SLTS092B datasheet(5/9 Pages) TI

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Application Notes

For technical support and more information, see inside back cover or visit www.ti.com

Adjusting the Output Voltage of the PT4120/

PT4140 Series of Isolated DC/DC Converters

The factory pre-set output voltage of Power Trends’

PT4120 and PT4140 series of isolated DC/DC converters

may be adjusted within ±10% of nominal. Adjustment is

made from the secondary side of the regulator1 with 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 6 (Vo adjust), and pin

4 (-Vout).

Adjust Down:

Add a resistor (R1), between pin 6 (Vo ad-

just) and pin 5 (+Vout).

Refer to Figure 1 and Table 2 for both the placement

and value of the required resistor, (R1) or R2.

Notes:

1. The PT4120 and PT4140 series of DC/DC converters

incorporate isolation between the Vin and Vo terminals.

Adjustment of the output voltage is made to the

regulation circuit on the secondary or output side of

the converter.

2. The maximum rated output power for this series is

20W. An increase in the output voltage may therefore

require a corresponding reduction in the maximum

output current (

see Table 1). The revised maximum

output current must be determined as follows:-

Io(max) =

or 5A, whichever is less.

Where Va is the adjusted ouput voltage.

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

location. Place the resistor as close to the ISR as possible.

Table 1

DC/DC CONVERTER ADJUSTMENT RANGE AND FORMULA PARAMETERS

Series Pt #

48V Bus

PT4126

PT4129

PT4127

PT4128

PT4121

PT4122

PT4125

PT4123

PT4124

24V Bus

PT4146

PT4147

PT4148

PT4141

PT4142

PT4143

PT4144

Max Current 2

3.8A

1.6A

1.3A

Vo(nom)

1.5

1.65

1.8

2.5

3.3

5.0

5.2V

12.0

15.0

Va(min)

1.35

1.49

1.62

2.25

2.95

4.5

4.75

10.8

13.5

Va(max)

1.65

1.81

1.98

2.75

3.65

5.5

5.75

13.2

16.5

1.225

2.5

Ko (V·k

Ω

Ω)

67.07

63.9

69.7

64.2

69.3

125.2

134.7

139.8

137.6

Rs (k

Ω

Ω)

43.2

66.5

110.0

187.0

243.0

110.0

90.9

Figure 1

(R1)

Adj Down

Adj

– V

PT4120/40

+V out

–V out

+V in

–Vin

Remote

On/Off

o(adj)

4. Never connect capacitors to Vo adjust. Any capacitance

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

the ISR.

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

be calculated using the following formulas.

(R1)

Ko (Va – Vr) – R

Ω

Vr (Vo – Va)

– Rs

Ω

(Va – Vo)

Where Vo = Original output voltage

Va = Adjusted output voltage

Vr = Reference voltage (Table 1)

Ko = Multiplier constant (Table 1)

Rs = Internal series resistance (Table 1)

PT4120/4140 Series

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