Rainbow-electronics MAX773 Bedienungsanleitung PDF herunterladen (Seite 10)

MAX770–MAX773

frequencies (up to 300kHz), allowing the use of tiny

external components.

As with traditional PFM converters, the power transistor

is not turned on until the voltage comparator senses

that the output is out of regulation. However, unlike tra-

ditional PFM converters, the MAX770–MAX773 switch

using the combination of a peak current limit and a pair

of one-shots that set the maximum on-time (16µs) and

minimum off-time (2.3µs); there is no oscillator. Once

off, the minimum off-time one-shot holds the switch

off for 2.3µs. After this minimum time, the switch either

1) stays off if the output is in regulation, or 2) turns on

again if the output is out of regulation.

The control circuitry allows the ICs to operate in contin-

uous-conduction mode (CCM) while maintaining high

efficiency with heavy loads. When the power switch is

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

Low I

, Step-Up DC-DC Controllers

______________________________________________________________________________________

MAX770

= 3V

REF

SHDN

AGND

GND

EXT

0.1µF

100µF

22µH

1N5817

MTP3055EL

SENSE

75mΩ

300µF

0.1µF

V+

OUT

= 5V

@ 1A

Figure 2a. 5V Preset Output, Bootstrapped Figure 2b. 12V Preset Output, Bootstrapped

Figure 2c. 12V Output, Non-Bootstrapped Figure 2d. 9V Output, Bootstrapped

MAX770

MAX771

MAX772

= 5V

REF

SHDN

AGND

GND

EXT

22µH

1N5817

18k

200µF

0.1µF

V+

68µF

OUT

= 12V

@ 0.5A

127k

SENSE

100mΩ

0.1µF

OUT

REF

R2 = (R1) ( -1)

REF

= 1.5V

MAX770

MAX771

MAX772

REF

SHDN

AGND

GND

EXT

47µF

20µH

1N5817

28k

100µF

0.1µF

V+

OUT

= 9V

140k

SENSE

0.1µF

OUT

REF

R2 = (R1) ( -1)

REF

= 1.5V

Si9410DY

= 4V

MAX771

= 5V

REF

SHDN

AGND

GND

EXT

0.1µF

68µF

22µH

1N5817

Si9410DY

SENSE

100mΩ

200µF

0.1µF

V+

OUT

= 12V

@ 0.5A

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 19 20

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