1.8V to 28V Input, PWM Step-Up
Controllers in µMAX
MAX668/MAX669
V
IN
= 3V to 12V
C1
68µF
20V
L1
4.7µH
V
OUT
= 12V @ 1A
D1
MBRS340T3
FDS6680
R1
0.02Ω
PGND
FB
GND
7
5
3
C7
220pF
R3
24.9k
1%
N1
C5
68µF
20V
C6
68µF
20V
C8
0.1µF
R2
218k
1%
1
C4
1µF
9
C2
0.1µF
LDO
EXT
8
6
MAX668
V
CC
CS+
10 SYNC/
SHDN
4
REF
C3
0.22µF
2
R4
100k
1%
FREQ
Figure 4. MAX668 High-Voltage Non-Bootstrapped Configuration
V
IN
= 2.7V to 5.5V
C1
68µF
10V
1
C2
1µF
9
V
CC
PGND
FB
GND
7
5
3
L1
4.7µH
8
6
R1
0.02Ω
V
OUT
= 12V @ 1A
D1
MBRS340T3
FDS6680
N1
C4
68µF
20V
C5
68µF
20V
C6
0.1µF
R2
218k
1%
LDO
EXT
MAX668
CS+
10 SYNC/
SHDN
4
REF
C3
0.22µF
2
R4
100k
1%
FREQ
C7
220pF
R3
24.9k
1%
Figure 5. MAX668 Low-Voltage Non-Bootstrapped Configuration
Non-Bootstrapped Operation
With non-bootstrapped operation, the IC is powered
from the input voltage (V
IN
) 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
CC
. 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
CC
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.
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11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
