LM3578A MWC National Semiconductor, LM3578A MWC Datasheet - Page 13

• Manufacturer Part Number: LM3578A MWC
• Description: Switching Regulator
• Manufacturer: National Semiconductor

Typical Applications
The circuit of Figure 19 converts a 5V supply into a 15V sup-
ply with 150 mA of output current, a load regulation of 14 mV
(30 mA to 140 mA), and a line regulation of 35 mV (4.5V
V
R1 = (V
R3 = V/(I
where:
I
I
in
L
L
= 2(I
is 200 mA in this example.
8.5V).
V
V
V
I
f
R1 = 140 k
R2 = 10 k
R3 = 0.15
o
osc
o
in
o
ripple
FIGURE 19. Boost or Step-Up Regulator
LOAD(min)
= 140 mA
L(max, DC)
= 15V
− 1) R2 where R2 = 10 k .
= 5V
= 50 kHz
FIGURE 18. Basic Boost Regulator
= 10 mV
)(V
+ 0.5 I
o
/V
in
)
L
)
R4 = 200 k
C1 = 1820 pF
C2 = 470 µF
C3 = 20 pF
C4 = 0.0022 µF
L1 = 330 µH
D1 = 1N5818
(Continued)
DS008711-9
DS008711-11
13
R4, C3 and C4 are necessary for continuous operation and
are typically 220 k , 20 pF, and 0.0022 µF respectively.
C1 is the timing capacitor found in Figure 1 .
D1 is a Schottky type diode such as a IN5818 or IN5819.
L1 is found as described in the buck converter section, using
the inductance chart for Figure 16 for the boost configuration
and 20% discontinuity.
INVERTING REGULATOR
Figure 20 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 be-
tween the magnitude of the input voltage and the output volt-
age is V
Figure 21 shows an LM1578A 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
where:
V, V
Boosted Output Current” section.
R5 is defined in the “Buck with Boosted Output Current” sec-
tion.
R6 serves the same purpose as R4 in the Boost Regulator
circuit and is typically 220 k .
C1, C3 and C4 are defined in the “Boost Regulator” section.
L1 is found as outlined in the section on buck converters, us-
ing the inductance chart of Figure 16 for the invert configura-
tion and 20% discontinuity.
I
L
= 2(I
BE1
, V
o
LOAD(min)
FIGURE 20. Basic Inverting Regulator
= V
sat
R1 = (|V
R4 = 10V
, and B
C2
C2
in
R3 = V/(I
x (t
)(V
V
I
I
o
o
on
o
in
f
| +1) R2 where R2 = 10 k .
in
|V
are defined in the “Buck Converter with
(V
BE1
/t
off
+|V
o
o
8.5V).
|/[f
B
).
L(max, DC)
− V
f
o
osc
/(I
|)/V
L (max, DC)
in
(|V
)/(f
IN
o
osc
| + V
+ 0.5 I
V
o
in
+ 0.5 I
) V
V
ripple
ripple
L
).
DS008711-10
).
]
L
)
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