Application Notes
For technical support and more information, see inside back cover or visit www.ti.com/powertrends
PT6900/6910 Series
Adjusting the Output Voltage of the PT6900/PT6910
Positive to Negative Converter Series
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).
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).
Adjust Down:
Add a resistor (R1), between pin 2 (Vo ad-
just) and pin 22 (Remote Sense Vo).
Refer to Figure 1 and Table 2 for both the placement and value
of the required resistor, either (R1) or R2 as appropriate.
Notes:
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 V
o adjust to either GND,
V
out, or the Sense pins. Any capacitance added to the
V
o 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 V
out 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.
i.e.
Iout (max)
=
12
Adc,
Va
where V
a is the adjusted output voltage.
Figure 1
The respective values of (R1) [adjust down], and R2 [ad-
just up], can also be calculated using the following formulas.
(R1)
=
24.9 (Va – Vr)
– Rs kΩ
(Vo – Va)
R2
=
24.9 Vr
– Rs
k
Ω
(Va – Vo)
Where:
Vo = Original output voltage
Va = Adjusted output voltage
Vr = Reference voltage in Table 1
Rs = The resistance given in Table 1
Table1
PT6900/PT6910ADJUSTMENTRANGEANDFORMULAPARAMETERS
Series Pt #
5.0V Bus
PT6903/13
PT6901/11
PT6902/12
3.3V Bus
PT6904/14
PT6905/15
Vo (nom)
-1.5V
-2.0V
-5.2V
Va (min)
-1.2V
-1.4V
-2.7V
Va (max)
-3.4V
-4.5V
-6.5V
Vr
-1.0V
-1.0V
-0.92V
Rs (kΩ
Ω
Ω
Ω
Ω)
12.7
10.0
17.4
C
in
+
C
out
R2
(Up)
(R1)
(Down)
COM
COM
Vout(-)
+Vin
PT6900/10
16 - 21
2
9 - 15
3 - 7
+Vin
-Vo
GND
Vo(adj)
Vo(sense)
22
8
GND(sense)
L
O
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