LM3578AM datasheet(16/20 Pages) NSC

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Typical Applications (Continued)

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 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

voltage is V

o =Vin x(ton/toff).

Figure 21 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

≤ 8.5V).

R1 = (|V

o| +1) R2 where R2 = 10 k

Ω.

R3 = V/(I

L(max, DC) + 0.5

∆I

L).

R4 = 10V

BE1Bf/(IL (max, DC) + 0.5

∆I

where:

V, V

BE1,Vsat, and Bf are defined in the “Buck Converter with

Boosted Output Current” section.

∆I

L = 2(ILOAD(min))(Vin +|Vo|)/VIN

R5 is defined in the “Buck with Boosted Output Current”

section.

R6 serves the same purpose as R4 in the Boost Regulator

circuit and is typically 220 k

Ω.

C1, C3 and C4 are defined in the “Boost Regulator” section.

≥ I

o |Vo|/[fosc(|Vo|+Vin)Vripple]

L1 is found as outlined in the section on buck converters,

using the inductance chart of Figure 16 for the invert con-

figuration and 20% discontinuity.

BUCK-BOOST REGULATOR

The Buck-Boost Regulator, shown in Figure 22, may step a

voltage up or down, depending upon whether or not the

desired output voltage is greater or less than the input

voltage. In this case, the output voltage is 12V with an input

voltage from 9V to 15V. The circuit exhibits an efficiency of

75%, with a load regulation of 60 mV (10 mA to 100 mA) and

a line regulation of 52 mV.

R1=(V

o − 1) R2 where R2 = 10 k

Ω

R3 = V/0. 75A

R4, C1, C3 and C4 are defined in the “Boost Regulator”

section.

D1 and D2 are Schottky type diodes such as the 1N5818 or

1N5819.

where:

d is the forward voltage drop of the diodes.

sat is the saturation voltage of the LM2578A output transis-

tor.

sat1 is the saturation voltage of transistor Q1.

≥ (V

in −Vsat −Vsat1)(ton/Ip)

00871110

FIGURE 20. Basic Inverting Regulator

00871112

in =5V

R4=190

Ω

o = −15V

R5 = 82

Ω

ripple =5mV

R6=220 k

Ω

o = 300 mA

C1 = 1820 pF

min = 60 mA

C2 = 1000 µF

osc =50kHz

C3=20pF

R1 = 160 k

Ω

C4 = 0.0022 µF

R2=10k

Ω

L1 = 150 µH

R3 = 0.01

Ω

D1 = 1N5818

FIGURE 21. Inverting Regulator

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