
Application Notes
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Adjusting the Output Voltage of the 10W-Rated
Excalibur Series of Isolated DC/DC Converters
The factory pre-set output voltage of Power Trends’ 10W
Excalibur series of isolated DC-DC converters may be
adjusted over a narrow 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 10 (Vo adjust), and
pins 6 & 7 (–Vout).
Adjust Down:
Add a resistor (R1), between pin 10 (Vo adjust)
and pins 8 & 9 (+Vout).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, (R1) or R2.
The values of (R1) [adjust down], and R2 [adjust up], can
also be calculated using the following formulas.
(R
1)
=
56.2 (V
a – 1.225)
– R
s
k
V
o – Va
Table 1
DC/DC CONVERTER ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
24V Bus
PT4247
PT4246
PT4241
PT4245
PT4242
PT4243
PT4244
48V Bus
PT4227
PT4226
PT4221
PT4225
PT4222
PT4223
PT4224
Rated Current 3
3A
2A
0.85A
Vo(nom)
1.3V
1.5V
1.8V
2.5V
3.3V
5.0V
12.0V
Vo(min)
1.2V
1.45V
1.7V
2.25V
2.95V
4.5V
10.8V
Vo(max)
1.4V
1.65V
1.98V
2.75V
3.65V
5.5V
13.2V
Rs (k
)
340.0
243.0
187.0
110.0
49.9
Figure 1
PT4220/4240
+ V out
-V out
+V in
-V in
Remote
On/Off
V
o(adj)
1
3
5
8, 9
6, 7
10
L
O
A
D
+V
in
-V
in
+V
O
–V
O
(R1)
Adj Down
R2
Adjust Up
R
2
=
68.845
– R
s
k
V
a – Vo
Where,
V
o
= Original output voltage
V
a
= Adjusted output voltage
R
s
= Internal resistance (Table 1)
Notes:
1. Use only a single 1% resistor in either the (R1) or R2
location. 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.
3. The output power is limited to 10W. If the output
voltage is increased, the maximum load current must be
derated according to the following equation.
I
o(max)
= 10
V
a
In any instance, the load current must not exceed the
converter’s rated current (See Table 1).
PT4220/4240 Series