PTH08T240FAS datasheet(9/37 Pages) TI

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APPLICATION INFORMATION

ADJUSTING THE OUTPUT VOLTAGE

=10k

SET

0.69

-0.69

-1.43kW

(1)

+Sense

−Sense

VoAdj

GND

PTH08T240F

+Sense

−Sense

GND

RSET

0.05 W

UDG−06077

PTH08T240F

www.ti.com........................................................................................................................................ SLTS277C – DECEMBER 2006 – REVISED DECEMBER 2008

The VOAdjust control (pin 8) sets the output voltage of the PTH08T240F. The adjustment range is 0.69 V to

2.0 V. The adjustment method requires the addition of a single external resistor, RSET, that must be connected

directly between the VOAdjust and – Sense pins. Table 1 gives the standard value of the external resistor for a

number of standard voltages, along with the actual output voltage that this resistance value provides.

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 13 shows the placement of the required

resistor.

Table 1. Standard Values of RSET for Standard Output Voltages

VO (Standard) (V)

RSET (Standard Value) (kΩ)

VO (Actual) (V)

1.8

4.75

1.807

1.5

6.98

1.510

1.2

12.1

1.200

1.1

15.4

1.100

20.5

1.004

0.9

31.6

0.899

(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 8 and 7, as close to the regulator as possible, using dedicated PCB traces.

(2)

Never connect capacitors to VOAdjust (pin 8). Any capacitance added to the VOAdjust pin affects the stability of the

regulator.

Figure 13. VO Adjust Resistor Placement

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