MAX669EUB/V-T 데이터 시트보기 (PDF) - Maxim Integrated
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MAX669EUB/V-T Datasheet PDF : 18 Pages
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1.8V to 28V Input, PWM Step-Up
Controllers in µMAX
VIN = 1.8V to 12V
C1
L1
1 LDO
C4
9 V+
MAX669
EXT 8
6
CS+
C2
10 SYNC/
SHDN
4 REF
C3
2
FREQ
7
PGND
5
FB
3
GND
R4
N1 D1
C5
R1
C6
R2
C7
R3
VOUT = 12V @ 0.5A
C8
Figure 2. MAX669 High-Voltage Bootstrapped Configuration
VIN = 1.8V to 5V
C1
68µF
L1
10V
4.7µH
C2
1µF
C3
0.22µF
1 LDO
9 VCC
MAX669
10 SYNC/
SHDN
4 REF
2
FREQ
R4
100k
1%
EXT 8
CS+
PGND
6
R1
0.02Ω
7
5
FB
3
GND
N1 D1
MBRS340T3
FDS6680
IRF7401
C4
68µF
10V
C7
220pF
C5
68µF
10V
R2
75k
1%
R3
24.9k
1%
VOUT = 5V @ 1A
C6
0.1µF
Figure 3. MAX669 Low-Voltage Bootstrapped Configuration
Bootstrapped Operation
With bootstrapped operation, the IC is powered from
the circuit output (VOUT). This improves efficiency
when the input voltage is low, since EXT drives the FET
with a higher gate voltage than would be available from
the low-voltage input. Higher gate voltage reduces the
FET on-resistance, increasing efficiency. Other (unde-
sirable) characteristics of bootstrapped operation are
increased IC operating power (since it has a higher
operating voltage) and reduced ability to start up with
high load current at low input voltages. If the input volt-
age range extends below 2.7V, then bootstrapped
operation with the MAX669 is the only option.
With VCC connected to VOUT, as in Figure 2, EXT volt-
age swing is 5V when VCC is 5.2V or more, and VCC -
0.2V when VCC is less than 5.2V. If the output voltage
does not exceed 5.5V, the on-chip regulator can be
disabled by connecting VCC to LDO (Figure 3). This
eliminates the LDO forward drop and supplies maxi-
mum gate drive to the external FET.
10 ______________________________________________________________________________________
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