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
Min
Typ
Max
Unit
Notes
Operating current range
µRAM2xxx
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.
0.02
0.02
20
30
A
A
µRAM3xxx
Operating input voltage
3.0
30
50
Vdc
Continuous
Transient output response
Load current step <1A/µsec
Step load change;
mVp-p
see Figures 9, 12, & 15, pp. 6-7
Transient output response
Load current step <1A/µsec
(CTRAN = 820µF)
Optional capacitance CTRAN can be used
50
mVp-p
mV
to increase transient current capability; See Figures
1 & 2 on p. 3 and Figures 10, 13, & 16 on pp. 6-7
VHR headroom voltage range(1)
@ 1A load
See Figures 5, 6 & 7
325
425
See Table 1 for headroom setting resistor values
Output ripple
10
5
mVp-p
mVrms
Ripple frequency 60Hz to 100kHz; optional capacitor
Input Vp-p = 100mV
CHR = 100µF required to increase low frequency
attenuation as shown in Figures 3a and 3b
see Figures 8, 11, & 14, pp. 6-7
Output ripple
10
5
mVp-p
mVrms
Ripple frequency 100kHz to 2MHz;
see Figures 8, 11, & 14, pp. 6-7
Input Vp-p = 500mV
SC output voltage(2)
OR’ing threshold
µRAM bias current
1.23
Vdc
mV
mA
See Table 1 RSC value
Vin – Vout
10
60
Power Dissipation
µRAM2xxx VHR = 380mV@1A
7.5
W
W
Vin = 28V; Iout = 20A
Vin = 28V; Iout = 30A
µRAM3xxx VHR = 380mV@1A
11.5
(1) Headroom is the voltage difference between the +Input and +Output pins.
RHR = (µRAM +Out/VHR) x 2.3k (see Table 1 for example values)
(2) 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 RSC resistor values)
RSC = ((µRAM +Out)/1.23V x 1k) – 2k
µRAM Out
3.0V
V
HR @ 1A
375mV
375mV
375mV
375mV
375mV
375mV
R
HR Value (ohms)
R
SC Value (ohms)
18.4k
0.439k
5.0V
30.6k
2.07k
12.0V
15.0V
24.0V
28.0V
73.6k
7.76k
92.0k
10.20k
147.2k
17.50k
171.7k
20.76k
Table 1—RHR and RSC 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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