bq24400 Programmable NiCd/NiMH Fast-Charge Management Device Features General Description Ø Safe management of fast charge for NiCd and NiMH battery packs. 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 peak voltahge (PVD), 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 bq24400 is a programmable, monolithic IC for fast-charge management of nickel cadmium (NiCd) and nickel metal-hydride (NiMH) batteries. The bq24400 provides a number of charge termination criteria: l Peak voltage, PVD (for NiCd and NiMH) l Maximum temperature l Maximum charge time For safety, the bq24400 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 bq24400 uses trickle-charge to condition the battery. For NiMH batteries, the bq24400 provides an optional top-off charge to maximize the battery capacity. The integrated high-frequency comparator allows the bq24400 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 SLUS498 -SEPTEMBER 2001 1 TS Temperature-sense input RC Timer-program input VCC Supply-voltage input MOD Modulation-control output bq24400 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 bq24400 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 bq24400 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 bq24400 4.0 V <V CC <6.0 V Charge Initialization V BAT <V SLP Battery Voltage (PVD checked at rate of MTO/64) Sleep Mode V SLP <V BAT <V CC V BAT <V MCV V TS >V HTF Charge Suspended V MCV <V BAT <V SLP Battery Temperature (checked 1,750 times per second) V TS <V HTF V BAT <V LBAT or V TS >V LTF V LBAT <V BAT <V MCV and V HTF <V TS <V LTF Battery Conditioning Current Regulation V LBAT <V BAT <V MCV and V HTF <V TS <V LTF PVD (after hold-off period), or V TS <V TCO or Time =MTO V CC Reset No Maintenance Charge Top-Off Selected? Yes Time =MTO or V TS <V TCO Top-Off V BAT >V MCV V BAT >V MCV V CC Reset or Battery Replacement Figure 2. State Diagram 3 Done UDG-01088 bq24400 Charge Termination Initiation and Charge Qualification Maximum Charge Time The bq24400 initiates a charge cycle when it detects l Application of power to VCC l Battery replacement l Exit from sleep mode The bq24400 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. The following equation shows the relationship between the RMTO and CMTO values and the maximum charge time (MTO) for the bq24400: Immediately following initiation, the IC enters a charge-qualification mode. The bq24400 charge qualification is based on battery voltage and temperature. If voltage on pin BAT is less than the internal threshold, VLBAT , the bq24400 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 bq24400 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. 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 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. During this period, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger. Similarly, the bq24400 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 bq24400 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 Peak Voltage Following qualification, the bq24400 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. The bq24400 uses a peak-voltage detection (PVD) scheme to terminate fast charge for NiCd and NiMH batteries. The bq24400 continuously samples the voltage on the BAT pin, representing the battery voltage, and triggers the peak detection feature if this value falls below the maximum sampled value by as much as 3.8 mV (PVD). 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. The resistor values RB1 And RB2 are calculated by the following equation: 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 bq24400 2 VCC VSS 7 bq24400 bq2000T CMTO RC 6 RMTO F2000T RCI.eps Figure 3. Typical Connection for the RC Input VCC 2 VSS 7 VCC bq24400 bq2000T RT1 5 TS RT2 N Battery T Pack C F2000TTMC.eps Figure 4. Temperature Monitoring Configuration BAT+ 2 VSS RB1 bq24400 bq2000T 4 BAT RB2 F2000TBVD.eps Figure 5. Battery Voltage Divider 5 bq24400 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 bq24400 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 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 R B1 = N−1 R B2 Table 4. Charge Status Display where N is the number of cells in series. Charge Action State The end-to-end input impedance of this resistive divider network should be at least 200kW and no more than 1MW. Initial Hold-Off Period The values of the external resistor and capacitor connected to pin RC set the initial hold-off period. During this period, the bq24400 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 = LEDStatus Battery absent 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 maximum time - out 32 Top-Off and Pulse-Trickle Charge 6 bq24400 Charge Current Control 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. The bq24400 controls the charge current through the MOD output pin. The current-control circuit supports a switching-current regulator with frequencies up to 500kHz. The bq24400 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): 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. IMAX = 0.05 RSNS If the voltage at the SNS pin is greater than VSNSLO or less than VSNSHI, the bq24400 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 bq24400 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 bq24400 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%. During top-off and trickle-charge, the bq24400 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). 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 R MTO 7 bq24400 DC+ + C6 47 mF D3 MMS D914LT C7 4.7 P F D6 BZT52-C5V1 C2 0.1 mF C8 0.33 mF R12 120 W R1 100kW R6 210 kW R4 12.4 kW + C5 10 mF C4 0.0022 mF D1 RED BAT+ D2 ZHCS 1000 D5 MMS D914LT C9 1000 P F + C3 10 mF R2 2 kW Q2 MMBT3904LT1 VCC R10 1 kW L1 47 mH Q1 FMMT718 D4 S 1A BQ24401 1 S NS MOD 8 2 VS S VCC 7 3 LED RC 6 4 BAT TS 5 R13 1.1 kW Q3 MMBT3904LT1 R11 220 W R7 105 kW THERM C1 0.1 mF R5 20 kW R8 6.81 kW BAT- R3 0.05 W Note s : 1. DC input volta ge : 9 V to 16 V 2. Cha rge curre nt: 1 A 3. L1: 3L globa l P /N P KS MD-1005-470K-1A UDG-01087 Figure 7. Three-Cell NiCd/NiMH 1A Charger 8 bq24400 Temperature Monitoring Sleep Mode The bq24400 measures the temperature by the voltage at the TS pin. This voltage is typically generated by a negative-temperature-coefficient thermistor. The bq24400 compares this voltage against its internal threshold voltages to determine if charging is safe. These thresholds are the following: The bq24400 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 bq24400 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. 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 bq24400 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 bq24400 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 bq24400 bq2000T Power Supply ground bq2000 ground bq24400 Table 3 summarizes these various conditions. 2000TCS.eps Charge Status Display The charge status is indicated by open-drain output LED. Table 4 summarizes the display output of the bq24400. Figure 8. Current-Sensing Circuit 9 bq24400 Absolute Maximum Ratings Symbol Parameter Minimum Maximum Unit VCC 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: 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. DC Thresholds (TA = TOPR; VCC = 5V ±20% unless otherwise specified) Symbol Parameter Temperature cutoff VTCO High-temperature fault VHTF VLTF Low-temperature fault Rating 0.225 * VCC 0.25 * VCC 0.5 * VCC Tolerance ±5% ±5% ±5% Unit Notes V Voltage at pin TS V Voltage at pin TS V Voltage at pin TS VBAT > VMCV inhibits V fast charge mV Voltage at pin BAT mV VMCV Maximum cell voltage 2.00 ±2.5% VLBAT PVD 950 3.8 ±5% ±20% 50 ±10 mV Voltage at pin SNS -50 ±10 mV Voltage at pin SNS VSLP Minimum cell voltage BAT input change for PVD detection 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 VCC - 1 ±0.5 V Applied to pin BAT VMCV - 0.1 ±0.02 V At pin BAT 10 bq24400 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. 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 Timing (TA = TOPR; VCC = 5V ±20% unless otherwise specified) Symbol Parameter Minimum Typical Maximum Unit dMTO MTO time-base variation -5 - +5 % fTRKL Pulse-trickle frequency 0.9 1.0 1.1 Hz 11 bq24400 Ordering Information bq24400 Package Option: P = 8-pin narrow plastic DIP D = 8-pin narrow SOIC PW = 8-pin TSSOP Device: bq24400 NiCd/NiMH Fast-Charge IC with ∆T/∆t Detection 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) Gag e Plane 0.200 (5,08) MAX S e ating 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 .0 1 0 (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 bq24400 8-Pin SOIC Narrow (D) 14 PINS S HOWN 0.050 (1,27) 0.020 (0,51) 0 .0 1 0 (0 ,2 5 ) 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) Gag e Plane 0.010 (0,25) 1 7 05- 85 A 0.044 (1,12) 0.016 (0,40) S e ating 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 4 0 4 0 0 4 7 / D 1 0 /9 6 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 bq24400 8-Pin TSSOP ~ PW Package Suffix 14 PINS S HOWN 0,30 0,65 0,19 14 0 ,1 0 M 8 0,15 NOM 4,50 4,30 6,60 6,20 Gag e Plane 0,25 1 7 05- 85 A 0,75 0,50 S e ating 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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