Starting Up under Load

The

Typical Operating Characteristics show the Start-

Up Voltage vs. Load Current graph for bootstrapped-

mode operation. This graph depends on the type

of power switch used. The MAX770–MAX773 are

not designed to start up under full load in boot-

strapped mode with low input voltages.

Layout Considerations

Due to high current levels and fast switching wave-

forms, which radiate noise, proper PC board layout is

essential. Protect sensitive analog grounds by using a

star ground configuration. Minimize ground noise by

connecting GND, the input bypass capacitor ground

lead, and the output filter capacitor ground lead to a

single point (star ground configuration). Also, minimize

lead lengths to reduce stray capacitance, trace resis-

tance, and radiated noise. Place input bypass capaci-

tor C2 as close as possible to V+ and GND.

Excessive noise at the V+ input may falsely trigger the

timing circuitry, resulting in short pulses at EXT. If this

occurs it will have a negligible effect on circuit efficien-

cy. If desired, place a 4.7µF directly across the V+ and

GND pins (in parallel with the 0.1µF C2 bypass capaci-

tor) to reduce the noise at V+.

5V/12V/15V or Adjustable, High-Efficiency,

______________________________________________________________________________________

19

Table 2. Component Suppliers

PRODUCTION

INDUCTORS

CAPACITORS

TRANSISTORS

Surface Mount

Matsuo

267 series

Sprague

595D series

Through Hole

Sumida

CD54 series

CDR125 series

Coiltronics

CTX20 series

Motorola

1N5817–1N5822

MUR115 (high voltage)

Nihon

EC10 series

DIODES

Sumida

RCH855 series

RCH110 series

Renco

RL1284-18

Sanyo

OS-CON series

Nichicon

PL series

United Chemi-Con

LXF series

NPN

Zetex

ZTX694B

Coiltronics

Matsuo

USA: (714) 969-2491

(714) 960-6492

Japan: 81-6-337-6450

81-6-337-6456

Nichicon

USA: (847) 843-7500

(847) 843-2798

Nihon

USA: (805) 867-2555

(805) 867-2698

Renco

USA: (516) 586-5566

(516) 586-5562

Sanyo

USA: (619) 661-6835

(619) 661-1055

Japan: 81-7-2070-6306

81-7-2070-1174

Sumida

USA: (847) 956-0666

Japan: 81-3-3607-5111

81-3-3607-5144

United Chemi-Con

USA: (714) 255-9500

(714) 255-9400

N-FET

Siliconix

Si9410DY

Si9420DY (high voltage)

Motorola

MTP3055EL

MTD20N03HDL

USA: (561) 241-7876

(561) 241-9339

SUPPLIER

PHONE

FAX

Zetex

USA: (516) 543-7100

(516) 864-7630

UK: 44-61-627-4963

44-61-627-5467