Application Notes
PT6900/6910 Series
Adjusting the Output Voltage of the PT6900/PT6910
Positive to Negative Converter Series
Figure 1
The negative output voltage of the Power Trends PT6900
Series ISRs may be adjusted higher or lower than the
factory trimmed pre-set voltage with the addition of a
single external resistor. Table 1 gives the allowable
adjustment range for each model in the series as Va (min)
and Va (max).
22
Vo(sense)
3
-
7
16 - 21
+Vin
-Vo
+Vin
PT6900/10
Vout(-)
GND
Vo(adj)
15
GND(sense)
8
9
-
2
(R1)
(Down)
L
O
A
D
+
Adjust Up: An increase in the output voltage is obtained
by adding a resistor R2, between pin 2 (Vo adjust) and
pin 8 (Remote Sense GND).
Cin
Cout
+
R2
(Up)
Adjust Down: Add a resistor (R1), between pin 2 (V ad-
o
COM
COM
just) and pin 22 (Remote Sense V ).
o
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, either (R1) or R2 as appropriate.
The respective values of (R1) [adjust down], and R2 [ad-
just up], can also be calculated using the following formulas.
Notes:
24.9 (Va – Vr)
(Vo – Va)
1. Only a single 1% resistor is required in either the (R1) or
R2 location. Do not use (R1) and R2 simultaneously.
Place the resistor as close to the ISR as possible.
2. Never connect capacitors from Vo adjust to either GND,
Vout, or the Sense pins. Any capacitance added to the
Vo adjust pin will affect the stability of the ISR.
3. If the sense pins are not being used, the resistors (R1) and
R2 can be connected to Vout and GND respectively.
4. An increase in the output voltage must be accompanied by
a corresponding reduction in the maximum output current.
The revised maximum output current must be reduced to
the equivalent of 12Watts.
(R1)
R2
=
=
– Rs kΩ
kΩ
24.9 Vr
(Va – Vo)
– Rs
Where:
Vo = Original output voltage
Va = Adjusted output voltage
Vr = Reference voltage in Table 1
Rs = The resistance given in Table 1
i.e.
12
Va
Iout (max)
=
Adc,
where Va is the adjusted output voltage.
Table1
PT6900/PT6910 ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
5.0V Bus
3.3V Bus
PT6903/13
PT6901/11
PT6904/14
PT6902/12
PT6905/15
V
(nom)
(min)
(max)
-1.5V
-1.2V
-3.4V
-1.0V
12.7
-2.0V
-1.4V
-4.5V
-1.0V
10.0
-5.2V
-2.7V
-6.5V
-0.92V
17.4
o
V
a
V
a
V
r
R
s
(kΩ)
For technical support and more information, see inside back cover or visit www.ti.com/powertrends
TI [ TEXAS INSTRUMENTS ]
