August 2000
ML4775
Adjustable Output Low Voltage
Boost Regulator with Shutdown
GENERAL DESCRIPTION
The ML4775 is a boost regulator designed for DC to DC
conversion in 1 to 3 cell battery powered systems. The
combination of BiCMOS process technology, internal
synchronous rectification, variable frequency operation,
and low supply current make the ML4775 ideal for 1 cell
applications. The ML4775 is capable of start-up with input
voltages as low as 1V, and the output voltage can be set
anywhere between 2.5V and 5.5V by an external resistor
divider connected to the SENSE pin.
Unlike regulators using external Schottky diodes, the
ML4775 isolates the load from the battery when the
SHDN pin is high. This is accomplished by an integrated
synchronous rectifier which 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 ML4775 requires a minimum number of
external components to build a very small regulator circuit
capable of achieving conversion efficiencies in excess of
90%.
FEATURES
s
s
s
s
s
s
s
Guaranteed start-up and operation at 1V input
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
Micropower operation
Adjustable output voltage (2.5V to 5.5V)
BLOCK DIAGRAM
L1
C
FF*
V
OUT
PWR
GND
8
V
L
6
5
V
OUT
V
IN
1
R
1
*C
IN
V
BAT
BOOST
CONTROL
FEEDBACK
SENSE
4
C
OUT
R
2
GND
3
REGULATION
&
SHUTDOWN
CONTROL
SHDN
2
FROM POWER
MANAGEMENT
*Optional
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
