ML4865 Datasheet, PDF (1/10 Pages) Fairchild Semiconductor – High Voltage High Current Boost Regulator

www.fairchildsemi.com
ML4865
High Voltage High Current Boost Regulator
Features
• Guaranteed full load start-up and operation at 1.8V input
• Continuous conduction mode for high output current
• Very low quiescent current
• Pulse frequency modulation and internal synchronous
rectification for high efficiency
• Maximum switching frequency > 200kHz
• Minimum external components
• Low ON resistance internal switching FETs
• Fixed 12V output can be adjusted to lower output voltages
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 effi-
ciencies approaching 90%.
Block Diagram
4
VL1
VIN
3
6
VL2
SHUTDOWN
CONTROL
SHDN
7
START-UP
SYNCHRONOUS
RECTIFIER
CONTROL
VOUT
8
+
–
BOOST
SHDN ^CONTROL
PWR GND
5
FEEDBACK
CONTROL
2.42V
GND
2
SENSE
1
REV. 1.0.2 8/10/01