PT6901 datasheet(3/5 Pages) TI

3 / 5 page

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Application

Notes

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 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 adjust) 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. 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 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.

i.e.

Iout (max)

Adc,

where Va is the adjusted output voltage.

Figure 1

The respective values of (R1) [adjust down], and R2 [adjust up],

can also be calculated using the following formulae.

(R1)

24.9 (2Va – Vo)

– Rs

Ω

2(Vo – Va)

24.9 Vo

– Rs

Ω

2(Va – Vo)

Where:

Vo = Original output voltage

Va = Adjusted output voltage

Rs = The resistance given in Table 1

Table1

PT6900 ADJUSTMENT RANGE AND FORMULA PARAMETERS

Series Pt #

PT6903

PT6901

PT6902

Vo (nom)

-1.5V

-2.0V

-5.2V

Va (min)

-1.1V

-1.4V

-3.7V

Va (max)

-2.9V

-4.4V

-8.9V

Rs (k

Ω

Ω)

12.7

10.0

17.4

330

µF

out

330

µF

(Up)

(R1)

(Down)

COM

Vout(-)

+Vin

PT6900

16 - 21

9 - 15

3 - 7

+Vin

-Vo

G N D

Vo(adj)

Vo(sense)

GND(sense)

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