BQ24050 Datasheet, PDF (15/37 Pages) Texas Instruments – 800mA Single Cell Li-Ion Battery Charger With Automatic Adaptor/USB Detection

bq24050
bq24052
bq24055
www.ti.com.................................................................................................................................... SLUS940A – SEPTEMBER 2009 – REVISED SEPTEMBER 2009
FUNCTIONAL GENERAL DESCRIPTION
The bq2405x is a highly integrate family of 2×2 or 2×3mm single cell Li-Ion 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, Over-Voltage 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 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 VLOWV 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.
Copyright © 2009, Texas Instruments Incorporated
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