The MAX8622 flyback switching regulator quickly and
efficiently charges high-voltage photoflash capacitors.
It is ideal for use in digital, film, cell-phone, and smartphone
cameras that use either 2-cell alkaline/NiMH or
single-cell Li+ batteries. An internal, low-on-resistance
n-channel MOSFET improves efficiency by lowering
switch power loss.
A current-limited, continuous-mode, transformer-switching
scheme quickly charges the output capacitor. The
cycle-by-cycle peak current-limit scheme has no inrush
current. Current limit is programmable to control the
maximum load drawn from the battery. An additional
input-voltage monitor loop extends battery life by
reducing the charge rate when the battery is nearly discharged.
This also permits the current limit to be set for
a faster charge rate under typical conditions, rather
than a level dictated by the worst-case discharge state
of the battery.
An open-drain DONE-bar output indicates when the photoflash
capacitor is completely charged. The MAX8622
automatically refreshes the output every 11s, efficiently
maintaining the capacitor charge level with minimum
battery drain.
The MAX8622 provides high charge accuracy by using
an external resistor-divider to monitor the output voltage.
Sensing directly at the transformer secondary prevents
output-capacitor discharge through feedback resistors
while still providing direct output sensing for optimum
voltage accuracy that is not transformer turns-ratio
dependent. The MAX8622 is offered in a 3mm x 3mm
10-pin TDFN package.
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