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MicroRam™
Output Ripple Attenuation Module
Features
• RoHS Compliant (with F or G pin option)
• >40 dB ripple attenuation from
1.1 KHz to 1 MHz
• >40 dB ripple attenuation from 100 Hz
to 1.1 KHz with additional component
• 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
Actual Size:
2.28 x 1.45 x 0.5 in
57,9 x 36,8 x 12,7 mm
Absolute Maximum Ratings
Parameter
Rating
+In to –In
Load current
VREF
Mounting torque
Vicor’s MicroRAM output ripple attenuation
module combines both active and passive
filtering to achieve greater than 40 dB of
noise attenuation from 1.1 KHz to 1 Mhz.
The lower frequency limit can be extended
down to 100 Hz, with greater than 40 dB of
attenuation, with the addition of a single
external capacitor. 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
can insure precise point of load voltage
regulation using its SC function.
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.
Notes
30
Vdc
Continuous
40
Vdc
100 ms
40
Adc
10 second pulse
Vin ± 1 V
Vdc
Continuous
100
mV
100 Hz 100 kHz
500
mV
100 kHz – 2 MHz
4–6
(0.45 – 0.68)
In. lbs
(Nm)
6 each, 4-40 screw
500 (260)
°F (°C)
<5 sec; wave solder
750 (390)
°F (°C)
<7 sec; wave solder
Ripple Input (Vp-p)
Product Highlights
Unit
Pin soldering temperature
Thermal Resistance
Parameter
Baseplate to sink
flat, greased surface
with thermal pad (P/N 20265)
Baseplate to ambient
free convection
1000 LFM
Typ
Unit
0.16
0.14
°C/Watt
°C/Watt
8.0
1.9
°C/Watt
°C/Watt
Part Numbering
µRAM 2
Product
Type
2 = 20 A
3 = 30 A
[1]
[2]
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
2
1
2
S
N
F
G
K
=
=
=
=
=
=
=
Pin Style
Short Pin
Long Pin
[1]
Short ModuMate [1]
Long ModuMate
Short RoHS
Long RoHS
[2]
Extra Long RoHS
Compatible with the ModuMate interconnect system for socketing and surface mounting
Not intended for socket or Surfmate mounting
Output Ripple Attenuation Module
Rev. 2.1
vicorpower.com
Page 1 of 19
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1
Baseplate
1 = Slotted
2 = Threaded
3 = Thru-hole
MicroRAM
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
Min
Operating current range
µRAM2XXX
Max
Unit
0.02
20
A
0.02
30
A
3.0
30
V
Transient output response
Load current step < 1 A/µsec
50
mVp-p
Step load change;
see Figures 20, 23, & 26, pp. 16–17
Transient output response
Load current step < 1 A/µsec
(CTRAN = 820 µF)
50
mVp-p
Optional capacitance CTRAN can be used
to increase transient current capability; See Figures
21, 24 & 27, pp. 16–17
425
mV
10
mVp-p
5
MVrms
µRAM3XXX
Operating input voltage
Recommended headroom voltage
range (VHR) @ 1A load.1
Typ
325
Output ripple
Input Vp-p = 100 mV
Output ripple
Input Vp-p = 500 mV
SC output voltage
2
Continuous
See Figures 4 and 5, pp. 5 for detailed explanation.
See Table 1 for typical headroom setting resistor values.
mVp-p
5
MVrms
–10
µRAM bias current
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.
10
1.23
OR’ing threshold
Notes
60
Ripple frequency of 60 Hz to 100 kHz; optional CHR
capacitor of 100µF required to increase low frequency
attenuation as shown in Figure 2, pp. 3
Ripple frequency of 100 kHz to 2 MHz;
as shown in Figure 2, pp. 3
Vdc
See table 1 for typical RSC values, note 2 for calculation.
mV
VIN – VOUT
mA
Power dissipation
µRAM2XXX VHR = 380 mV @ 1 A
7.5
W
VIN = 28 V; IOUT = 20 A
µRAM3XXX VHR = 380 mV @ 1 A
11.5
W
VIN = 28 V; IOUT = 30 A
1 The headroom voltage VHR is the voltage difference between the V
IN + and the VOUT + pins of the μRAM.
RHR =
VOUT +
* 2.3k
VHR
(See Table 1 for example RHR values)
2 The SC resistor is used to trim the converter’s output voltage (V
NOM ) to compensate for the headroom voltage drop
of the μRAM when remote sense is not used. This feature can only be used with converter’s that have a trim reference range
between 1.21 and 1.25V.
RSC =
(VNOM * 1 k)
–2k
1.23 V
(See Table 1 for example RSC values)
µRAM output voltage
VHR @ 1A
RHR Value (Ω)
3V
375 mV
18.2 k
442
5V
375 mV
30.9 k
2.05 k
12 V
375 mV
73.2 k
7.68 k
15 V
375 mV
90.9 k
10.20 k
24 V
375 mV
147.0 k
17.40 k
28 V
375 mV
174.0 k
21.00 k
Table 1 – Calculated values of RSC and RHR for a headroom voltage of 375 mV.
Use notes 1 and 2 to compute RSC and RHR values for different headroom voltages.
Output Ripple Attenuation Module
Rev. 2.1
vicorpower.com
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RSC Value (Ω)
MicroRAM
MICRORAM THEORY OF OPERATION:
VHR
PARD Attenuation
Passive
Vicor’s MicroRAM uses both active and passive filtering to
attenuate PARD (Periodic and Random Deviations), typically
associated with a DC to DC converter’s output voltage.
The passive filter provides effective attenuation in the 50 KHz
to 20 MHz range. The low frequency range of the passive filter
(ie; resonant frequency) can be lowered by adding capacitance
to the CTRAN pin to ground and will improve the transient
load capability, as is shown in Figure 7. The active filter
provides attenuation from lower frequencies up to 2 MHz.
The lower frequency range of the active filter can be extended
down by adding an external by-pass cap across the RHR
resistor.
VDIODE
Active
VIN+
VOUT+
2.3 k
CTRAN
VIN-
57 μF
9.4 μF
VREF
CHR
(Optional)
VOUT-
RHR
Figure 1 — Simplified MicroRAM Block Diagram
Figure 2 — MicroRAM attenuation with and without an additional CHR capacitor.
The plots in Figure 2 show the increase in attenuation range that can be realized by adding an additional capacitor, CHR, across the RHR resistor, as shown in
Figure 1. These plots represent the total attenuation, due to both the active and passive filtering, before and after adding an additional 100 µF of capacitance
for CHR. There are practical limitations to the amount of capacitance that can be added, which is explained in more detail under the VREF section.
Output Ripple Attenuation Module
Rev. 2.1
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MicroRAM
PARD Attenuation (Continued)
Active attenuation is achieved by using power MOSFETs as a
variable resistor that can dynamically change its impedance in
order to maintain a constant output voltage, equal to the
voltage programmed on its reference pin. When the input is
lower, the active loop reduces the FET’s resistance, lowering
the overall voltage drop across the MicroRAM. When the input
is higher, the resistance is increased, increasing the voltage
drop across the MicroRAM. The bandwidth of the active loop
must be sufficiently higher than the converters control loop so
it does not introduce significant phase shift to the sense loop of
the converter.
There are both upper and lower limits to the range of resistance
variations. The lower limit is based on the path resistance
between VIN+ and VOUT+ and the amount of current passing
through the MicroRAM. On the high end, the resistance of the
FET, and therefore the maximum voltage drop, is limited to the
voltage when the body diode of the FET starts to conduct and
ripple passes through it to the output, exhibiting positive peaks
of ripple at the load.
The waveforms in Figure 3 are representative of a typical
ripple signal, riding on a DC voltage. The headroom voltage
across the MicroRAM (VHR) is the difference in DC voltage
between VIN and VOUT. This headroom is programmed via
RHR, shown in Figure 1. The headroom voltage should be
selected such that the headroom voltage minus half the peak to
peak ripple does not cross the minimum headroom limit, or
that the headroom voltage plus half the peak to peak ripple
does not exceed the voltage drop of the FET’s intrinsic body
diode voltage drop, that is current and temperature dependent.
The headroom must be properly set below the point of diode
conduction. In either of these two cases if the headroom is
depleted or the diode conducts, the ripple at the CTRAN node
will be exhibited as peaks of the ripple voltage amplitude at the
load, negating the active attenuation.
If the fundamental switching frequency of the converter is
above the resonant frequency of the passive LC filter
(see Figure 8) the fundamental switching and harmonic
frequencies will be reduced at the rate of 40 dB per decade in
frequency. The active filter will be presented with lower peak
to peak ripple and will have sufficient dynamic range to
attenuate the ripple. If the fundamental is below the resonant
frequency of the LC filter, then the active circuit will attenuate
the full noise signal.
The plot in Figure 4 illustrates the “effective” headroom
voltage over the full operating current range of the MicroRAM.
The reduction in headroom voltage, seen across the
MicroRAM over the full 30 A load current range, is due to two
factors; the effects of the slope adjust and the insertion
resistance of the MicroRAM. The two green shaded areas
represent the minimum and maximum recommended headroom
voltages listed in the MicroRAM’s specification table.
The gray area is the voltage drop due to the MicroRAM’s
insertion resistance, from the positive input to the positive
output, of the MicroRAM, multiplied by the load current.
This insertion resistance is typically 5 mΩ at 25°C and can
increase to 6.5 mΩ at 100°C.
VIN + VDIODE
VIN[p-p]
VIN[DC]
VHR1
VHR2
VIN + ( IIN * R[uRAM] )
VOUT
Figure 3 — Active Attenuation and the Effects of Headroom
Output Ripple Attenuation Module
Rev. 2.1
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MicroRAM
0.45
0.40
Headroom Voltage
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
5
10
15
20
25
30
Load Current
VHR, 30 A, Min HR
VHR, 30 A, Max HR
Insertion Loss
Figure 4 — MicroRAM headroom voltage reduction over full load current range.
As the load current is increased, the internal slope adjust of the
MicroRAM will reduce the headroom voltage across the
MicroRAM at a rate of about 2 mV/A for the 30 A version
(4 mV/A for 20 A version) in an effort to reduce the power loss
across the MicroRAM. This headroom reduction,
in conjunction with the increased voltage drop across the
MicroRAM due to its resistance, reduces the effective
headroom voltage and therefore the MicroRAM’s ability
to attenuate PARD at higher load currents.
0.35
0.30
Headroom Voltage
0.25
0.20
0.15
0.10
0.05
0.00
0
5
10
15
20
Load Current
VHR, 20 A, Min HR
VHR, 30 A, Min HR
Rds drop
Figure 5 — Slope adjust comparison of 20 A and 30 A MicroRAM.
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Rev. 2.1
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25
30
MicroRAM
The plots in Figure 5 show the difference in the slope adjust
effect between the two versions of the MicroRAM and that the
minimum recommended headroom of 325 mV will still leave
an effective headroom voltage of about 140 mV at 20A, using
the 20 A MicroRAM. When using the 30 A version at 30 A,
the headroom would be about 120 mV, so a higher initial
headroom voltage might be required.
The recommended minimum and maximum headroom
voltages, stated on page two, are listed as reference points for
designers and should not be considered as absolutes when
designing with the MicroRAM. At lower operating currents, a
lower initial headroom voltage can be used with no detrimental
effects on the MicroRAM’s ability to attenuate PARD. The
designer should have a good idea of the amount of PARD, at
the maximum operating current, the MicroRAM is to filter
when selecting the MicroRAM’s headroom voltage. He could
use the slope adjust rate to calculate what the headroom
voltage should be at the minimum load to determine his
headroom programming resistor value. The attenuation plots,
shown in Figure 2, are of a MicroRAM with 300 mV of
headroom initially programmed, running at 10 A load with 115
mVp-p of ripple on the input voltage. Lowering the headroom
voltage will reduce the MicroRAM’s transient performance, so
Figure 6 — Normal transient load response
consideration of the filter’s performance priorities should be
used when determining the best headroom setting.
For example: a designer needs to filter 100 mV of ripple
at 10 A, and is using a 20 A MicroRAM. He should have
100 mV of headroom plus 50 mV for the insertion resistance
at 10 A, or 150 mV of programmed headroom. At minimum
load, the programmed headroom voltage would be 150 mV
plus 40 mV (10 A multiplied by 4 mV/A slope adjust), or
190 mV of programmed headroom. This will ensure enough
attenuation headroom voltage at the 10 A max load and save
power making the overall system more efficient.
CTRAN
CTRAN is the passive filtered node that feeds into the active
filter portion of the MicroRAM. Adding extra storage
capacitors here can improve the overall system response to
load transients.
The waveforms in Figures 6 and 7 represent the MicroRAM’s
response to a step in load current, from 10 A to 14 A, with
and without an additional 470 µF capacitor on CTRAN.
Figure 7 — Transient response with added CTRAN capacitor
Channel 1(blue) is VIN+ from the converter, Channel 2 (light blue) is VOUT+, Channel 3 (pink) is CTRAN and Channel 4 (green) is the output step load current.
Channels 1 through 3 are DC measured with a 5 V offset and referenced to the same point on the y (voltage) axis. Channel 4 has no offset and is the step
load added to the continuous 10 A static load, which is not shown.
Output Ripple Attenuation Module
Rev. 2.1
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MicroRAM
PASSIVE ATTENUATION
Figure 8 — MicroRAM’s Passive Filter Attenuation with VHR = 300 mV, IOUT = 10 A
The affects of input voltage on the internal ceramic capacitors in the LC circuit shifts the resonant bump higher
in frequency as capacitance goes down with increased DC potential. The attenuation shape changes with the
addition of electrolytic capacitance (with relatively low ESR compared with ceramic) at CTRAN lowering the
resonant frequency and quality factor (Q) of the tank.
VREF / SLOPE ADJUST
VREF is the headroom programming pin for the MicroRAM.
The voltage on this pin will be the voltage seen on the
MicroRAM’s output. This pin is used to program the voltage
drop across the MicroRAM. Its value is calculated using the
following equation:
RHR =
2.3 k x VOUT
VHR
Where:
RHR = MicroRAM headroom programming resistor,
VOUT = voltage seen on the MicroRAM’s output pins,
VHR = desired headroom voltage across the MicroRAM.
“Slope Adjust” is the MicroRAM’s built-in headroom adjust
feature that takes advantage of Vicor’s 2nd generation
converter product characteristic of presenting lower ripple
amplitude and higher fundamental switching frequencies with
increased load current. The MicroRAM slope adjust feature
improves the filter’s efficiency by sensing the load current and
is designed to maintain a constant power drop across the
MicroRAM as the load current varies. As the load current
increases, the slope adjust circuit reduces the headroom
linearly based on the slope of the changing load current. The
typical passive filter within the MicroRAM will increase losses
with increased current. The Slope Adjust feature will decrease
the headroom voltage by about 50 mV from minimum load to
max load, for either the 20 A or 30 A version of the filter.
There is a limit to how much additional capacitance can be
added to the VREF pin. Depending on the low frequency ripple
component of the converter’s output (especially off-line
converters), a low frequency (5 to 20 Hz) oscillation may occur
at the MicroRAM output due to excessive lag of the
MicroRAM’s output vs. the converter’s, when additional
VREF capacitance is greater than 50 µF.
Output Ripple Attenuation Module
Rev. 2.1
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MicroRAM
SC
The SC pin of the MicroRAM provides a means of headroom
voltage drop compensation for the converter, when remote
sensing is not possible, as with the Vicor’s 2nd Generation
Micro converter product line. The equivalent circuit is shown
in Figure 9 and consists of a current source, whose nominal
source current can be calculated as the MicroRAM’s headroom
voltage, divided by 1,000 Ω. Internally, this current source is
fed into a reference circuit consisting of a 1.23 V reference
with a 1 K series resistor. Since the MicroRAM’s
SC circuit generates a fixed current, part of that current gets
shunted away by the internal reference circuit, the rest flows
into the converter’s SC pin. The value of RSC determines how
much of the MicroRAM’s SC current goes to the converter’s
SC circuit.
RSC =
MicroRAM In
IμSC
μSC
ISC
Converter Out
SC
GAIN =
VNOM/1.23 V
RSC
1K
1K
IINT
I SC
1.23 V
1.23V
μRAM
1 k x VNOM
– 2k
1.23 V
Converter
Figure 9 — MicroRAM’s SC control circuit.
ORing
Where:
VNOM = nominal converter output voltage
The attenuation MOSFETs used in the MicroRAM are
orientated such that they form an OR’ing circuit between the
converter’s output and the load. Less than 50 mA will flow
from the output to the input terminal of the MicroRAM over
the full output voltage range while the input is shorted.
In Figure 10, a 48 V to 12 V Vicor Mini converter is used to
create a 9 V output supply. The converter is trimmed down
from 12 V to 9 V, using a 3.01 K resistor from the converter’s
The internal reference circuit of the MicroRAM is designed
to match the 1.23 V reference circuit of Vicor’s “Brick”
converters, which limits the voltage range that the SC pin can
span. This function will not work with Vicor’s 1st Gen
converters due to its 2.5 V internal reference voltage.
TYPICAL CIRCUIT APPLICATIONS
V48B12C250BN
48 V to 12 V
VIN+
1
VIN+
2
PC
RSENSE
VOUT+
9
SENSE+
8
SC
3
VIN-
4
PR
SENSEVOUT-
VIN-
MicroRAM
CRS
22uF
7
RTRIM
6 3.01K
1
VIN+
2
SC
3
CTRAN
4
VIN-
5.1Ω
VOUT+ 7
VREF
6
VOUT-
5
VOUT+
RHR
54.9K
*CHR
VOUT-
5
*CTRAN
* Optional Components
Figure 10 — Typical configuration using Remote Sense control and a 12 V converter trimmed down to 9 V. RHR set for 375 mV of headroom voltage
*QSTART
IRLML6401
VIN+
1
2
3
VIN-
4
VIN+
PC
PR
VIN-
20 K
MicroRAM
VOUT+ 7
SC
*CSTART
*RSTART
V48C5C100BN
48 V to 5 V
6
VOUT- 5
1
RSC
VIN+
2
2.05K
SC
3
CTRAN
4
VIN-
*CTRAN
1 uF
VOUT+
7
VREF
6
VOUT-
5
VOUT+
RHR
30.9 K
*CHR
VOUT-
* Optional Components
Figure 11 — Typical SC control configuration and an optional start-up circuit. RHR set for 375 mV of headroom voltage.
Output Ripple Attenuation Module
Rev. 2.1
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MicroRAM
Figure 12 — Normal startup waveforms.
Figure 13 — Startup waveforms with the optional
startup circuitry.
SC to its VOUT- pins, then uses the remote sense pins, along
with the RRS and CRS components, to maintain proper output
voltage and converter stability. Again, the headroom voltage is
designed to be 375 mV.
MicroRAM’s output voltage, the internal active circuit will
turn-off the MOSFET’s and the difference between the input
and output is the MOSFET’s body diode voltage drop. As the
voltage on VREF continues to increase in value, the output
voltage starts to follow the VREF voltage until it reaches the
programmed headroom offset voltage.
The circuit shown in Figure 11 is of a Vicor Micro 48 V to 5 V
DC to DC converter with a MicroRAM, set to have 375 mV
of headroom voltage drop across it. To compensate for the
headroom drop, the MicroRAM’s SC circuit is used to adjust
the converter to have 5.375 V on its output, so the voltage seen
on the MicroRAM’s output is 5 V.
Figure 11 also shows an optional start-up circuit that might be
required in some designs which are sensitive to any voltage
“glitches” during the initial start-up of the MicroRAM. The
waveforms in Figures 12 and 13 show a comparison of typical
startup waveforms, with and without the optional startup
circuit. In Figure 12, the voltage on the MicroRAM’s VIN+
(Ch1, blue) and VOUT+ (Ch2, light blue) pin are equal at
startup. This is due to the VREF voltage (Ch3, pink) being
much lower than VIN+. The time required to charge the
internal VREF cap, and any external CHR caps that where
added, through the 2.3 K internal resistor (Figure 1) is the
cause of the delay. This voltage difference forces the active
circuit to drive the attenuation MOSFET’s to their minimum
rdson value, essentially shorting the input and output together.
Once the VREF voltage is within a diode voltage drop of the
The waveforms in Figure 13 demonstrate the optional startup
circuit’s ability to eliminate the startup glitch by shorting the
VREF pin (Ch3, violet) to VIN+ (Ch1, blue) for a short period
of time, determined by the RC components connected to the
gate of the PFET. The circuit releases the VREF pin to
discharge down to its programmed value and creates the
headroom voltage needed for attenuation. VOUT+
(Ch3, light blue) can be seen following the VREF voltage.
*NOTE: In any design using the MicroRAM, a minimum
output load of 20 mA is required for proper operation.
Without this load, the internal circuitry of the MicroRAM
can force the output rail to be as much as 8 V greater
than the input rail.
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MicroRAM
CONVERTER TRIMMING USING A MICRORAM: Remote Sense
RSENSE
5.1 Ω
VIN
+IN
+OUT
PC
+SENSE
DC-DC
Converter
PR
CRS
22 µF
SC
SC
RUP
–SENSE
RDWN
RTN
–IN
VOUT
+OUT
+IN
+
CTRAN
µRAM
–IN
RHR
Vref
CHR
optional
–OUT
GND
–OUT
Figure 14 — Configuration for trimming a converter’s output up/down using remote sensing.
When trimming up a converter in a remote sense configuration, the designer must be aware that the voltage the trim-up resistor is
connected to, the output of the converter, is not just the desired trim-up voltage but also the headroom voltage of the filter. The
voltage programmed on the converter’s SC pin is based on just the trimmed up voltage alone.
Vicor recommends that the value of RSENSE resistor in Figure 14 should be 5.1 Ω for proper operation. For converter's other than
Vicor's, this value can be increased up to 10 x (51Ω) to help with system stability.
When trimming down a converter in remote sense, there are no other voltage drops to take into consideration so the equation is
much simpler.
Trim Down equation:
Trim up equation:
RUP =
1 k (VNOM x (VOUT + VHR) – (VOUT x 1.23 V) )
1.23 V (VOUT – VNOM)
RDWN =
1 k x VOUT
VNOM – VOUT
Where:
Where:
RUP = trim up resistor
RDWN = trim down resistor
VNOM = nominal converter output voltage
VNOM = nominal converter output voltage
VOUT = desired output voltage, seen on MicroRAM’s output
VOUT = desired output voltage, seen on MicroRAM’s output
VHR = headroom voltage drop across the MicroRAM
1 k = converter’s internal series resistor
1.23 V = converter’s internal reference voltage
1 k = converter’s internal series resistor
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MicroRAM
CONVERTER TRIMMING USING A MICRORAM: SC Controlled Trimming
VIN
+OUT
+IN
PC
PR
RTN
DC-DC
Converter
–IN
SC
SC
RSC
RDWIN
CTRAN
µRAM
RHR
VREF
–OUT
–IN
–OUT
VOUT
+OUT
+IN
RUP
CHR
optional
GND
Figure 15 — Configuration for trimming a converter’s output up/down using SC.
When trimming up a converter using SC control, the designer would calculate the trim-up resistor based on the designed trimmed up
voltage without regard for the headroom voltage drop. The SC circuit will adapt the converter’s output for the additional headroom
voltage drop of the filter.
Converter’s Trim Up/Down Resistor Equations:
RUP =
1 k x VOUT x (VNOM – 1.23 V)
1.23 V x (VOUT – VNOM)
Where:
RDWN =
1 k x VOUT
(VNOM – VOUT)
Where:
RUP = trim up resistor
RDWN = trim up resistor
VNOM = nominal converter output voltage
VNOM = nominal converter output voltage
VOUT = desired output voltage, seen on MicroRAM’s output
VOUT = desired output voltage, seen on MicroRAM’s output
1.23 V = converter’s internal reference voltage
1k = converter’s internal series resistor
1 k = converter’s internal series resistor
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MicroRAM
µRAM’S SC RESISTOR CALCULATION
WITH A TRIM-UP RESISTOR
The equation to calculate the RSC resistor is as follows:
RSC =
RSC’s value is the found by taking the difference in the voltage
between the MicroRAM’s SC pin and the converter’s SC pin,
and dividing that by the current required from the MicroRAM
to source into the converter’s SC pin.
VµSC – VSC
ISC
Where:
RSC = resistor that programs the trim up current
from the MicroRAM
VµSC = the voltage seen on the MicroRAM’s SC pin
VSC = the voltage seen on the converter’s SC pin
ISC = the trim current generated by the MicroRAM
µRAM’S SC RESISTOR CALCULATION
WITH A TRIM-DOWN RESISTOR
The equations to calculate the RSC resistor and the VSC voltage
are the same when trimming a converter up or down.
When trimming a converter down, current is drawn out of the
converter’s SC pin through the RDWN resistor.
This current can be calculated using the following equation:
To calculate RSC, the three missing terms must be calculated.
To find the value of VSC use the following:
VSC =
I=
(VOUT + VHR) x 1.23 V
VNOM
Where:
VHR = programmed voltage drop (headroom) across
the MicroRAM
VSC is the trimmed up voltage measured on the converter’s SC
pin to produce the trimmed up VOUT with the VHR (filter
headroom voltage) added. The current required to elevate the
SC voltage can be calculated using the following equation:
I=
(VSC – 1.23 V)
1k
The current I is the total current needed by the SC pin to create
the desired trimmed up voltage. This current is made up of the
current from the RUP resistor and the current from the
MicroRAM. With the value of the trim-up resistor is known,
the current provided by RUP can be calculated as follows:
IUP =
(VOUT + VHR – VSC)
RUP
The current required from the MicroRAM is the difference
between the total current (I)
and the current provided by the RUP resistor (IUP).
(1.23 V – VSC)
1k
To determine the amount of current drawn through the trim
down resistor, IDWN, use the following equation:
IDWN =
VSC
RDWN
Since RDWN is calculated without adding the MicroRAM’s
headroom voltage, its value is lower than if it were trimming
down with the headroom added. The current through RDWN is
greater than the current that must be drawn from the
converter’s SC pin, so the MicroRAM must source its current
into RDWN to get proper regulation. The current required from
the MicroRAM can be calculated as follow:
ISC = IDWN – I
The same equation is used to calculate the voltage on the
MicroRAM’s SC pin as when trimming up:
VµSC = 1.23 V + VHR – ISC x 1 k
The value of RSC can now be calculated using:
RSC =
ISC = I – IUP
The last term to find is the voltage measured on the
MicroRAM’s SC pin (VµSC), which can be calculated using
the following equation:
VµSC = 1.23 V + VHR – ISC x 1 k
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(VµSC – VSC)
ISC
MicroRAM
PARALLELING APPLICATIONS
Figure 16 — Recommended paralleling connections of Vicor converter’s and paired MicroRAM’s.
A MicroRAM doesn’t have the capability to current share when paralleling with another filter. To use the MicroRAM in
parallel/redundant designs, the recommended method is to have one converter act as the “master” controller of the system,
forcing the paralleled converters to act as “slave” devices, regulated by the master via the PR pins. Figure 17 shows a simplified
version of the circuit. For more detailed information, please refer to these Vicor application notes:
http://cdn.vicorpower.com/documents/application_notes/an2_pr-pin.pdf
http://cdn.vicorpower.com/documents/application_notes/AN_Designing%20High-Power%20Arrays.pdf
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MicroRAM
PICOR’S FILTER CALCULATOR APPLICATION
To make the task of calculating the required external resistors much easier, Picor has developed a filter calculator program that is
designed to be used with Vicor’s MicroRAM output filter, as well as with Picor’s QPO output filters. The filter program will
automatically calculate any trim resistors that might be required, in either remote sense or SC control modes, and all the external
resistors required by the filter. The resulting values are of standard 1% tolerance resistors.
Figure 17 — Screen shots of Picor’s Filter Calculator program for determining the external resistor values used in the circuits of Figures 10 and 11.
The screen shots shown in Figure 17 are of Picor’s output filter calculator program, a tool which can be used to calculate the resistor values needed in the
circuits shown in Figure 10 and Figure 11. This program is a Windows based executable file that is available to Vicor Applications Engineering, and which can
also made available to our customers upon request. To request a copy of the program please contact your local Vicor Field Applications Engineer or email
your request to [email protected]
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MicroRAM
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 are based on circuit simulation and should be considered when point of load
capacitance is used with the MicroRAM in order to maintain a minimum of 30° of phase margin.
Using ceramic load capacitance with <1milliohm ESR and <1nH ESL:
20 µF to 200 µF requires 20 nH of trace/wire load path inductance
200 µF to 1,000 µF requires 60 nH of trace/wire load path inductance
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:
20 µF to 200 µF load capacitance needs an ESL of >50 nH
200 µF to 1,000 µF load capacitance needs an ESL of >5 nH
Adding low ESR capacitance directly at the output terminals of MicroRAM is not recommended and may cause stability problems.
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.
RECOMMENDED PCB LAYOUT
To achieve the best attenuation, proper routing of the power nodes must be followed. The VIN- and VOUT- are internally connected
within the MicroRAM module and should not be connected externally. Doing so will create a ground loop and will degrade
attenuation results. All measurements should be made using the VOUT- of the MicroRAM as reference ground. If possible, waveform
measurements should be made with an oscilloscope that is AC line isolated from other test equipment, and should use probes without
the grounding clip attached. Please contact [email protected] for of proper PARD measurements techniques.
Figure 18 — Recommended copper patterns, top view.
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MicroRAM
µRAM2xxx
Figure 19 — V375A28C600B and µRAM;
Input and output ripple @50% (10 A) load CH1=Vi; CH2=Vo;
Vi-Vo=332 mV; RHR=178 k
Figure 20 — V375A28C600B and µRAM; Input and output dynamic
response no added CTRAN; 20% of 20 A rating load step of 4 A
(10 A – 14 A); RHR = 178 k (Configured as in Figure 7 w/o Trim)
Figure 21 — V375A28C600B and µRAM;
Input and output dynamic response CTRAN=820 µF Electrolytic; 32.5%
of load step of 6.5 A (10 A – 16.5 A); RHR=178 k
(Configured as in Figure 7 w/o Trim)
Figure 22 — V375B12C250B and µRAM;
Input and output [email protected]% (10 A) load CH1=Vi; CH2=Vo; ViVo=305 mV; RHR=80 k
(Configured as in Figure 7 w/o Trim)
Figure 23 — V300B12C250B and µRAM;
Input and output dynamic response no added CTRAN; 17.5% of 20 A rating
load step of 3.5 A (10 A – 13.5 A);RHR=80 k
(Configured as in Figure 7 w/o Trim)
Figure 24 — V300B12C250B and µRAM;
Input and output dynamic response CTRAN = 820 µF Electrolytic; 30% of
load step of 6 A (10 A – 16 A); RHR=80 k
(Configured as in Figure 8 w/o Trim)
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MicroRAM
µRAM2xxx
Figure 25 — V48C5C100B and µRAM; Input and output ripple
@50% (10 A) load CH1 = Vi; CH2 = Vo;
Vi-Vo= 327mV; RHR = 31k (Configured as in Figure 8)
Figure 26 — V48C5C100B and µRAM; Input and output dynamic
response no added CTRAN; 22.5% of 20 A rating load step of 4.5 A
(10 A – 14.5 A);RHR=31k (Configured as in Figure 8)
Figure 27 — V48C5C100B and µRAM; Input and output dynamic
response CTRAN=820 µF Electrolytic; 35% of load step of 7 A
(10 A – 17 A);RHR=31 k (Configured as in Figure 8)
Notes: The measurements in Figures 20–28 were taken with a µRAM2C21 and standard scope probes with a 20 MHz bandwidth scope setting. The criteria for transient
current capability was as follows: The transient load current step was incremented from 10 A to the peak value indicated, then stepped back to 10 A until the resulting output
peak to peak was around 40 mV.
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MicroRAM
MECHANICAL DRAWINGS
uRAM Pins
No. Function Label
1
+In
+
2
Control
SC
3
C ext. CTRAN
4
–In
–
5
–Out
–
6
7
Reference
+Out
Vref
+
DIMENSION L
PIN SHORT – .54 [13.7]
PIN LONG–– .62 [15.7]
PIN EXTRA LONG–––- .71 [18.0]
NOTES:
1. MATERIAL:
BASE: 6000 SERIES ALUMINUM
COVER: LCP, ALUMINUM 3003 H14
PINS:
RoHS PINS GOLD PLATE 30 MICRO INCH MIN; NON-RoHS
PINS:
TIN/LEAD 90/10 BRIGHT
2. DIMENSIONS AND VALUES IN BRACKETS ARE METRIC
3. MANUFACTURING CONTROL IS IN PLACE TO ENSURE THAT THE SPACING
BETWEEN THE MODULES LABEL SURFACE TO THE PRINTED CIRCUIT BOARD
OF THE APPLICATION RANGES FROM DIRECT CONTACT (ZERO), TO THE
MAXIMUM GAP AS CALCULATED FROM THE TOLERANCE STACK-UP
AND IS NOT SUBJECT NEGATIVE TOLERANCE ACCUMULATION
Figure 28 — Module outline
0.062 ±0.010
1,57 ±0,25
PCB THICKNESS
0.800*
INBOARD
SOLDER
MOUNT
ONBOARD
SOLDER
MOUNT
SHORT PIN STYLE
0.094 ±0.003
2,39 ±0,08
LONG PIN STYLE
0.094 ±0.003
2,39 ±0,08
20,32
0.525*
13,34
PLATED
THRU HOLE
DIA
0.275*
6,99
0.145*
3,68
0.133
3,38
1
2
3
4
ALUMINUM
BASEPLATE
1.734**
44,04
2.000*
50,80
7
R
(7X)
ALL MARKINGS
THIS SURFACE
6
PINS STYLES
SOLDER:TIN/LEAD PLATED
MODUMATE: GOLD PLATED COPPER
RoHS: GOLD PLATED COPPER
5
0.06
(4X)
1,5
.400*
10,16
1.090**
27,69
0.45
11,5
*DENOTES TOL = ±0.003
±0,08
0.53
13,5
Unless otherwise specified,
dimensions are in inches
mm
Decimals
**PCB WINDOW
0.XX
Tol.
±0,25
0.XXX
±0.005
±0,127
Figure 29 — PCB mounting specifications
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Angles
±0.01
±1°
MicroRAM
Vicor’s comprehensive line of power solutions includes high density AC-DC and DC-DC modules and
accessory components, fully configurable AC-DC and DC-DC power supplies, and complete custom
power systems.
Information furnished by Vicor is believed to be accurate and reliable. However, no responsibility is assumed by Vicor for its use. Vicor makes no
representations or warranties with respect to the accuracy or completeness of the contents of this publication. Vicor reserves the right to make
changes to any products, specifications, and product descriptions at any time without notice. Information published by Vicor has been checked and
is believed to be accurate at the time it was printed; however, Vicor assumes no responsibility for inaccuracies. Testing and other quality controls
are used to the extent Vicor deems necessary to support Vicor’s product warranty. Except where mandated by government requirements, testing of
all parameters of each product is not necessarily performed.
Specifications are subject to change without notice.
Vicor’s Standard Terms and Conditions
All sales are subject to Vicor’s Standard Terms and Conditions of Sale, which are available on Vicor’s webpage or upon request.
Product Warranty
In Vicor’s standard terms and conditions of sale, Vicor warrants that its products are free from non-conformity to its Standard Specifications (the
“Express Limited Warranty”). This warranty is extended only to the original Buyer for the period expiring two (2) years after the date of shipment
and is not transferable.
UNLESS OTHERWISE EXPRESSLY STATED IN A WRITTEN SALES AGREEMENT SIGNED BY A DULY AUTHORIZED VICOR SIGNATORY, VICOR
DISCLAIMS ALL REPRESENTATIONS, LIABILITIES, AND WARRANTIES OF ANY KIND (WHETHER ARISING BY IMPLICATION OR BY OPERATION OF LAW)
WITH RESPECT TO THE PRODUCTS, INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OR REPRESENTATIONS AS TO MERCHANTABILITY,
FITNESS FOR PARTICULAR PURPOSE, INFRINGEMENT OF ANY PATENT, COPYRIGHT, OR OTHER INTELLECTUAL PROPERTY RIGHT, OR ANY OTHER
MATTER.
This warranty does not extend to products subjected to misuse, accident, or improper application, maintenance, or storage. Vicor shall not be liable
for collateral or consequential damage. Vicor disclaims any and all liability arising out of the application or use of any product or circuit and assumes
no liability for applications assistance or buyer product design. Buyers are responsible for their products and applications using Vicor products and
components. Prior to using or distributing any products that include Vicor components, buyers should provide adequate design, testing and
operating safeguards.
Vicor will repair or replace defective products in accordance with its own best judgment. For service under this warranty, the buyer must contact
Vicor to obtain a Return Material Authorization (RMA) number and shipping instructions. Products returned without prior authorization will be
returned to the buyer. The buyer will pay all charges incurred in returning the product to the factory. Vicor will pay all reshipment charges if the
product was defective within the terms of this warranty.
Life Support Policy
VICOR’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS
PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF VICOR CORPORATION. As used herein, life support
devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and whose failure to perform
when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the
user. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or system or to affect its safety or effectiveness. Per Vicor Terms and Conditions of Sale, the user of Vicor products
and components in life support applications assumes all risks of such use and indemnifies Vicor against all liability and damages.
Intellectual Property Notice
Vicor and its subsidiaries own Intellectual Property (including issued U.S. and Foreign Patents and pending patent applications) relating to the
products described in this data sheet. No license, whether express, implied, or arising by estoppel or otherwise, to any intellectual property rights is
granted by this document. Interested parties should contact Vicor's Intellectual Property Department.
Vicor Corporation
25 Frontage Road
Andover, MA, USA 01810
Tel: 800-735-6200
Fax: 978-475-6715
email
Customer Service: [email protected]
Technical Support: [email protected]
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