bq2903 Rechargeable Alkaline Charge/Discharge Controller IC Features General Description ➤ Safe charge of three or four rechargeable alkaline batteries such as Renewal® from Rayovac® The bq2903 is a cost-effective charge controller for rechargeable alkaline batteries such as Renewal batteries from Rayovac. The bq2903 combines sensitive, full-charge detection for three to four rechargeable alkaline cells, with a low-battery cut-off for over-discharge protection. ➤ Pulsed charge terminated with maximum voltage limit ➤ LED outputs indicate charge status ➤ Automatic charge control simplifies charger design Designed for integration into a threeor four-cell system, the bq2903 can improve the service life of the rechargeable alkaline cells by properly managing the charge and discharge. The bq2903 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. ➤ Available in 14-pin 300-mil DIP or 150-mil SOIC Charge completion is indicated when the average charge rate falls below Pin Connections Pin Names ➤ Selectable end-of-discharge voltage prevents overdischarge and improves cycle life ➤ Optional external FET drive allows high current loads ➤ Pre-charge qualification indicates fault conditions BAT1N 1 14 BAT1P BAT2N 2 13 DC BAT3N 3 12 LRTN2 NSEL 4 11 VSS VSEL 5 10 VSS DONE 6 9 LRTN1 CHG 7 8 DRV approximately 6% of the fast charge rate. Status outputs are provided to indicate charge in progress, charge complete, or fault condition. The bq2903 avoids over-depleting the battery by using the internal end-of-discharge control circuitry. The bq2903 also eliminates the external power switching transistors needed to separately charge individual Renewal cells. To reduce external component count, the discharge and charge control FETs are internal to the bq2903; however, if the discharge load is greater than 400mA, a DRV pin is provided to drive an external N-FET, reducing the effective discharge path resistance for the system. For safety, charging is inhibited if the voltage of any cell is greater than 3.0V during charge or if the voltage of any cell is less than 0.4V when not charging (open-circuit voltage). DC Charging supply input BAT1N Battery 1 negative input CHG Battery status output 1 BAT2N Battery 2 negative input DONE Battery status output 2 BAT3N Battery 3 negative input NSEL Number of cells input VSS Battery 4 negative input/ IC ground VSEL End of discharge voltage select input LRTN1, 2 System load returns Battery 1 positive input DRV External FET drive output BAT1P 14-Pin Narrow DIP or SOIC PN290301.eps 6/99 C 1 bq2903 = BAT1P selects an EDV of 1.10V. VSEL floating selects EDV = 1.0V. VSEL =VSS selects EDV = 0.9V. Pin Descriptions DC DC supply input BAT1P This input is used to recharge the rechargeable alkaline cells and power the bq2903 during charge. This input must be connected to a voltage-limited current source. CHG This input connects to the positive terminal of the battery designated BAT1 (see Figure 3). This pin also provides power to the bq2903 when DC is not present. Charge status BAT1N This open-drain output is used to signify the battery charging status and is valid only when DC is applied. See Figure 4 and Table 1. DONE Charge done BAT2N BAT3N Number of cells input Battery 3 negative input This input connects to the negative terminal of the battery designated BAT3 (see Figure 3). VSS End-of-discharge select input Battery 4 negative input/IC ground This input connects to the negative terminal of the battery designated BAT4 (see Figure 3). This three-level input selects the desired endof-discharge cut-off voltage for the bq2903. VSEL DC Battery 2 negative input This input connects to the negative terminal of the battery designated BAT2 (see Figure 3). This input selects whether the bq2903 charges 3 or 4 cells. NSEL = BAT1P selects 4 cells, and NSEL = VSS selects 3 cells. VSEL Battery 1 negative input This input connects to the negative terminal of the battery designated BAT1 (see Figure 3). This open-drain output is used to signify charge completion and is valid only when DC is applied. NSEL Battery 1 positive input 13 4 NSEL 5 VSEL 6 DONE 14 BAT 1P Control/Status Logic 1 BAT 1N 2 BAT 2N 3 BAT 3N 8 DRV 9 LRTN1 12 LRTN CHG 7 2 10 VSS 11 VSS BD290301.eps Figure 1. Functional Block Diagram 2 bq2903 (VOCV<0.4V). If the VOCV of any cell is below VMIN, the bq2903 enters a charge-pending mode and indicates a fault (see Table 1). LRTN1, 2 Load returns These open-drain pull-down outputs are typically used as low-side load switches. High-side load switching is also possible with the addition of an external P-FET DRV If all cells are above VMIN and the minimum operating voltage VOP(min)=2.7V at the DC pin is met, the bq2903 will initiate a charge cycle. A charge cycle consists of pulse charging the battery and then checking for a termination condition. External FET drive output This push-pull output drives an optional external N-FET (see Figure 4). See page 5 for a full description. Charge Termination Once a charge cycle begins, the bq2903 terminates charge when the average charge rate falls below 6% of the maximum charge rate. The bq2903 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). Functional Description Figure 1 is a block diagram outlining the major components of the bq2903. Figure 2 illustrates the charge control and display status during a bq2903 cycle. Table 1 outlines the various operational states and their associated conditions which are described in detail in the following section. Charge Re-Initiation If DC remains valid, the bq2903 will suspend all charge activity after full-charge termination. A charge cycle is reinitiated 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. DC Input This input is used to charge the rechargeable alkaline cells and power the bq2903 during a charge. To charge the batteries, this input should be connected to a current source limited to 300mA. If the DC input current is greater than 300mA, the power dissipation limits of the package will be exceeded. The DC input should also be capable of supplying a minimum of 2.0V*N, where N is the number of cells to be charged. The DC input should not exceed 10V. Charge Status Indication Table 1 and Figure 2 outline the various charge action states and the associated BAT1P, CHG, and DONE output states. The charge status outputs are designed to work with individual or tri-color LED indicators. In all cases, if the voltage at the DC pin is less than the voltage at the BAT1P pin, CHG and DONE outputs are held in a high-impedance condition. Charge Pre-Qualification After DC is applied, the bq2903 checks the open-circuit voltage (VOCV) of each cell for an undervoltage condition Table 1. bq2903 Operational Summary Charge Action State DC absent Charge initiation Charge pending/ fault BAT1P Input CHG Output DONE Output VDC < VBAT1P - Z Z DC applied - - - Conditions 1 VOCV < 0.4V or VCCV > 3.0V 2 - 1 6 sec = Low 1 sec = Z 6 Z Charge pulse VOCV ≤ 1.63V before pulse Charge pulsed @ 100Hz per Figure 1 Low Z Pulse skip VOCV > 1.63V before pulse Pulse skipped per Figure 1 Low Z Average charge rate falls below 6% of the fast charge rate Charge complete Z Low Charge complete Notes: 1. VOCV = Open-circuit voltage of each cell between positive and negative leads. 2. VCCV = Closed-circuit voltage. 3 bq2903 Charging End-of-Discharge Control The bq2903 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 100 Hz rate on the BAT1P pin. When DC is less than the voltage on BAT1P, the bq2903 is powered by the battery at BAT1P. In this state, the batteries discharge down to the level determined by the VSEL pin. The end-of-discharge voltage (VEDV) is selectable by connecting the VSEL pin as outlined in Table 2. If the voltage across any cell is below the voltage specified by the VSEL input, the bq2903 disconnects the battery stack from the load by turning the internal discharge FET off. The DRV output is also driven low, disabling the external FET. After disconnecting power (the battery stack) to the load, the standby current in the bq2903 is reduced to less than 1µA. Typically, higher discharge loads (>200mA) should use a lower discharge voltage cut-off to maximize battery capacity. The bq2903 pulse charges the battery for approximately 7.5ms of every 10ms, when conditions warrant. The bq2903 measures the open circuit voltage (VOCV) of each battery cell during the idle period. If a single-cell potential 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 6% of the maximum charge rate. Once charging is terminated, the internal charging FET remains off, and the DONE output becomes active per Table 1 and Figure 2. With DC applied, the internal discharge FET will always remain on, and the DRV output will remain high. After disconnecting the battery stack from the load, the internal discharge FET remains off, and the DRV output remains low until the batteries are replaced or DC is reapplied, initiating a new charge cycle. DC Valid Charge Complete Charging 2 Pending 1 tP 10ms tPW 7.5ms 3 4 BAT1P 1/6 sec. CHG DONE Notes: 1. 2. 3. 4. Charging Pending: 0.4 < VOCV < 0.4V per cell, VCCV > 3.0V per cell. Charging: 0.4 < VOCV < 1.63V, VCCV < 3.0V. Pulses skipped when VOCV > 1.63V. Charge complete when average charge rate falls below approximately 6% of the fast charge rate. Figure 2. bq2903 Example of Charge Action Events 4 bq2903 DRV Pin Table 2. bq2903 EDV Selections End-of-Discharge Voltage Pin Connection 1.10V VSEL = BAT1P 1.00V VSEL = Z 0.90V VSEL = VSS The bq2903 controls battery discharge with two internal FETs between LRTN1, LRTN2, and VSS. The current through each switch should be limited to 200mA. LRTN1 can be tied to LRTN2 for discharge current of up to 400mA. To reduce the effective discharge switch resistance, or for high current loads, the DRV pin can control an external N-FET, as shown in Figure 4. DRV is “high” when a valid charging voltage is applied to the DC pin and remains “high” during discharge. DRV goes “low” during discharge to turn off the external FET when an end-of-discharge condition is met. This pin should not be connected if the external FET option is not used. Number-of-Cell Selection NSEL is used to select whether the bq2903 will charge 3 or 4 cells. Figure 3 shows the proper connection for a 3or 4-cell system. For 4 cell operation, NSEL = BAT1P. For 3 cell operation, NSEL = VSS and the BAT2N pin should be connected to the BAT3N pin. BAT1P BAT1 BAT2 BAT3 BAT4 BAT1P BAT1 NSEL BAT1N BAT2 BAT2N NSEL BAT1N BAT2N BAT3N BAT3 VSS BAT3N VSS bq2903 bq2903 4-Cell 3-Cell FG290301.eps Figure 3. NSEL Connection Diagram 5 bq2903 DC+ R1 C1 D1 CHG/RED D2 DONE/GREEN 13 7 6 4 5 10 11 DC CHG DONE NSEL VSEL VSS VSS 14 1 2 3 8 9 12 BAT1P BAT1N BAT2N BAT3N DRV LRTN1 LRTN2 C2 R2 C3 C4 R3 R4 Load C5 bq2903 DCQ1 IRF7102 Dual N-Channel MOSFET Optional for Higher Discharge Current or Lower Series Loss Battery and Load Note: Load must be disconected from battery stack while changing FG290302.eps Figure 4. bq2903 Application Example, 4–Cell and 1.0V EDV 6 bq2903 Absolute Maximum Ratings Symbol Parameter Minimum Maximum Unit Notes DCIN VDC -0.3 11.0 V VT DC threshold voltage applied on any pin, excluding DC pin -0.3 11.0 V TOPR Operating ambient temperature 0 +70 °C TSTG Storage temperature -40 +85 °C TSOLDER Soldering temperature - +260 °C IDC DC charging current - 400 mA ILOAD Discharge current - 500 mA No external FET IOL Output current - 20 mA CHG, DONE Note: Commercial 10 sec max. 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. 7 bq2903 DC Thresholds Symbol VMAX VEDV (TA = 25°C; VDC =10V) Parameter Maximum open-circuit voltage End-of-discharge voltage Rating Tolerance Unit Notes 1.63 ± 3% V VOCV > VMAX inhibits or terminates charge pulses 0.90 ± 5% V VSEL = VSS 1.00 ± 5% V VSEL = Z 1.10 ± 5% V VSEL = BAT1P VFLT Maximum closed-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 all cells re-initiates charge Note: Each 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%. Timing Symbol (TA = 25°C) Parameter Minimum Typical Maximum Unit Notes tP Pulse period - 10 - ms See Figure 2 tPW Pulse width - 7.5 - ms See Figure 2 8 bq2903 DC Electrical Characteristics (TA = TOPR) Symbol Parameter Minimum Typical Maximum Unit Notes VIH Logic input high VBAT1P - 0.1 - VBAT1P V VSEL, NSEL VIL Logic input low VSS - VSS + 0.1 V VSEL, NSEL VOL - - 1.0 V Logic output low DONE, CHG, IOL = 5mA - - 0.4 V IOL = 1.0mA, DRV (Greater of VBAT1P or VDC) - 1.0 - - V DRV, IOH = -1.0mA 5 - - mA VOL = VSS + 1.0V, DONE 1 - - mA DRV = VSS + 1.0V VOH Gate drive output IOL Output current CHG, IDC Supply current - 35 250 µA Outputs unloaded, VDC = 10.0V ISB1 Standby current - 25 40 µA VDC = 0, VOCV > VEDV, BAT1P-3N ISB2 End-of-discharge standby current - - 1 µA VDRV = 0V, VDC = 0 IL Input leakage - - ±1 µA NSEL IOZ Output leakage in high-Z state - - ±5 µA CHG, DONE RDSON Discharge on resistance - 0.5 - Ω ILOAD Discharge current without external N-FET - - 400 mA No external FET; LRTN1 (pin 9) must be tied to LRTN2 (pin 12). IIL Logic input low - - 70 µA V= GND to GND + 0.5V, VSEL IIH Logic input high -70 - - µA V = VDC -0.5 to VDC, VSEL IIZ Logic input float -2 - 2 µA VSEL IDC DC charging current - - 300 mA VOP Operating voltage 2.7 - 10 V Note: All voltages relative to VSS. 9 Discharge FETs; VBAT1P = 2.7V, LRTN1 (pin 9) must be tied to LRTN2 (pin 12) bq2903 PN: 14-Pin DIP (0.300") 14-Pin PN (0.300" DIP) Inches Dimension Millimeters Min. Max. Min. Max. A 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 0.740 0.770 18.80 19.56 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 0.070 0.090 1.78 2.29 SN: 14-Pin SN (0.150" SOIC) 14-Pin SN (0.150" SOIC) Inches Dimension 10 Millimeters Min. Max. Min. Max. A 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 0.335 0.350 8.51 8.89 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 bq2903 Data Sheet Revision History Change No. Page No. 1 1 Pin connections LRTN1 (pin 9) was LRTN, LRTN2 (pin 12) was LRTN 1 2 Functional block diagram Updated block diagram 1 3 Pin description Added descriptions for LRTN1 and LRTN2 1 5 DRV pin Clarified LRTN1 and LRTN2 description 1 6 Application example Corrected schematic 1 9 RDSON and ILOAD specification Added notes on LRTN1 and LRTN2 2 7 TOPR Deleted industrial temperature range Notes: Description Nature of Change Change 1 = May 1999 B changes from July 1996. Change 2 = June 1999 C changes from May 1999 B Ordering Information bq2903 Package Option: PN = 14-pin narrow plastic DIP SN = 14-pin narrow SOIC Device: bq2903 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. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER’S RISK. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI’s publication of information regarding any third party’s products or services does not constitute TI’s approval, warranty or endorsement thereof. Copyright 1999, Texas Instruments Incorporated