MAX1724 View Datasheet(PDF) - Maxim Integrated
Part Name
Description
Manufacturer
MAX1724 Datasheet PDF : 12 Pages
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1.5µA IQ, Step-Up DC-DC Converters
in Thin SOT23-5
BATT
R2
SHDN
R1
DAMPING
SWITCH
MAX1724
STARTUP
CIRCUITRY
ZERO-
CROSSING
DETECTOR
ERROR
COMPARATOR
1.235V REFERENCE
CONTROL
LOGIC
DRIVER
CURRENT
LIMIT
OUT
P
LX
N
GND
Figure 2. MAX1724 Simplified Functional Diagram
1.2V TO VOUT
10µF
10µH
SHDN
LX
OUT
MAX1723
GND
FB
D1
VOUT = 3.6V
R2
2.37MΩ
10µF
R1
1.24MΩ
Figure 3. MAX1723 Single-Cell Operation
up voltage is a function of load current (see Typical
Operating Characteristics). This circuit is powered from
the BATT pin for the MAX1722/MAX1724, guaranteeing
startup at input voltages as low as 0.91V. The MAX1723
lacks a BATT pin; therefore, this circuit is powered
through the OUT pin. Adding a Schottky diode in paral-
lel with the P-channel synchronous rectifier allows for
startup voltages as low as 1.2V for the MAX1723
(Figure 3). The external Schottky diode is not needed
for input voltages greater than 1.8V. Once started, the
output maintains the load as the battery voltage
decreases below the startup voltage.
Shutdown (MAX1723/MAX1724)
The MAX1723/MAX1724 enter shutdown when the
SHDN pin is driven low. During shutdown, the body
diode of the P-channel MOSFET allows current to flow
from the battery to the output. VOUT falls to approxi-
mately VIN - 0.6V and LX remains high impedance.
Shutdown can be pulled as high as 6V, regardless of
the voltage at BATT or OUT. For normal operation, con-
nect SHDN to the input.
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