PI3303-00-EVAL1 Datasheet, PDF (35/42 Pages) Vicor Corporation – Cool-Power® ZVS Switching Regulators

Device
R1
R2
PI3311-x0-LGIZ
1kΩ
Open
PI3318-x0-LGIZ
0.806kΩ
1.0kΩ
PI3312-x0-LGIZ
1.5kΩ
1.0kΩ
PI3301-x0-LGIZ
2.61kΩ
1.13kΩ
PI3302-x0-LGIZ
4.53kΩ
1.13kΩ
PI3303-x0-LGIZ
11.0kΩ
1.0kΩ
PI3305-x0-LGIZ
14.0kΩ
1.0kΩ
Table 3 — PI33xx-x0 Internal divider values
R4
100Ω
100Ω
100Ω
100Ω
100Ω
100Ω
100Ω
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:
( ) ^{( ) Rhigh =}
1
V_OUT – 1
R1
–
1
R2
(1)
( ) _{( )} ^Rlow
=
1
R1 V_OUT
1
–1
–
1
R1
(2)
If, for example, a 4.0V output is needed, the user should choose
the regulator with a trim range covering 4.0V from Table 2. For
this example, the PI3301 is selected (3.3V set voltage). First step
would be to use Equation (1) to calculate R_high 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 = 2.61kΩ and R2 = 1.13kΩ. Inserting these
values in to Equation (1), R_high is calculated as follows:
( ) 3.78kΩ = (4.0 – 1 )
2.61kΩ
1
–
1
1.13kΩ
(3)
Resistor R_high should be connected as shown in Figure 60 to
achieve the desired 4.0V 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 1V setting. The following Equation (4) can be used
calculate Rhigh values for the PI3420 regulators.
R = _{high (1V)}
1
( V_OUT ^– 1)
(4)
R1
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-x0
regulators. By adding an additional external capacitor to the TRK
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 • I_TRK ) – 100 • 10 ^-9
(5)
Where t_TRK is the soft-start time and I_TRK is a 50µA 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)
t
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).
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^® ZVS Switching Regulators
Page 35 of 42
Rev 2.4
02/2017
vicorpower.com
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