PT6903N datasheet(3/7 Pages) TI1

3 / 7 page

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 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 Va (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

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,

out, or the Sense pins. Any capacitance added to the

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)

Adc,

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)

24.9 Vr

– Rs

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/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)

-1.5V

-2.0V

-5.2V

Va (min)

-1.2V

-1.4V

-2.7V

Va (max)

-3.4V

-4.5V

-6.5V

-1.0V

-0.92V

Rs (k

Ω

Ω)

12.7

10.0

17.4

out

(Up)

(R1)

(Down)

COM

Vout(-)

+Vin

PT6900

16 - 21

9 - 15

3 - 7

+Vin

-Vo

GND

Vo(adj)

Vo(sense)

GND(sense)

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