Datasheet

R
SET
=10k xW
0.69
V -0.69
O
-1.43k W
PTH08T230W
GND
GND
VoAdj
7
5
+Sense
+Sense
−Sense
−Sense
V
O
V
O
R
1%
SET
0.05W
3
6
4
PTH08T230W, PTH08T231W
SLTS265L –NOVEMBER 2005– REVISED AUGUST 2011 www.ti.com
APPLICATION INFORMATION
ADJUSTING THE OUTPUT VOLTAGE
The V
O
Adjust control (pin 7) sets the output voltage of the PTH08T230/231W. The adjustment range is 0.69 V to
5.5 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 the –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 required resistor value can either be calculated using the following formula, or
simply selected from the values given in Table 2. Figure 11 shows the placement of the required resistor.
(1)
Table 1. Preferred Values of R
SET
for Standard Output Voltages
V
O
(Standard) (V) R
SET
(Standard Value) (kΩ) V
O
(Actual) (V)
5.0
(1)
0.169 5.01
3.3 1.2 3.30
2.5 2.37 2.51
1.8 4.7 1.81
1.5 6.98 1.51
1.2
(2)
12.1 1.20
1.0
(2)
20.5 1.01
0.7
(2)
681 0.70
(1) For V
O
> 3.6 V, the minimum input voltage is (V
O
+ 1) V.
(2) For output voltages ≤ 1.2V, at nominal operating frequency, the output ripple may increase (typically
2×) when operating at input voltages greater than (V
O
× 11). When using the SmartSync feature,
review the SmartSync application section 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 7 and 6, as close to the regulator as possible, using dedicated PCB traces.
(2) Never connect capacitors from V
O
Adjust to either GND, V
O
, or +Sense. Any capacitance added to the V
O
Adjust pin
affects the stability of the regulator.
Figure 11. V
O
Adjust Resistor Placement
12 Copyright © 2005–2011, Texas Instruments Incorporated