PT6905A Datasheet, PDF (3/7 Pages) Texas Instruments – 12 Watt 5V/3.3V Input Plus to Minus Voltage Converter

Application Notes
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 addi-
tion of a single external resistor. Table 1 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 ad-
just) 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. 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.
I_out (max)
=
12
V_a
Adc,
where V_a is the adjusted output voltage.
Figure 1
+Vin
C_in
3-7
+Vin
22
Vo(sense)
PT6900
16 - 21
-Vo
GND Vo(adj)
9 - 15 2
GND(sense)
8 _(R1)
(Down)
+
R2
(Up)
COM
Vout(-)
L
O
C _out
A
D
COM
The respective values of (R1) [adjust down], and R2 [ad-
just up], can also be calculated using the following formulas.
(R1)
=
24.9 (V_a – V_r)
(V_o – V_a)
– R_s kΩ
R2
=
24.9 V_r
(V_a – V_o)
–
R_s
kΩ
Where:
V_o = Original output voltage
V_a = Adjusted output voltage
V_r = Reference voltage in Table 1
R_s = The resistance given in Table 1
Table1
PT6900/PT6910 ADJUSTMENT RANGE AND FORMULA PARAMETERS
Series Pt #
5.0V Bus
PT6903/13
PT6901/11
PT6902/12
3.3V Bus
PT6904/14
PT6905/15
Vo (nom)
Va (min)
Va (max)
Vr
Rs (kΩ)
-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
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