Datasheet

LM2578A, LM3578A
SNVS767E –AUGUST 2000–REVISED APRIL 2013 www.ti.com
V
in
= 5V R4 = 200 kΩ
V
o
= 15V C1 = 1820 pF
V
ripple
= 10 mV C2 = 470 μF
I
o
= 140 mA C3 = 20 pF
f
osc
= 50 kHz C4 = 0.0022 μF
R1 = 140 kΩ L1 = 330 μH
R2 = 10 kΩ D1 = 1N5818
R3 = 0.15Ω
Figure 32. Boost or Step-Up Regulator
R1 = (V
o
− 1) R2 where R2 = 10 kΩ.
R3 = V/(I
L(max, DC)
+ 0.5 ΔI
L
)
where:
ΔI
L
= 2(I
LOAD(min)
)(V
o
/V
in
)
ΔI
L
is 200 mA in this example.
R4, C3 and C4 are necessary for continuous operation and are typically 220 kΩ, 20 pF, and 0.0022 μF
respectively.
C1 is the timing capacitor found in Figure 14.
C2 ≥ I
o
(V
o
− V
in
)/(f
osc
V
o
V
ripple
).
D1 is a Schottky type diode such as a 1N5818 or 1N5819.
L1 is found as described in the buck converter section, using the inductance chart for Figure 29 for the boost
configuration and 20% discontinuity.
INVERTING REGULATOR
Figure 33 shows the basic configuration for an inverting regulator. The input voltage is of a positive polarity, but
the output is negative. The output may be less than, equal to, or greater in magnitude than the input. The
relationship between the magnitude of the input voltage and the output voltage is V
o
= V
in
× (t
on
/t
off
).
Figure 33. Basic Inverting Regulator
Figure 34 shows an LM2578A configured as a 5V to −15V polarity inverter with an output current of 300 mA, a
load regulation of 44 mV (60 mA to 300 mA) and a line regulation of 50 mV (4.5V ≤ V
in
≤ 8.5V).
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