MAX1800EHJ 查看數據表（PDF） - Maxim Integrated
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MAX1800EHJ Datasheet PDF : 24 Pages
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Digital Camera Step-Up
Power Supply
OUT
IC POWER
2.35V
ONM
REF
GND
OSC
FBM
COMPM
FB1
COMP1
DCON1
1.25V
FB2
COMP2
DCON2
FB3
COMP3
DCON3
AI
ON1
ON2
ON3
ONA
UNDERVOLTAGE LOCKOUT
EN
ON
RDY
REFERENCE
REF
MAX1800
EN
STARTUP
OSCILLATOR
Q
MAIN PWM
CONTROLLER
D
Q1
EN
OSCILLATOR
EN
OSC Q2
FB COMP
EN AUX1
OSC
FB
Q
COMP
DUTY
EN AUX2
OSC
FB
Q
COMP
DUTY
EN AUX3
OSC
FB
Q
COMP
DUTY
GAIN
BLOCK
VREF
EN
0.9VREF
POUT
POUT
P
LX
LX
N
PGND
PGND
DL1
DL2
DL3
AO
RDYM
N
Figure 2. Simplified Functional Diagram
the output voltage. The controller forces the inductor cur-
rent to rise above the 300mA Idle Mode threshold to
ensure pulse skipping and improved efficiency at light
loads.
Auxiliary DC-DC Controllers
The MAX1800 auxiliary controllers operate in a low-noise,
fixed-frequency, PWM mode, with output power limited by
the external components. The controllers regulate their out-
put voltages by modulating the pulse width of the drive sig-
nal for an external N-channel MOSFET switch. The auxiliary
controllers are inactive until the main output has started.
Figure 3 shows a block diagram for a MAX1800 auxil-
iary PWM controller. A sawtooth oscillator signal at OSC
governs the internal timing. At the beginning of each
cycle, DL_ goes high to turn on the external MOSFET
switch. The MOSFET switch turns off when the internally
level-shifted sawtooth rises above COMP_ or when the
maximum duty cycle is exceeded. The switch remains
off until the beginning of the next cycle. An internal
transconductance amplifier establishes an integrated
error voltage at COMP_, thereby increasing the loop
gain for improved regulation accuracy.
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