
Application Notes
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Adjusting the Output Voltage of the 30W-Rated
PT3400 Series of Isolated DC/DC Converters
The output voltage of the PT3400 Excalibur series of
isolated DC/DC converters may be adjusted over a limited
range from the factory-trimmed nominal value. Adjust-
ment is accomplished with a single external resistor. The
placement the resistor determines the direction of adjust-
ment, either up or down, and the value of the resistor the
magnitude of adjustment. Table 3-1 gives the allowable
adjustment range for each model in the series as Va (min)
and Va (max) respectively. Note that converters with an
output voltage of 1.8V or less can only be adjusted up 1.
Adjust Up:
An increase in the output voltage is obtained
by adding a resistor, R1 between Vo Adj (pin 6), and –Vsense
(pin 7).
Adjust Down
(PT3401, PT3402, & PT3408 Only):
Add a
resistor (R2), between Vo Adj (pin 6) and +Vsense (pin 14).
Refer to Figure 3-1 and Table 3-2 for both the placement and
value of the required resistor, R1 or (R2).
The values of R1 [adjust up], and (R2) [adjust down], can
also be calculated using the following formulas.
R1
=
2 Ro
– Rs
k
Va – Vo
(R2)
=
Ro (Va – 2)
– Rs
k
Vo – Va
Where, Va = Adjusted output voltage
Vo = Original output voltage
Ro = Resistor constant in Table 3-1
Rs = Internal series resistance in Table 3-1
Figure 3-1
Notes:
1. The output voltage of the PT3401 (3.3V),
PT3402 (2.5V), and PT3408 (5V) may be adjusted either
higher or lower. All other models, which have an output
voltage of 1.8V or less, can only be adjusted higher.
2. Use only a single 1% resistor in either the R1 or (R2)
location. Place the resistor as close to the converter as
possible.
3. Never connect capacitors to Vo Adj. Any capacitance added
to this pin will affect the stability of the converter.
4. If the output voltage is increased, the maximum load
current must be derated according to the following
equation.
Io(max)
=
Vo × Io(rated)
Va
In any instance, the load current must not exceed the
converter’s rated output current Io(rated) in Table 3-1.
PT3400 Series
L
O
A
D
* Remote Sense (–)
Remote Sense (+)
+V
OUT
–V
OUT
+V
IN
–V
IN
C
OUT
330F
+
R
1
Ad j ust Up
(R
2)
Adj Down
PT3400
1
2
11–13
8–10
14
7
3
4
–V
IN
+V
IN
EN 1
EN 2
SEQ
V
o Adj
6
5
+V
OUT
–V
OUT
+V
SENSE
–V
SENSE