The MAX1874 charges a single-cell Li+ battery from
both USB and AC adapter sources. It also includes battery-to-input power switchover, so the system can be
powered directly from the power source rather than
from the battery.
In its simplest application, the MAX1874 needs no
external MOSFET or diodes, and accepts input voltages
up to 6.5V; however, DC input overvoltage protection
up to 18V can be added with a single SOT PFET.
On-chip thermal limiting simplifies printed circuit board
(PCB) layout and allows optimum charging rate without
the thermal limits imposed by worst-case battery and
input voltage. When the MAX1874 thermal limit is
reached, the charger does not shut down but simply
reduces charging current.
Ambient or battery temperature can be monitored with
an external thermistor. When the temperature is out of
range, charging pauses.
Other features include an active-low CHG output to indicate when
battery current tapers below a predetermined level. DC
power-OK (active-low DCOK), USB power-OK (active-low UOK), and power-on
(PON) outputs indicate when valid power is present.
These outputs drive logic or power-selection MOSFETs
to disconnect the charging sources from the load and
to protect the MAX1874 from overvoltage.
The MAX1874 contains no logic for communication with
the USB host. It must receive instructions from a local
microcontroller. The MAX1874 is available in a 16-pin
5mm x 5mm thin QFN package and operates over the
-40°C to +85°C temperature range.
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