRAM to the load.
The OR’ing feature prevents current flowing from the output
of the MicroRAM back through it’s input terminal in a
redundant system configuration in the event that a converter
output fails. When the converter output supplying the
MicroRAM droops below the OR’ed output voltage potential
of the redundant system, the input of the MicroRAM is
isolated from it’s output. Less than 50mA will flow out of the
input terminal of the MicroRAM over the full range of input
voltage under this condition.
+In
SC
C
TRAN
–In
Passive
Block
Active
Block
+Out
SC
Control
Vref
–Out
Block Diagram
APPLICATION NOTES
Load capacitance can affect the overall phase margin of the
MicroRAM active loop as well as the phase margin of the
converter loop. The distributed variables such as inductance of
the load path, the capacitor type and value as well as its ESR
and ESL also affect transient capability at the load. The
following guidelines should be considered when point of load
capacitance is used with the MicroRAM in order to maintain a
minimum of 30 degrees of phase margin.
2) For the case where load capacitance is connected
directly to the output of the MicroRAM, i.e. no
trace inductance, and the ESR is >1 milliohm:
(a) 20
µF
to 200
µF
load capacitance needs an ESL
of >50 nH
(b) 200
µF
to 1,000
µF
load capacitance needs an
ESL of >5 nH
3) Adding low ESR capacitance directly at the output
terminals of MicroRAM is not recommended and
may cause stability problems.
4) In practice the distributed board or wire inductance at a load
or on a load board will be sufficient to isolate the output of
the MicroRAM from any load capacitance and minimize
any appreciable effect on phase margin.
1) Using ceramic load capacitance with < 1milliohm
ESR and <1nH ESL:
(a) 20
µF
to 200
µF
requires 20 nH of trace/wire
load path inductance
(b) 200
µF
to 1,000
µF
requires 60 nH of trace/wire
load path inductance
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
MicroRAM Data Sheet
Rev. 1.4
Page 4 of 10
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μRAM2xxx
Ripple Attenuation @ 28 V (Room Temp.)
20.00
0.00
Gain (dB)
-20.00
-40.00
-60.00
-80.00
10
100
1,000
10,000
100,000
1,000,000 10,000,000
Freq. (Hz)
10 A, 100
uF
Vref
Figure 3a
10 A, No Vref Cap
Ripple Attenuation @ 5 V (Room Temp.)
20.00
0.00
Gain (dB)
-20.00
-40.00
-60.00
-80.00
10
100
1,000
10,000
100,000
1,000,000
10,000,000
Freq. (Hz)
10 A, 100
uF
Vref
10 A, No Vref Cap
Figure 3a, 3b
—
Curves demonstrating the small signal attenuation performance as measured on a network analyzer with a
typical module at (a) 28 V and 10 A output and (b) 5 V and 10 A. The low frequency attenuation can be enhanced by connecting a
100 µF capacitor, CHR, to the VREF pin as shown in Figures 1 and 2.
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
MicroRAM Data Sheet
Rev. 1.4
Page 5 of 10
Set your site on VICOR at www.vicorpower.com
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