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SMB135E View Datasheet(PDF) - Summit Microelectronics

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Description
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SMB135E Datasheet PDF : 34 Pages
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SMB135
GENERAL DESCRIPTION
The SMB135 is a fully programmable battery charger for
single-cell Li-Ion and Li-Polymer battery packs. The
device’s high-efficiency, switch-mode operation reduces
heat dissipation and allows for higher current capability
for a given package size. The SMB135 provides four
main charging phases: trickle-charge, pre-conditioning
(pre-charge), constant current and constant voltage.
The overall system accuracy of the SMB135 is 1%,
allowing for a higher capacity utilization versus other
conventional solutions.
When a battery or an external supply is inserted and the
EN (ENABLE) input is asserted, the SMB135 performs
the pre-qualification checks before initiating a charging
cycle. The input voltage needs to be higher than the
UVLO threshold and the cell temperature needs to be
within the temperature limits for the charging cycle to
start. As soon as the input supply is removed, the
SMB135 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.
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 SMB135 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
SMB135 enters the pre-charge mode. This mode
replenishes deeply depleted cells and minimizes heat
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.
When the battery voltage reaches the pre-charge to fast-
charge voltage level, the SMB135 enters the constant
current (fast charge) mode. The fast charge current
level is programmable in two ways: a) via an external
sense resistor and b) via the corresponding register.
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 from
25mA to 130mA in 15mA increments.
After the charge cycle has terminated, the SMB135
continues to monitor the battery voltage. If the battery
voltage falls below the recharge threshold (typically
115mV below float voltage), the SMB135 can
automatically top-off the battery.
A wide range of protection features is also included in
the SMB135. These include input and output over-
voltage protection, battery missing detector and thermal
monitor for continuous cell temperature monitoring and
pre-qualification.
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:
Battery (float) voltage
Fast charge current
Pre-conditioning voltage threshold
Pre-conditioning charge current
Termination current
Safety charge timers
Temperature window
The SMB135 also offers three programmable PWM
switching frequencies ranging from 750kHz to 1250kHz
in 250kHz increments.
Summit Microelectronics, Inc
2106 3.1 11/4/2008
2
 

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