PT6621 datasheet(3/5 Pages) TI

3 / 5 page

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Application

Notes

PT6620 Series

More Application Notes

Adjusting the Output Voltage of the

PT6620 7Amp12V Bus Converter Series

The output voltage of the Power Trends PT6650 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

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 14 (Vo adjust) and pins 7-10

(GND).

Adjust Down:

Add a resistor (R1), between pin 14 (Vo adjust)

and pins 11-13 (Vout).

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 Remote Sense pin. Any capacitance added to

the Vo adjust pin will affect the stability of the ISR.

3. If the Remote Sense feature is being used, connecting the

resistor (R1) between pin 14 (Vo adjust) and pin 1 (Remote

Sense) can benefit load regulation.

4. The minimum input voltage required by the part is Vout + 3,

or 9V, whichever is higher.

5. The maximum output current must be limited to the equiva-

lent of 30Watts.

i.e.

Iout (max)

Adc,

where Va is the adjusted output voltage.

Figure 1

330

µF

out

330

µF

(R1)

Adj Down

Adjust Up

COM

Vin

PT6620

11,12,13

7,8,9,10

4,5,6

Vin

V o

G N D

Vo(adj)

STBY

Vsense

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

also be calculated using the following formulae.

Ro (Va – 1.25)

(R1)

(Vo – Va)

– Rs

kΩ

1.25 Ro

– Rs

kΩ

Va - Vo

Where:

Vo = Original output voltage

Va = Adjusted output voltage

Ro = The resistance value in Table 1

Rs = The series resistance from Table 1

Table 1

PT6620 ADJUSTMENT AND FORMULA PARAMETERS

Series Pt #

PT6622

PT6623

PT6621

PT6624

PT6625

PT6626

Vo (nom)

1.5V

2.5V

3.3V

3.6V

5.0V

9.0V

Va (min)

1.4V

1.9V

2.3V

2.5V

2.9V

5.2V

Va (max)

2.7V

3.7V

4.5V

4.8V

6.5V

10.0V

Ro (k

Ω

Ω)

4.99

10.0

12.1

16.2

12.1

Rs (k

Ω

Ω)

2.49

4.99

12.1

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