MAX1947
Shutdown
The MAX1947 enters shutdown mode when SHDN is
driven low. During shutdown, the synchronous rectifier
disconnects the output from the input, eliminating the DC
conduction path that normally exists with traditional boost
converters in shutdown mode. The output is actively dis-
charged to ground through an internal 500Ω resistor. The
quiescent current is reduced to 2µA while in shutdown
mode. Drive SHDN high for normal operation. The output
reaches regulation approximately 650µs after SHDN
goes high.
Applications Information
Inductor Selection
An inductor value of 4.7µH performs well in most appli-
cations. The MAX1947 also works with inductors in the
2.2µH to 6.8µH range. Smaller inductance values typi-
cally offer a smaller physical size for a given series
resistance, allowing the smallest overall circuit dimen-
sions but with lower output-current capability. Circuits
using larger inductance values exhibit higher output-
current capability, but are larger for the same series
resistance and current rating.
The inductor’s incremental saturation current rating
should be greater than the peak switch-current limit.
However, it is generally acceptable to bias the inductor
into saturation by as much as 20%, although this
slightly reduces efficiency (see the Electrical
Characteristics for the MAX1947 NFET current limit).
Table 1 lists the suggested components for several typ-
ical applications. Also, the inductor’s DC resistance sig-
nificantly affects efficiency.
Low Input/Output Voltage
Step-Up DC-DC Converter with
RESET
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