PI33XX Datasheet, PDF (36/42 Pages) Vicor Corporation – 8V to 36Vin Cool-Power ZVS B uck Regulator Family

Resistor R-high would be connected as in Figure 4 to
achieve the 4.0V regulator output. No R_low resistor
would be used since in this example the trim is
above the regulator set voltage.
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 100nF and a fixed charge current to provide
a minimum startup time of 2ms (typical) for all
PI33XX 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:
(
)
Where, t_TRK is the soft-start time and I_TRK is a 50uA
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 devices TRK pins
together. This type of tracking will force all
connected regulators to startup and reach regulation
at the same time (see Figure 5 (a)).
VOUT 1
VOUT 2
(a)
Master VOUT
VOUT 2
(b)
t
Figure 5 - PI33XX tracking methods
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
vicorpower.com
800 735.6200
PI33XX-X0
through a divider (Figure 6) with the same ratio as
the slave’s feedback divider (see Table 4 for values).
Master VOUT
PI33XX
R1
TRK
Slave
R2
SGND
Figure 6 - Voltage divider connections for direct tracking
All connected regulators’ soft-start slopes will track
with this method. Direct tracking timing is
demonstrated in Figure 5 (b). All tracking regulators
should have their Enable (EN) pins connected
together to work properly.
Inductor Pairing
The PI33XX utilizes an external inductor. This
inductor has been optimized for maximum efficiency
performance. Table 5 details the specific inductor
value and part number utilized for each PI33XX
device and are manufactured by either Picor or
Cooper Bussman Coiltronics accordingly.
Device
PI3311-X0
PI3318-X0
PI3312-X0
PI3301-X0
PI3302-X0
PI3303-X0
PI3305-X0
Inductor
[nH]
125
155
200
200
200
230
230
Inductor
Part Number
PI6125-00-FPIZ
PI6155-00-FPIZ
FPT705-200-R
FPT705-200-R
FPT705-200-R
FPT705-230-R
FPT705-230-R
Manufacturer
Picor
Picor
Coiltronics
Coiltronics
Coiltronics
Coiltronics
Coiltronics
Table 5 - PI33XX Inductor pairing
Thermal Derating
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
Rev 1.4
11/2012
Cool-Power^®
Page 36 of 42