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APPLICATION INFORMATION

Adjusting the Output Voltage of the PTH04070W Wide-Output Adjust Power Modules

Rset + 10 kW

0.891 V

Vout * 0.9 V

* 3.24 kW

Inhibit

GND

GND

RSET

0.05 W

1%

C1

Ceramic

C2

Ceramic

PTH04070W

2

4

3

1

5

VO Adj

GND

VO

VIN

47-

µF

47-

µF

VI

VO

Inhibit

PTH04070W

SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007

The VOAdjust control (pin 4) sets the output voltage of the PTH04070W product. The adjustment range is from

0.9 V to 3.6 V. The adjustment method requires the addition of a single external resistor, RSET, that must be

connected directly between the VOAdjust and GND pin 2. Table 1 gives the standard external resistor for a

number of common bus voltages, along with the actual voltage the resistance produces.

For other output voltages, the value of the required resistor can either be calculated using the following formula,

or simply selected from the range of values given in Table 2. Figure 9 shows the placement of the required

resistor.

Table 1. Standard Values of Rset for Common Output

Voltages

VO (V)

RSET (kΩ)

VO(V)

(Required)

(Standard Value)

(Actual)

3.3(1)

0.475

3.298

2.5(1)

2.32

2.502

2

4.87

1.999

1.8

6.65

1.801

1.5

11.5

1.504

1.2

26.1

1.204

1

84.5

1.001

0.9

Open

0.9

(1)

The minimum input voltage is 3 V or (VO + 1.1) V, whichever is

greater.

(1)

A 0.05-W rated resistor may be used. The tolerance should be 1%, with a temperature stability of 100 ppm/

°C (or

better). Place the resistor as close to the regulator as possible. Connect the resistor directly between pins 4 and 2

using dedicated PCB traces.

(2)

Never connect capacitors from VOAdjust to either GND or VO. Any capacitance added to the VOAdjust pin will affect

the stability of the regulator.

Figure 9. VO Adjust Resistor Placement

Copyright © 2004–2007, Texas Instruments Incorporated

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Product Folder Link(s): PTH04070W