Datasheet

LM26484
www.ti.com SNVS573F –SEPTEMBER 2008–REVISED MARCH 2013
LOW DROPOUT OPERATION
The LM26484 can operate at 100% duty cycle (no switching; PMOS switch completely on) for low dropout
support of the output voltage. In this way the output voltage will be controlled down to the lowest possible input
voltage. When the device operates near 100% duty cycle, output voltage ripple is approximately 25 mV. The
minimum input voltage needed to support the output voltage is
V
IN,
MIN = I
LOAD
* (R
DSON, PFET
+ R
INDUCTOR
) + V
OUT
(3)
I
LOAD
Load current
R
DSON, PFET
Drain to source resistance of
PFET switch in the triode region
R
INDUCTOR
Inductor resistance
Component Selection
SW1, SW2 OPERATION
Table 4. Buck1/2 Configuration and Component Selection Guide
Actual V
OUT
Actual V
OUT
Target Ideal Resistor Values Common R Values Delta from Feedback Capacitors
with Com/R (V)
Target (V)
V
OUT
(V) R1/3 (KΩ) R2/4 (KΩ) R1/3 (KΩ) R2/4 (KΩ) (V) (V) C3/6 (pF) C4/8 (pF)
0.8 120 200 121 200 0.803 0.002 15 none
0.9 160 200 162 200 0.905 0.005 15 none
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
1.4 360 200 357 200 1.393 -0.008 10 none
1.5 400 200 402 200 1.505 0.005 10 none
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
2.8 460 100 464 100 2.82 0.02 8.2 33
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
3.4 580 100 576 100 3.38 -0.02 6.8 33
3.5 600 100 604 100 3.52 0.02 6.8 33
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