When charging from the USB port, the host controller can use the ISET2 pin to select a charging rate of 100mA or 500mA. A low signal sets the current to 100 mA, and a high signal sets the current to 500 mA. High z input disables USB charging

Voltage regulation feedback through the output pins. This input is connected directly to the positive terminal of the battery pack. The bqTINY-II monitors the battery pack voltage between the output and the VSS pin. When the battery voltage rises to the VO(REG) threshold, the voltage regulation phase begins and the charge current begins to decrease.

As a safety backup, bqTINY-II can also monitor charging time. If charging is not terminated within the time specified by t(CHG), the bqTINY-II shuts down the charger and asserts a fault code on the STATx pin. See the Timer Failover section for details.

The bqTINY-II monitors the charging current during the voltage regulation phase. When a taper threshold I(taper) is detected, bqTINY-II starts a taper timer t(taper). Charging terminates after the timer expires. A resistor connected between ISET1 and VSS (RSET) determines the taper detection level. The V (taper) and K (set) parameters are specified in the specification table. Note that this applies to both AC and USB charging.

The bqTINY-II will reset the cone timer if the charging current exceeds the cone threshold I (cone). In addition to cone current detection, the bqTINY-II will terminate charging if the charging current falls below the I(TERM) threshold. This feature allows quick identification of battery removal, or insertion of a fully charged battery. Note that both the charge timer and cone timer are ignored. A resistor connected between ISET1 and VSS (RSET) determines the taper detection level. The V(TERM) and K(SET) parameters are specified in the specification table. Note that this applies to both AC and USB charging.

After charging, the bqTINY-II restarts charging when the output pin voltage falls below the V(RCH) threshold. This feature keeps the battery fully charged all the time.

The bq24026 and bq24027 monitor the charge current during the voltage regulation phase. Once the taper threshold I (taper) is detected, the bq24026/27 will terminate charging. This version has no cone timer (t(cone)).

A resistor connected between ISET1 and VSS (RSET) determines the taper detection level of the AC input. For USB charging, the taper level is fixed at 10% for a 100 or 500mAh charge rate.

Also note that there is an I(TERM) assay in bq24026 and bq24027.

If both AC and USB are removed from the circuit, the bqTINY-II will enter a low-power sleep mode. This feature prevents draining the battery without input power.

bqTINY-II provides a recovery method for handling temporal fault conditions. The following discussion summarizes this approach:

Condition #1: The charging voltage is higher than the charging threshold (V(RCH)), and the timeout fault occurs. Recovery method: bqTINY-II waits for the battery voltage to be lower than the charging threshold. This may be due to battery load, self-discharge or battery removal. When the battery voltage falls below the charge threshold, the bqTINY-II clears the fault and begins a new charge cycle. Toggling POR, CE or TTE can also clear the error.

Condition #2: Charge voltage is below charge threshold (V(RCH)), timeout fault occurs Recovery method: In this scenario, bqTINY-II applies the I(fault) current. This small current is used to detect a battery removal condition and remains on as long as the battery voltage is below the charge threshold. If the battery voltage exceeds the charge threshold, the bqTINY-II disables the I (fault) current and performs the recovery method described in Condition #1. When the battery voltage falls below the charge threshold, the bqTINY-II clears the fault and begins a new charge cycle. Toggling POR, CE or TTE can also clear the error.

bqTINY-II is packaged in a thermally enhanced MLP package. The package includes a thermal pad to provide effective thermal contact between the device and the printed circuit board (PCB). The complete PCB design guidelines for this package are contained in the Application Notes QFN/SON PCB Attachment Application Notes (TI literature number SLUA271).

The most common measure of package thermal performance is the thermal impedance (θJA) measurement (or simulation) from surrounding equipment connected to the air package surface (ambient). The mathematical expression of θJA is:

Location: ? TJ = Device Junction Temperature ? TA = Ambient Temperature ? P = Device Power Dissipation Factors that can greatly affect θJA measurements and calculations include: ? Is the device board mounted? Track size, composition, thickness, and geometry? Orientation (vertical or horizontal)? Volume and airflow_lus549 of ambient air surrounding the test device? Are other surfaces close to the device being tested

The power dissipation P of the device is a function of the charge rate and voltage drop of the internal power FETs. Calculated by the following formula:

Due to the charging characteristics of Li-xx batteries, their maximum power consumption generally occurs at the beginning of the charging cycle, when the battery voltage is at its lowest