Datasheet

bq24050

bq24052

bq24055

www.ti.com

SLUS940B –SEPTEMBER 2009–REVISED JUNE 2012

FUNCTIONAL GENERAL DESCRIPTION

The bq2405x is a highly integrate family of 2×2 or 2×3mm single cell Li-Ion and Li-Pol chargers. The charger can

be used to charge a battery, power a system or both. The charger has three phases of charging: Pre-charge to

recover a fully discharged battery, fast-charge constant current to supply the buck charge safely and voltage

regulation to safely reach full capacity. The charger is very flexible, allowing programming of the fast-charge

current, pre-charge current and termination. This charger is designed to work with a USB connection or Adaptor

(DC out). The charger also checks to see if a battery is present.

The charger also comes with a full set of safety features: JEITA Temperature Standard, Overvoltage Protection,

DPM-IN, Safety Timers, and ISET short protection. All of these features and more are described in detail below.

The charger is designed for a single power path from the input to the output to charge a single cell Li-Ion or

Li-Pol battery pack. Upon application of a 5VDC power source the D+, D– detection routine is run to determine if

the source is an Adaptor or a USB port. This feature is useful, when the battery is discharged (USB transceiver

dead) or there is no transceiver, by early detection of an adaptor, thus allowing initial charging at the adaptor

level. ISET and OUT short checks are performed in parallel with the detection routine to assure a proper charge

cycle.

If the battery voltage is below the LOWV threshold, the battery is considered discharged and a preconditioning

cycle begins. The amount of precharge current can be programmed using the PRE-TERM pin which programs a

percent of fast charge current (10 to 100%) as the precharge current. This feature is useful when the system load

is connected across the battery “stealing” the battery current. The precharge current can be set higher to account

for the system loading while allowing the battery to be properly conditioned. The PRE-TERM pin is a dual

function pin which sets the precharge current level and the termination threshold level. The termination "current

threshold" is always half of the precharge programmed current level.

Once the battery voltage has charged to the V

LOWV

threshold, fast charge is initiated and the fast charge current

is applied. The fast charge constant current is programmed using the ISET pin. The constant current provides the

bulk of the charge. Power dissipation in the IC is greatest in fast charge with a lower battery voltage. If the IC

reaches 125°C the IC enters thermal regulation, slow the timer clock by half and reduce the charge current as

needed to keep the temperature from rising any further. Figure 23 shows the charging profile with thermal

regulation. Typically under normal operating conditions, the IC’s junction temperature is less than 125°C and

thermal regulation is not entered.

Once the cell has charged to the regulation voltage the voltage loop takes control and holds the battery at the

regulation voltage until the current tapers to the termination threshold. The charge termination can be disabled if

desired. The CHG pin is low (LED on) during the first charge cycle only and turns off once the charge termination

threshold is reached, regardless if termination is enabled or disabled.

The TS pin monitors the voltage across the pack thermistor and implements the JEITA standard. This allows for

reduced voltage regulation at hot temperatures and reduced charge currents at low temperatures. The TS pin

incorporates a chip disable feature when pulled low and an Termination and Timer Disable Mode (TTDM) feature

when left floating or pulled high.

Further details are mentioned in the Operating Modes section.