Datasheet

APPLICATION INFORMATION
ADJUSTING THE OUTPUT VOLTAGE
R =10k x
SET
W
0.69
V -0.69
O
-1.43kW
(1)
5
3 4
6
7
GND GND
8
GND
+Sense
V
O
−Sense
V Adj
O
PTH08T220W/221W
R
SET
1%
0.05W
+Sense
V
O
−Sense
C
O
PTH08T220W , PTH08T221W
www.ti.com ................................................................................................................................................... SLTS252K – NOVEMBER 2005 – REVISED JUNE 2009
The V
o
Adjust control (pin 8) sets the output voltage of the PTH08T220/221W. The adjustment range of the
PTH08T220/221W 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 – 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 12 shows the placement of the required
resistor.
Table 1. Standard Values of R
SET
for Standard Output Voltages
V
O
(Standard) R
SET
(Standard Value) V
O
(Actual)
5.0 V
(1)
169 Ω 5.005 V
3.3 V 1.21 k Ω 3.304 V
2.5 V 2.37 k Ω 2.506 V
1.8 V 4.75 k Ω 1.807 V
1.5 V 6.98 k Ω 1.510 V
1.2 V
(2)
12.1 k Ω 1.200 V
1.0 V
(2)
20.5 k Ω 1.004 V
0.7 V
(2)
681 k Ω 0.700 V
(1) For V
O
> 3.6 V, the minimum input voltage is (V
O
+ 2) 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 8 and 7, 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 12. V
O
Adjust Resistor Placement
Copyright © 2005 – 2009, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Link(s): PTH08T220W PTH08T221W