Rainbow-electronics MAX8514 Manual de usuario descargar pdf (Pagina 26)

MAX8513/MAX8514

Wide-Input, High-Frequency, Triple-Output Supplies

with Voltage Monitor and Power-On Reset

26 ______________________________________________________________________________________

This gain between f

and f

is also set by the ratio of

R3/R1, where R1 is selected in the OUT1 Voltage

Setting section. Therefore:

And similar to Case 1, C5 can be calculated as:

Set the error-amplifier third pole, f

, at approximately

1/2 the switching frequency. The gain of the error

amplifier at f

(between f

and f

) is set by the ratio

of R3/R

and is also equal to:

where R

is:

Therefore:

Similar to Case 1, R4, C11, and C12 can be calculated as:

Below is a numerical example to calculate the error-

amplifier compensation values for Case 2:

= 12V (nomimal input voltage)

RAMP

= 1V

OUT1

= 3.3V

FB1

= 1.25V

L1A = 6.2µH

C4 = 560µF/ 10V OS-Con capacitor, with ESR = 0.015Ω

= 300kHz

Pick R2 = 8.06kΩ. Then:

Pick f

= 50kHz, which is less than f

/ 5.

Use 20kΩ.

Use 12nF.

Use 2.2kΩ.

Use 3.9nF.

Pick f

3 = f

/ 2 = 150kHz.

Rf k kHz

ZESR

222 1895

382

××

ππΩ

RRG k k

I MOD fc

()

=× = × =

32000923 1 846

11331846

13 3 1 846

214

ΩΩ

Ω

1- -

Rf k kHz

PMOD

20 2 7

11 8

××

ππΩ

kHz

kHz kHz

kHz

RRG k k

MOD DC

EA fZ fZ

PMOD

ZESR MOD fc

EA fZ fZ

()

.. .

=×

=× = × =

−

18 95 50

0 0923

18 95 0 0923

1 543

31 1331543 20 48

12-

ΩΩ

MOD DC

RAMP

1806

125

1133

()

=× =

ΩΩ-

LA C

kHz

PMOD

ZESR

ESR

××

21 4

262 560

20015 560

18 95

π µµ

π µΩ

CRf

ZESR

253 1

××

×××

RR G G

I MOD fc D

()

=× ×3

EA fc

MOD fc

()

PMOD

××π

PMOD

ZESR MOD fc

()

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 34 35

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Rainbow-electronics MAX8514 Manual de usuario Pagina 26

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