MAX618EEE Ver la hoja de datos (PDF) - Maxim Integrated
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MAX618EEE Datasheet PDF : 15 Pages
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MAX618
28V Internal Switch, Step-Up DC-DC Converter
Detailed Description
The MAX618 pulse-width modulation (PWM) DC-DC
converter with an internal 28V switch operates in a wide
range of DC-DC conversion applications including boost,
SEPIC, and flyback configurations. The MAX618 uses
fixed-frequency PWM operation and Maxim’s proprietary
Idle Mode control to optimize efficiency over a wide range
of loads. It also features a shutdown mode to minimize
quiescent current when not in operation.
PWM Control Scheme and
Idle Mode Operation
The MAX618 combines continuous-conduction PWM
operation at medium to high loads and Idle Mode opera-
tion at light loads to provide high efficiency over a wide
range of load conditions. The MAX618 control scheme
actively monitors the output current and automatically
switches between PWM and Idle Mode to optimize
efficiency and load regulation. Figure 2 shows a functional
diagram of the MAX618’s control scheme.
The MAX618 normally operates in low-noise, continuous-
conduction PWM mode, switching at 250kHz. In PWM
mode, the internal MOSFET switch turns on with each
clock pulse. It remains on until either the error comparator
trips or the inductor current reaches the 2A switch-current
limit. The error comparator compares the feedback-error
signal, current-sense signal, and slope-compensation
signal in one circuit block. When the switch turns off,
energy transfers from the inductor to the output capacitor.
Output current is limited by the 2A MOSFET current limit
IDLE MODE
CURRENT LIMIT
MAX618
PWM
CURRENT LIMIT
CURRENT-
SENSE
CIRCUIT
VL
PGND IN
ERROR
COMPARATOR
PWM
LOGIC
NMOS
R
LX
OUT
250kHz
GND
OSCILLATOR
14R
FB
SLOPE
COMPENSATION
REFERENCE
INTEGRATOR
COMP
SHDN
SHUTDOWN
THERMAL
SHUTDOWN
LINEAR
REGULATOR
IN
VL
Figure 2. Functional Diagram
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