
Application Notes
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PT6725 Series
Adjusting the Output Voltage of the PT6725
Series of Integrated Switching Regulators
The PT6725 series of ISRs are non-programmable
versions of the PT6721/2 Excalibur regulators. The
regulators have a fixed output voltage, which may be
adjusted higher or lower than the factory pre-set voltage
using a single external resistor. Table 1 gives the adjust-
ment range for each model in the series as V
a
(min) and
V
a
(max).
Adjust Up:
An increase in the output voltage is obtained by
adding a resistor R
2
, between pin 1 (V
o
Adjust) and pin 7
(Remote Sense GND).
Adjust Down:
and pin 17 (Remote Sense V
out
).
Add a resistor
(R
1
)
, between pin 1 (V
o
Adjust)
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, either
(R
1
)
or R
2
as appropriate.
The values of
(R
)
[adjust down], and R
[adjust up], can
also be calculated using the following formulas.
R
o
( V
a
–V
r
)
V
o
– V
a
(R
1
)
=
– R
s
k
R
o
·V
r
V
a
– V
o
– R
s
k
R
2
=
Where: V
o
= Original output voltage
= Adjusted output voltage
= The reference voltage (Table 1)
R
o
= The multiplier resistance (Table 1)
R
s
= The internal series resistance (Table 1)
V
a
V
r
Figure 1
Notes:
1. Use only a single 1% resistor in either the
(R
1
)
or R
2
location. Place the resistor as close to the regulator as
possible.
2. Never connect capacitors from V
o
Adjust to either GND,
V
out
, or the Remote Sense pins. Adding capacitance to the
V
o
Adjust pin will affect the stability of the ISR.
3. If the Remote Sense feature is not being used, pin 7 must
be connected to pin 8 for optimum output voltage
accuracy. The resistors
(R
1
)
and R
2
may then be connected
from ‘V
o
Adjust’ to either V
out
or GND respectively.
L
O
A
D
(R1)
Adj Down
R2
Adjust Up
C
out
+
C
in
+
COM
+5V
Vo
COM
PT6725
Sns(+)
Sns(-)
V
out
GND
Vo(adj)
V
in
Stby*
13
–
16
17
7
1
8
–
12
4,5,6
2