Datasheet
SET
O
0.7
R 30.1 (k ) 6.49 (k )
V 0.7
æ ö
= W ´ - W
ç ÷
-
è ø
+Sense
V
O
-Sense
GND
V
O
Adj
PTH08T250W
10
17
11
16
13 4 181298
V
O
GND GND GND AGND
R
SET
1%
0.05 W
C
O
+
+Sense
V
O
-Sense
GND
UDG-07049
PTH08T250W
www.ti.com
SLTS278G –NOVEMBER 2010–REVISED MARCH 2009
APPLICATION INFORMATION
ADJUSTING THE OUTPUT VOLTAGE
The V
o
Adjust control sets the output voltage of the PTH08T250W. The adjustment range of the PTH08T250W is
0.7 V to 3.6 V. The adjustment method requires the addition of a single external resistor, R
SET
, that must be
connected directly between pins V
o
Adjust (pin 18) and AGND (pin 4). 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 11 shows the placement of the required
resistor.
(1)
Table 1. Standard Values of R
SET
for Standard Output Voltages
V
O
(Standard) (V) R
SET
(Standard Value) (kΩ) V
O
(Actual) (V)
3.3 1.62 3.298
2.5 5.23 2.498
2.0 9.76 1.997
1.8 12.7 1.798
1.5 19.6 1.508
1.2 35.7 1.199
1.0
(1)
63.4 1.001
0.7
(1)
Open 0.700
(1) The maximum input voltage is duty cycle limited to (V
O
× 12) or 14 volts, whichever is less. The
maximum allowable input voltage is a function of switching frequency, and may increase or decrease
when the SmartSync feature is utilized. Please review the SmartSync section of the Application
Information for further guidance.
(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 18 and 4, as close to the regulator as possible, using dedicated PCB traces.
(2) Never connect capacitors from V
O
Adjust to either + Sense, GND, or V
O
. Any capacitance added to the V
O
Adjust pin
affects the stability of the regulator.
Figure 11. V
O
Adjust Resistor Placement
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Product Folder Link(s): PTH08T250W