Application Notes
PT4220/4240 Series
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).
68.845
Va – Vo
R2
=
– Rs
kΩ
Where, Vo = Original output voltage
Va = Adjusted output voltage
Rs = Internal resistance (Table 1)
Notes:
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).
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.
Adjust Down: Add a resistor (R1), between pin 10 (Vo adjust)
and pins 8 & 9 (+Vout).
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.
RefertoFigure1andTable2forboththeplacementandvalue
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.
10
Va
Io(max)
=
(R1)
=
56.2 (Va – 1.225)
Vo – Va
In any instance, the load current must not exceed the
converter’s rated current (See Table 1).
– Rs
kΩ
Table 1
DC/DC CONVERTER ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
24V Bus
PT4247
PT4227
3A
PT4246
PT4226
3A
PT4241
PT4221
3A
PT4245
PT4225
3A
PT4242
PT4222
3A
PT4243
PT4223
2A
PT4244
PT4224
0.85A
48V Bus
Rated Current 3
Vo(nom)
Vo(min)
Vo(max)
Rs (kΩ)
1.3V
1.2V
1.4V
340.0
1.5V
1.8V
1.7V
1.98V
243.0
2.5V
3.3V
5.0V
4.5V
5.5V
110.0
12.0V
10.8V
13.2V
49.9
1.45V
1.65V
243.0
2.25V
2.75V
187.0
2.95V
3.65V
187.0
Figure 1
+Vin
+VO
5
3
8, 9
6, 7
+V in
+V out
-Vout
PT4220/4240
(R1)
Adj Down
-Vin
Remote
V
o(adj)
-Vin
On/Off
L
1
10
O
A
D
R2
Adjust Up
–VO
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TI [ TEXAS INSTRUMENTS ]
