bq24401 Programmable NiCd/NiMH Fast-Charge Management Device Features General Description Ø Safe management of fast charge for NiCd and NiMH Ø High-frequency switching controller for efficient and simple charger design Ø Ø Pre-charge qualification for detecting shorted, damaged, or overheated cells Fast-charge termination by ∆T/∆t maximum temperature, and maximum charge time Ø Selectable top-off mode for achieving maximum capacity in NiMH batteries Ø Programmable trickle-charge mode for reviving deeply discharged batteries and for postcharge maintenance Ø Built-in battery removal and insertion detection Ø Sleep mode for low power consumption Pin Connections The bq24401 is a programmable, monolithic IC for fast-charge management of nickel cadmium (NiCd) and nickel metal-hydride (NiMH). Depending on the chemistry, the b q 2 44 0 1 p r o v i de s a n u m b e r o f charge termination criteria: l Rate of temperature rise, ∆T/∆t (for NiCd and NiMH) l Maximum temperature l Maximum charge time For safety, the bq24401 inhibits fast charge until the battery voltage and temperature are within user-defined limits. If the battery voltage is below the low-voltage threshold, the bq24401 uses trickle-charge to condition the battery. For NiMH batteries, the bq24401 provides an optional top-off charge to maximize the battery capacity. The integrated high-frequency comparator allows the bq24401 to be the basis for a complete, high-efficiency power-conversion circuit. Pin Names SNS 1 8 MOD VSS 2 7 VCC LED 3 6 RC BAT 4 5 TS SNS Current-sense input VSS System ground LED Charge-status output BAT Battery-voltage input 8-Pin DIP or Narrow SOIC or TSSOP PN-2000.eps SLUS497–SEPTEMBER 2001 1 TS Temperature-sense input RC Timer-program input VCC Supply-voltage input MOD Modulation-control output bq24401 Pin Descriptions SNS RC Current-sense input Timer-program input RC input used to program the maximum charge-time, hold-off period, and trickle rate during the charge cycle, and to disable or enable top-off charge Enables the bq24401 to sense the battery current via the voltage developed on this pin by an external sense-resistor connected in series with the battery pack VSS System Ground VCC Supply-voltage input LED Charge-status output MOD Modulation-control output Open-drain output that indicates the charging status by turning on, turning off, or flashing an external LED BAT Push-pull output that controls the charging current to the battery. MOD switches high to enable charging current to flow and low to inhibit charging- current flow. Battery-voltage input Functional Description Battery-voltage sense input. A simple resistive divider, across the battery terminals, generates this input. TS The bq24401 is a versatile, NiCd, NiMH battery-charge control device. See Figure 1 for a functional block diagram and Figure 2 for the state diagram. Temperature-sense input Input for an external battery-temperature monitoring circuit. An external resistive divider network with a negative temperature-coefficient thermistor sets the lower and upper temperature thresholds. TS Voltage Reference BAT OSC Voltage Comparator ADC ∆T/∆t ALU Clock Phase Generator Timer Charge Control LED Voltage Comparator MOD RC Internal OSC SNS VCC VSS BD2000T.eps Figure 1. Functional Block Diagram 2 bq24401 4.0 V < VCC < 6.0 V Charge Initialization VBAT < VSLP Sleep Mode Battery Voltage (checked at all times) VMCV < VBAT < VSLP VSLP < VBAT < VCC VBAT < VMCV VTS > VHTF Charge Suspended Battery Temperature (sampled every 16 seconds for dT/dt) VTS <VHTF VLBAT < VBAT < VMCV and VHTF < VTS < VLTF VBAT < VLBAT or VTS > VLTF Battery Conditioning Current Regulation VLBAT < VBAT < VMCV and VHTF < VTS < VLTF ∆T/∆t (after hold-off period), or VTS < VTCO or Time = MTO VCC Reset Maintenance Charge No Top-Off Selected? Yes Time = MTO or VTS < VTCO VBAT > VMCV Top-Off Done VBAT > VMCV VCC Reset or Battery Replacement Figure 2. State Diagram 3 UDG-01087 bq24401 Initiation and Charge Qualification Charge Termination The bq24401 initiates a charge cycle when it detects Maximum Charge Time l Application of power to VCC l Battery replacement l Exit from sleep mode The bq24401 sets the maximum charge-time through pin RC. With the proper selection of external resistor and capacitor, various time-out values may be achieved. Figure 3 shows a typical connection. Immediately following initiation, the IC enters a charge-qualification mode. The bq24401 charge qualification is based on battery voltage and temperature. If voltage on pin BAT is less than the internal threshold, VLBAT , the bq24401 enters the charge-pending state. This condition indicates the possiblility of a defective or shorted battery pack. In an attempt to revive a fully depleted pack, the bq24401 enables the MOD pin to trickle-charge at a rate of once every 1.0s. As explained in the section “Top-Off and Pulse-Trickle Charge,” the trickle pulse-width is user-selectable and is set by the value of the resistance connected to pin RC. The following equation shows the relationship between the RMTO and CMTO values and the maximum charge time (MTO) for the bq24401: During this period, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger. A negative-coefficient thermistor, referenced to VSS and placed in thermal contact with the battery, may be used as a temperature-sensing device. Figure 4 shows a typical temperature-sensing circuit. MTO = RMTO ∗ CMTO ∗ 35,988 MTO is measured in minutes, RMTO in ohms, and CMTO in farads. (Note: RMTO and CMTO values also determine other features of the device. See Tables 2 and 3 for details.) Maximum Temperature Similarly, the bq24401 suspends fast charge if the battery temperature is outside the VLTF to VHTF range. (See Table 4.) For safety reasons, however, it disables the pulse trickle, in the case of a battery over-temperature condition (i.e., VTS < VHTF). Fast charge begins when the battery temperature and voltage are valid. During fast charge, the bq24401 compares the battery temperature to an internal high-temperature cutoff threshold, VTCO. As shown in Table 4, high-temperature termination occurs when voltage at pin TS is less than this threshold. NiCd and NiMH Batteries DT/Dt Following qualification, the bq24401 fast-charges NiCd or NiMH batteries using a current-limited algorithm. During the fast-charge period, it monitors charge time, temperature, and voltage for adherence to the termination criteria. This monitoring is further explained in later sections. Following fast charge, the battery is topped off, if top-off is selected. The charging cycle ends with a trickle maintenance-charge that continues as long as the voltage on pin BAT remains below VMCV. When fast charging, the bq24401 monitors the voltage at pin TS for rate of temperature change detection, ∆T/∆t. The bq24401 samples the voltage at the TS pin every 16s and compares it to the value measured 2 samples earlier. This feature terminates fast charge if this voltage declines at a rate of VCC V 161 Min Figure 4 shows a typical connection diagram. Table 1. Charge Algorithm Battery Chemistry NiCd or NiMH Charge Algorithm 1. Charge qualification 2. Trickle charge, if required 3. Fast charge (constant current) 4. Charge termination (∆T/∆t, time) 5. Top-off (optional) 6. Trickle charge 4 bq24401 Table 2. Summary of NiCd or NiMH Charging Characteristics Parameter Value Maximum cell voltage (VMCV) 2V Minimum pre-charge qualification voltage (VLBAT) 950mV High-temperature cutoff voltage (VTCO) 0.225 ∗ VCC High-temperature fault voltage (VHTF) 0.25 ∗ VCC Low-temperature fault voltage (VLTF) 0.5 ∗ VCC bq24401 fast-charge maximum time out (MTO) RMTO ∗ CMTO ∗ 35,988 Fast-charge charging current (IMAX) 0.05/RSNS Hold-off period MTO/32 Top-off charging current (optional) IMAX/16 Top-off period (optional) MTO Trickle-charge frequency 1Hz Trickle-charge pulse-width See Figure 6 Table 3. Temperature-Monitoring Conditions Temperature Condition Action VTS > VLTF Cold battery—checked at all times Suspends fast charge or top-off and timer Allows trickle charge—LED flashes at 1Hz rate during pre-charge qualification and fast charge VHTF < VTS < VLTF Optimal operating range Allows charging VTS < VHTF Suspends fast-charge initiation, does not allow Hot battery—checked during charge qualifitrickle charge—LED flashes at 1Hz rate during cation and top-off and trickle-charge pre-charge qualification VTS < VTCO Battery exceeding maximum allowable temTerminates fast charge or top-off perature—checked at all times Initial Hold-Off Period Table 4. Charge Status Display The values of the external resistor and capacitor connected to pin RC set the initial hold-off period. During this period, the bq24401 avoids early termination by disabling the ∆T/∆t feature. This period is fixed at the programmed value of the maximum charge time divided by 32. hold-off period = Charge Action State Battery absent maximum time - out 32 5 LED Status High impedance Pre-charge qualification 1Hz flash Trickle charge (before fast charge) 1Hz flash Fast charging Low Top-off or trickle High impedance Charge complete High impedance Sleep mode High impedance Charge suspended (VTS > VLTF) 1Hz flash bq24401 2 VCC VSS 7 bq24401 bq2000T CMTO RC 6 RMTO F2000T RCI.eps Figure 3. Typical Connection for the RC Input VCC 2 VSS 7 VCC bq24401 bq2000T RT1 5 TS RT2 N Battery T Pack C F2000TTMC.eps Figure 4. Temperature Monitoring Configuration BAT+ 2 VSS bq24401 bq2000T 4 RB1 BAT RB2 F2000TBVD.eps Figure 5. Battery Voltage Divider 6 bq24401 Charge Current Control Top-Off and Pulse-Trickle Charge The bq24401 controls the charge current through the MOD output pin. The current-control circuit supports a switching-current regulator with frequencies up to 500kHz. The bq24401 monitors charge current at the SNS input by the voltage drop across a sense-resistor, RSNS, in series with the battery pack. See Figure 8 for a typical current-sensing circuit. RSNS is sized to provide the desired fast-charge current (IMAX): Top-off may be desirable on batteries that have a tendency to terminate charge before reaching full capacity. To enable this option, the capacitance value of CMTO connected to pin RC (Figure 3) should be greater than 0.13µF, and the value of the resistor connected to this pin should be less than 15kΩ. To disable top-off, the capacitance value should be less than 0.07µF. The tolerance of the capacitor needs to be taken into account in component selection. IMAX = Once enabled, the top-off is performed over a period equal to the maximum charge time at a rate of 1 16 that of fast charge. 0.05 RSNS If the voltage at the SNS pin is greater than VSNSLO or less than VSNSHI, the bq24401 switches the MOD output high to pass charge current to the battery. When the SNS voltage is less than VSNSLO or greater than VSNSHI, the bq24401 switches the MOD output low to shut off charging current to the battery. Figure 7 shows a typical multi-chemistry charge circuit. Following top-off, the bq24401 trickle-charges the battery by enabling the MOD to charge at a rate of once every 1.0 second. The trickle pulse-width is user-selectable and is set by the value of the resistor RMTO, which is on pin RC. Figure 6 shows the relationship between the trickle pulse-width and the value of RMTO. The typical tolerance of the pulsewidth below 150kΩ is ±10%. Voltage Input As shown in Figure 5, a resistor voltage-divider between the battery pack’s positive terminal and VSS scales the battery voltage measured at pin BAT. During top-off and trickle-charge, the bq24401 monitors battery voltage and temperature. These functions are suspended if the battery voltage rises above the maximum cell voltage (V MCV ) or if the temperature exceeds the high-temperature fault threshold (VHTF). The resistor values RB1 and RB2 are calculated by the following equation: RB1 = N−1 RB2 where N is the number of cells in series. The end-to-end input impedance of this resistive divider network should be at least 200kΩ and no more than 1MΩ. 160 140 120 Shows Tolerance Pulsewidth—ms 100 80 60 40 20 4 3 2 1 2 4 6 8 10 50 100 150 200 250 RMTO—kΩ 2000PNvB3.eps Figure 6. Relationship Between Trickle Pulse-Width and Value of RMTO 7 bq24401 DC+ L1 47 mH Q1 FMMT718 D4 S1A BAT+ + D3 MMSD914LT R7 1 kW C6 47 mF D2 ZHCS1000 D5 MMSD914LT C8 1000 PF VCC + C3 10 mF R2 2 kW Q2 MMBT3904LT1 C7 4.7 PF C9 0.33 mF R9 120 W R1 100kW R4 210 kW R13 10.5 kW + C5 10 mF C4 0.0022 mF BQ24401 1 SNS MOD 8 2 VSS VCC 7 3 LED RC 6 Q3 MMBT3904LT1 D1 RED R8 220 W R5 105 kW R12 100 kW 4 D6 BZT52-C5V1 C2 0.1 mF BAT TS THERM 5 C1 0.1 mF R10 1.1 kW R11 6.81 kW C10 0.01 mF R14 23.2 kW BAT- R3 0.05 W Notes: 1. DC input voltage: 9 V to 16 V 2. Charge current: 1 A 3. L1: 3L global P/N PKSMD-1005-470K-1A Figure 7. Three-Cell NiCd/NiMH 1A Charger 8 bq24401 Temperature Monitoring Sleep Mode The bq24401 measures the temperature by the voltage at the TS pin. This voltage is typically generated by a negative-temperature-coefficient thermistor. The bq24401 compares this voltage against its internal threshold voltages to determine if charging is safe. The bq24401 features a sleep mode for low power consumption. This mode is enabled when the voltage at pin BAT is above the low-power-mode threshold, VSLP. During sleep mode, the bq24401 shuts down all internal circuits, drives the LED output to high-impedance state, and drives pin MOD to low. Restoring BAT below the VMCV threshold initiates the IC and starts a fast-charge cycle. These thresholds are the following: l l l High-temperature cutoff voltage: VTCO = 0.225 ∗ VCC This voltage corresponds to the maximum temperature (TCO) at which fast charging is allowed. The bq24401 terminates fast charge if the voltage on pin TS falls below VTCO. High-temperature fault voltage: VHTF = 0.25 ∗ VCC This voltage corresponds to the temperature (HTF) at which fast charging is allowed to begin. Low-temperature fault voltage: VLTF = 0.5 ∗ VCC This voltage corresponds to the minimum temperature (LTF) at which fast charging or top-off is allowed. If the voltage on pin TS rises above VLTF, the bq24401 suspends fast charge or top-off but does not terminate charge. When the voltage falls back below VLTF, fast charge or top-off resumes from the point where suspended. Trickle-charge is allowed during this condition. Rf RSNS 1 SNS Cf 2 BAT- VSS bq2000T bq24401 Power Supply ground bq2000 ground bq24401 2000TCS.eps Table 3 summarizes these various conditions. Charge Status Display The charge status is indicated by open-drain output LED. Table 4 summarizes the display output of the bq24401. Figure 8. Current-Sensing Circuit Absolute Maximum Ratings Minimum Maximum Unit VCC Symbol VCC relative to VSS -0.3 +7.0 V VT DC voltage applied on any pin, excluding VCC relative to VSS -0.3 +7.0 V TOPR Operating ambient temperature -20 +70 °C TSTG Storage temperature -40 +125 °C TSOLDER Soldering temperature - +260 °C Note: Parameter Notes 10s 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. 9 bq24401 DC Thresholds (TA = TOPR; VCC = 5V ±20% unless otherwise specified) Symbol VTCO VHTF VLTF Parameter Temperature cutoff High-temperature fault Low-temperature fault Rating 0.225 * VCC 0.25 * VCC 0.5 * VCC Tolerance ±5% ±5% ±5% Unit V V V VMCV Maximum cell voltage 2.00 ±2.5% V VLBAT Minimum cell voltage ±5% mV VTHERM TS input change for ∆T/∆t detection 950 VCC − 161 ±25% V/Min 50 ±10 mV Voltage at pin SNS -50 ±10 mV Voltage at pin SNS VSLP High threshold at SNS, resulting in MOD-low Low threshold at SNS, resulting in MOD-high Sleep-mode input threshold VRCH Recharge threshold VSNSHI VSNSLO Notes Voltage at pin TS Voltage at pin TS Voltage at pin TS VBAT > VMCV inhibits fast charge Voltage at pin BAT VCC - 1 ±0.5 V Applied to pin BAT VMCV - 0.1 ±0.02 V At pin BAT Impedance Symbol Parameter Minimum Typical Maximum Unit RBAT Battery input impedance 10 - - MΩ RTS TS input impedance 10 - - MΩ RSNS SNS input impedance 10 - - MΩ Minimum Typical Maximum Unit Timing Symbol (TA = TOPR; VCC = 5V ±20% unless otherwise specified) Parameter dMTO MTO time-base variation -5 - +5 % fTRKL Pulse-trickle frequency 0.9 1.0 1.1 Hz 10 bq24401 Recommended DC Operating Conditions (TA = TOPR) Symbol Condition Minimum Typical Maximum Unit Notes VCC Supply voltage 4.0 5.0 6.0 V ICC Supply current - 0.5 1 mA Exclusive of external loads ICCS Sleep current - - 5 µA VBAT = VSLP VTS Thermistor input 0.5 - VCC V VTS < 0.5V prohibited VOH Output high VCC - 0.2 - - V MOD, IOH = 20mA VOL Output low - - 0.2 V MOD, LED, IOL = 20mA IOZ High-impedance leakage current - - 5 µA LED Isnk Sink current - - 20 mA MOD, LED RMTO Charge timer resistor 2 - 250 kΩ CMTO Charge timer capacitor 0.001 - 1.0 µF Note: All voltages relative to VSS except as noted. Ordering Information bq24401 Package Option: P = 8-pin narrow plastic DIP D = 8-pin narrow SOIC PW = 8-pin TSSOP Device: bq24401 NiCd/NiMH Fast-Charge IC with ∆T/∆t Detection 11 bq24401 8-Pin DIP (P) 0.400 (10,60) 0.355 (9,02) 8 5 0.260 (6,60) 0.240 (6,10) 1 4 0.070 (1,78) MAX 0.325 (8,26) 0.300 (7,62) 0.020 (0,51) MIN 0.015 (0,38) Gage Plane 0.200 (5,08) MAX Seating Plane 0.010 (0,25) NOM 0.125 (3,18) MIN 0.100 (2,54) 0.021 (0,53) 0.015 (0,38) 0.430 (10,92) MAX 0 .010 (0 ,2 5) M 4040082/D 05/98 NOTES: A. All linear dimensions are in inches (millimeters). B. This drawing is subject to change without notice. C. Falls within JEDEC MS-001 12 bq24401 8-Pin SOIC Narrow (D) 14 PINS SHOWN 0.050 (1,27) 0.020 (0,51) 0.010 (0,25) M 0.014 (0,35) 14 8 0.008 (0,20) NOM 0.244 (6,20) 0.228 (5,80) 0.157 (4,00) 0.150 (3,81) Gage Plane 0.010 (0,25) 1 7 05- 85 A 0.044 (1,12) 0.016 (0,40) Seating Plane 0.069 (1,75) MAX 0.010 (0,25) 0.004 (0,10) 0.004 (0,10) PINS ** 8 14 16 A MAX 0.197 (5,00) 0.344 (8,75) 0.394 (10,00) A MIN 0.189 (4,80) 0.337 (8,55) 0.386 (9,80) DIM 4040047 / D 10/96 NOTES: A. All linear dimensions are in inches (millimeters). B. This drawing is subject to change without notice. C. Body dimensions do not include mold flash or protrusion, not to exceed 0.006 (0,15). D. Falls within JEDEC MS-012 13 bq24401 8-Pin TSSOP ~ PW Package Suffix 14 PINS SHOWN 0,30 0,65 0,19 14 0,10 M 8 0,15 NOM 4,50 4,30 6,60 6,20 Gage Plane 0,25 1 7 05- 85 A 0,75 0,50 Seating Plane 0,15 0,05 1,20 MAX PINS ** DIM 0,10 8 14 16 20 24 28 A MAX 3,10 5,10 5,10 6,60 7,90 9,80 A MIN 2,90 4,90 4,90 6,40 7,70 9,60 4040064/F 01/97 NOTES: A. All linear dimensions are in millimeters. B. This drawing is subject to change without notice. C. Body dimensions do not include mold flash or protrusion not to exceed 0,15. D. Falls within JEDEC MO-153 14 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. 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