SMB239
GENERAL DESCRIPTION
The SMB239 is a fully programmable, linear battery
charger for single-cell Li-Ion and Li-Polymer battery
packs. The device’s simple, linear-mode operation and
ultra-small package significantly reduce component
count and required board space. The SMB239 provides
four main charging phases: trickle-charge, pre-
conditioning (pre-charge), constant current and constant
voltage. The overall system accuracy of the SMB239 is
1%, allowing for a higher capacity utilization versus other
conventional solutions.
When a battery or an external supply is inserted the
SMB239 performs the pre-qualification checks before
initiating a charging cycle. The input voltage needs to be
higher than the UVLO threshold for the charging cycle to
start. As soon as the input supply is removed, the
SMB239 enters a shutdown mode, thereby saving
battery power. A programmable option also exists that
allows the user to prevent battery charging until an I2C
command has been issued.
Once the final float voltage (programmable) has been
reached, the battery charger will enter a constant voltage
mode in which the battery voltage is kept constant,
allowing the charge current to gradually taper off. The
constant-voltage charging mode will continue until the
charge current drops below the termination current
threshold, or until the fast charge timer has expires. The
termination current threshold is programmable.
After the charge cycle has terminated, the SMB239
continues to monitor the battery voltage. If the battery
voltage falls below the recharge threshold (typically
115mV below float voltage), the SMB239 can
automatically top-off the battery.
An option exists for preventing charging initiation upon
power cycling unless the battery voltage is 220mV,
390mV or 550mV (VCH) below the float voltage level.
This prevents over-stressing of the battery via
continuous charging cycles in systems with short run
times and frequent power cycling (IN power
connect/disconnect).
A wide range of protection features is also included in
the SMB239. These include input and output (battery)
over-voltage protection, battery missing detector and
thermal monitor for continuous cell temperature
monitoring and pre-qualification.
If the battery voltage is below 2.0V (trickle-charge to pre-
charge threshold), the device will apply a trickle-charge
current of 10mA (typical). This allows the SMB239 to
reset the protection circuit in the battery pack and bring
the battery voltage to
a
higher level without
compromising safety.
Once the battery voltage crosses the 2.0V threshold, the
SMB239 enters the pre-charge mode. This mode
replenishes deeply depleted cells and minimizes heat
The following charging parameters can be adjusted
dynamically via the I2C interface, for optimizing battery
management real-time. These parameters can also be
programmed statically via a user-friendly GUI interface:
dissipation during the initial charge cycle.
The
preconditioning current is programmable, with the default
value at C/10. If the battery voltage does not reach the
preconditioning voltage level (programmable) within a
specified amount of time (pre-charge timeout), the safety
timer expires and the charge cycle is terminated.
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•
•
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•
•
Battery (float) voltage
Fast charge current
Pre-conditioning voltage threshold
Pre-conditioning charge current
Termination current
When the battery voltage reaches the pre-charge to fast-
charge voltage level, the SMB239 enters the constant
current (fast charge) mode. The fast charge current
level is programmable via the corresponding register.
Temperature window
•
Safety charge timers.
Summit Microelectronics, Inc
2129 3.0 2/23/2009
2
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
