Maxi Family
Rev 9.0
vicorpower.com
Page 12 of 15
4/2013
800 735.6200
375 V Input
Parallel Operation
The PR pin supports paralleling for increased power with N+1
(N+M) redundancy. Modules of the same input voltage, output
voltage, and power level will current share if all PR pins are
suitably interfaced.
Compatible interface architectures include the following:
AC coupled single-wire interface.
All PR pins are connected
to a single communication bus through 0
.
001
µ
F (500 V)
capacitors. This interface supports current sharing and is fault
tolerant except for the communication bus. Up to three
converters may be paralleled by this method. See Figure 9.
Transformer coupled interface.
For paralleling four or more
converters a transformer coupled interface is required. See
Figure 10.
For details on parallel operation please refer to the
Design Guide & Applications Manual for Maxi, Mini, Micro Family.
Figure 9
—
AC coupled single-wire interface.
* See Maxi, Mini, Micro Design Guide.
+IN
PC
PR
–IN
+IN
PC
PR
–IN
Module 2
Module 1
+
Parallel
Bus
–
0.2 µF
0.001 µF
0.2 µF
0.001 µF
Low inductance
ground plane
or bus
4.7 nF
4.7 nF
4.7 nF
4.7 nF
Z1
*
Z1
*
+IN
PC
PR
–IN
+IN
PC
PR
–IN
Module 2
Module 1
T1
T2
+
–
0.2 µF
0.2 µF
Parallel
Bus
4.7 nF
4.7 nF
4.7 nF
4.7 nF
Z1
*
Z1
*
Figure 10
—
Transformer-coupled interface.
PARALLEL BUS - PR PIN
Output Voltage Programming
The output voltage of the converter can be adjusted or
programmed via fixed resistors, potentiometers or voltage
DACs. See Figure 8.
Figure 8
—
Output voltage trim down and trim up circuit.
–OUT
+S
SC
Error Amplifier
+
0.033 uF
–
+
-S
+OUT
Load
Rd
Trim Down
Ru
Trim Up
1.23 V
1 k
Ω
100
Ω
typ.
1,000 Vout
Vnom – Vout
R
d
(ohms) =
1,000 (Vout –1.23) Vnom
1.23 (Vout – Vnom)
R
U
(ohms) =
– 1,000
Trim Down
1. This converter is not a constant power device – it has a
constant current limit. Hence, available output power is
reduced by the same percentage that output voltage is
trimmed down. Do not exceed maximum rated output current.
2. The trim down resistor must be connected between the SC
and -S pins. Do not bypass the SC pin directly with a
capacitor.
Trim Up
1. The converter is rated for a maximum delivered power. To
ensure that maximum rated power is not exceeded, reduce
maximum output current by the same percentage increase in
output voltage.
2. The trim up resistor must be connected between the SC
and +S pins. Do not bypass the SC pin directly with a
capacitor.
3. Do not trim the converter above maximum trim range
(typ10%) or the output over voltage protection
circuitry may be activated.
SECONDARY CONTROL - SC PIN
Trim resistor values calculated automatically:
On-line calculators for trim resistor values are available on the
vicor website at:
asp.vicorpower.com/calculators/calculators.asp?calc=1
Resistor values can be calculated for fixed trim up, fixed trim
down and for variable trim up or down.
