LM3578AM datasheet(18/30 Pages) TI

18 / 30 page

LM2578A, LM3578A

SNVS767E – AUGUST 2000 – REVISED APRIL 2013

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Vin = 5V

R4 = 200 k

Vo = 15V

C1 = 1820 pF

Vripple = 10 mV

C2 = 470

μF

Io = 140 mA

C3 = 20 pF

fosc = 50 kHz

C4 = 0.0022

μF

R1 = 140 k

L1 = 330

μH

R2 = 10 k

D1 = 1N5818

R3 = 0.15

Figure 32. Boost or Step-Up Regulator

R1 = (Vo − 1) R2 where R2 = 10 kΩ.

R3 = V/(IL(max, DC) + 0.5 ΔIL)

where:

ΔIL = 2(ILOAD(min))(Vo/Vin)

ΔIL is 200 mA in this example.

R4, C3 and C4 are necessary for continuous operation and are typically 220 k

Ω, 20 pF, and 0.0022 μF

respectively.

C1 is the timing capacitor found in Figure 14.

≥ Io (Vo − Vin)/(fosc Vo Vripple).

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 Vo = Vin × (ton/toff).

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

≤ Vin ≤ 8.5V).

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