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,

10

______________________________________________________________________________________

MAX770

REF

SHDN

FB

AGND

GND

N

7

EXT

CS

C2

0.1

µF

C1

100

µF

L1

22

µH

D1

1N5817

MTP3055EL

75m

Ω

C4

300

µF

C3

0.1

µF

5

4

3

6

1

8

2

V+

@ 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

REF

SHDN

AGND

GND

N

7

EXT

CS

FB

L1

22

µH

D1

1N5817

R1

18k

C4

200

µF

C3

0.1

µF

5

4

6

1

8

3

2

V+

C1

68

µF

@ 0.5A

R2

127k

100m

Ω

C2

0.1

µF

R2 = (R1)

(

-1

)

MAX770

MAX771

MAX772

REF

SHDN

AGND

GND

N

7

EXT

CS

FB

C1

47

µF

L1

20

µH

D1

1N5817

R1

28k

C4

100

µF

C3

0.1

µF

5

4

6

1

8

3

2

V+

R2

140k

C2

0.1

µF

R2 = (R1)

(

-1

)

Si9410DY

MAX771

REF

SHDN

FB

AGND

GND

N

7

EXT

CS

C2

0.1

µF

C1

68

µF

L1

22

µH

D1

1N5817

Si9410DY

100m

Ω

C4

200

µF

C3

0.1

µF

5

4

3

6

1

8

2

V+

@ 0.5A