MAX863EEE Ver la hoja de datos (PDF) - Maxim Integrated
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MAX863EEE Datasheet PDF : 16 Pages
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Dual, High-Efficiency, PFM, Step-Up
DC-DC Controller
VIN = 2.7V TO 11V
L1
10µH
2A
C3
100µF
20V
≤0.1Ω
C2
0.1µF
C4
100µF
20V
≤0.1Ω
L2
10µH
1A
VOUT1 = 12V
C1
100µF
16V
≤0.1Ω
C8
R8
10pF
1M
1%
C9
R9
82pF
115k
1%
D1
R5
MBRS340T3
R6
D2
MBRS140
N1.A
R7
100k
LOW-BATTERY
DETECTOR OUTPUT
R1
50mΩ
VDD
EXT1
LBI
EXT2
CS1
CS2
N1.B
IRF7301
R2
R3
100mΩ
1M
MAX863
1%
LBO
FB2
FB1
SENSE1
BOOT PGND
SHDN1
SHDN2
REF
GND
ON/OFF
R4
56k
1%
C7
0.1µF
VOUT2 = 24V
C5
22µF
35V
0.1Ω
C6
15pF
C10
270pF
Figure 4b. Adjustable Non-Bootstrapped Typical Operating Circuit
Low-Voltage Start-Up Oscillator
(BOOT Pin)
The MAX863 features a low-voltage start-up oscillator
that guarantees start-up in bootstrapped configuration
down to 1.5V. At these low supply voltages, the error
comparator and internal biasing of the IC are locked
out. The low-voltage oscillator switches the external
MOSFET with around 30% duty cycle until the voltage
at VDD rises above 2.7V. At this point, the error com-
parator and one-shot timing circuitry turn on. The low-
voltage oscillator is enabled by connecting the BOOT
pin to VDD. When BOOT is high, VDD must be connect-
ed to VOUT1.
Use the start-up oscillator in the bootstrapped configu-
ration only, since the MAX863 operates in an open-loop
state while the start-up oscillator is active. When using
a non-bootstrapped circuit configuration, connect
BOOT to GND to disable the start-up oscillator. This
prevents the output from rising too high when VDD is
between 1.5V and 2.7V, such as during power-up and
low-battery conditions.
Bootstrapped/Non-Bootstrapped Modes
Figures 2 and 4 show standard applications in boot-
strapped and non-bootstrapped modes. In boot-
strapped mode, the IC is powered from the output (VDD
is connected to OUT1, BOOT is connected to VDD).
Bootstrapped-mode operation is useful for increasing
the gate drive to the MOSFETs in low-input-voltage
applications, since EXT1 and EXT2 swing from VDD to
GND. Increasing the gate-drive voltage reduces MOS-
FET on-resistance, which improves efficiency and
increases the load range. For supply voltages below
5V, bootstrapped mode is recommended. In boot-
strapped mode, the output connected to VDD must not
exceed 11V. If BOOT is high, VDD must be connect-
ed to OUT1.
In non-bootstrapped mode, the IC is powered by a
direct connection from the input voltage to VDD. Since
the voltage swing applied to the gate of the external
MOSFET is derived from VDD, the external MOSFET on-
resistance increases at low input voltages. The mini-
mum input voltage is 2.7V. For operation down to 4V,
use logic-level MOSFETs. For lower input voltages, use
low-threshold logic-level MOSFETs. When both output
voltages are set above 11V, non-bootstrapped mode is
mandatory.
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