Datasheet

VIND
1,2
VINC
EN
AGND
PGND
FB
SW
LM26420
V
IN
C
F
R
F
C
IN
V =
1
2.5V
0.8V
1 + 2x
1 
3.5%  1.5%
= 1.4%
V =
1
V
OUT
V
FB
1 + 2x
1 
TOL  I
VIND
VINC
EN
AGND
PGND
FB
SW
LM26420
V
OUT
L
OUT
C
OUT
R1
R2
LM26420
SNVS579F –FEBRUARY 2009–REVISED MARCH 2013 www.ti.com
Figure 37. Programming V
OUT
To determine the maximum allowed resistor tolerance , use the following equation:
(15)
where TOL is the set point accuracy of the regulator, Φ is the tolerance of V
FB
.
Example:
VOUT = 2.5V, with a set point accuracy of +/- 3.5%.
(16)
Choose 1% resistors. If R2 = 10kΩ, then R1 is 21.25kΩ.
VINC FILTERING COMPONENTS
Additional filtering is required between VINC and AGND in order to prevent high frequency noise on VIN from
disturbing the sensitive circuitry connected to VINC. A small RC filter can be used on the VINC pin as shown in
Figure 38.
Figure 38. RC filter on VINC
In general, R
F
is typically between 1Ω and 10Ω so that the steady state voltage drop across the resistor due to
the VINC bias current does not affect the UVLO level. C
F
can range from 0.22 µF to 1.0 µF in X7R or X5R
dielectric, where the RC time constant should be at least 2 µS. C
F
should be placed as close as possible to IC
with a direct connection from VINC and AGND.
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