PRELIMINARY
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
(C
TRAN
= 820µF)
V
HR
headroom voltage range
(1)
@ 1A load
Output ripple
Input Vp-p = 100mV
325
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 C
TRAN
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 60Hz to 100kHz; optional capacitor
C
HR
= 100µF required to increase low frequency
attenuation as shown in Figures 3a and 3b
see Figures 8, 11, & 14, pp. 6-7
Ripple frequency 100kHz to 2MHz;
see Figures 8, 11, & 14, pp. 6-7
See Table 1 R
SC
value
Vin – Vout
50
mVp-p
425
10
5
mV
mVp-p
mVrms
Output ripple
Input Vp-p = 500mV
SC output voltage
(2)
OR’ing threshold
µRAM bias current
Power Dissipation
µRAM2xxx V
HR
= 380mV@1A
µRAM3xxx V
HR
= 380mV@1A
7.5
11.5
1.23
10
10
5
mVp-p
mVrms
Vdc
mV
60
mA
W
W
Vin = 28V; Iout = 20A
Vin = 28V; Iout = 30A
(1)
Headroom is the voltage difference between the +Input and +Output pins.
R
HR
= (µRAM +Out/V
HR
) x 2.3k (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)/1.23V x 1k) – 2k
(2)
µRAM Out
3.0V
5.0V
12.0V
15.0V
24.0V
28.0V
V
HR
@ 1A
375mV
375mV
375mV
375mV
375mV
375mV
R
HR
Value (ohms)
18.4k
30.6k
73.6k
92.0k
147.2k
171.7k
R
SC
Value (ohms)
0.439k
2.07k
7.76k
10.20k
17.50k
20.76k
Table 1—R
HR
and R
SC
are computed values for a 375mV 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. 1.1
Page 2 of 8
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