PI3740-00 Datasheet, PDF (22/48 Pages) Vicor Corporation – Parallel capable with single wire current sharing

Application Description
Output Voltage Trim
The output voltage can be adjusted by feeding back a portion
of the desired output through a voltage divider to the error
amplifier’s input (see Figure 37). Equation 1 can be used to
determine resistor values needed for the voltage divider.
( ) ^{R1 = R2 •}
V_OUT
1.7
-1
(1)
The R2 value is selected by the user; a 1.65kΩ resistor value
is recommended.
If, for example, a 12V output is needed, the user can select a
1.65kΩ (1%) resistor for R2 and use Equation (1) to calculate R1.
Once R1 value is calculated, the user should select the nearest
resistor value available. In this example, R1 is 9.997kΩ so a
10.0kΩ should be selected.
Soft-Start Adjustment and Tracking
The TRK pin offers a means to increase the regulator’s soft-start
time or to track with additional regulators. The soft-start slope is
controlled by an external capacitor and a fixed charge current to
provide the startup ramp. The following equation can be used to
calculate the proper capacitor for a desired soft-start time:
C_TRK =
(t_TRK • I_SS )
1.7
– 56 • 10 ^-12
(2)
Where t_TRK is the desired soft-start time and I_SS is the TRK pin
source current (see Electrical Characteristics for limits).
The PI3740-00 allows the tracking of multiple like regulators.
Two methods of tracking can be chosen: proportional or direct
tracking. Proportional tracking will force all connected
regulators to startup and reach regulation at the same time
(see Figure 38 (a)). To implement proportional tracking, simply
connect all devices TRK pins together.
V_OUT 1
V_OUT 2
ProporƟonal
Tracking
(a)
Master V_OUT
V_OUT 2
Direct
Tracking
(b)
t
Figure 38 — PI3740-00 tracking methods
PI3740-00
For Direct Tracking, choose the regulator with the highest output
voltage as the master and connect the master to the TRK pin
of the other regulators through a divider (Figure 39) with the
same ratio as the slave’s feedback divider (see Output Voltage
Trim). The TRK pin should not be driven without 1kΩ minimum
series resistance.
Master V_OUT
PI3740
R1
TRK
Slave
R2
SGND
Figure 39 — Voltage divider connections for direct tracking
All connected regulators’ soft-start slopes will track with this
method. Direct tracking timing is demonstrated in Figure 38
(b). All tracking regulators should have their Enable (EN) pins
connected together for proper operation.
Inductor Pairing
Operations and characterization of the PI3740-00 was
performed using a 420nH inductor, Part # HCV1206-R42-R,
manufactured by Eaton. This Inductor has a form factor of
12.5mm x 10mm x 5mm. No other inductor is recommended for
use with the PI3740-00. For additional inductor information and
sourcing, please contact Eaton directly.
Cool-Power^® ZVS Switching Regulators
Page 22 of 48
Rev 1.4
04/2017
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