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BQ2954SN Datasheet(PDF) 3 Page - Texas Instruments |
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BQ2954SN Datasheet(HTML) 3 Page - Texas Instruments |
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3 / 18 page  Functional Description The bq2954 functional operation is described in terms of the following (Figure 1): I Charge algorithm I Charge qualification I Charge status display I Configuring the display and termination I Voltage and current monitoring I Battery insertion and removal I Temperature monitoring I Maximum time--out I Charge regulation I Recharge after fast charge Charge Algorithm The bq2954 uses a two-phase fast-charge algorithm. In phase 1, the bq2954 regulates constant current until the voltage on the BAT pin, VBAT, rises to the internal threshold, VREG. The bq2954 then transitions to phase 2 and regulates constant voltage (VBAT =VREG) until the charging current falls below the programmed IMIN threshold. Fast charge then terminates, and the bq2954 enters the Charge Complete state. (See Figure 2.) Charge Qualification The bq2954 starts a charge cycle when power is applied while a battery is present or when a battery is inserted. Figure 2 shows the state diagram for the bq2954. The bq2954 first checks that the battery temperature is within the allowed, user-configurable range. If the tem- perature is out of range, the bq2954 remains in the QUALIFICATION state (S01) and waits until the battery temperature and voltage are within the allowed range. If during any state of charge, a temperature excursion occurs HOT, the bq2954 proceeds to the DONE state (S04) and indicates this state on the LED outputs and provides no current. If this occurs, the bq2954 remains in the DONE state unless the following two conditions are met: I Temperature falls within valid charge range I VBAT falls below the internal threshold,VRCHG If these two conditions are met, a new charge cycle be- gins. During any state of charge, if a temperature ex- cursion occurs COLD, the bq2954 terminates charge and returns to the QUALIFICATION state (S01). Charge re- starts if VBAT and temperature are in valid range. When the temperature and voltage are valid, the bq2954 enters the CONDITIONING state (S02) and regulates current to ICOND (=IMAX/10). After an initial holdoff pe- riod tHO (which prevents the IC from reacting to tran- sient voltage spikes that may occur when charge current is first applied), the IC begins monitoring VBAT.IfVBAT does not rise to at least VMIN before the expiration of 3 bq2954 BD2954.eps Voltage Reference Charge Control State Machine PWM Regulator Display Control Power-On Reset MTO Timer Oscillator DSEL CSEL LED1 LED2 BTST CHG LCOM MOD ICOMP VCC TM TPWM ITERM VSS TS VCOMP BAT SNS Figure 1. Functional Block Diagram |
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