Datasheet

O UT
OUT
FB_DCDC1
FB_DCDC1
R1 + R2 V
V = V R1 = R2 R2
R2 V
´
æ ö
´ -
ç ÷
è ø
OUT
OUT FB_LDOx
FB_LDO1
R3 + R4 V
V = V R3 = R4 R4
R4 V
´
æ ö
´ -
ç ÷
è ø
TPS65720
TPS65721
www.ti.com SLVS979 –OCTOBER 2009
APPLICATION INFORMATION
OUTPUT VOLTAGE SETTING
DCDC1
The output voltage of the DCDC converter can be set with external resistor network on Pin FB_DCDC1. The
feedback voltage is 0.6V.
It is recommended to set the total resistance of R1 + R2 to less than 1MΩ. Route the FB_DCDC1 trace separate
from noise sources, such as the inductor trace (L1).
V
FB-DCDC1
= 0.6V
(1)
Typical resistor values:
OUTPUT VOLTAGE R1 R2 NOMINAL VOLTAGE
3.3V 680k 150k 3.32V
3.0V 510k 130k 2.95V
2.85V 560k 150k 2.84V
2.5V 510k 160k 2.51V
2.05V 360k 150k 2.04V
2.0V 470k 200k 2.01V
1.8V 300k 150k 1.80V
1.6V 200k 120K 1.60V
1.5V 300k 200k 1.50V
1.2V 330k 330k 1.20V
A feed-forward capacitor in parallel to the resistor from Vout to FB_DCDC1 is required. It´s value should be
based on transient performance and will be in the range from 4.7pF to 22pF.
LDO1
For TPS65720, the output voltage of LDO1 is set by register LDO_CTRL with the I2C compatible interface. The
default output voltage is programmed to 1.85V. The programmable voltage range is 0.8V to 3.3V.
For the TPS65721, the output voltage for LDO1 is externally adjustable using a resistor divider at pin FB_LDO1.
The feedback voltage is 0.8V and the total resistance of the voltage divider should be kept in the 100kΩ to 1MΩ
range. A feed-forward capacitor in parallel to the resistor from Vout to FB_LDO1 is required. It´s value should be
based on transient performance and will be in the range from 4.7pF to 22pF.
The output voltage with an internal reference voltage V
FB-LDO1
=0.8V is:
(2)
Typical resistor values:
OUTPUT VOLTAGE R3 R4 NOMINAL VOLTAGE
3.3V 470k 150k 3.31V
1.85V 200k 150k 1.86V
1.8V 300k 240k 1.80V
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