Datasheet
APPLICATION INFORMATION
ADJUSTING THE OUTPUT VOLTAGE
R =10k x
SET
W
0.69
V -0.69
O
-1.43kW
(1)
+Sense
−Sense
VoAdjGND
PTH08T240F
3
5
6
7
8
+Sense
−Sense
GND
4
GND
+
V
O
V
O
R
SET
1%
0.05 W
UDG−06077
C
O
PTH08T240F
SLTS277D – DECEMBER 2006 – REVISED MARCH 2009 ...............................................................................................................................................
www.ti.com
The V
O
Adjust 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, R
SET
, that must be connected
directly between the V
O
Adjust 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 R
SET
for Standard Output Voltages
V
O
(Standard) (V) R
SET
(Standard Value) (k Ω ) V
O
(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
1 20.5 1.004
0.9 31.6 0.899
(1) R
SET
: 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 V
O
Adjust (pin 8). Any capacitance added to the V
O
Adjust pin affects the stability of the
regulator.
Figure 13. V
O
Adjust Resistor Placement
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