PTH08T255WAS datasheet(8/35 Pages) TI1

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APPLICATION INFORMATION

ADJUSTING THE OUTPUT VOLTAGE

SET

0.7

8.25

)

0.7

30.1

(1)

+Sense

-Sense

GND

Adj

PTH08T255W

GND GND GND

AGND

SET

0.05 W

+Sense

-Sense

GND

UDG-08145

PTH08T255W

SLTS290 – NOVEMBER 2008 ........................................................................................................................................................................................... www.ti.com

The Vo Adjust control sets the output voltage of the PTH08T255W. The adjustment range of the PTH08T255W is

3.0 V to 5.25 V. The adjustment method requires the addition of a single external resistor, RSET, that must be

connected directly between pins Vo Adjust (pin 18) and AGND (pin 4). Figure 6 shows the placement of the

required resistor.

To set the output voltage, the value of the required resistor can either be calculated using the following formula,

or simply selected from the range of standard resistor values given in Table 2.

Table 2. Output Voltage Set-Point Resistor Values

VO Required (V)

RSET (kΩ)

VO Required (V)

RSET (kΩ)

3.0

100

4.2

6.81

3.1

63.4

4.3

5.90

3.2

45.3

4.4

4.99

3.3

34.0

4.5

4.22

3.4

27.4

4.6

3.48

3.5

22.1

4.7

2.87

3.6

18.2

4.8(3)

2.32

3.7

15.4

4.9(3)

1.82

3.8

13.0

5.0(3)

1.37

3.9

11.0

5.1(3)

0.931

4.0

9.31

5.2(3)

0.549

4.1

8.06

5.25(3)

0.374

(1)

RSET: Use a 0.05-W resistor with a tolerance of 1% and temperature stability of 100 ppm/°C (or better). Connect the

resistor directly between pins 18 and 4, as close to the regulator as possible, using dedicated PCB traces.

(2)

Any capacitance added to the VO Adjust pin affects the stability of the regulator.

(3)

When setting the output voltage to 4.8V or greater, the Auto-Track pin must be directly connected to VI if the feature

is not used. If the Auto-Track feature is utilized, a 100k

Ω resistor must connect the Auto-Track pin to VI.

Figure 6. VO Adjust Resistor Placement

Product Folder Link(s): PTH08T255W

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