PT4662 datasheet(13/16 Pages) TI1

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Application Notes

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Adjusting the Output Voltage of the PT4660

& PT4680 Series of Dual-Output Converters

The dual output voltages from the PT4660 (48-V Bus),

and PT4680 (24-V Bus) series of DC/DC converters can

be independently adjusted by up to 10 %, higher or lower

than the factory trimmed pre-set voltage. The adjustment

method requires the addition of a single external resistor 1.

Table 3-1 gives the adjustment range of Vo1 and Vo2 for

each model in the series as Va(min) and Va(max).

Vo1 Adjust Down:

Add a resistor (R1), between pin 13

(Vo1 Adj) and pin 12 (Vo1) 2.

Vo1 Adjust Up:

To increase the output, add a resistor R2

between pin 13 (Vo1 Adj) and pin 14 (COM) 2, 4.

Vo2 Adjust Down:

Add a resistor (R3) between pin 20

(Vo2 Adj) and pin 21 (Vo2) 2.

Vo2 Adjust Up:

Add a resistor R4 between pin 20

(Vo2 Adj) and pin 19 (COM) 2, 4.

Refer to Figure 3-1 and Table 3-2 for both the placement and

value of the required resistor.

Notes:

1. Adjust resistors are not required if Vo1 and Vo2 are to

remain at their respective nominal set-point voltage.

In this case, Vo1 Adj (pin 13) and Vo2 Adj (pin 20) are

left open-circuit

2. Use only a single 1% resistor in either the (R1) or R2

location to adjust Vo1, and in the (R3) or R4 location

to adjust Vo2. Place the resistor as close to the converter

as possible.

Figure 3-1; Placement of Output Adjust Resistors

3. Vo2 must always be at least 0.3 V lower than Vo1.

4. The over-voltage protection threshold is fixed, and is set

nominally 25 % above the set-point output voltage.

Adjusting Vo1 or Vo2 higher will reduce the voltage

margin between the respective steady-state output

voltage and its over-voltage (OV) protection threshold.

This could make the module sensitive to OV fault

detection, as a result of random noise and load tran-

sients.

Note: An OV fault is a latched condition that shuts down

both outputs of the converter. The fault can only be cleared

by cycling one of the Enable control pins (EN1* / EN2), or

by momentarily removing the input power to the module.

5. Never connect capacitors to either the Vo1 Adj or

Vo2 Adj pins. Any capacitance added to these control

pins will affect the stability of the respective regulated

output.

The adjust up and adjust down resistor values can also be

calculated using the following formulas. Be sure to select

the correct formula parameter from Table 3-1 for the

output and model being adjusted.

(R1) or (R3)

Ro · (Va – Vr )

– Rs

Ω

(Vo – Va)

R2 or R4

Ro ·

– Rs

Ω

Va – Vo

Where: Vo = Original output voltage, (Vo1 or Vo2)

Va = Adjusted output voltage

Vr = The reference voltage from Table 3-1

Ro = The resistance constant in Table 3-1

Rs = The series resistance from Table 3-1

PT4660 & PT4680 Series

PT4660

+Vin

EN 1*

EN 2

–Vin

1 adj

2 adj

COM

9–12

21–24

14–19

–V

COM

* Inverted logic

(R1)

(R3)

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