PI354X-00 Datasheet, PDF (27/39 Pages) –

Output Voltage Set Point
The PI354x-00 family of Buck Regulators utilizes an internal
reference (V_REF). The output voltage setting is accomplished using
external resistors as shown in Figure 51. Select R2 to be at or
around 1kΩ for best noise immunity. Use Equations (1) and (2) to
determine the proper value based on the desired output voltage.
-
+ V_REF
R_ZI
C_HF
-
LGH
+ V_LGH-REF
EAIN
EAO
COMP
V_OUT
R1
R2
Figure 51 — External resistor divider network
V_OUT = V_REF •
R1 + R2
R2
(1)
( ) _{R1 = R2 •} V_OUT – V_REF
(2)
V_REF
where V_REF = V_EAIN
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 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
(3)
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 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).
PI354x-00
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.
Master V_OUT
PI354x
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
Inductor
(nH)
340
Inductor
Part Number
FPT1006-340-R
PI3543-00
420
HCV1206-R42-R
PI3545-00
420
HCV1206-R42-R
PI3546-00
900
HCV1206-R90-R
Table 2 — PI354x-00 Inductor pairing
Manufacturer
Eaton
Eaton
Eaton
Eaton
Cool-Power^® ZVS Switching Regulators
Page 27 of 39
Rev 1.6
03/2017
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