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3
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 (800) 531-5782 Fax: (630) 393-6902 http://www.powertrends.com
Application
Notes
PT3320/3340 Series
Adjusting the Output Voltage of the PT3320 /
PT3340 Series of Isolated DC-DC Converters
The factory pre-set output voltage of Power Trends’ PT3320
and PT3340 series DC-DC converters may be adjusted within a
nominal ±10% range. This is accomplished with the addition of
a single external resistor. For the input voltage range specified in
the data sheet, Table 1 gives the allowable adjustment range for
each model as Vo (min) and Vo (max).
Adjust Up:
An increase in the output voltage is obtained by
adding a resistor, R2 between pin 18 (Vo adjust), and pin 13
(-Remote Sense).
See note 4.
Adjust Down:
Add a resistor (R1), between pin 18 (Vo adjust)
and pin 19 (+Remote Sense).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, (R1) or R2.
Notes:
1. Use only a single 1% resistor in either the (R1) or R2 loca-
tion. Place the resistor as close to the ISR as possible.
2. Never connect capacitors to Vo adjust. Any capacitance
added to the Vo adjust control pin will affect the stability of
the ISR.
Table 1
DC-DC CONVERTER ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
24V Bus
PT3341
PT3342
PT3343
PT3344
48V Bus
PT3325
PT3326
PT3321
PT3322
PT3323
PT3324
Vo(nom)
2.0V
2.5
3.3
5.0
12.0
15.0
Vo(min)
1.8V
2.25
2.95
4.5
10.8
13.5
Vo(max)
2.2
2.75
3.65
5.5
13.2
16.5
Vr
1.225
2.5
Ro (k
)
80.6
33.2
18.2
14.3
11.0
Rs (k
)
150.0
121.0
150.0
121.0
90.9
80.6
Figure 1
(R1)
Adj Down
R2
Adj Up
Cin
100
F
100V
(Optional)
+
Cout
330
F
+
L
O
A
D
+V
-V
+V
in
-V
in
PT3320/3340
18
4, 5, 6
7, 8, 9
+Vin
+Vout
-Vin
Vo(adj)
Inhibit
2
Sns(+)
19
10 - 12
-Vout
14 - 17
Sns(-)
13
3. If the remote sense pins are not being used, the resistors (R1)
and R2 can be connected to +Vout or -Vout respectively.
4. The adjusted output voltage Va effectively sets the voltage
across pins 13 and 19 (±Remote Sense). When using the
remote sense pins, Vout (measured directly across pins 10–12,
and 14–17) can be significantly higher than Va, and may
exceed Vo (max). If Va is adjusted upward, the alternative is
to increase the minimum input voltage by the same percent-
age as Vout exceeds Vo(max).
The values of (R1) [adjust down], and R2 [adjust up], can also be
calculated using the following formulas.
(R1)
=
Ro (Vo – Vr)(Va – Vr)
– Rs
k
Vr (Vo – Va)
R2
=
Ro (Vo – Vr)
– Rs
k
(Va – Vo)
Where
Vo = Original output voltage
Va = Adjusted output voltage
Vr = Reference voltage (Table 1)
Ro = Multiplier resistance (Table 1)
Rs = Series resistance (Table 1)