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BQ24273RGET Datasheet(PDF) 10 Page - Texas Instruments |
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BQ24273RGET Datasheet(HTML) 10 Page - Texas Instruments |
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10 / 27 page  bq24273 SLUSB08 – JUNE 2012 www.ti.com Battery Charging Process When the battery is deeply discharged or shorted (VBAT<VBATSHRT), the bq24273 applies a 50mA current to close the pack protector switch and bring the battery voltage up to acceptable charging levels. Once the battery rises above VBATSHRT, the charge current is regulated to the value set in the I 2C register. If the die temperature does heat up, the thermal regulation circuit reduces the charge current to maintain a die temperature less than 125°C. The slew rate for fast charge current is controlled to minimize the current and voltage over-shoot during transient. The charge current is regulated to IOCHARGE until the battery is charged to the regulation voltage. Once the battery voltage is close to the regulation voltage, VBATREG, the charge current is tapered down as shown in Figure 2. The voltage regulation feedback occurs by monitoring the battery-pack voltage between the BAT and PGND pins. The bq24273 is a fixed single-cell voltage version, with adjustable regulation voltage (3.5V to 4.44V) programmed using the I2C interface. The bq24273 monitors the charging current during the voltage regulation phase. Once the termination threshold, ITERM, is detected and the battery voltage is above the recharge threshold, the bq24273 terminates the charge cycle and enters battery detection. The termination current level is programmable. To disable the charge current termination, the host sets the charge termination bit (TE) of charge control register to 0, refer to I2C section for details. A new charge cycle is initiated when one of the following conditions is detected: 1. The battery voltage falls below the VBATREG-VRCH threshold. 2. CE bit toggle or RESET bit is set 3. HI-Z bit toggle Battery Detection When termination conditions are met, a battery detection cycle is started. During battery detection, IDETECT is pulled from VBAT for tDETECT to verify there is a battery. If the battery voltage remains above VDETECT for the full duration of tDETECT, a battery is determined to present and the IC enters “Charge Done”. If VBAT falls below VDETECT, a “Battery Not Present” fault is signaled and battery detection continues. The next cycle of battery detection, the bq2427x turns on IBATSHORT for tDETECT. If VBAT rises to VDETECT, the current source is turned off and after tDETECT, the battery detection continues through another current sink cycle. Battery detection continues until charge is disabled or a battery is detected. Once a battery is detected, the fault status clears and a new charge cycle begins. Battery detection is not run when termination is disabled. DEFAULT Mode DEFAULT mode is used when I2C communication is not available. DEFAULT mode is entered in the following situations: 1. When the charger is enabled and VBAT<3.6V before I 2C communication is established 2. When the watchdog timer expires without a reset from the I2C interface and the safety timer has not expired. 3. When the device comes out of any fault condition (sleep mode, OVP, faulty adapter mode, etc.) before I2C communication is established In default mode, the I2C registers are reset to the default values. The 27 min safety timer is reset and starts when DEFAULT mode is entered. The default value for VBATREG is 3.6V, and the default value for ICHARGE is 1A. The input current limit for the IN input is set to 1.5A. Default mode is exited by programming the I2C interface. Note that if termination is enabled and charging has terminated, a new charge cycle is NOT initiated when entering DEFAULT mode. Safety Timer and Watchdog Timer At the beginning of charging process, the bq24273 starts the safety timer. This timer is active during the entire charging process. If charging has not terminated before the safety timer expires, charging is halted and the CE bit is written to a “1”. The length of the safety timer is selectable using the I2C interface. A single 128 μs pulse is sent on the STAT and INT outputs and the STATx bits of the status registers are updated in the I2C. The /CE bit must be toggled in order to clear the safety timer fault. The safety timer duration is selectable using the TMR_X bits in the Safety Timer Register/ NTC Monitor register. Changing the safety timer duration resets the safety timer. If the safety timer expires, charging is disabled (CE changed to a “1”). This function prevents continuous charging of a defective battery if the host fails to reset the safety timer. 10 Submit Documentation Feedback Copyright © 2012, Texas Instruments Incorporated Product Folder Link(s) :bq24273 |
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