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SMB139

Programmable Linear Battery Charger in 1.3 x 2.1 uCSP™

Summit Microelectronics 

SMB139

Preliminary Information

GENERAL DESCRIPTION

The SMB139 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 SMB139 provides

four main charging phases: trickle-charge, pre-

conditioning (pre-charge), constant current and constant

voltage. The overall system accuracy of the SMB139 is

1%, allowing for a higher capacity utilization versus other

conventional solutions.

When a battery or an external supply is inserted and the

ENABLE input is asserted, the SMB139 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

SMB139 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 3mA (typical). This allows the SMB139 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

SMB139 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 SMB139 enters the constant

current (fast charge) mode. The fast charge current

level is programmable 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.

After the charge cycle has terminated, the SMB139

continues to monitor the battery voltage. If the battery

voltage falls below the recharge threshold (typically

125mV below float voltage), the SMB139 can

automatically top-off the battery.

A wide range of protection features is also included in

the SMB139. These include input and output (battery)

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.

Summit Microelectronics, Inc

2121 3.0 6/19/2008

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