PT6900 Datasheet, PDF (3/5 Pages) Texas Instruments – 12 WATT PLUS TO MINUS VOLTAGE CONVERTER

Application Notes
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PT6900 Series
More Application Notes
Adjusting the Output Voltage of the
PT6900 Positive to Negative Converter Series
The negative output voltage of the Power Trends PT6900 Se-
ries ISRs may be adjusted higher or lower than the factory
trimmed pre-set voltage with the addition of a single external
resistor. Table 1 accordingly gives the allowable adjustment
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 R2, between pin 2 (V_o adjust) and pin 8
(Remote Sense GND).
Adjust Down: Add a resistor (R1), between pin 2 (V_o adjust) 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.
Notes:
1. Use only a single 1% resistor in either the (R1) or R2 loca-
tion. 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.
Figure 1
+Vin
3-7
+Vin
22
Vo(sense)
PT6900
16 - 21
-Vo
C _in
+
3 3 0 µF
GND Vo(adj)
9 - 15 2
GND(sense)
8 _(R1)
(Down)
R2
(Up)
COM
Vout(-)
L
O
C _out
A
330µF D
COM
The respective values of (R1) [adjust down], and R2 [adjust up],
can also be calculated using the following formulae.
(R1) =
24.9 (2V_a – V_o)
2(V_o – V_a)
– R_s
kΩ
R2
=
24.9 V_o
2(V_a – V_o)
– R_s
kΩ
Where:
V_o = Original output voltage
V_a = Adjusted output voltage
R_s = The resistance given in Table 1
i.e.
I_out (max)
=
12
V_a
Adc,
where V_a is the adjusted output voltage.
Table1
PT6900 ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
PT6903
PT6901
PT6902
Vo (nom)
Va (min)
Va (max)
Rs (kΩ)
-1.5V
-1.1V
-2.9V
12.7
-2.0V
-1.4V
-4.4V
10.0
-5.2V
-3.7V
-8.9V
17.4
Power Trends, Inc. 27715 Diehl Road, Warrenville, IL 60555 [phone] Fax: [phone] http://www.powertrends.com
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