PI3542-00-LGIZ Datasheet, PDF (26/37 Pages) Vicor Corporation – 36 Vin to 60 Vin Cool-Power ZVS Buck Regulator & LED Driver

(R1 + R2)
V =V
OUT
ref
•
R2
(1)
(Vref – V )
R1 = –R2 •
OUT
(2)
Vref
where, Vref = 1 V
Soft-Start Adjust 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 internal capacitor and a fixed
charge current to provide a Soft-Start Time tSS for all
PI354x-00 regulators. By adding an additional external
capacitor to the TRK pin, the soft-start time can be increased
further. The following equation can be used to calculate the
proper capacitor for a desired soft-start times:
C_TRK = (t_TRK • I_TRK ) – 47 • 10^-9,
Where, t_TRK is the soft-start time and I_TRK is a 50 μA internal
charge current (see Electrical Characteristics for limits).
There is typically either proportional or direct tracking
implemented within a design. For proportional tracking
between several regulators at startup, simply connect all
PI354x-00 device TRK pins together. This type of tracking
will force all connected regulators to startup and reach
regulation at the same time (see Figure 52a).
V_OUT 1
V_OUT 2
(a)
Master V_OUT
V_OUT 2
(b)
t
Figure 52 — PI354x-00 tracking methods
For Direct Tracking, choose the PI354x-00 with the highest
output voltage as the master and connect the master to the
TRK pin of the other PI354x-00 regulators through a divider
(Figure 53) with the same ratio as the slave’s
feedback divider.
Cool-Power®
Page 26 of 37
Rev 1.3
2/2016
PI354x-00
Master V_OUT
PI3
x
R1
TRK
Slave
R2
SGND
Figure 53 — Voltage divider connections for direct tracking
All connected PI354x-00 regulator soft-start slopes will track
with this method. Direct tracking timing is demonstrated in
Figure 52b. All tracking regulators should have their Enable
(EN) pins connected together to work properly.
Inductor Pairing
The PI354x-00 utilizes an external inductor. This inductor
has been optimized for maximum efficiency performance.
Table 2 details the specific inductor value and part number
utilized for each PI354x-00.
Device
PI3542-00
PI3543-00
PI3545-00
PI3546-00
Inductor
(nH)
340
420
420
900
Inductor
Part Number
FPT1006-340-R
HCV1206-R42-R
HCV1206-R42-R
HCV1206-R90-R
Manufacturer
Eaton
Eaton
Eaton
Eaton
Table 2 — PI354x-00 Inductor pairing
Thermal De-rating
Thermal de-rating curves are provided that are based on
component temperature changes versus load current, input
voltage and air flow. It is recommended to use these curves
as a guideline for proper thermal de-rating. These curves
represent the entire system and are inclusive to both the
Picor regulator and the external inductor. Maximum thermal
operation is limited by either the MOSFETs or inductor
depending upon line and load conditions.
Thermal measurements were made using a standard
PI354x-00 Evaluation board which is 2.5 x 4 inches in area
and uses 4-layer, 2oz copper. Thermal measurements were
made on the three main power devices, the two internal
MOSFETs and the external inductor, with air flows of 0, 200,
and 400 LFM.
Small Signal Model - Constant Voltage Mode
The PI354X product family is a variable frequency CCM/DCM
ZVS Buck Regulator. The small signal model for this
powertrain is that of a voltage controlled current source
which has a trans-conductance that varies depending on the
operating mode. When the converter is operating at its
normal frequency, it is in discontinuous mode. As the load
increases to the point at which the boundary between
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