July 2000
ML4875*
Low Voltage Boost Regulator with Shutdown
GENERAL DESCRIPTION
The ML4875 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 ML4875 ideal for 1 cell
applications. The ML4875 is capable of start-up with input
voltages as low as 1V and is available in 5V, 3.3V, and 3V
output versions with an output voltage accuracy of ±3%.
Unlike regulators using external Schottky diodes, the
ML4875 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 ML4875 requires only one inductor and two
capacitors to build a very small regulator circuit capable
of achieving conversion efficiencies in excess of 90%.
The circuit contains a
RESET
output which goes low when
the DETECT input drops below 200mV.
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
5V, 3.3V, and 3V output versions
*Some Packages Are End Of Life Or Obsolete
BLOCK DIAGRAM
L1
V
OUT
PWR
GND
8
V
L
6
5
V
OUT
V
IN
1
FEEDBACK
*C
IN
V
BAT
BOOST
CONTROL
C
OUT
GND
3
REGULATION
&
SHUTDOWN
CONTROL
REF
+
–
SHDN
2
DETECT
4
*R
A
RESET
7
FROM POWER
MANAGEMENT
*R
B
5V
*Optional
1
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
