PI3301-20-LGIZ Datasheet, PDF (35/42 Pages) Vicor Corporation – 8 V to 36 Vin Cool-Power ZVS Buck Regulator Family

Device
R1
R2
R4
PI3311-x0-LGIZ
1k
Open
100
PI3318-x0-LGIZ
0.806 k
1.0 k
100
PI3312-x0-LGIZ
1.5 k
1.0 k
100
PI3301-x0-LGIZ
2.61 k
1.13 k
100
PI3302-x0-LGIZ
4.53 k
1.13 k
100
PI3303-x0-LGIZ
11.0 k
1.0 k
100
PI3305-x0-LGIZ
14.0 k
1.0 k
100
Table 3 — PI33xx-x0 Internal divider values
By choosing an output voltage value within the ranges stated in
Table 2, V_OUT can simply be adjusted up or down by selecting the
proper R_high or R_low value, respectively. The following equations
can be used to calculate R_high and R_low values:
If, for example, a 4.0 V output is needed, the user should choose
the regulator with a trim range covering 4.0 V from Table 2. For
this example, the PI3301 is selected (3.3 V set voltage). First step
would be to use Equation (1) to calculate Rhigh since the required
output voltage is higher than the regulator set voltage. The
resistor-divider network values for the PI3301 are can be found in
Table 3 and are R1 = 2.61 kΩ and R2 = 1.13 kΩ. Inserting these
values in to Equation (1), R_high is calculated as follows:
PI33xx-x0
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 x I_TRK) – 100 x 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 devices TRK pins
together. This type of tracking will force all connected regulators
to startup and reach regulation at the same time (see Figure 61(a).
V_OUT 1
V_OUT 2
(a)
Master V_OUT
V_OUT 2
(b)
+
Figure 61 — PI33xx-x0 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 through a divider (Figure 62) with the same
ratio as the slave’s feedback divider (see Table 3 for values).
Resistor R_high should be connected as shown in Figure 60 to
achieve the desired 4.0 V regulator output. No external R_low
resistor is need in this design example since the trim is above the
regulator set voltage.
The PI3420 output voltage can only be trimmed higher than
the factory 1 V setting. The following Equation (3) can be used
calculate Rhigh values for the PI3420 regulators.
1
!_!!"!(!!) = _{!"#$ − 1}                                        (3)      
!1
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 100 nF and a fixed charge current to
provide a minimum startup time of 2 ms (typical) for all PI33xx-x0
regulators. By adding an additional external capacitor to the TRK
Master V_OUT
PI33xx
R1
TRK
Slave
R2
SGND
Figure 62 — Voltage divider connections for direct tracking
All connected regulators’ soft-start slopes will track with this
method. Direct tracking timing is demonstrated in Figure 61(b). All
tracking regulators should have their Enable (EN) pins connected
together to work properly.
Cool-Power®
Page 35 of 42
Rev 2.0
02/2016
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