The BQ2409X family of devices is highly integrated for Li-Ion and Li-Polymer linear chargers for portable applications where device protection space is limited. Device - 6.6 V overvoltage protection can be operated via USB port or AC adapter. The - input voltage dynamic power management for high input voltage range, input overvoltage protection supports low cost unregulated adapters. -125°C thermal regulation; 150°C thermal

Shutdown Protection The BQ2409X has a single power output that can charge the battery. System loads can be paralleled - OUT short circuit protection and ISET short circuit with battery as long as average system load detection will not allow battery to fully charge in the process JEITA Range 10 hour safety timer for battery operation. NTC - Fast charge current when cool, 4.06V battery is charged in three stages: thermal regulation, bq24092/3 constant current and constant voltage. During all charge fixed 10 hour safety timer phases, an internal control loop monitors the IC system junction temperature and reduces the charge current automatically terminating and the timer disabled if the internal temperature threshold is exceeded.

The charger power stage and charge current sensing functions are fully integrated. The charger features highly accurate current and voltage regulation loops, charge status display and charge termination pre-charge current and termination current thresholds programmed via external resistors. The fast charge current value can also be programmed via an external resistor.

Pin Configuration and Functional Diagram

The BQ2409X is a family of highly integrated single-cell Li-Ion and Li-polymer chargers. The charger can be used to charge the battery, power the system, or both. The charger has three charging stages: pre-charge to restore a fully discharged battery, fast-charge constant current, safely provide step-down charging and voltage regulation to safely reach full load. The charger is very flexible and can program fast charge current and precharge/termination current. This charger is designed for use with a USB connection or an adapter (DC output). The charger also checks for the presence of batteries. The charger also has a full set of safety features: JEITA temperature standard, overvoltage protection, DPM-IN, safety timer and ISET short circuit protection. All of these features and more are described in detail below. The charger is designed to charge a single-cell Li-Ion or LiPol battery pack with a single power path from input to output. When applying 5VDC power, perform ISET and OUT short-circuit checks to ensure proper charge cycles.

If the battery voltage is below the LOWV threshold, the battery is considered discharged and a preconditioning cycle begins. The precharge current can be programmed using the PRE-TERM pin to program a percentage of the fast charge current (10 to 100%) as the precharge current. This is useful when the system is loading to "steal" battery current through the battery connection. The precharge current can be set higher for system loading while allowing the battery to regulate properly. The PRE-TERM pin is a dual function pin that sets the precharge current level and termination threshold level. The termination "current threshold" is always half the precharge programming current level. Once the battery voltage is charged to the VLOWV threshold, fast charge is initiated and fast charge current is applied; is applied. Use the ISET pin to program fast charge constant current. Constant current provides most of the cost. The IC consumes the most power during fast charging when the battery voltage is low. If ICIC enters thermal regulation after reaching 125°C, halve the timer clock and reduce the charge current

Need to keep the temperature from rising. The figure below shows a charge curve gauge with heat. Typically under normal operating conditions, the IC has a junction temperature below 125°C without input thermal regulation. Once the battery is charged to the regulated voltage, the voltage loop controls and maintains the battery at the regulated voltage until the current tapers off to the termination threshold. Termination can be disabled if desired. The CHG pin is low only for the first charge cycle (LED on) and turns off when the termination threshold is off, which is reached regardless of whether charge current is enabled or not.

Function description

Power-down or under-voltage lockout (UVLO)

If the IN pin voltage is lower than UVLO, the BQ2409X series is in power-down mode. This part is considered "dead", all pins are high impedance. Once the IN voltage rises above the UVLO threshold, the IC enters sleep mode or active mode, depending on the OUT pin (battery) voltage.

UVLO

If the IN pin voltage is lower than VUVLO, the BQ2409X series is in power-down mode. The part is considered "dead" and all pins are high impedance.

Power-up After the IN voltage rises above UVLO (see sleep mode), the IC is active, resets all logic and timers, and then starts executing a number of continuous monitoring routines. Usually the input voltage will rise quickly ICLO declares a good power UVLO and sleep state, start qualifying charge at 100mA, set the input current limit threshold based on the ISET2 pin, start the safety timer and enable the CHG pin see the figure below.

sleep mode

If the IN pin voltage is between VOUT + VDT and UVLO, the charge current is disabled, i.e. the safety timer count is stopped (not reset), and the PG and CHG pins are high impedance. As the input voltage rises, the charger exits sleep mode, the PG pin goes low, the safety timer continues to count, charging is enabled and the CHG pin returns to its previous state. See Figure 16.

new charge cycle

When good power is applied, start a new charge cycle, perform chip disable/enable (TS pin), exit terminal and timer disable mode (TTDM), detect battery insertion or OUT voltage drops below VRCH threshold. The CHG pin is only active low during the first charge cycle, so exiting TTDM or if the CHG pin is already high impedance, falling below VRCH will not turn on the CHG pin FET.

Overvoltage Protection (OVP) - Continuous Monitoring

If overvoltage is applied to the input source, the conducting FET (if previously on) turns off tBLK (OVP) after deglitching. The timer expires and the CHG and PG pins go into a high impedance state. Once the overvoltage returns to normal voltage, the PG pin goes low, the timer continues to run, continues to charge, and the CHG pin spikes low after 25ms. The PG pin is optional on some packages.

Power Good Indicator (PG)

With 5V applied, the input voltage rises above the UVLO and sleep thresholds (VIN > VBAT + VDT), but less than OVP (VIN

CHG pin indication

The charge pin has an internal open-drain FET that is turned on (pulled down to VSS) only during the first charge (independent of TTDM) and turned off once the battery reaches voltage regulation and the charge current tapers off to the value set by the PRE-TERM resistor. Termination threshold. The charge pin is high impedance in sleep mode, and OVP (if PG is high impedance) returns to its previous state as indicated once removed. Cycling input power, pulling the TS pin low and releasing or entering precharge mode causes the CHG pin to go into reset (going low if power is good and a discharged battery is connected) and is considered the first charge Start.

CHG and PG LED pull-up power supply

For host monitoring, use a pull-up resistor between the STATUS pin and the host's VCC for visual indication. A resistor in series with the LED is connected between the STATUS pin and the power supply. If the CHG or PG source can exceed 7V, a 6.2V Zener diode should be used to clamp the voltage. If the source is the OUT pin, be aware that the brightness of the LED changes when the battery changes voltage.

BQ2409X power-on flow chart

PRE_TERM - Precharge and Termination Programmable Thresholds

PRE_TERM is used to program the precharge current and termination current thresholds. The precharge current level is two times higher than the termination current level. Termination can be set between 5% and 50% of the programmed output current level set by ISET. If left unconnected, termination and precharge are internally set to 10/20%, respectively. The precharge to fast charge Vlowv threshold is set to 2.5V. RPRE-TERM = %Term × KTERM = %Pre-CHG × KPRE-CHG where

Term is the percentage of fast charge current when termination occurs

Pre-CHG is the percentage of fast charge current required during precharge

KTERM and KPRE-CHG are gain factors in electrical specifications (1)

ISET2

ISET2 is a three-state input that sets the input current limit/regulation threshold. A low program a adjusts the fast charge current through the ISET resistor and is any maximum allowed input/output current ISET2 setting, Float will program a 100mA current limit, and High will program a 500mA current limit. Below is what drives the 3-state ISET2 pin.