PI3318-01-LGIZ Datasheet, PDF (21/26 Pages) Vicor Corporation – 8V to 36Vin, 15A Cool-Power ZVS Buck Regulator

Application Description
Output Voltage Trim
The PI33XX-X1 family of Buck Regulators provides
four common output voltages: 1.0V, 1.8V, 2.5V, and
3.3V. A post-package trim step is implemented to
offset any resistor divider network errors ensuring
maximum output accuracy. With a single resistor
connected from the ADJ pin to SGND or REM, each
device’s output can be varied above or below the
nominal set voltage (with the exception of the
PI3311-X1 which can only be above the set voltage
of 1V).
Device
PI3311-X1-LGIZ
PI3318-X1-LGIZ
PI3312-X1-LGIZ
PI3301-X1-LGIZ
Output Voltage
Set
Range
1.0V 1.0 to 1.4V
1.8V 1.4 to 2.0V
2.5V 2.0 to 3.1V
3.3V 2.3 to 4.1V
Table 3 - PI33XX-X1 family output voltage ranges
The remote pin (REM) should always be connected
to the VOUT pin, if not used, to prevent an output
voltage offset. Figure 4 shows the internal feedback
voltage divider network.
R4
R1
-
+
R2
1.0Vdc
VOUT
REM
ADJ
R_low
SGND
R_high
Figure 4 - Internal resistor divider network
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 value for each
regulator is listed below in Table 4.
vicorpower.com
800 735.6200
PI33XX-X1
Device
PI3311-X1-LGIZ
PI3318-X1-LGIZ
PI3312-X1-LGIZ
PI3301-X1-LGIZ
R1
R2
R4
1k Open 100
0.806k 1.0k 100
1.5k 1.0k 100
2.61k 1.13k 100
Table 4 - PI33XX-X1 Internal divider values
By choosing an output voltage value within the
ranges stated in Table 3, 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 4.0V output is needed, the user
should choose the regulator with a trim range
covering 4.0V from Table 3. 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 4 and
are R1=2.61kΩ and R2=1.13kΩ. Inserting these
values in to Equation (1), R_high is calculated as
follows:
(
)(
)
Resistor R-high would be connected as in Figure 4 to
achieve the 4.0V regulator output. No R_low resistor
would be used since in this example the trim is
above the regulator set voltage.
The PI3311-X1 output voltage can only be trimmed
higher than the factory 1V setting. The following
Rev 1.3
09/2015
Cool-Power^®
Page 21 of 26