Datasheet

LM26480
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SNVS543I JANUARY 2008REVISED MAY 2013
Ideal Resistor Values Common R Values Actual VOUT Feedback Capacitors
Target Actual VOUT
Delta from
R1 (K) R2 (K) R1 (K) R2 (K) C1(pF) C2(pF)
Vout (V) W/ Com/R (V)
Target (V)
1 200 200 200 200 1 0 15 none ^
1.1 240 200 240 200 1.1 0 15 none |
1.2 280 200 280 200 1.2 0 12 none |
1.3 320 200 324 200 1.31 0.01 12 none Buck1
1.4 360 200 357 200 1.393 -0.008 10 none And
1.5 400 200 402 200 1.505 0.005 10 none Buck2
1.6 440 200 442 200 1.605 0.005 8.2 none |
1.7 427 178 432 178 1.713 0.013 8.2 none |
1.8 463 178 464 178 1.803 0.003 8.2 none |
1.9 498 178 499 178 1.902 0.002 8.2 none |
2 450 150 453 150 2.01 0.01 8.2 none >
2.1 480 150 475 150 2.083 -0.017 8.2 none ^
2.2 422 124 422 124 2.202 0.002 8.2 none |
2.3 446 124 442 124 2.282 -0.018 8.2 none |
2.4 471 124 475 124 2.415 0.015 8.2 none |
2.5 400 100 402 100 2.51 0.01 8.2 none |
2.6 420 100 422 100 2.61 0.01 8.2 none |
2.7 440 100 442 100 2.71 0.01 8.2 33 Buck2
2.8 460 100 464 100 2.82 0.02 8.2 33 Only
2.9 480 100 475 100 2.875 -0.025 8.2 33 |
3 500 100 499 100 2.995 -0.005 6.8 33 |
3.1 520 100 523 100 3.115 0.015 6.8 33 |
3.2 540 100 536 100 3.18 -0.02 6.8 33 |
3.3 560 100 562 100 3.31 0.01 6.8 33 |
The output voltages of the bucks of the LM26480 are established by the feedback resistor dividers R1 and R2
shown on the application circuit above. The equation for determining V is: V
OUT
= V
FB
(R1+R2)/R2 where V
FB
is
the voltage on the Buck FBx pin.
The Buck control loop will force the voltage on V
FB
to be 0.50 V ±3%.
The above table shows ideal resistor values to establish buck voltages from 0.8V to 3.3 V along with common
resistor values to establish these voltages. Common resistors do not always produce the target value, error is
given in the delta column.
In addition to the resistor feedback, capacitor feedback C1 is always required, and depending on the output
voltage capacitor C2 is also required. See External Component Selection for these requirements.
Inductor Value Unit Description Notes
L
SW
1,2 2.2 µH SW1,2 inductor D.C.R. 70 m
Output Inductors & Capacitors for SW1 AND SW2
There are several design considerations related to the selection of output inductors and capacitors:
Load transient response;
Stability;
Efficiency;
Output ripple voltage; and
Over-current ruggedness.
The LM26480 has been optimized for use with nominal values 2.2 µH and 10 µF. If other values are needed for
the design, please contact Texas Instruments sales with any concerns.
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