Rainbow-electronics MAX8614B Manual de usuario descargar pdf (Pagina 12)

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

12 ______________________________________________________________________________________

For stability, the inverter output filter capacitor, C2,

should satisfy the following:

C2 > (6L V

REF

INVMAX

) /

D- (V

REF

- V

INV

) V

INV

)

where R

= 0.0175 (MAX8614B), and 0.040

(MAX8614A). D- is 1 minus the inverter switch duty cycle

and is:

D- = V

/ V

INV

Table 2 lists representative low-ESR capacitor suppliers.

Input Bypass Capacitor

Although the output current of many MAX8614A/

MAX8614B applications may be relatively small, the

input must be designed to withstand current transients

equal to the inductor current limit. The input bypass

capacitor reduces the peak currents drawn from the

voltage source, and reduces noise caused by the

MAX8614A/MAX8614B switching action. The input

source impedance determines the size of the capacitor

required at the input. As with the output filter capacitor,

a low-ESR capacitor is recommended. A 4.7µF, low-

ESR capacitor is adequate for most applications,

although smaller bypass capacitors may also be

acceptable with low-impedance sources or if the source

supply is already well filtered. Bypass AV

separately

from V

with a 0.1µF ceramic capacitor placed as

close as possible to the AV

and GND pins.

PC Board Layout and Routing

Proper PC board layout is essential due to high-current

levels and fast-switching waveforms that radiate noise.

Breadboards or protoboards should never be used

when prototyping switching regulators.

Table 1. Inductor Selection Guide

OUTPUT VOLTAGES

AND LOAD CURRENT

INDUCTOR L (µH) DCR (mΩ)I

SAT

(A) SIZE (mm)

TOKO

DB3018C, 1069AS-2R0

2.0 72 1.4 3 x 3 x 1.8

TOKO

DB3018C, 1069AS-4R3

4.3 126 0.97 3 x 3 x 1.8

TOKO

S1024AS-4R3M

4.3 47 1.2 4 x 4 x 1.7

Sumida

CDRH2D14-4R7

4.7 170 1 3.2 x 3.2 x 1.55

15V, 50mA

-7.5V, 100mA

TOKO

S1024AS-100M

10 100 0.8 4 x 4 x 1.7

Sumida

CDRH2D11-100

10 400 0.35 3.2 x 3.2 x 1.2

Sumida

CDRH2D14-100

10 295 0.46 3.2 x 3.2 x 1.55

15V, 20mA

-7.5V, 40mA

Murata

LQH32CN100K33

10 300 0.45 3.2 x 2.5 x 2

Table 2. Component Suppliers

SUPPLIER PHONE WEBSITE

INDUCTORS

Murata 770-436-1300 www.murata.com

Sumida 847-545-600 www.sumida.com

TOKO 847-297-0070 www.tokoam.com

DIODES

Central

Semiconductor

(CMHSH5-2L)

631-435-1110 www.centralsemi.com

Motorola

(MBR0540L)

602-303-5454 www.motorola.com

CAPACITORS

Taiyo Yuden 408-573-4150 www.t-yuden.com

TDK 888-835-6646 www.TDK.com

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