bq2902 Rechargeable Alkaline Charge/Discharge Controller IC Features General Description ➤ Safely charges two rechargeable alkaline batteries such as Renewal® from Rayovac® The bq2902 is a low-cost charger for rechargeable alkaline batteries such as Renewal® batteries from Rayovac®. The bq2902 combines sensitive, fullcharge detection for two rechargeable alkaline cells, with a low-battery cut-off for overdischarge protection. ➤ Terminates pulsed charge with maximum voltage limit ➤ Contains LED charge status output ➤ Features a pin-selectable low-battery cut-off ➤ Pre-charge qualification indicates fault condition ➤ Available in 8-pin 300-mil DIP or 150-mil SOIC Pin Connections Designed for system integration into a two-cell system, the bq2902 can improve the service life of the rechargeable alkaline cells by properly managing the charge and discharge. The bq2902 requires a voltage limited current source to generate the proper charge pulses for the Renewal® cell. Each cell is individually monitored to ensure full charge without a damaging overcharge. Charge completion is indicated when the average charge rate falls below approximately 3% of the fast charge rate. A status output is provided to indicate charge in progress, charge complete, or fault indication. The bq2902 avoids over-depleting the battery by using the internal end-of-discharge control circuit. The bq2902 also eliminates the external power switching transistors needed to separately charge individual Renewal cells. For safety, charging is inhibited if the per-cell voltage is greater than 3.0V during charge (closed-circuit voltage), or if the cell voltage is less than 0.4V (open-circuit voltage). Pin Names VSEL 1 8 CHG BAT1N 2 7 VSS BAT1P 3 6 VSS DC 4 5 LRTN DC Charging supply input CHG Battery status output BAT1P Battery 1 positive input BAT1N Battery 1 negative input VSS Battery 2 negative input IC ground LRTN System load return VSEL End-of-discharge voltage select input 8-Pin Narrow DIP or SOIC PN290201.eps 5/99 C 1 bq2902 BAT1P Pin Descriptions DC This input connects to the positive terminal of the battery designated BAT1 (see Figure 3). This pin also provides power to the bq2902 when DC is not present. DC supply input This input is used to charge the rechargeable alkaline cells and power the bq2902 during charge. To charge the batteries, this input should be connected to a current-source limited to 300 mA. If the DC input current is greater than 300mA, the power dissipation limits of the package may be exceeded. The DC input should also be capable of supplying a minimum of 3.3V and should not exceed 5.5V. CHG BAT1N Battery 1 negative input This input connects to the negative terminal of the battery designated BAT1 (see Figure 3). VSS Battery 2 negative input/IC ground This input connects to the negative terminal of the battery designated BAT2 (see Figure 3). Charge status LRTN This open-drain output is used to signify the battery charging status and is valid only when DC is applied. VSEL Battery 1 positive input Load return This open-drain pull-down output is typically used as a low-side switch. High-side load switching is also possible with the addition of an external P-FET. End-of-discharge select input This three-level input selects the desired end-of-discharge cut-off voltage for the bq2902. VSEL = BAT1P selects an EDV of 1.10V. VSEL floating selects EDV = 1.0V. VSEL = VSS selects EDV = 0.9.V Functional Description Figure 1 is a block diagram outlining the major components of the bq2902. Figure 2 illustrates the charge control and display status during a bq2902 cycle. Table 1 outlines the vari- DC VSEL CHG 4 3 BAT1P 1 8 Control/Status Logic 2 5 6 7 BAT1N LRTN VSS VSS BD290201.eps Figure 1. Functional Block Diagram 2 bq2902 ous operational states and their associated conditions which are described in detail in the following section. Figure 3 is an application example. Charge Re-Initiation If DC remains valid, the bq2902 suspends all charge activity after full-charge termination. A charge cycle is re-initiated when all cell potentials fall below 1.4V. The rechargeable alkaline cells, unlike other rechargeable chemistries, do not require a maintenance charge to keep the cells in a fully charged state. The self-discharge rate for the Renewal cells is typically 4% per year at room temperature. Charge Initiation The bq2902 always initiates and performs a charge cycle whenever a valid DC input is applied. A charge cycle consists of pulse charging the battery and then checking for a termination condition. The charging section explains charging in greater detail. Charge Status Indication Charge Pre-Qualification Table 1 and Figure 2 outline the various charge action states and the associated BAT 1P, and CHG output states. The charge status output is designed to work with an LED indicator. In all cases, if DC is not present at the DC pin, or if the DC supply is less than the voltage at the BAT1P pin, the CHG output is held in a highimpedance condition. After DC is applied, the bq2902 checks the open-circuit voltage (VOCV) of each cell for an undervoltage condition (VMIN = 0.4V) and begins a charge cycle when the VOCV of all cells is above VMIN. If VOCV of any cell is below VMIN, the bq2902 enters a charge-pending mode and indicates a fault condition (see Table 1). The bq2902 remains in a charge-pending mode until VOCV of each cell is above VMIN. Charging Charge Termination The bq2902 controls charging by periodically connecting the DC current-source to the battery stack, not to the individual battery cells. The charge current is pulsed from the internal clock at approximately a 80Hz rate on the BAT1P pin. Once a charge cycle begins, the bq2902 terminates charge when the average charge rate falls below 3% of the maximum charge rate. The bq2902 also terminates charge when the closed-circuit voltage (VCCV) of any cell exceeds 3.0V (VFLT) during charge and indicates a fault condition on the CHG output (see Table 1). The bq2902 pulse charges the battery for approximately 10ms of every 12.5ms, when conditions warrant. The bq2902 measures the open-circuit voltage (VOCV) of each battery cell during the idle period. If a single-cell poten- Table 1. bq2902 Operational Summary Conditions BAT1P Input CHG Output VDC < VBAT1P Low battery detection per VSEL Z Charge initiation DC applied - - Charge pending/ fault VOCV < 0.4V1 or VCCV > 3.0V2 - VOCV ≤ 1.63V before pulse Charge pulsed @ 80Hz per Figure 2 VOCV > 1.63V before pulse Pulse skipped per Figure 2 Average charge rate falls below 3% of the fast charge rate Charge complete Charge Action State DC absent Charge pulse Pulse skip Charge complete Notes: 1. VOCV = Open-circuit voltage of each cell between positive and negative leads. 2. VCCV = Closed-circuit voltage. 3 sec = Low sec = Z 2 3 2 3 1 1 sec = Low 6 sec = Z 6 1 sec = Low 6 sec = Z 6 1 Low bq2902 discharge voltage (VEDV) is selectable by connecting the VSEL pin as outlined in Table 2. Typically, higher discharge loads (>200mA) should use a lower discharge voltage cut-off to maximize battery capacity. tial of any battery is above the maximum open-circuit voltage (VMAX = 1.63V ±3%), the following pulses are skipped until all cell potentials fall below the VMAX limit. Charging is terminated when the average charge rate falls below approximately 3% of the maximum charge rate. Once charging is terminated, the internal charging FET remains off, and the CHG output becomes active per Table 1 and Figure 2. With DC applied, the internal discharge FET will always remain on. End-of-Discharge Control When DC is not present or less than the voltage present on the BAT1P pin, the bq2902 power is supplied by the voltage present at the BAT1P pin. In this state, the batteries discharge down to the level determined by the VSEL pin. The bq2902 monitors the cell voltage of the rechargeable alkaline cells. Table 2. bq2902 EDV Selections If the voltage across any cell is below the voltage specified by the VSEL input, the bq2902 disconnects the battery stack from the load by turning the internal discharge FET off. The discharge FET remains off until either the batteries are replaced or DC is reapplied, initiating a new charge cycle. After disconnecting the battery stack from the load, the standby current in the bq2902 is reduced to less than 1µA. The end-of- End-of-Discharge Voltage Pin Connection 1.10V VSEL = BAT1P 1.00V VSEL = Z 0.90V VSEL = VSS DC Valid Charge Complete Charging 1 Pending 12.5ms 2 10ms 3 BAT1P 2/3 sec. 1/6 sec. CHG Notes: 1. Charging: 0.4 < VOCV < 1.63V, VCCV < 3.0V. 2. Pulses skipped when VOCV > 1.63V. 3. Charge complete when average charge falls below 3% of fast charge rate TD290201.eps Figure 2. bq2902 Application Diagram 4 bq2902 bq2902 DC+ D1 C1 LED R1 4 8 7 6 DC CHG VSS VSS BAT1P BAT1N LRTN VSEL 3 2 5 1 Battery 1 C2 R2 Load C3 Battery 2 DCBattery and Load Note: Load must be disconnected from battery stack while charging. FG290201.eps Figure 3. bq2902 Application Example, 1.0V EDV 5 bq2902 Absolute Maximum Ratings Symbol Parameter Minimum Maximum Unit Notes DCIN VDC relative to GND -0.3 7.0 V VT DC threshold voltage applied on any pin, excluding the DC pin, relative to GND -0.3 7.0 V TOPR Operating ambient temperature 0 +70 °C Commercial Industrial TSTG Storage temperature TSOLDER Soldering temperature IDC DC charging current - 400 mA ILOAD Discharge current - 500 mA IOL Output current - - mA Note: VMAX VEDV +85 °C +85 °C - +260 °C 10 sec max. CHG Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Exposure to conditions beyond the operational limits for extended periods of time may affect device reliability. DC Thresholds Symbol -40 -40 (TA = 25°C; VDC = 5.5V) Parameter Maximum open-circuit voltage End-of-discharge voltage Rating Tolerance Unit Notes 1.63 ± 3% V VOCV > VMAX inhibits/terminates charge pulses 0.90 ± 5% V VSEL = BAT2N 1.00 ± 5% V VSEL = Z 1.10 ± 5% V VSEL = BAT1P VFLT Maximum open-circuit voltage 3.00 ± 5% V VCCV > VFLT terminates charge, indicates fault VMIN Minimum battery voltage 0.40 ± 5% V VOCV < VMIN inhibits charge VCE Charge enable 1.40 ± 5% V VOCV < VCE on both cells reinitiates charge Note: Each DC threshold parameter above has a temperature coefficient associated with it. To determine the coefficient for each parameter, use the following formula: Tempco = ParameterRating * -0.5mV/°C 1.63 The tolerance for these temperature coefficients is 10%. 6 bq2902 Timing Symbol (TA = TOPR) Parameter Minimum Typical Maximum Unit Notes tP Pulse period - 12.5 - ms See Figure 2 tPW Pulse width - 10 - ms See Figure 2 Note: Typical is at TA = 25°C. DC Electrical Characteristics (TA = TOPR) Symbol Parameter Minimum Typical Maximum Unit Notes VIH Logic input high VBAT1P - 0.1 - VBAT1P V VSEL VIL Logic input low VSS - VSS + 0.1 V VSEL VOL Logic output low - - 0.8 V IOL = 10mA IOL Output current 10 - - mA @VOL = VSS + 0.8V ICC Supply current - - 250 µA Outputs unloaded, VDC = 5.5V ISB1 Standby current - - 25 µA VDC = 0V, VOCV > VEDV ISB2 End-of-discharge standby current - - 1 µA VDC = 0V IL Input leakage - - ±1 µA VSEL IOZ Output leakage in high-Z state -5 - - µA CHG RDSON On resistance - 0.5 - Ω IIL Logic input low - - 70 µA VSEL IIH Logic input high -70 - - µA VSEL IIZ Logic input float -2 - 2 µA VSEL IDC DC charging current - - 300 mA VDC DC charging voltage 3.3 - 5.5 V ILOAD Discharge current - - 400 mA VOP Operating voltage 1.8 - 5.5 V 7 Discharge FET;VBAT1P = 1.8V DC BAT1P bq2902 8-Pin DIP (PN) 8-Pin PN (0.300" DIP) Inches D E1 E A B1 A1 L C B S e G 8 Millimeters Dimension A Min. Max. Min. Max. 0.160 0.180 4.06 4.57 A1 0.015 0.040 0.38 1.02 B 0.015 0.022 0.38 0.56 B1 0.055 0.065 1.40 1.65 C 0.008 0.013 0.20 0.33 D 0.350 0.380 8.89 9.65 E 0.300 0.325 7.62 8.26 E1 0.230 0.280 5.84 7.11 e 0.300 0.370 7.62 9.40 G 0.090 0.110 2.29 2.79 L 0.115 0.150 2.92 3.81 S 0.020 0.040 0.51 1.02 bq2902 8-Pin SOIC Narrow (SN) 8-Pin SN (0.150" SOIC) Inches 9 Millimeters Dimension A Min. Max. Min. Max. 0.060 0.070 1.52 1.78 A1 0.004 0.010 0.10 0.25 B 0.013 0.020 0.33 0.51 C 0.007 0.010 0.18 0.25 D 0.185 0.200 4.70 5.08 E 0.150 0.160 3.81 4.06 e 0.045 0.055 1.14 1.40 H 0.225 0.245 5.72 6.22 L 0.015 0.035 0.38 0.89 bq2902 Data Sheet Revision History Change No. Page No. 1 2 Notes: Description Figure 1. Functional Block Diagram Change 1 = May 1999 C changes from Jan. 1997 B. 10 Nature of Change Updated block diagram bq2902 Ordering Information bq2902 Package Option: PN = 8-pin plastic DIP SN = 8-pin narrow SOIC Device: bq2902 Rechargeable Alkaline Charge/Discharge Controller IC 11 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. 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