19-2278; Rev 0; 4/02 Advanced Li+ Battery-Pack Protectors In case of a fault condition, on-board drivers control external P-channel MOSFETs, which disconnect the cells from the pack external terminals. The external protection MOSFETs are connected in a common-source configuration that does not require external pullup resistors. The MAX1894/MAX1924 use only one current-sense resistor to achieve the protection features. All protection thresholds and delays do not require any external components and are trimmed at the factory. If any cell voltage drops below the undervoltage threshold, the MAX1894/MAX1924 disconnect the pack from the load and power down to prevent deep discharge of the pack. The MAX1894/MAX1924 offer a trickle-charge feature, which provides a low-current path to safely charge a deeply discharged pack. The MAX1894/ MAX1924 also have two logic-level inputs, which can be used by a microcontroller to disable the protection MOSFETs and to put the device in shutdown. The MAX1894/MAX1924 have low quiescent current (30µA typ) and ultra-low shutdown current (0.8µA typ) to prevent deep-cell discharge. Features ♦ Protect Against Cell Overvoltage Factory Programmable Limits from 4V to 4.4V Accurate to ±0.5% ♦ Protect Against Cell Undervoltage Factory Programmable Limits from 2V to 3.2V Accurate to ±2.0% ♦ Protect Against Charge, Discharge, and PackShort Current Faults ♦ Automatically Trickle Charges Deeply Discharged Cells ♦ Fully Integrated MOSFET Drivers Do Not Require Pullup Resistors ♦ 0.8µA (typ) Shutdown Supply Current Prevents Deep Discharge of Cells ♦ 30µA (typ) Operating Supply Current ♦ 28V (max) Input Voltage ♦ Available in Small 16-Pin QSOP Package Pin Configuration TOP VIEW B4P 1 16 SRC VCC 2 15 DSO B3P 3 14 CGO IC3 4 The MAX1894X is designed for 4-series battery packs, without hysteresis on the protection thresholds. The MAX1924V and MAX1924X include hysteresis for the 3and 4-series packs, respectively. B2P 5 Applications 13 TKO MAX1894 MAX1924 12 SHDN IC2 6 11 CTL B1P 7 10 PKN IC1 8 9 3- or 4-Series Li+ Battery Packs BN QSOP Ordering Information PART TEMP RANGE PIN-PACKAGE CELLS OVERVOLTAGE OVERVOLTAGE THRESHOLD HYSTERESIS MAX1894XEEE -40°C to +85°C 16 QSOP 4 4.25V* No MAX1924VEEE -40°C to +85°C 16 QSOP 3 4.35V* Yes MAX1924XEEE -40°C to +85°C 16 QSOP 4 4.35V* Yes *Contact factory for alternative threshold voltages. Typical Applications Circuits appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1894/MAX1924 General Description The MAX1894/MAX1924 are lithium-ion/lithium-polymer (Li+) battery-pack protector ICs for 3- or 4-series Li+ battery packs. The MAX1894/MAX1924 enhance the useful operating life of Li+ batteries by monitoring individual cell voltages and preventing over/undervoltage conditions. The MAX1894/MAX1924 also protect the battery pack against charge current, discharge current, and packshort fault conditions. MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors ABSOLUTE MAXIMUM RATINGS SRC, IC2, IC3, VCC to BN.......................................-0.3V to +28V IC1 to BN ..................................................................-0.3V to +6V DSO, TKO, CGO to BN.............................-0.3V to (VSRC + 0.3V) B4P to B3P ...............................................................-0.3V to +6V B3P to B2P ...............................................................-0.3V to +6V B2P to B1P ...............................................................-0.3V to +6V B1P to BN .................................................................-0.3V to +6V CTL, SHDN to PKN...................................................-0.3V to +6V PKN to BN ...................................................................-2V to +2V ESD Protection on All Pins ...............................................±2000V Continuous Power Dissipation (TA = +70°C) 16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VSRC = VB4P + 0.1V, each battery cell voltage (VCELL) = 3.6V, VCTL = VSHDN = VPKN, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SRC Input Current TYP 20 MAX 40 No faults 30 45 µA Undervoltage without charge source 0.8 2 µA Top Cell Sampling Current (Note 2) VCELL = 3.6V 60 µA Intermediate Cell Input Bias Current (Note 3) VCELL = 3.6V 500 pA VCC Undervoltage Lockout Threshold Rising edge, hysteresis = 1% falling edge 4.5 V Charge-Mode Detection Threshold VSRC - VB4P Supply Current (Note 1) Shutdown Supply Current SYMBOL ISUP ISHDN CONDITIONS VSRC - VB_P = 1V 100 4.225 4.250 4.275 MAX1924X, MAX1924V cell voltage rising 4.325 4.350 4.375 VOV_TH Overvoltage Threshold Hysteresis VOV_HYT MAX1924X, MAX1924V cell voltage falling Undervoltage Threshold (Note 4) VUV_TH Cell voltage falling PKN to BN Discharge Current Fault Threshold PKN to BN Charge Current Fault Threshold 2 25 MAX1894X cell voltage rising Overvoltage Threshold (Note 4) PKN to BN Discharge Current Fault Threshold, Pack-Short Condition Discharge or Charge Current Fault to DSO, CGO, TKO Transition Delay Time Discharge Current Fault to DSO Transition Time Delay for PackShort Condition MIN 200 UNITS µA mV V mV 2.260 2.300 2.340 V VOD_TH 130 145 160 mV VOC_TH -120 -100 -80 mV VPS_TH 385 405 425 mV tI-DELAY 2.5 3 3.5 ms tP-DELAY 400 450 500 µs _______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors (VSRC = VB4P + 0.1V, each battery cell voltage (VCELL) = 3.6V, VCTL = VSHDN = VPKN, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Charge-Voltage Comparator Threshold for Resetting Discharge-Current Fault Latch Discharge-Voltage Comparator Threshold for Resetting ChargeCurrent Fault Latch DSO, CGO, and TKO Sink Current SYMBOL DSO, CGO, and TKO Source Current Under/Overvoltage to DSO, CGO, TKO Transition Delay CONDITIONS MIN TYP MAX UNITS VSRC - VB4P 25 100 mV VB4P - VSRC 25 100 mV VSRC = 12V, VPIN = 5V (Note 5) 100 200 µA VSRC = 12V, VPIN = 10V VCTL = 3V (Note 5) 3.5 5 mA 270 320 tV-DELAY SHDN, CTL Input High (Note 6) Rising edge SHDN, CTL Input Low (Note 6) Falling edge SHDN, CTL Input Leakage Current PKN = BN SHDN, CTL Delay to Output Change 370 2.4 ms V 1.2 V 1 µA 50 ns DSO, CGO, TKO Output High (Note 7) VB_P = 4V, VCTL = 3V -0.1 V DSO, CGO, TKO Output Low (Note 7) VB_P = 4V -14 V _______________________________________________________________________________________ 3 MAX1894/MAX1924 ELECTRICAL CHARACTERISTICS (continued) MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors ELECTRICAL CHARACTERISTICS (VSRC = VB4P + 0.1V, each battery cell voltage (VCELL) = 3.6V, VCTL = VSHDN = VPKN, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER SYMBOL SRC Input Current Supply Current (Note 1) Shutdown Supply Current ISUP ISHDN Charge-Mode Detection Threshold CONDITIONS MIN TYP MAX UNITS µA VSRC - VB_P = 1V 40 No faults 50 µA Undervoltage without charge source 2 µA 25 100 mV MAX1894X cell voltage rising 4.21 4.29 MAX1924X, MAX1924V cell voltage rising 4.32 4.38 Cell voltage falling 2.24 2.36 V VSRC - VB4P V Overvoltage Threshold (Note 4) VOV_TH Undervoltage Threshold (Note 4) VUV_TH PKN to BN Discharge-Current Fault Threshold VOD_TH 120 170 mV PKN to BN Charge-Current Fault Threshold VOC_TH -130 -70 mV VPS_TH 345 465 mV tI-DELAY 2 4 ms tP-DELAY 370 480 µs VSRC - VB4P 25 100 mV VB4P - VSRC 25 100 mV DSO, CGO, and TKO Sink Current VSRC = 12V, VPIN = 5V (Note 5) 100 µA DSO, CGO, and TKO Source Current VSRC = 12V, VPIN = 10V VCTL = 3V (Note 5) 3.5 mA PKN to BN Discharge-Current Fault Threshold, Pack Short Condition Discharge- or Charge-Current Fault to DSO, CGO, TKO Transition Delay Time Discharge-Current Fault to DSO Transition Time Delay for Pack Short Condition Charge-Voltage Comparator Threshold for Resetting Discharge-Current Fault Latch Discharge-Voltage Comparator Threshold for Resetting ChargeCurrent Fault Latch Under/Overvoltage to DSO, CGO, TKO Transition Delay 270 tV-DELAY SHDN, CTL Input High (Note 6) Rising edge SHDN, CTL Input Low (Note 6) Falling edge 370 ms 1.2 V 2.4 V Note 1: Average current from the top of the battery pack. Measured at VCC. Note 2: Typical supply current for the top cell during the 0.5ms sampling period. Note 3: Input bias current for this measurement is valid when all cell voltages are equal and the measurement is made over a time greater than 3 seconds. Note 4: Each cell voltage is sampled individually and a differential measurement is made (VB4P - VB3P, VB3P - VB2P, VB2P - VB1P, and VB1P - BN). Note 5: VPIN represents VDSO, VCGO, or VTKO. Note 6: Inputs to SHDN and CTL pins are referred to PKN. Note 7: Measurements are with respect to VSRC. 4 _______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors SUPPLY CURRENT vs. TEMPERATURE 40 SUPPLY CURRENT (µA) 1.0 4-SERIES BATTERY PACK 0.9 0.8 0.7 0.6 2.310 MAX1894 toc03 4-SERIES BATTERY PACK 2.305 CELL VOLTAGE (V) 1.1 SUPPLY CURRENT (µA) 50 MAX1894 toc01 1.2 UNDERVOLTAGE THRESHOLD vs. TEMPERATURE MAX1894 toc02 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 30 20 B1P B3P 2.300 B4P B2P 2.295 10 0.5 0 -40 -15 10 35 60 2.290 -40 85 -15 -40 10 35 60 85 CHARGE-CURRENT FAULT THRESHOLD vs. TEMPERATURE CHARGE-CURRENT FAULT RECOVERY THRESHOLD vs. TEMPERATURE 100 90 B3P 4.350 B4P B2P VB4P - VSRC (mV) 80 B1P 110 100 90 70 60 50 40 4.345 80 30 70 4.340 -40 -15 10 35 60 20 -40 85 -15 10 35 60 -40 85 -15 10 35 60 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) DISCHARGE-CURRENT FAULT THRESHOLD vs. TEMPERATURE DISCHARGE-CURRENT FAULT RECOVERY THRESHOLD vs. TEMPERATURE PACK-SHORT CURRENT FAULT THRESHOLD vs. TEMPERATURE 145 140 410 VPKN - VBN (mV) VB4P - VSRC (mV) 80 85 MAX1894 toc09 90 150 415 MAX1894 toc08 100 MAX1894 toc07 155 VPKN - VBN (mV) -15 TEMPERATURE (°C) 120 VBN - VPKN (mV) CELL VOLTAGE (V) 4.355 85 MAX1894 toc05 MAX1924X 60 130 MAX1894 toc04 4.360 35 TEMPERATURE (°C) TEMPERATURE (°C) OVERVOLTAGE THRESHOLD vs. TEMPERATURE 10 MAX1894 toc06 0.4 70 60 50 40 405 400 30 135 20 -40 -15 10 35 TEMPERATURE (°C) 60 85 395 -40 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX1894/MAX1924 Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) DISCHARGE-CURRENT FAULT TIMING CHARGE-CURRENT FAULT TIMING PACK-SHORT CURRENT FAULT TIMING MAX1894 toc11 MAX1894 toc10 MAX1894 toc12 0 VPKN - VBN 100mV/div VPKN - VBN 200mV/div VPKN - VBN 100mV/div 0 0 DSO 5V/div 0 1ms/div DSO 5V/div CGO 5V/div 0 0 1ms/div 100µs/div Pin Description 6 PIN NAME 1 B4P Cell 4 Positive Connection. Short B4P to B3P for MAX1924V. FUNCTION 2 VCC Supply Input. Connect this pin to the top of the battery pack through a diode and a capacitor (see the Typical Application Circuit). 3 B3P Cell 3 Positive Connection 4 IC3 Internal Connection. Float this pin. 5 B2P Cell 2 Positive Connection 6 IC2 Internal Connection. Float this pin. 7 B1P Cell 1 Positive Connection 8 IC1 Internal Connection. Float this pin. 9 BN Battery Negative. Connection for the cell 1 negative terminal and the top of the current-sense resistor RSENSE. BN is also chip ground. 10 PKN Pack Negative. The sense resistor (RSENSE) is connected between BN and PKN. 11 CTL Control Input. Drive CTL low for normal operation. Drive CTL high to turn off the three external protection MOSFETs. 12 SHDN Shutdown. Drive SHDN low for normal operation. Drive SHDN high to put the device into shutdown if no charger is present. 13 TKO Trickle-Charge Driver Output. TKO drives the gate of an external P-channel trickle-charge MOSFET low (on) in normal operation. 14 CGO Fast-Charge Driver Output. CGO drives the gate of an external P-channel fast-charge MOSFET low (on) in normal operation. 15 DSO Discharge Driver Output. DSO drives the gate of an external P-channel discharge control MOSFET low (on) in normal operation. 16 SRC Common Source Connection for MOSFETs. SRC provides the bias for gate drivers DSO, TKO, and CGO. _______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors Modes of Operation Table 1. Flow Chart Symbol Table SYMBOL DESCRIPTION VOC_TH Charge-Current Fault Threshold (Negative Value) VOD_TH Discharge-Current Fault Threshold VPS_TH Pack-Short Discharge-Current Fault Threshold VUV_TH Undervoltage Threshold VOV_TH Overvoltage Threshold VSRC MOSFET Common Source Voltage VRSENSE Sense Resistor Voltage VOV_HYT Overvoltage Threshold Hysteresis Shutdown Mode OVF Overvoltage Sample Counter The MAX1894/MAX1924 go into shutdown mode under two conditions: the SHDN pin is driven high without a charger applied, or a battery cell undervoltage fault is detected, also without a charger applied. In shutdown mode, the device consumes 0.8µA (typ) on the VCC pin and all MOSFETs are off. The MAX1894/MAX1924 stay in shutdown mode as long as no charging voltage is applied to the battery pack (VSRC is less than the pack voltage). When the battery pack is connected to a charger (VSRC > VB4P + 0.1V) and the pack voltage is above 4.5V, the device goes into normal operating mode and begins monitoring the pack (see Figure 2). UVF Undervoltage Sample Counter Normal Mode In the normal mode of operation, the MAX1894/MAX1924 are in either a standby mode (29µA typ) or sample mode (160µA typ). The device enters the standby mode from shutdown mode. The standby mode lasts for 79ms; then the device goes into the sample mode. During sample mode, the MAX1894/MAX1924 check each cell for overvoltage and undervoltage. Sample mode lasts for 0.5ms; then the MAX1894/MAX1924 return to standby mode. During sample mode, the MAX1894/MAX1924 do not introduce cell mismatch. During normal mode operation, the MAX1894/MAX1924 continuously monitor the voltage across RSENSE for charge or discharge current faults, or battery pack-short faults. Protection Features Overvoltage Protection The MAX1894/MAX1924 provide overvoltage protection to avoid overcharging cells. When an overvoltage fault is detected in four consecutive samples, CGO and TKO go high, stopping the charging process. The MAX1894/MAX1924 continue to sample the cell voltages, and if no overvoltage is detected, CGO and TKO are returned to the normal low state (see Figure 3). The MAX1924 also includes a hysteresis of 200mV. The overvoltage threshold is preprogrammed and requires no external components. The overvoltage threshold is factory set at 4.25V (typ) for the MAX1894 and 4.35V (typ) for the MAX1924. Contact Maxim for more information on threshold levels between 4V and 4.4V. Undervoltage Protection The MAX1894/MAX1924 provide undervoltage protection to avoid overdischarging the cells. With no battery charger present, and an undervoltage fault is detected in four consecutive samples, DSO, CGO, and TKO go high and the device goes into shutdown mode (see Figure 4). If a battery charger is applied to the battery pack and one or more cells are below VUV_TH, then only TKO goes low, allowing trickle-charge current to flow. If no undervoltage is detected in any sample, DSO, CGO, and TKO all go low. The undervoltage threshold is preprogrammed at 2.30V (typ). Contact Maxim for more information on threshold levels between 2V and 3.2V. Charge-Current Fault Protection The MAX1894/MAX1924 protect against excessive charge current by monitoring the voltage developed across RSENSE. RSENSE is connected between BN and PKN. If V RSENSE exceeds the charge-current fault threshold (VOC_TH, typically 100mV) for more than 3ms, the charge current comparator is tripped, setting CGO and TKO high. The charge-current fault condition is latched and is not reset until the MAX1894/MAX1924 detect a reversal in _______________________________________________________________________________________ 7 MAX1894/MAX1924 Detailed Description The MAX1894/MAX1924 battery-pack protectors supervise the charging and discharging process of Li+ cells. Designed for 3-series (MAX1924V) and 4-series (MAX1894X/MAX1924X) applications, these devices monitor the voltage across each cell to provide protection against undervoltage, overvoltage, and overcurrent damage. Output pins CGO, TKO, and DSO control external MOSFET gates. These MOSFETs, in turn, control the fast-charging, trickle-charging, and discharge processes of the battery pack (Figure 1). MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors OVERDISCHARGE PROTECTION PACK + R5 10Ω C5 2.2µF TRICKLE CHARGE 16 15 OVERCHARGE PROTECTION RTKO 510Ω 14 13 D1 CMPSH-3 2 1 R4 51Ω R3 1kΩ R2 1kΩ DSO CGO TKO VCC B4P C6 0.1µF MAX1894X MAX1924X C4 1µF 3 C3 0.1µF BN SRC 4 5 B3P IC3 B2P SHDN C2 0.1µF R1 1kΩ 6 CTL 7 C1 0.1µF 8 9 RSENSE 0.02Ω IC2 12 11 MICROCONTROLLER B1P IC1 BN PKN 10 PACK - Figure 1. Typical Applications Circuit with Trickle Charge the direction of current flow. To reverse the current flow, the charger has to be removed (Figure 5). The sustaining condition for the latch is a 100mV (max) voltage drop across SRC and B4P. Since the charge-current fault threshold between BN and PKN is also 100mV (typ), the RDS_ON of the overcharge protection MOSFET must be greater than the sense resistor in order to ensure a latched state. Discharge-Current Fault Protection The MAX1894/MAX1924 protect against excessive discharge-current by monitoring the voltage developed across RSENSE. If VRSENSE exceeds the discharge-current fault threshold (VOD_TH, typically 145mV) for more 8 than 3ms, the discharge-current comparator is tripped, setting DSO, CGO, and TKO high. Discharge-current fault is latched and is not reset until the MAX1894/MAX1924 detect a reversal in the direction of current flow. To reverse the current flow, a charger must be applied (Figure 6). Pack-Short Current Fault Protection The MAX1894/MAX1924 protect against a shorted pack by monitoring the voltage developed across RSENSE. If VRSENSE exceeds the pack-short threshold (V PS_TH, typically 405mV) for more than 450µs, the pack-short comparator is tripped, setting CGO, DSO, and TKO high. _______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors MAX1894/MAX1924 VUV_TH = 2.3V typ & VOV_TH = 4.25V typ SHUTDOWN PIN OPERATION SHUTDOWN NORMAL OPERATION DSO, CGO, TKO = H VSRC > VB4P + 0.1V NO YES NO TKO = L VCC > 4.5V SHDN = H NO YES YES STANDBY = 79ms NO SHUTDOWN DSO, CGO, TKO = H VCELL < VUV_TH NO YES RESET UVF LATCH UVF = UVF + 1 NO YES VCELL > VOV_TH DSO, CGO, TKO = H YES RESET OVF LATCH OVF = OVF + 1 MAX1924 VOV_HYT = 200mV MAX1894 VOV_HYT = 0 TKO, CGO = H VSRC > VB4P + 0.1V YES CONTROL PIN OPERATION OVF = 4 NORMAL OPERATION NO RESET VOV_TH = 4.25V typ NO NO UVF = 4 CTL = H YES YES DSO, CGO, TKO = H VSRC > VB4P + 0.1V NO YES CGO = DSO = H Figure 2. Undervoltage and Overvoltage Protection Flow Chart Pack-short current fault is latched and is not reset until the MAX1894/MAX1924 detect a reversal in the direction of current flow. A charger must be applied to reverse the current flow (Figure 7). Figure 3. Shutdown and Control Pin Flow Charts Design Procedure Fast and Trickle-Charge Paths The MAX1894/MAX1924 offer the designer the flexibility of two charging paths: a fast charging path and a trickle-charge path (see Figure 1). Trickle charging is enabled and TKO is set low when one or more cells are belows VUV_TH. _______________________________________________________________________________________ 9 MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors UNDERVOLTAGE CONDITION 320ms UNDERVOLTAGE THRESHOLD CELL VOLTAGE SAMPLING DSO, CGO, TKO OVERVOLTAGE CONDITION (MAX1894, NO HYSTERESIS) 320ms 80ms OVERVOLTAGE THRESHOLD CELL VOLTAGE SAMPLING TKO, CGO OVERVOLTAGE CONDITION (MAX1894, WITH HYSTERESIS) 320ms OVERVOLTAGE THRESHOLD CELL VOLTAGE OVERVOLTAGE THRESHOLD HYSTERESIS SAMPLING TKO, CGO Figure 4. Undervoltage and Overvoltage Timing Diagrams 10 ______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors NO OC FAULT VRSENSE < VOC_TH FOR 3ms NO OD FAULT VRSENSE > VOD_TH FOR 3ms YES YES DSO, TKO, CGO = H TKO, CGO = H NO VB4P > VSRC + 0.1V MAX1894/MAX1924 NORMAL OPERATION NORMAL OPERATION YES Figure 5. Charge-Current Fault Set the nominal values of the trickle charge current by selecting resistor RTKO based on the following equation: RTKO = (VCHRG - VPACK)/ITKO where VCHRG is the charger output voltage, VPACK is the battery-pack voltage, and ITKO is the trickle-charge current. When the trickle-charge option is not used, float CGO and connect TKO to the gate of the overcharge protection MOSFET (see Figure 9). When a charger is applied and the voltage on one or more cells is less than VUV_TH, the MAX1894/MAX1924 modulate the TKO output until all cells exceed VUV_TH. NO VSRC > VB4P + 0.1V YES Figure 6. Discharge-Current Fault RSENSE Selection All current faults are detected using a current-sense resistor connected between BN and PKN. The value of this resistor sets the fault current levels. Charge-current fault is given by: IOC _ TH = VOC _ TH RSENSE = 100mV RSENSE Discharge-current fault is given by: IOD _ TH = VOC _ TH RSENSE = 145mV RSENSE Protection FET Drivers All three external MOSFETs have their source pins connected to the SRC pin. When a MOSFET is turned off, FET drivers pull the gate to the SRC voltage. Additional external pullup resistors are not needed. When the MOSFET is turned on, the VGS is limited to -14V by a clamp circuit built in the drivers. This allows use of MOSFETs with maximum VGS of -20V. All three drivers have the same circuitry and drive capability. The quiescent current in normal operation is less than 3µA per driver. Pack-short current fault is given by: IPS _ TH = VPS _ TH RSENSE = 405mV RSENSE Select RSENSE to obtain the desired fault current levels. For example, a 20mΩ RSENSE sets the charge current fault at 5A. Choose an RSENSE that can withstand the dissipation during normal operation and current fault conditions. For example, pack-short current is given by: ______________________________________________________________________________________ 11 MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors Table 2. State Table STATE Undervoltage CTL STATE SHDN STATE CHARGER APPLIED GOES INTO SHUTDOWN MODE TKO CGO DSO L L Yes No L H H L L No Yes H H H Overvoltage L L X No H H L Charge Current Fault L L Yes No H H L Discharge Current Fault L L No No H H H Pack Short Current Fault L L No No H H H Forced Shutdown by External µP X H No Yes H H H X H Yes No H H H CTL H L X No H H H Deep Discharge (VCC < 4.5V) L L Yes No L H H Normal Operation L L X No L L L X: Don’t care. IPS = VCELL × NS N RDSON _ DSO + RDSON _ CGO + RSENSE + RCELL × S NP where NS is the number of cells in series, NP is number of cells in parallel, and V CELL is the cell voltage. Dissipation during pack-short current fault condition is given by: PPS = (IPS )2 × RSENSE The RSENSE chosen should be able to withstand PPS dissipation. Verify power dissipation in normal operation and other current fault conditions as well. Choosing External MOSFETs The external P-channel MOSFETs act as switches to enable or disable charging and discharging of batteries. Different P-channel MOSFETs may be selected depending on the charge and discharge currents anticipated. In most applications, the requirements for fast-charge and discharge MOSFETs are similar and the same type of MOSFETs can be used. The trickle-charge MOSFET can be a small-signal type to minimize cost. The MAX1894/MAX1924 MOSFET drivers have a VGS clamp of -14V typical and MOSFETs with maximum VGS of -20V can be used. MOSFETs must have a V DS greater than the maximum pack voltage. 12 The power dissipation in the MOSFETs is given by: P = I2 RDSON The MOSFET should be chosen to withstand power dissipation during normal operation and all current fault conditions. Additional MOSFETs can be added in parallel to help these requirements. Table 3 lists some suitable MOSFETs in a small SO-8 package. Decoupling Considerations The MAX1894/MAX1924 must have a reliable VCC bias to function properly. A severe overload, such as a short circuit at the pack terminals, can collapse the batterypack voltage below the V CC undervoltage lockout threshold. The use of a diode-capacitor peak detector on the VCC input ensures continued operation during voltage transients on the battery (Figure 1). Since the MAX1894/MAX1924 typically consume only 30µA, D1 and C6 can be small, low-cost components. A 30V Schottky diode with a few mA current capability and a 0.1µF capacitor are sufficient. The MAX1894/MAX1924 continuously monitor the differential voltage between the B4P and SRC inputs to detect the application of a charger. RC filters with similar time constants must be added to both inputs to ensure the differential voltage is not corrupted by noise. ______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors MAX1894/MAX1924 Table 3. MOSFET Selection P-CHANNEL MOSFETS MAXIMUM DRAIN CURRENT (A) IRF7404 6.7 IRF7406 5.8 Si4431 5.8 Si4947 (dual) 3.5 EA NORMAL OPERATION NO VRSENSE > VPS_TH FOR 450µs Protecting and Filtering Cell Inputs Resistors in series with each B_P pin are recommended to limit the current in case there is a short between adjacent B_P pins (see Figure 1). The intermediate cell input bias current is typically 0.5nA. A 1kΩ resistor in series with any intermediate cell moves the overvoltage trip point by typically 0.5mV, which is insignificant compared to the ±25mV tolerance in the overvoltage threshold. The top cell input bias current during sampling period is typically 60µA. To reduce the voltage change on the top cell input due to sampling current, a filter resistance of 10Ω to 50Ω should be added in series with the top cell. To attain the desired filter characteristics, the capacitance across the two top cell input pins should be 1µF. The MAX1894/MAX1924 have internal ESD diodes on each B_P pin for ESD protection up to 2kV. When higher ESD ratings are needed, capacitors (typically 0.1µF) can be added across adjacent B_P pins (see Figure 1). The RC filters improve the device immunity to ESD and filter the noise spikes on B1P–B4P to prevent the MAX1894/MAX1924 from being triggered and latched prematurely by noise spikes. Control Pins SHDN and CTL SHDN and CTL allow external logic or microprocessors to control the MAX1894/MAX1924 gate drivers. Drive CTL high to turn off the three protection MOSFETs: DSO, CGO, and TKO. Drive SHDN high to force the MAX1894/ MAX1924 into shutdown mode (with no charger applied). SHDN and CTL do not affect the state machine. Toggling these two pins does not change the state or reset any fault conditions. If external control circuitry or a microprocessor is not used, connect SHDN and CTL to PKN. YES SET OD = 1 DSO, CGO, TKO = H NO VSRC > VB4P + 0.1V YES Figure 7. Pack-Short Current Fault Layout Considerations Good layout is important to minimize the effects of noise on the system and to ensure accurate voltage and current measurements. Use the appropriate trace widths for the high-current paths and keep traces short to minimize parasitic inductance and capacitance. Minimize current-sense resistor trace lengths and make use of Kelvin connections to the resistor. Provide adequate space and board area for the external MOSFETs and sense resistor to dissipate the heat required. Place RC filters close to B1P–B4P pins. Chip Information TRANSISTOR COUNT: 4259 ______________________________________________________________________________________ 13 MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors SHDN CTL B4P B3P SRC CELL SELECTOR RDY CLOCK HV DRIVER B2P BN OV FAULT B1P CMP REF OVER AND UNDER THRESHOLDS STATE MACHINE DSO SRC UV FAULT FAULT LOGIC HV DRIVER CGO HYSTERESIS BN SRC CMP +145mV HV DRIVER CHARGE CURRENT FAULT PKN CMP -100mV SET/RESET TIMER DISCHARGE-CURRENT FAULT BN PACK-SHORT CURRENT FAULT MAX1894 MAX1924 CMP +405mV BN TKO VCC CMP -50mV DSCHG Q S LATCH ON BIAS 3.5V REG R B4P SRC CMP +50mV CHG RDY UV FAULT SHDN Figure 8. Simplified Functional Diagram 14 ______________________________________________________________________________________ Advanced Li+ Battery-Pack Protectors MAX1894/MAX1924 OVERDISCHARGE PROTECTION R5 10Ω PACK + C5 2.2µF 16 15 OVERCHARGE PROTECTION 14 13 D1 CMPSH-3 2 1 R4 51Ω C4 1µF R3 1kΩ C3 0.1µF R2 1kΩ C2 0.1µF R1 1kΩ C1 0.1µF BN CGO TKO VCC B4P C6 0.1µF 3 4 5 6 7 8 9 RSENSE 0.02Ω SRC DSO B3P MAX1894X MAX1924X IC3 B2P SHDN IC2 CTL B1P 12 11 MICROCONTROLLER IC1 BN PKN 10 PACK - Figure 9. Typical Applications Circuit without Trickle Charge ______________________________________________________________________________________ 15 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QSOP.EPS MAX1894/MAX1924 Advanced Li+ Battery-Pack Protectors Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.