PTH08080WAST datasheet(7/16 Pages) TI

7 / 16 page

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APPLICATION INFORMATION

Adjusting the Output Voltage of the PTH08080W Wide-Output Adjust Power Modules

= 10 k

SET

0.891 V

- 0.9 V

out

- 1.82 kW

GND

RSET

0.05 W

PTH08080W

V Adj

GND

Inhibit

D1 (See Note 3)

PTH08080W

SLTS235A – FEBRUARY 2005 – REVISED MARCH 2005

The VO Adjust control (pin 4) sets the output voltage of the PTH08080W product. The adjustment range is from

0.9 V to 5.5 V. The adjustment method requires the addition of a single external resistor, RSET, that must be

connected directly between the VO Adjust 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 10 shows the placement of the required

resistor.

Table 1. Standard Values of RSET for Common Output

Voltages

Rset

(Required)

(Standard Value)

(Actual)

5 V

348

Ω

5.010 V

3.3 V (1)

1.87 k

Ω

3.315 V

2.5 V (1)

3.74 k

Ω

2.503 V

2 V

6.19 k

Ω

2.012 V

1.8 V

8.06 k

Ω

1.802 V

1.5 V

13.0 k

Ω

1.501 V

1.2 V

27.4 k

Ω

1.205 V

1 V

86.6 k

Ω

1.001 V

0.9 V

Open

0.9 V

(1)

The minimum input voltage is 4.5 V or (VO + 2) V, whichever is

greater. The maximum input voltage is 18 V or (VO *10) V,

whichever is lesser.

(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 VO Adjust to either GND or VO. Any capacitance added to the VO Adjust pin affects the

stability of the regulator.

(3)

The protection diode, D1, is required whenever the output voltage setpoint is adjusted to 5.25 V (or higher) and VI is

16 V or greater.

Figure 10. VO Adjust Resistor Placement

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