BQ24040 Datasheet, PDF (14/31 Pages) Texas Instruments – 800mA Single-Input Single Cell Li-Ion Battery Charger With Auto Start

bq24040
bq24041
SLUS941A – SEPTEMBER 2009 – REVISED SEPTEMBER 2009.................................................................................................................................... www.ti.com
FUNCTIONAL GENERAL DESCRIPTION
The bq2404x is a highly integrate family of 2×2 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 and
Pre-charge/Termination Current (bq24040 only). 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 (bq24040 only),
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 ISET and OUT short checks are performed 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 votlage.
If the IC reaches 125°C the IC enters thermal requlation, slows 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 termination can be disabled if desired.
The CHG pin is low (LED on) during the first charge cycle only and turns off once the termination threshold is
reached, regardless if termination, for charge current, is enabled or disabled.
Further details are mentioned in the Operating Modes section.
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