July 2000
ML4865
High Voltage High Current Boost Regulator
GENERAL DESCRIPTION
The ML4865 is a high voltage, continuous conduction
boost regulator designed for DC to DC conversion in
multiple cell battery powered systems. Continuous
conduction allows the regulator to maximize output
current for a given inductor. The maximum switching
frequency can exceed 200kHz, allowing the use of small,
low cost inductors. The ML4865 is capable of start-up with
input voltages as low as 1.8V and generates a 12V output
with output voltage accuracy of ±4%.
Unlike most boost regulators, the ML4865 isolates the
load from the battery when the SHDN pin is high. An
integrated synchronous rectifier eliminates the need for an
external Schottky diode and provides a lower forward
voltage drop, resulting in higher conversion efficiency. In
addition, low quiescent battery current and variable
frequency operation result in high efficiency even at light
loads. The ML4865 requires only one inductor and two
capacitors to build a very small regulator circuit capable
of achieving conversion efficiencies approaching 90%.
FEATURES
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Guaranteed full load start-up and operation at 1.8V
input
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Continuous conduction mode for high output current
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Very low quiescent current
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Pulse frequency modulation and internal synchronous
rectification for high efficiency
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Maximum switching frequency > 200kHz
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Minimum external components
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Low ON resistance internal switching FETs
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Fixed 12V output can be adjusted to lower output
voltages
BLOCK DIAGRAM
4
VL1
6
VL2
SHUTDOWN
CONTROL
SHDN
7
VIN
3
START-UP
SYNCHRONOUS
RECTIFIER
CONTROL
VOUT
+
–
8
+
–
SHDN
BOOST
CONTROL
+
–
FEEDBACK
CONTROL
2.42V
SENSE
1
PWR GND
5
GND
2
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
