MAX668 Maxim, MAX668 Datasheet - Page 11

• Manufacturer Part Number: MAX668
• Description: 1.8V to 28V Input / PWM Step-Up Controllers in MAX
• Manufacturer: Maxim

With non-bootstrapped operation, the IC is powered
from the input voltage (V
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-
Figure 4. MAX668 High-Voltage Non-Bootstrapped Configuration
Figure 5. MAX668 Low-Voltage Non-Bootstrapped Configuration
V
IN
V
= 2.7V to 5.5V
IN
= 3V to 12V
0.1 F
1 F
1 F
______________________________________________________________________________________
C3
0.22 F
C3
0.22 F
C2
C4
C2
Non-Bootstrapped Operation
IN
R4
100k
1%
R4
100k
1%
10
10
1
9
4
2
1
9
4
2
) or another source, such as
V
SYNC/
SHDN
REF
FREQ
LDO
V
SYNC/
SHDN
REF
FREQ
LDO
CC
CC
MAX668
MAX668
1.8V to 28V Input, PWM Step-Up
PGND
PGND
68 F
GND
68 F
GND
EXT
CS+
EXT
CS+
20V
10V
FB
FB
C1
C1
5
5
8
6
7
3
8
6
7
3
0.02
0.02
R1
R1
N1
FDS6680
N1
FDS6680
L1
4.7 H
L1
4.7 H
nect to V
used with non-bootstrapped operation.
If the input voltage does not exceed 5.5V, the on-chip
regulator can be disabled by connecting V
(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.
MBRS340T3
MBRS340T3
D1
D1
Controllers in µMAX
CC
220pF
220pF
C4
68 F
20V
C5
68 F
20V
C7
C7
. Also note that only the MAX668 can be
C5
68 F
20V
C6
68 F
20V
R3
24.9k
1%
R3
24.9k
1%
R2
218k
1%
R2
218k
1%
C8
0.1 F
C6
0.1 F
V
V
OUT
OUT
= 12V @ 1A
= 12V @ 1A
CC
to LDO
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