PI352X-00 Datasheet, PDF (27/34 Pages) Vicor Corporation – 30VIN to 60VIN Cool-Power ZVS Buck Regulator

Application Description
Output Voltage Set Point
The PI352x-00 family of Buck Regulators utilizes V_REF, an internal
reference for regulating the output voltage. The output voltage
setting is accomplished using external resistors as shown in
Figure 58. Select R2 to be at or around 1kΩ for best noise
immunity. Use Equations (2) and (3) to determine the proper value
based on the desired output voltage.
-
+ V_REF
R_ZI
C_HF
EAIN
C_EAIN-INT
EAO
COMP
V_OUT
R1
R2
Figure 58 — External resistor divider network
V_OUT = V_REF •
R1 + R2
R2
(2)
R1
=
R2
•
V_OUT – V_REF
V_REF
(3)
where V_REF = V_EAIN
Note: When using the above method of trimming by adjusting the value
of R1, the compensation of the control loops is modified and additional
Cout may be needed depending on the model. When the PI3526-00-LGIZ
is trimmed below 10V, the effective C_OUT must be at least 120µF, including
tolerance and voltage coefficient.
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 t_SS for all PI352x-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 time
in excess of t_SS:
C_TRK = (t_TRK • I_TRK ) – C_{TRK_INT}
(4)
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 PI352x-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 59a).
Cool-Power^® ZVS Switching Regulators
Page 27 of 34
Rev 1.3
06/2017
PI352x-00
V_OUT 1
V_OUT 2
(a)
Master V_OUT
V_OUT 2
(b)
t
Figure 59 — PI352x-00 tracking responses
For Direct Tracking, choose the PI352x-00 with the highest output
voltage as the master and connect the master to the TRK pin of
the other PI352x-00 regulators through a divider (Figure 59) with
the same ratio as the slave’s feedback divider.
Master V_OUT
PI352x
R1
TRK
Slave
R2
SGND
Figure 60 — Voltage divider connections for direct tracking
All connected PI352x-00 regulator soft-start slopes will track
with this method. Direct tracking timing is demonstrated in
Figure 59b. All tracking regulators should have their Enable (EN)
pins connected together to work properly.
Inductor Pairing
The PI352x-00 utilizes an external inductor. This inductor has
been optimized for maximum efficiency performance. Table 3
details the specific inductor value and part number utilized for
each PI352x-00.
Product
System
Value (nH) Manufacturer
PI3525-00-LGIZ
230
Eaton
PI3526-00-LGIZ
480
Eaton
Table 3 — PI352x-00 Inductor pairing
Part Number
FP2207R1-R230-R
HCV1707R1-R48-R
Inductor Part
Number
FP2207R1-R230-R
Thermal Impedances
φ_INT-TOP φ_INT-LEADS φ_INT-BELLY
(°C / W) (°C / W) (°C / W)
Max Operating
Temperature
T_INT-IND
(°C)
8.75
4.77
5.99
125
HCV1707R1-R48-R 65.41
8.87
20.46
125
Table 4 — Inductor thermal model parameters
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