19-3169; Rev 0; 1/04 Power-Source Selector for Dual-Battery Systems Features The MAX1538 selector provides power-source control for dual-battery systems. The device selects between an AC adapter and dual batteries based on the presence of the three power sources and the state of charge of each battery. The MAX1538 includes analog comparators to detect AC/airline-adapter presence and determine battery undervoltage. Fast analog circuitry allows the device to switch between power sources to implement a break-before-make time, which allows hot swapping of battery packs. The MAX1538 independently performs power-source monitoring and selection, freeing the system power-management µP for other tasks. This simplifies the development of µP power-management firmware and allows the µP to enter standby, reducing system power consumption. ♦ Automatically Detects and Responds to Low-Battery Voltage Condition Battery Insertion and Removal AC-Adapter Presence Airline-Adapter Presence ♦ Step-Down and Step-Up Charger Compatibility ♦ Fast Break-Before-Make Selection Allows Hot Swapping of Power Sources No External Schottky Diodes Needed The MAX1538 supports “relearn mode,” which allows the system to measure and fully utilize battery capacity. In this state, the part allows the selected battery to be discharged even when an AC adapter is present. The MAX1538 can also be used to power the system in an aircraft. On detecting an airline adapter, the MAX1538 automatically disables charging or discharging of battery packs and only allows the system to be powered from the adapter. ♦ Simplifies Power-Management µP Firmware ♦ 4.75V to 28V AC-Adapter Input Voltage Range ♦ Small 28-Pin Thin QFN Package (5mm x 5mm) ♦ 50µA Maximum Battery Quiescent Current ♦ Implements Battery Capacity Relearning ♦ Allows Usage of Aircraft Supply ♦ Direct Drive of P-Channel MOSFETs Ordering Information PART TEMP RANGE PIN-PACKAGE MAX1538ETI -40°C to +85°C 28 Thin QFN The MAX1538 is available in a space-saving 28-pin thin QFN package with a maximum footprint of 5mm x 5mm. Notebook and Subnotebook Computers Internet Tablets ADAPTER SYSTEM LOAD Applications Typical Operating Circuit ACDET CHRG BATSEL RELRN OUT2 AIRDET Dual-Battery Portable Equipment ADPIN REVBLK OUT1 OUT0 EXTLD BATTERY CHARGER MAX1538 ADPBLK VDD CHG_OUT CHGIN MINVA Pin Configuration appears at end of data sheet. CHGA MINVB CHGB DISB GND DISA BATB BATTERY A BATTERY B BATA BATSUP ________________________________________________________________ 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 MAX1538 General Description MAX1538 Power-Source Selector for Dual-Battery Systems ABSOLUTE MAXIMUM RATINGS VEXTLD, VBATSUP, VADPIN, VBATA, VBATB, VCHGIN to GND .................................................-0.3V to +30V VADPPWR to GND...................................-0.3V to (VADPIN + 0.3V) VREVBLK, VADPBLK to GND ...................-0.3V to (VEXTLD + 0.3V) VCHGA, VCHGB, VDISBAT to GND ..........-0.3V to (VCHGIN + 0.3V) VDISA to GND..........................................-0.3V to (VBATA + 0.3V) VDISB to GND..........................................-0.3V to (VBATB + 0.3V) VDD, VCHRG, VBATSEL, VRELRN, VOUT0, VOUT1, VOUT2, VMINVA, VMINVB, VAIRDET, VACDET to GND..........-0.3V to +6V Continuous Power Dissipation (TA = +70°C) 28-Pin Thin QFN 5mm x 5mm (derate 20.8mW/°C above +70°C) ..........................1666.7mW Operating Temperature Range MAX1538ETI ....................................................-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 (VBATA = VBATB = VCHGIN = 16.8V, CVDD= 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER ADPIN, EXTLD Supply Voltage Range CHGIN, BATA, BATB and BATSUP Supply Voltage Range ADPIN, BATA, BATB, BATSUP Quiescent Current (Current from the Highest Voltage Supply) CONDITIONS VBATA = 4.75V to 19V, VBATB = 4.75V to 19V, VBATSUP = 4.75V to 19V, VADPIN = 4.75V to 28V, no external load at VDD MIN TYP MAX UNITS 4.75 28.00 V 4.75 19.00 V VADPIN = highest, VADPPWR = high 21 50 VADPIN = highest, VADPPWR = low 23 54 VBATA = highest, VDISA = high 21 42 VBATA = highest, VDISA = low 24 50 VBATB = highest, VDISB = high 21 42 VBATB = highest, VDISB = low 24 50 VBATSUP = highest 18 40 ADPIN Quiescent Current (ADPIN Current When Not the Highest Voltage) VADPIN = 4.75V to 18V, no external load at VDD VADPPWR = high 0.01 0.5 VADPPWR = low 2.6 6 BATA Quiescent Current (BATA Current When Not the Highest Voltage) VBATA = 4.75V to 19V, no external load at VDD VDISA = high 3.9 6.0 VDISA = low 7.0 12 BATB Quiescent Current (BATB Current When Not the Highest Voltage) VBATB = 4.75V to 19V, no external load at VDD VDISB = high 3.9 6.0 VDISB = low 7.0 12 Adapter selected (REVBLK or ADPBLK pins low) 3.0 6.1 Adapter not selected (REVBLK and ADPBLK pins high) 0.02 1.0 AC or airline state (CHGA, CHGB, and DISBAT pins high) 0.03 1.5 Charge state (CHGA or CHGB pin low, DISBAT pin high) 3.1 6.2 Discharge or relearn state (CHGA or CHGB pin low, DISBAT pin low) 6.1 12.1 EXTLD Quiescent Current CHGIN Quiescent Current 2 µA µA µA µA _______________________________________________________________________________________ µA µA Power-Source Selector for Dual-Battery Systems (VBATA = VBATB = VCHGIN = 16.8V, CVDD= 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 3.270 3.3 3.330 V LINEAR REGULATOR VDD Output Voltage IVDD = 0 to 100µA VDD Power-Supply Rejection Ratio VDD Undervoltage Lockout VBATA or VBATB = 5V to 19V, VADPIN = 5V 1.0 VBATA = VBATB = 5V, VADPIN = 5V to 28V 1.0 VBATA, VBATB, or VADPIN = 5V to 19V, sawtooth at 10V/µs, other supplies = 12V Rising edge, relative to regulation point mV / V 1 -55 -10 mV 0 5.5 V 0.1 1 µA 2.0 2.03 COMPARATORS ACDET, AIRDET Input Voltage Range ACDET, AIRDET Input Bias Current VAIRDET = VACDET = 3V ACDET, AIRDET Trip Threshold Input falling 1.97 ACDET, AIRDET Hysteresis 20 MINV_ Operating Voltage Range MINV_ Input Bias Current BAT_ Minimum Voltage Trip Threshold VMINV_ = 0.93V to 2.6V VBAT_ falling 0.93 2.60 V -50 +50 nA VMINV_ = 0.93V 4.605 4.65 4.695 VMINV_ = 1.5V 7.455 7.5 7.545 VMINV_ = 2.6V 12.93 13 13.07 BAT_ Minimum Voltage Hysteresis BAT_ Pack Removal Detection Threshold 125 VBAT_ falling V mV 1.90 BAT_ Pack Removal Hysteresis 2.0 V mV 2.10 85 V mV GATE DRIVERS (Note 1) ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Source Current (PMOS Turn-Off) VSOURCE = 15V, VPIN = 7.5V 18 60 VSOURCE = 15V, VPIN = 13V 3 15 ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Sink Current (PMOS Turn-On) VSOURCE = 15V, VPIN = 15V 20 70 VSOURCE = 15V, VPIN = 9.5V 10 55 ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-On Clamp Voltage (VPIN to VSOURCE) VSOURCE = 8V to 19V (ADPPWR, REVBLK, and AOPBLK, VSOURCE = 8V to 28V) -11.0 -9.0 VSOURCE = 4.75V to 8V -8.00 mA mA -7.0 V -3.65 _______________________________________________________________________________________ 3 MAX1538 ELECTRICAL CHARACTERISTICS (continued) MAX1538 Power-Source Selector for Dual-Battery Systems ELECTRICAL CHARACTERISTICS (continued) (VBATA = VBATB = VCHGIN = 16.8V, CVDD= 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-On Time VSOURCE = 15V, VPIN = 13V to VPIN = 9V 0.3 0.88 µs ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-Off Time VSOURCE = 15V, VPIN = 9V to VPIN = 13V 0.3 0.88 µs 0.8 V STATE SELECTION INPUTS CHRG, BATSEL, RELRN Input Low Voltage CHRG, BATSEL, RELRN Input High Voltage 2.1 CHRG, BATSEL, RELRN Input Leakage Current VCHRG = VBATSEL = VRELRN = 5.5V V 0.1 1 µA STATE OUTPUTS OUT0, OUT1, OUT2 Sink Current OUT0, OUT1, OUT2 Leakage Current VOUT_ = 0.4V 1 VOUT_ = 5.5V 25 VOUT_ = 5.5V mA 0.1 1 µA TRANSITION TIMES MINV_ Comparator Delay tMINV VBAT_ = 5.5V to VBAT_ = 4.45V 5.5 11 µs AIRDET and ACDET Comparator Delay tADP Falling edge with -20mV overdrive 2.7 6.0 µs 31 ms 10 µs BAT_ Removal Comparator Delay Battery-Insertion Blanking Time Falling edge with -20mV overdrive 10 tBBLANK 13 21 tTRANS 5 7.5 State-Machine Delay MOSFET Turn-On Delay 4 µs 50 _______________________________________________________________________________________ ns Power-Source Selector for Dual-Battery Systems (VBATA = VBATB = VCHGIN = 16.8V, CVDD = 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) MIN MAX UNITS ADPIN, EXTLD Supply Voltage Range PARAMETER 4.75 28.00 V CHGIN, BATA, BATB, and BATSUP Supply Voltage Range 4.75 19.00 V ADPIN, BATA, BATB, BATSUP Quiescent Current (Current from the Highest Voltage Supply) CONDITIONS VBATA = 4.75V to 19V, VBATB = 4.75V to 19V, VBATSUP = 4.75V to 19V, VADPIN = 4.75V to 28V, no external load at VDD VADPIN = highest, VADPPWR = high 50 VADPIN = highest, VADPPWR = low 54 VBATA = highest, VDISA = high 42 VBATA = highest, VDISA = low 50 VBATB = highest, VDISB = high 42 VBATB = highest, VDISB = low 50 VBATSUP = highest 40 1 VADPPWR = low 9 ADPIN Quiescent Current (ADPIN Current When Not the Highest Voltage) VADPIN = 4.75V to 18V, no external load at VDD VADPPWR = high BATA Quiescent Current (BATA Current When Not the Highest Voltage) VBATA = 4.75V to 19V, no external load at VDD VDISA = high 7.5 VDISA = low 16 BATB Quiescent Current (BATB Current When Not the Highest Voltage) VBATB = 4.75V to 19V, no external load at VDD VDISB = high 7.5 VDISB = low 16 EXTLD Quiescent Current CHGIN Quiescent Current µA µA µA µA Adapter selected (REVBLK or ADPBLK pins low) 9.5 Adapter not selected (REVBLK and ADPBLK pins high) 1.0 AC or airline state (CHGA, CHGB, and DISBAT pins high) 1.5 Charge state (CHGA or CHGB pin low, DISBAT pin high) 10 Discharge or relearn state (CHGA or CHGB pin low, DISBAT pin low) µA µA 18.5 LINEAR REGULATOR VDD Output Voltage IVDD = 0 to 100µA VDD Undervoltage Lockout Rising edge, relative to regulation point 3.270 3.330 V -60 -10 mV 0 5.5 V 1.94 2.06 V 0.93 2.60 V VMINV_ = 0.93V 4.59 4.72 VMINV_ = 1.5V 7.4 7.6 VMINV_ = 2.6V 12.86 13.14 COMPARATORS ACDET, AIRDET Input Voltage Range ACDET, AIRDET Trip Threshold Input falling MINV_ Operating Voltage Range BAT_ Minimum Voltage Trip Threshold VBAT_ falling V _______________________________________________________________________________________ 5 MAX1538 ELECTRICAL CHARACTERISTICS MAX1538 Power-Source Selector for Dual-Battery Systems ELECTRICAL CHARACTERISTICS (continued) (VBATA = VBATB = VCHGIN = 16.8V, CVDD = 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL BAT_ Pack Removal Detection Threshold CONDITIONS VBAT_ falling MIN MAX UNITS 1.88 2.12 V GATE DRIVERS (Note 1) ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Source Current (PMOS Turn-Off) VSOURCE = 15V, VPIN = 7.5V 18 VSOURCE = 15V, VPIN = 13V 3 ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Sink Current (PMOS Turn-On) VSOURCE = 15V, VPIN = 15V 20 VSOURCE = 15V, VPIN = 9.5V 10 ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-On Clamp Voltage (VPIN to VSOURCE) VSOURCE = 8V to 19V (ADPPWR, REVBLK, and ADPBLK, VSOURCE = 8V to 28V) -11.7 VSOURCE = 4.75V to 8V -8.00 mA mA -6.5 V -3.50 ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-On Time VSOURCE = 15V, VPIN = 13V to VPIN = 9V 0.88 µs ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, CHGB Turn-Off Time VSOURCE = 15V, VPIN = 9V to VPIN = 13V 0.88 µs 0.8 V STATE SELECTION INPUTS CHRG, BATSEL, RELRN Input Low Voltage CHRG, BATSEL, RELRN Input High Voltage 2.1 V STATE OUTPUTS OUT0, OUT1, OUT2 Sink Current VOUT_ = 0.4V 1 VOUT_ = 5.5V 25 mA TRANSITION TIMES MINV_ Comparator Delay tMINV VBAT_ = 5.5V to VBAT_ = 4.45V 11 µs AIRDET and ACDET Comparator Delay tADP Falling edge with -20mV overdrive 6 µs Battery-Insertion Blanking Time MOSFET Turn-On Delay tBBLANK 12 31 ms tTRANS 5 10 µs Note 1: VPIN refers to the voltage of the driver output. VSOURCE refers to the power source for the driver. ADPPWR, REVBLK, ADPBLK, DISBAT, DISA, DISB, CHGA, and CHGB gate drivers correspond to sources at ADPIN, EXTLD, EXTLD, CHGIN, BATA, BATB, CHGIN, and CHGIN, respectively. Note 2: Guaranteed by design. Not production tested. 6 _______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems VDD vs. TEMPERATURE 3.305 BATTERY INPUT CURRENT (µA) 3.297 35 MAX1538 toc02 MAX1538 toc01 3.298 IBAT_ vs. VBAT_ 3.310 VDD (V) 3.295 3.294 3.300 3.295 3.293 3.292 3.290 30 25 20 15 10 5 3.291 BAT_ HIGHEST SUPPLY 3.290 3.285 0.05 0.10 0.15 0.20 0 -40 -20 VDD LOAD CURRENT (mA) 0 20 40 60 80 4 TEMPERATURE (°C) 6 8 10 12 14 16 BATTERY VOLTAGE (V) ADAPTER INSERTION IBAT_ vs. VBAT_ MAX1538 toc05 4.0 MAX1538 toc04 0 BAT_ NOT HIGHEST SUPPLY 3.5 BATTERY INPUT CURRENT (µA) VDD (V) 3.296 MAX1538 toc03 VDD LOAD REGULATION 3.299 VADPIN 20V VADPIN AND 10V VEXTLD 3.0 VEXTLD VREVBLK 2.5 2.0 0V 20V V ADPBLK 1.5 10V tADP VREVBLK 1.0 0V VADPBLK 0.5 5V VOUT1 0 0V 0 5 10 15 20 10.0µs/div BATTERY VOLTAGE (V) _______________________________________________________________________________________ 7 MAX1538 Typical Operating Characteristics (Circuit of Figure 1. TA = +25°C, unless otherwise noted.) MAX1538 Power-Source Selector for Dual-Battery Systems Typical Operating Characteristics (continued) (Circuit of Figure 1. TA = +25°C, unless otherwise noted.) BATTERY REMOVAL BATTERY INSERTION MAX1538 toc07 MAX1538 toc06 A CONTACT BOUNCE 10V 10V SYSTEM LOAD = 3A B 0V 0V VBATA 0V VOUT0 (10V/div) 0V VEXTLD 10V 5.00ms/div 5.00ms/div A: CONTACT BOUNCE B: BATTERY INSERTION BLANKING TIME = 22ms SOURCE SELECTION CHANGE BATTERY REMOVAL TIMING VBATA = 16.8V BATTERY B REMOVED 5 x MINV 20V VEXTLD 10V MAX1538 toc08 VBATB = 16.8V VBATA = 10V 20V VBATA = 10V MAX1538 toc09 10.2V 10V (tADP FOR t TRANS ADAPTER REMOVAL TIMING) VDISB tTRANS 0V 0V VDISA 10V (10V/div) CBATB = 1µF VDISA 0V VOUT0 (10V/div) SYSTEM LOAD = 3A 2.00µs/div 4.00µs/div SOURCE SELECTION CHANGE MAX1538 toc10 10V 0V 5V 0V VBATSEL VOUT0 VDISB 10V (10V/div) 20V tTRANS INDUCTIVE KICK VDISA 10V (10V/div) NO CAPACITOR AT BATB VBATB AC-COUPLED (5V/div) 2.00µs/div 8 VOUT0 INDUCTIVE KICK 10V SYSTEM LOAD = 3A VBATSEL 10V VDISB (10V/div) 20V 9.6V 10V 10V 0V 5V 0V VEXTLD 9.8V tMINV VOUT0 (10V/div) 10V VDISB (10V/div) 10V VDISA 0V 10V VDISB (10V/div) 10V VDISA 0V VBATB = 16.8V VBATA _______________________________________________________________________________________ VBATB AC-COUPLED (5V/div) Power-Source Selector for Dual-Battery Systems BREAK-BEFORE-MAKE TIMING FIRST SOURCE INSERTION MAX1538 toc11 MAX1538 toc12 5V OUT1 0V OUT2, OUT0 tTRANS 16V MOSFET TURN-OFF TIME MOSFET TURN-ON TIME MOSFET FOR INITIAL DISCHARGE PATH 14V 20V VADPIN 12V MOSFET DRIVERS 10V VREVBLK 10V 8V 0V POWER-UP TIME MOSFET FOR FINAL DISCHARGE PATH 20V 10V VEXTLD 0V 1.00µs/div 200µs/div Pin Description PIN NAME FUNCTION 1 MINVA Minimum Battery A Voltage Set Point. Battery A discharge is prevented if VBATA has fallen below 5 x VMINVA. 2 MINVB Minimum Battery B Voltage Set Point. Battery B discharge is prevented if VBATB has fallen below 5 x VMINVB. 3 BATSEL Battery-Selection Input. Drive to logic low to charge battery A or give discharge preference to battery A. Drive to logic high to charge battery B or give discharge preference to battery B. 4 RELRN Battery-Relearn Logic-Level Input. Drive RELRN high to enable battery-relearn mode. 5 CHRG Charge-Enable Logic-Level Input. Drive CHRG high to enable the charging path from the charger to the battery selected by BATSEL. 6 OUT0 7 OUT1 8 OUT2 9 ACDET AC-Adapter Detection Input. When VACDET is greater than the ACDET trip threshold (2V typ), adapter presence is detected. 10 AIRDET Airline-Adapter Detection Input. When VAIRDET > 2V and VACDET < 2V, the airline-adapter presence is detected. Charging is disabled when an airline adapter is detected. 11 ADPIN Adapter Input. When VADPIN > VBATSUP, the MAX1538 is powered by ADPIN. ADPIN is the supply rail for the ADPPWR MOSFET driver. 12 ADPPWR Adapter-Power P-Channel MOSFET Driver. Connect ADPPWR to the gate of P1 (Figure 1). P1 disconnects the adapter from the system during relearn mode. Exclude P1 and leave ADPPWR disconnected if relearn is not used. ADPPWR is driven relative to ADPIN. ADPPWR and REVBLK are driven with the same control signal. 13 REVBLK Gate Drive for the Reverse-Blocking P-Channel MOSFET. Connect REVBLK to the gate of P2 (Figure 1). P2 enables and disables the AC adapter’s power path. REVBLK is driven relative to EXTLD. REVBLK and ADPPWR are driven with the same control signal. Selector-State Output. This open-drain output indicates the state of the MAX1538. See Table 1 for information on decoding. _______________________________________________________________________________________ 9 MAX1538 Typical Operating Characteristics (continued) (Circuit of Figure 1. TA = +25°C, unless otherwise noted.) MAX1538 Power-Source Selector for Dual-Battery Systems Pin Description (continued) 10 PIN NAME 14 ADPBLK 15, 21 N.C. FUNCTION Gate Drive for the Adapter-Blocking P-Channel MOSFET. Connect ADPBLK to the gate of P3 (Figure 1). P3 enables and disables the battery discharge path. ADPBLK is driven relative to EXTLD. ADPBLK and DISBAT are driven with the same control signal. Not Internally Connected 16 EXTLD External Load. EXTLD is the supply rail for REVBLK and ADPBLK. 17 CHGIN Charger Node Input. CHGIN is the supply rail for DISBAT, CHGA, and CHGB. 18 DISBAT Gate Drive for the Battery-Discharge P-Channel MOSFET. Connect DISBAT to the gate of P4 (Figure 2). P4 disconnects the battery from the system load when charging from a step-up converter. Exclude P4 and leave DISBAT disconnected if using a step-down charger. DISBAT is driven relative to CHGIN. DISBAT and ADPBLK are driven by the same control signal. 19 CHGA Gate Drive for the Charge Battery A P-Channel MOSFET. Connect CHGA to the gate of P6 (Figure 1). P6 enables and disables the charge path into battery A. CHGA is driven relative to CHGIN. CHGA and DISA are driven by the same control signal. 20 CHGB Gate Drive for the Charge Battery B P-Channel MOSFET. Connect CHGB to the gate of P7 (Figure 1). P7 enables and disables the charge path into battery B. CHGB is driven relative to CHGIN. CHGB and DISB are driven by the same control signal. 22 BATB Battery B Voltage Input. Battery undervoltage and absence is determined by measuring BATB. BATB is the supply rail for DISB. 23 DISB Gate Drive for the Discharge from Battery B P-Channel MOSFET. Connect DISB to the gate of P8 (Figure 1). P8 enables and disables the discharge path from battery B. DISB is driven relative to BATB. DISB and CHGB are driven by the same control signal. 24 DISA Gate Drive for the Discharge from Battery A P-Channel MOSFET. Connect DISA to the gate of P5 (Figure 1). P5 enables and disables the discharge path from battery A. DISA is driven relative to BATA. DISA and CHGA are driven by the same control signal. 25 BATA Battery A Voltage Input. Battery undervoltage and absence is determined by measuring BATA. BATA is the supply rail for DISA. 26 BATSUP 27 GND Ground 28 VDD Linear-Regulator Output. Bypass with a 1µF capacitor from VDD to GND. BATSUP powers the MAX1538. Diode OR BATA and BATB to BATSUP externally. ADPIN is diode connected to BATSUP internally. Bypass with a 0.1µF capacitor from BATSUP to GND. ______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems MAX1538 ADAPTER R1 R2 R3 CADAPTER ACDET CHRG AIRDET BATSEL ADPIN ADPPWR FOR RELEARN P1 MODE ONLY RELRN STEP-DOWN CHARGER MAX1538 REVBLK P2 SYSTEM LOAD CSYS RSNS CHARGER INPUT IN EXTLD LOGIC SUPPLY C2 CHARGER OUTPUT P3 ADPBLK CCHG OUT2 OUT P7 P6 CHGIN OUT1 CHGA OUT0 VDD CHGB DISB P8 P5 DISA MINVA BATB CBATB C1 0.1µF R10 R11 BATA D1 D2 CBATA BATSUP GND MINVB R12 C3 0.1µF R13 BATTERY B BATTERY A Figure 1. Step-Down Typical Application Circuit ______________________________________________________________________________________ 11 MAX1538 Power-Source Selector for Dual-Battery Systems ADAPTER R1 EXTERNAL AC/AIRDETECTION CIRCUIT R2 + R3 OUT CADAPTER ACDET CHRG AIRDET BATSEL ADPIN ADPPWR FOR RELEARN P1 MODE ONLY RELRN LOGIC SUPPLY STEP-UP CHARGER MAX1538 CHARGER INPUT IN OUT2 C2 CHARGER OUTPUT P2 OUT1 REVBLK CCHG SYSTEM LOAD OUT0 OUT EXTLD VDD CSYS P3 ADPBLK MINVA DISBAT P4 C1 1µF R10 R11 CHGIN R12 P7 P6 CHGA MINVB CHGB R13 DISB GND P8 P5 DISA BATB CBATB D1 CBATA BATTERY B BATA BATSUP D2 C3 0.1µF BATTERY A Figure 2. Typical Application Circuit for Step-Up/Step-Down Charger 12 ______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems MAX1538 4R BATB R BATTERY B UNDERVOLTAGE LATCH Q S 0.4V ADPIN ADPPWR R Q MINVB EXTLD 4R REVBLK BATA R BATTERY A UNDERVOLTAGE LATCH Q S 0.4V R ADPBLK CHGIN Q MINVA DISBAT ACDET CHGA STATE MACHINE 2V CHGB AIRDET BATA CHRG BATSEL RELRN DISA ADPIN BATSUP BATB LDO VDD DISB REF GND OUT0 OUT1 OUT2 MAX1538 N N N Figure 3. Functional Diagram ______________________________________________________________________________________ 13 OUT1, and OUT0 indicate the state of the selector so the host can properly respond. The MAX1538 can be configured for use with a stepdown battery charger, as shown in Figure 1, or with a step-up/step-down battery charger, as shown in Figure 2. The minimum MAX1538 system requires only six MOSFETs. The MAX1538 provides relearn-mode support with the addition of P1. Relearn mode allows the system to relearn the battery’s capacity without user intervention. Table 1 summarizes the possible states and configurations of the MAX1538. Detailed Description The MAX1538 performs power path selection between an adapter input and two batteries, relieving the host system from the burden of real-time response to powersource changes. The integrated selector implements a fixed break-before-make timer to ensure that power sources are not connected together and yet the load is not left unserviced. The MAX1538 monitors battery and adapter state and presence to determine which source to select and whether to charge the battery. Logic inputs CHRG, BATSEL, and RELRN allow the host to enable/disable charging, select which battery to use, and impose battery discharge even with adapter presence. The MAX1538 automatically detects airline adapters and prevents charging when an airline adapter is detected. Open-drain logic outputs OUT2, Table 1. MAX1538 State Table BATT B (CHGB and DISB) On Off 1 1 0 Charge A A B BATSEL BATT A (CHGA and DISA) RELRN Battery (ADPBLK and DISBAT) OUT0 MOSFET STATE (See Figure 4) OUT1 LOGIC INPUTS Battery OUT2 SOURCE STATE CHG MAX1538 Power-Source Selector for Dual-Battery Systems System (ADPPWR and REVBLK) X X 1 0 0 On Off AC X X 1 0 1 On Off Off On 1 1 1 Charge B AC N X X 1 0 Off On On Off 1 0 0 Relearn A AC X N X 1 1 Off On Off On 1 0 1 Relearn B On Off Off Off 0 1 0 AC adapter On Off Off Off 0 1 1 Airline Off On On Off 0 0 0 Discharge A Off On Off On 0 0 1 Discharge B Off Off Off Off 0 0 0 Idle Adapter AC AC Otherwise AIR X X X X Absent Absent X N X X X 0 N U X X X Absent X N X X 1 Absent U N X X X Absent U U X X X STATE Legend AC AIR Absent AC adapter is present. VACDET and VAIRDET are both above 2V. Airline adapter is present. VACDET is below 2V and VAIRDET is above 2V. External adapter is absent. VACDET and VAIRDET are both below 2V. N N indicates the battery is normal. The battery is normal when it has not tripped the undervoltage latch (5 x VMINV_). See the Battery Presence and Undervoltage Detection section. U U indicates the battery has tripped the undervoltage comparator. An undervoltage battery is detected when VBAT_ goes below 5 x VMINV_. See the Battery Presence and Undervoltage Detection section. Otherwise covers all cases not explicitly shown elsewhere in the table. Otherwise X 14 X X X X X indicates don’t care. The output does not depend on any inputs labeled X. ______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems ADAPTER ADAPTER SWITCH ADAPTER ADAPTER SWITCH SYSTEM SYSTEM BATTERY SWITCH CHARGER ADAPTER SWITCH BATTERY SWITCH CHARGER "A" SWITCH BATTERY SWITCH CHARGER "B" "A" SWITCH SWITCH "B" "A" SWITCH SWITCH BATTERY B DISCHARGE/ RELEARN "B" SWITCH BATTERY A BATTERY B BATTERY A BATTERY B BATTERY A CHARGE SYSTEM AC/AIR Figure 4. MAX1538 Selection States Battery Presence and Undervoltage Detection The MAX1538 determines battery absence and undervoltage and does not allow discharge from an undervoltage battery. A battery is considered undervoltage when VBAT_ < 5 x VMINV_, and remains classified as undervoltage until VBAT_ falls below 2V and again rises above 5 x V MINV . The undervoltage latch is also cleared when the charge path is enabled. Set the battery undervoltage threshold using resistive voltagedividers R10, R11, R12, and R13, as shown in Figure 1. The corresponding undervoltage threshold is: VBATA _ Undervoltage = 5 × VDD × R11 R10 + R11 VBATB _ Undervoltage = 5 × VDD × R13 R12 + R13 To minimize error, use 1% or better accuracy divider resistors, and ensure that the impedance of the divider results in a current about 100 times the MINV_ input bias current at the MINV_ threshold voltage. To optimize error due to 50nA input bias current at MINV_ and minimize current consumption, typically choose resistors (R10 + R11) or (R12 + R13) smaller than 600kΩ. Since batteries often exhibit large changes in their terminal voltage when a load current is removed, further discharge after the undervoltage latch has been set is not allowed until the battery is removed or the charge path to the battery is selected. Battery removal is detected when VBAT_ falls below 2V. For correct detection of battery removal, ensure that the leakage current into BAT_ is lower than the leakage current out of BAT_ so that BAT_ falls below 2V when the battery is removed. The contributors to leakage current into BAT_ are D1, D2, P6, and P7. Battery Relearn Mode The MAX1538 implements a battery relearn mode, which allows for host-device manufacturers to implement a mode for coulomb-counting fuel gauges (such as the MAX1781) to measure battery capacity without user intervention. In battery relearn mode, the AC adapter is switched off and battery discharge is selected. In this implementation, the host system could prompt users when their battery capacity becomes inaccurate, use the host system as a load to discharge the battery, and then recharge the battery fully. Coulomb-counting fuel-gauge accuracy is increased after a relearning cycle. Battery relearn mode requires the addition of MOSFET P1, which blocks current from the adapter to the system. To enable relearn mode, drive RELRN high and drive BATSEL low to relearn battery A or high to relearn battery B. Relearn mode overrides the functionality of the CHG pin. Battery relearn mode does not occur when the selected battery’s undervoltage latch has been set, or when the selector is in airline mode (see the Airline Mode and AC Adapter section.) The RELRN pin only applies when an AC adapter is present. If the AC adapter is absent and RELRN is ignored, OUT[2:1] = 10 when the MAX1538 is in battery relearn mode. If CHG = 0, only OUT2 is needed to indicate that the MAX1538 was properly placed in relearn mode. If the selected battery trips the undervoltage latch when in relearn mode, the AC adapter is switched in without causing a crash to the system. OUT2 can indicate that the relearn cycle is terminated due to battery undervoltage. Typically, after the host system performs a battery relearn cycle, it either charges the discharged battery or begins a relearn cycle on the other battery. To switch to charge mode, drive RELRN low and CHG high. Since RELRN overrides CHG, in many applications it is best to permanently keep CHG high and reduce the IO needed to control the selector. When the AC adapter is available, it is used as the power source for EXTLD unless the RELRN pin is high. In this state, the charger can be enabled and a battery charged. ______________________________________________________________________________________ 15 MAX1538 ADAPTER MAX1538 Power-Source Selector for Dual-Battery Systems Airline Mode and AC Adapter The MAX1538 provides compatibility with airline adapters. For airplane safety, the use of an airline adapter requires that the battery charger or charge path is disabled. The MAX1538 disables the charge path when an airline adapter is detected. In airline mode, ADPPWR and REVBLK drive P1 and P2 on, and all other MOSFETs are off, regardless of the state of RELRN, CHG, BATSEL, or the batteries. If the AC threshold is above the airline threshold, select a resistive voltage-divider (as shown in Figure 1) according to the following equations: VAC _ Threshold = VACDET _ Threshold × R1+ R2 + R3 R3 VAir _ Threshold = VAIRDET _ Threshold × R1+ R2 + R3 R2 + R3 where VACDET_Threshold and VAIRDET_Threshold are typically 2.0V (see the Electrical Characteristics). An AC adapter is detected when the adapter voltage is above VAC_Threshold, and an airline adapter is detected when the adapter voltage is between V AC_Threshold and VAIR_Threshold. To minimize error, use 1% accuracy or better divider resistors, and ensure that the impedance of the divider results in a current about 100 times the ACDET and AIRDET input bias current. To optimize error due to 1µA input bias current at ACDET/AIRDET and minimize current consumption, typically choose R3 less than 20kΩ. See the Adapter Removal Debouncing section for more information regarding R1, R2, and R3. Short R2 to disable airline-adapter mode. Optionally, an external circuit can be implemented to determine the presence of an AC/airline adapter. The circuit in Figure 5 provides fast detection of an airline adapter, yet allows external circuitry to discriminate between airline and AC adapters. If VAC_Threshold < V AIR_Threshold, this circuit must be used for airlineadapter detection. Other permutations that directly drive AIRDET instead do not work properly on the MAX1538 because adapter removal is not detected fast enough, causing the system load to crash. OUT[2:0] = 011 if the MAX1538 is in airline-adapter mode. If RELRN = 0 and CHG = 0, only OUT[1:0] are necessary to indicate airline-adapter mode. ADAPTER INSERTION EXTERNAL AC/AIRLINE DETECTION CIRCUIT ADAPTER R1 R2 + R3 ACDET MUST WAIT OUT ADPIN FOR AC ADAPTER ACDET P1 FOR AIRLINE ADAPTER AIRDET ADPIN ADPPWR ACDET MAX1538 P2 ADAPTER REMOVAL REVBLK EXTLD ACDET MAY OCCUR BEFORE OR AFTER ADPIN ADPIN FOR AC ADAPTER FOR AIRLINE ADAPTER ACDET Figure 5. Using an External Adapter Detection Circuit 16 ______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems Single Transition Break-Before-Make Selection The MAX1538 guarantees that no supplies are connected to each other during any transition by implementing a fixed delay time (tTRANS, the break-before-make transition timer). This is necessary as the batteries have very low impedances, and momentarily shorting batteries together can cause hundreds of amps to flow. For example, when adapter removal is detected, ADPPWR and REVBLK begin to turn off less than 10µs before ADPBLK and DISBAT begin to turn on, connecting the appropriate battery. For example, upon switching from one battery to another, DISA and CHGA begin turning off less than 10µs before DISB and CHGB begin to turn on. To guarantee a break-before-make time, ensure that the turn-off time of the MOSFETs is smaller than tTRANS (see the MOSFET Selection section). The MAX1538 also guarantees that any change does not cause unnecessary power-source transitions. When switching from battery to battery; battery to adapter; or adapter to battery because of adapter or battery insertion or removal, or due to a change at BATSEL, a single set of MOSFETs are turned off followed by another set of MOSFETs turned on. No additional transitions are necessary. The only exception occurs when RELRN is high and the adapter is inserted because it is first detected as an airline adapter and later detected as an AC adapter. This results in a transition from discharge mode to AC mode, followed by a transition from AC mode to relearn mode. Although this extra transition is generally harmless, it can be avoided by disabling relearn mode when the adapter is absent. case the system holdup capacitor is not large enough to sustain the system load. Battery insertion is automatically debounced using the battery-insertion blanking time (tBBLANK). A battery is not discharged unless the battery has been above the 5 x VMINV threshold for 21ms (typ). After tBBLANK is expired, VBAT_ must exceed 5 x VMINV_ or the battery is detected as undervoltage. Applications Information MOSFET Selection Select P-channel MOSFETs P1–P8 according to their power dissipation, R DSON , and gate charge. Each MOSFET must be rated for the full system load current. Additionally, the battery discharge MOSFETs (P3, P5, P6, P7, and P8) should be selected with low on-resistance for high discharge efficiency. Since for any given switch configuration at least half of the MOSFETs are off, dual MOSFETs can be used without reducing the effective MOSFET power dissipation. When using dual ADAPTER ADPIN FOR RELEARN MODE ONLY P1 ADPPWR MAX1538 STEP-DOWN BATTERY CHARGER SYSTEM LOAD IN P2 REVBLK EXTLD ADPBLK P3 DUAL FDS4935A OUT CHGIN DUAL FDS4935A P7 P6 CHGB DISB DUAL FDS4935A P8 P5 Blanking The MAX1538 implements sophisticated blanking at the adapter and the batteries to correctly determine battery/adapter insertion and removal. Logic inputs CHRG, RELRN, and BATSEL should be debounced to ensure that fast repetitive transitions do not occur, in which CHGA DISA BATB BATA BATTERY B BATTERY A Figure 6. Optimal Use of Power Dissipation Using Dual MOSFETs ______________________________________________________________________________________ 17 MAX1538 CHG Control Toggle CHG to enable the charge path to the battery. Charge control is overridden by RELRN (see the Battery Relearn Mode section) or airline mode (see the Airline Mode and AC Adapter section). When CHG is enabled, the MAX1538 connects the selected battery (BATSEL = 0 for battery A and BATSEL = 1 for battery B) to the charger. OUT[2:1] = 11 if the MAX1538 is in charge mode. When the charge path is enabled, the corresponding battery undervoltage latch is cleared. This allows charging of protected battery packs. In typical applications, connect CHRG to VDD to reduce the system I/O. MAX1538 Power-Source Selector for Dual-Battery Systems MOSFETs, they should be paired as shown in Figure 6 for optimal power dissipation. The MAX1538 provides asymmetric MOSFET gate drive, typically turning MOSFETs on faster than they are turned off. The tTRANS timer ensures that the MOSFETs that are turning on begin to turn on 10µs after those MOSFETs that are turning off begin to turn off. Choose MOSFETs with low enough gate charge that all off-transitioning MOSFETs turn off before any on-transitioning MOSFET turns on. Use the following equations to estimate the worst-case turn-on and turn-off times: t ON = t ON = QG ∆V1 ∆V2 QG + = × 0.93kΩ VG IOFF1 IOFF2 VG slows down as the MOSFET approaches off. See the Typical Operating Characteristics for a scope shot showing MAX1538 turn-on and turn-off times when driving FDS6679 MOSFETs. The MAX1538 typically turns the FDS6679 on in 0.7µs and off in 1µs. Combining the MAX1538 with a Charger To configure the MAX1538 for use with a step-down charger, use the circuit of Figure 7. Connect the charger’s power input to EXTLD. Do not connect the charger’s power input to ADPIN. This ensures that the charger does not bias ADPIN through its high-side MOSFET. System Holdup Capacitor CSYS must be capable of sustaining the maximum system load during the transition time between source selection. Size the capacitor so that: 5V QG QG × = × 0.25kΩ VG ION VG 5 × VMINV − (tMINV + t TRANS + t ON ) × where tON is the turn-on time, tOFF is the turn-off time, QG is the MOSFET’s total gate charge specified at voltage VG, IOFF1 is the 18mA (min) gate current when driving the gate from 7.5V gate drive to 2V gate drive, ∆V1 is the voltage change during the 18mA gate drive (5.5V), IOFF2 is 3mA gate current when driving the gate from 2V to 0V, ∆V2 is the 2V change, and ION is the turn-on current. The MAX1538’s gate-drive current is nonlinear and is a function of gate voltage. For example, the gate driver ISYS _ MAX > VSYS _ MIN CSYS where tMINV is the battery undervoltage comparator delay, t TRANS is the fixed time between switching MOSFETs off and switching MOSFETs on, tON is the time to turn a MOSFET on (see the MOSFET Selection section), VMINV is the lower of VMINVA and VMINVB, ISYS_MAX is the maximum system load, VSYS_MIN is the minimum allowable system voltage before system ADAPTER CADAPTER MAX1538 1µF ADPIN MAX1908 MAX1909 OR MAX1535 SYSTEM LOAD CSYS DCIN P2 CSSP CSSN REVBLK EXTLD C2 P3 ADPBLK BATT CHGIN Figure 7. Combining the MAX1538 with a Charger 18 ______________________________________________________________________________________ Power-Source Selector for Dual-Battery Systems MAX1538 OTHER POWER SOURCE 5 x VMINV OR AC/AIR THRESHOLD EXTLD MAX1538 VSYS_MIN tMINV OR tADP CSOURCE ISOURCE tOFF ADPBLK/REVBLK tTRANS tON PARASITIC INDUCTANCE (LSOURCE) REVBLK/ADPBLK TO BATTERY OR ADAPTER Figure 8. System Holdup Capacitor Timing crash, and CSYS is the total system holdup capacitance, which does not need to be near the MAX1538. The timing related to the system holdup capacitance is shown in Figure 8. Charger output capacitance contributes to CSYS for the step-down charger topology (Figure 1), but not for the step-up/step-down charger topology (Figure 2). Leakage Current into BAT_ Leakage current into BATA or BATB can interfere with proper battery-removal detection. D1 and D2 must be low leakage to ensure that battery removal is properly detected. Choose MOSFETs P6 and P7 with low offleakage current. Board leakage current can also be a problem. For example, neighbor pins BATA and BATSUP should have greater than 50MΩ impedance between each other. Proper battery-removal detection requires that: IBoard + IDS _ OFF(P6) + IDS _ OFF(P7) + ID1_ leakage + ID2 _ leakage < IBAT _ Sink @ 2V where IBoard is board leakage current, IDS_OFF is the off-leakage current of MOSFETs P6 and P7, ID_Leakage is the reverse leakage current of the diodes, and IBAT_Sink@2V is the BAT_ leakage current at 2V (0.4µA; see the Typical Operating Characteristics). Figure 9. Inductive Kick Upon Source Disconnect Inductive “Kick” When the adapter or a battery is delivering a significant current to the system and that path is disabled (typically to enable another path), a voltage spike is generated at the source. This is due to a parasitic inductance shown in Figure 9. When the adapter is disconnected, a positive voltage spike occurs at ADPIN. When a discharging battery is disconnected, a positive voltage spike occurs at BAT_. Connect a capacitor from BAT_ or ADPIN to GND to limit this inductive kick. Choose the source capacitance according to the following equation: CSOURCE > LSOURCE × ISYS _ MAX 302 − VSOURCE 2 2 where V SOURCE is the maximum DC voltage of the source in question, ISYS_MAX is the maximum system load, and L SOURCE (parasitic inductance) and CSOURCE are shown in Figure 9. During battery charge, the voltage spike during battery disconnect is negative. To ensure that this negative voltage spike does not go below 0V, choose CBAT_ according to the following equation: CBAT _ > LBAT _ × ICHG _ MAX 2 2 VBAT _ _ MIN ______________________________________________________________________________________ 19 BATB 21 N.C. 20 CHGB 19 CHGA BATSEL 3 MAX1538 * RELRN 4 18 DISBAT CHRG 5 17 CHGIN OUT0 6 16 EXTLD OUT1 7 15 N.C. IBAT *EXPOSED PADDLE 9 ADPBLK 10 11 12 13 14 8 REVBLK 19V × CBAT _ where IBAT_ is the 3.9µA BAT_ quiescent current (due to a 5MΩ internal resistor), and CBAT_ is the capacitance from BAT_ to GND. When CBAT_ = 1µF, tAbsence_delay corresponds to a 5s time constant. If this time is unacceptable, use a smaller capacitance or connect a resistor or current sink from BAT_ to GND. 20 MINVA 1 MINVB 2 ADPPWR t Absence _ delay = DISA VDD 28 27 26 25 24 23 22 Battery-Absence-Detection Delay When a selected battery is removed, the system load quickly pulls BAT_ below 5 x V MINV_ and another source is selected. The battery is considered present and undervoltage until VBAT_ falls below 2V. Although another power source is quickly switched to the system load, capacitance at BAT_ (see the Inductive "Kick" section) delays the detection of the removed battery. If another battery is inserted before this delay has passed, it is considered undervoltage. Calculate the delay using the following equation: DISB Pin Configuration where VAdapter is the AC-adapter voltage when removing an AC adapter and airline-adapter voltage when removing an airline adapter, CADPIN is the capacitance at ADPIN, and tBounce is the 5ms debounce time. See the Airline Mode and AC Adapter section for a definition of V_Threshold. BATSUP ) BATA ( ADPIN V_ Threshold × tBounce C ADPIN × VAdapter − V_ Threshold AIRDET R1 + R2 + R3 < Because BATA and BATB are high-impedance nodes, prevent leakage current between BATA/BATB and other high-voltage sources by carefully routing traces. Note that flux remaining on the board can significantly contribute to leakage current. See the Leakage Current into BAT_ section. Minimize parasitic inductance in the BATA and BATB path to reduce inductive kick during battery disconnect. This reduces the capacitance requirement at BATA and BATB. GND Adapter Removal Debouncing Upon adapter removal the adapter’s connector may bounce. To avoid false detection of adapter reinsertion select R1, R2, and R3 according to the following equation: Layout The MAX1538 selector fits in a very small layout. Ensure that C1 is placed close to V DD and GND. Connect the paddle to GND directly under the IC. A complete layout example is shown in Figure 10. OUT2 where V BAT__MIN is the minimum battery voltage, ICHG_MAX is the maximum charge current, and LBAT_ is the battery’s inductance. CBAT_ values of 0.01µF are adequate for typical applications. Adding capacitance at BAT_ pins lengthens the time needed to detect battery removal. See the Battery-Absence-Detection Delay section. ACDET MAX1538 Power-Source Selector for Dual-Battery Systems THIN QFN (5mm x 5mm) Chip Information TRANSISTOR COUNT: 5431 PROCESS: BiCMOS ______________________________________________________________________________________ GND BATTERY A GND R11 GND C1 R3 OUT1 7 OUT0 6 CHRG 5 RELRN 4 BATSEL 3 MINVB 2 MINVA 1 4 P5 8 9 10 11 12 13 14 * EXPOSED PADDLE MAX1538 28 27 26 25 24 23 22 VDD OUT2 R2 CBATA GND ACDET 3 BATSUP AIRDET 2 BATA ADPIN R1 CBATSUP R10 P8 DISA ADPPWR 1 DISB REVBLK BATTERY B BATB ADPBLK CBATB 15 N.C. 16 EXTLD 17 CHGIN 18 DISBAT 19 CHGA 20 CHGB 21 N.C. 8 7 5 P3 SYSTEM 1 2 P2 3 6 4 1 8 5 P6 2 7 3 6 P7 6 7 4 5 8 GND CADAPTER ADAPTER CHARGER MAX1538 GND Power-Source Selector for Dual-Battery Systems Figure 10. MAX1538 Layout Example ______________________________________________________________________________________ 21 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.) D2 0.15 C A D b CL D/2 PIN # 1 I.D. QFN THIN.EPS MAX1538 Power-Source Selector for Dual-Battery Systems 0.10 M C A B D2/2 k 0.15 C B PIN # 1 I.D. 0.35x45∞ E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e CL CL L L e e 0.10 C A C 0.08 C A1 A3 PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL COMMON DIMENSIONS DOCUMENT CONTROL NO. REV. 21-0140 C 1 2 EXPOSED PAD VARIATIONS NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL DOCUMENT CONTROL NO. REV. 21-0140 C 2 2 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. 22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.