PT3321 datasheet(3/5 Pages) TI

3 / 5 page

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Application

Notes

PT3320/3340 Series

More Application Notes

Adjusting the Output Voltage of the PT3320 /

PT3340 Series of Isolated DC-DC Converters

The factory pre-set output voltage of Power Trends’ PT3320

and PT3340 series DC-DC converters may be adjusted within a

nominal ±10% range. This is accomplished with the addition of

a single external resistor. For the input voltage range specified in

the data sheet, Table 1 gives the allowable adjustment range for

each model as Vo (min) and Vo (max).

Adjust Up:

An increase in the output voltage is obtained by

adding a resistor, R2 between pin 18 (Vo adjust), and pin 13

(-Remote Sense).

See note 4.

Adjust Down:

Add a resistor (R1), between pin 18 (Vo adjust)

and pin 19 (+Remote Sense).

Refer to Figure 1 and Table 2 for both the placement and value

of the required resistor, (R1) or R2.

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 to Vo adjust. Any capacitance

added to the Vo adjust control pin will affect the stability of

the ISR.

Table 1

DC-DC CONVERTER ADJUSTMENT RANGE AND FORMULA PARAMETERS

Series Pt #

24V Bus

PT3341

PT3342

PT3343

PT3344

48V Bus

PT3325

PT3326

PT3321

PT3322

PT3323

PT3324

Vo(nom)

2.0V

2.5

3.3

5.0

12.0

15.0

Vo(min)

1.8V

2.25

2.95

4.5

10.8

13.5

Vo(max)

2.2

2.75

3.65

5.5

13.2

16.5

1.225

2.5

Ro (k

Ω

Ω)

80.6

33.2

18.2

14.3

11.0

Rs (k

Ω

Ω)

150.0

121.0

150.0

121.0

90.9

80.6

Figure 1

(R1)

Adj Down

Adj Up

Cin

100

µF

100V

(Optional)

Cout

330

µF

-V

PT3320/3340

4, 5, 6

7, 8, 9

+Vin

+Vout

-Vin

Vo(adj)

Inhibit

Sns(+)

10 - 12

-Vout

14 - 17

Sns(-)

3. If the remote sense pins are not being used, the resistors (R1)

and R2 can be connected to +Vout or -Vout respectively.

4. The adjusted output voltage Va effectively sets the voltage

across pins 13 and 19 (±Remote Sense). When using the

remote sense pins, Vout (measured directly across pins 10–12,

and 14–17) can be significantly higher than Va, and may

exceed Vo (max). If Va is adjusted upward, the alternative is

to increase the minimum input voltage by the same percent-

age as Vout exceeds Vo(max).

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

calculated using the following formulas.

(R1)

Ro (Vo – Vr)(Va – Vr)

– Rs

Ω

Vr (Vo – Va)

Ro (Vo – Vr)

– Rs

Ω

(Va – Vo)

Where

Vo = Original output voltage

Va = Adjusted output voltage

Vr = Reference voltage (Table 1)

Ro = Multiplier resistance (Table 1)

Rs = Series resistance (Table 1)

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