AME, Inc.
Low Power
DC/DC Boost Converter
AME5131
n Detailed Description
Operation
The AME5131 is a boost converter with a smart control
scheme that operates in a pulse frequency modulation
(PFM) with constant peak current control.
The smart control schemes utilize a reference voltage,
minimum off-time, maximum on-time and current-limited
control scheme. The switch turns off as the inductor cur-
rent reaches the internally set peak current of 400mA
(typical). The second criteria that turns off the switch is
the maximum on-time of 6ms (typical). As the switch is
turned off the external Schottky diode is forward biased
delivering the current to the output. The switch remains
off for a minimum of 400 ns (typical), or until the feedback
voltage drops below the reference voltage.
Using this PFM peak current control scheme the con-
verter operates in discontinuous conduction mode (DCM)
where the switching frequency depends on the output
current, which results in high efficiency over the entire
load current range. This regulation scheme is inherently
stable, allowing a wider selection range for the inductor
and output capacitor.
Soft-start
Soft-start is provided on the AME5131 to minimize in-
rush current. All inductive boost converters exhibit high
inrush current during start-up if no special precaution is
made. This can cause voltage drops at the input rail dur-
ing start up and may result in an unwanted or early sys-
tem shut down.
The soft-start time is set by increasing the current limit
in two steps starting from 100mA for 256 cycles to 200mA
for the next 256 cycles, and then full current limit.
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AME [ ANALOG MICROELECTRONICS ]
