ML4871 Datasheet, PDF (1/9 Pages) Micro Linear Corporation – High Current Boost Regulator

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July 2000
ML4871
High Current Boost Regulator
GENERAL DESCRIPTION
The ML4871 is a 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 ML4871
is capable of start-up with input voltages as low as 1.8V
and is available in 5V and 3.3V output versions with an
output voltage accuracy of ±3%.
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 ML4871 requires only one inductor and two
capacitors to build a very small regulator circuit capable
of achieving conversion efficiencies approaching 90%.
The circuit also contains a RESET output which goes low
when the DETECT input drops below 1.25V.
FEATURES
s Guaranteed full load start-up and operation
at 1.8V Input
s Continuous conduction mode for high output current
s Very low supply current (20µA output referenced) for
Micropower operation
s Pulse Frequency Modulation and Internal Synchronous
Rectification for high efficiency
s Maximum switching frequency > 200kHz
s Minimum external components
s Low ON resistance internal switching FETs
s 5V and 3.3V output versions
BLOCK DIAGRAM
VIN
2
1
VL1
4
DETECT
VREF
7
RESET
+
COMP
–
6
VL2
START-UP
SYNCHRONOUS
RECTIFIER
CONTROL
VOUT
5
+
–
BOOST
CONTROL
1.25V
PWR GND
8
GND
3
1