July 2000
PRELIMINARY
ML4770*
2 Cell, Adjustable Output, High Current
Boost Regulator with Load Disconnect
GENERAL DESCRIPTION
The ML4770 is a continuous conduction mode boost
regulator designed for DC to DC conversion in multiple
cell battery power 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 ML4770 is capable of start-up with input voltages as
low as 1.8V. The output voltage can be set anywhere
between 3.0V and 5.5V by an external resistor divider
connected to the SENSE pin.
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 current and variable
frequency operation result in high efficiency even at light
loads. The ML4770 requires only a few external
components to build a very small regulator capable of
achieving conversion efficiencies approaching 85%.
The SHDN input allows the user to stop the regulator from
switching, and provides complete isolation of the load
from the battery.
FEATURES
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Guaranteed full load start-up and operation at
1.8V input
Continuous conduction mode for high output current
Pulse Frequency Modulation and internal synchronous
rectification for high efficiency
Isolates the load from the input during shutdown
Minimum external components
Low ON resistance internal switching FETs
Low supply current
Adjustable output voltage (3V to 5.5V)
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* Some Packages Are Obsolete
BLOCK DIAGRAM
1
6
VL1
VL2
SHUTDOWN
CONTROL
SHDN
7
VIN
2
START-UP
SYNCHRONOUS
RECTIFIER
CONTROL
VOUT
+
–
5
+
–
SENSE
BOOST
CONTROL
+
–
4
2.57V
SHDN
PWR GND
8
GND
3
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
