Rainbow-electronics MAX669 Instrukcja Użytkownika Pobierz pdf (Strona 11)

Non-Bootstrapped Operation

With non-bootstrapped operation, the IC is powered

from the input voltage (V

) or another source, such as

a logic supply. Non-bootstrapped operation (Figure 4)

is recommended (but not required) for input voltages

above 5V, since the EXT amplitude (limited to 5V by

LDO) at this voltage range is no higher than it would be

with bootstrapped operation. Note that non-boot-

strapped operation is

required

if the output voltage

exceeds 28V, since this level is too high to safely con-

nect to V

. Also note that only the MAX668 can be

used with non-bootstrapped operation.

If the input voltage does not exceed 5.5V, the on-chip

regulator can be disabled by connecting V

to LDO

(Figure 5). This eliminates the regulator forward drop

and supplies the maximum gate drive to the external

FET for lowest on-resistance. Disabling the regulator

also reduces the non-bootstrapped minimum input volt-

age from 3V to 2.7V.

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up

Controllers in µMAX

______________________________________________________________________________________ 11

MAX668

LDO

CS+

REF

FREQ

SYNC

SHDN

PGND

GND

EXT

= 2.7V to 5.5V

0.22µF

1µF

100k

0.02Ω

218k

24.9k

220pF

MBRS340T3

68µF

20V

68µF

20V

0.1µF

OUT

= 12V @ 1A

68µF

10V

4.7µH

FDS6680

Figure 5. MAX668 Low-Voltage Non-Bootstrapped Configuration

MAX668

LDO

CS+

REF

FREQ

PGND

GND

EXT

= 3V to 12V

0.22µF

1µF

0.1µF

100k

0.02Ω

218k

24.9k

220pF

MBRS340T3

68µF

20V

68µF

20V

0.1µF

OUT

= 12V @ 1A

68µF

20V

4.7µH

FDS6680

SYNC/

SHDN

Figure 4. MAX668 High-Voltage Non-Bootstrapped Configuration

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 17 18

MAX668/MAX669 1
Controllers in µMAX 1

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