FPV1006-85-R datasheet(24/30 Pages) VICOR

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R1, R2, and R4 are all internal 1.0 % resistors and R_low and

R_high are external resistors for which the designer can add

to modify VOUT to a desired output. The internal resistor

values for each regulator are listed next in Table 3.

By choosing an output voltage value within the ranges stated

in Table 2, VOUT 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 PI3423 is selected (3.3 V 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 PI3423 can be found in Table 3 and are

R1 = 2.61k Ω and R2 = 1.13 kΩ. Inserting these values in to

Equation (1), R_HIGH is calculated as follows:

Resistor R_high should be connected as shown in Figure 38

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.

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 tSS for all for all

PI34xx-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:

CTRK = (tTRK xITRK) – 100 x 10 -9,

where, tTRK is the soft-start time and ITRK is a 50 μA internal

charge current (see Electrical Characteristics for limits).

There is typically either a proportional or direct tracking

method implemented within a tracking 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 39 (a)).

For Direct Tracking, choose the regulator with the highest

output voltage as the master and connect the master TRK pin

to the TRK pin of the other regulators through a divider

(Figure 40) with the same ratio as the slave’s feedback

divider (see Table 3 for values).

All connected regulators’ soft-start slopes will track with this

method. Direct tracking timing is demonstrated in

Figure 39 (b).

Cool-Power®

Rev 1.3

vicorpower.com

Page 24 of 30

12/2015

800 927.9474

PI34xx-00

ADJ

REM

OUT

SGND

low

high

1.0 Vdc

Figure 38 — Internal resistor divider network

Table 3 — PI34xx-00 Internal divider values

(b)

(a)

OUT

Master V

OUT

Figure 39 — PI34xx-00 tracking methods

Device

PI3420-00-LGIZ

1 k

∞

100

PI3421-00-LGIZ

0.806 k

1.0 k

100

PI3422-00-LGIZ

1.5 k

1.0 k

100

PI3423-00-LGIZ

2.61 k

1.13 k

100

PI3424-00-LGIZ

4.53 k

1.13 k

100

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