9-0756; Rev 0; 1/07 KIT ATION EVALU E L B A IL AVA SMBus Level 2 Battery Charger with Remote Sense The MAX8731A is an SMBus™ programmable multichemistry battery charger. The MAX8731A uses a minimal command set to easily program the charge voltage, charge current, and adapter current limit. The MAX8731A charges one to four Li+ series cells and delivers up to 8A charge current. The MAX8731A drives n-channel MOSFETs for improved efficiency and reduced cost.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ABSOLUTE MAXIMUM RATINGS DCIN, CSSN, CSIN, FBSA, FBSB to GND..............-0.3V to +28V CSSP to CSSN, CSIP to CSIN, PGND to GND ......-0.3V to +0.3V BST to GND ............................................................-0.3V to +32V BST to LX..................................................................-0.3V to +6V DHI to LX.................................................-0.3V to +(VBST + 0.3)V DLO to PGND.......................................
SMBus Level 2 Battery Charger with Remote Sense (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF, VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ELECTRICAL CHARACTERISTICS (continued) (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF, VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS LDO Output Voltage 8.
SMBus Level 2 Battery Charger with Remote Sense (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF, VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.0625 0.125 0.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ELECTRICAL CHARACTERISTICS (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF , VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 16.968 V % CHARGE-VOLTAGE REGULATION 16.
SMBus Level 2 Battery Charger with Remote Sense (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF , VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 103.3 116.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ELECTRICAL CHARACTERISTICS (continued) (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF , VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 2.007 2.089 V 10 30 mV 0 200 mV 0.9 1.
SMBus Level 2 Battery Charger with Remote Sense (VDCIN = VLX = VCSSP = VCSSN = 19V, VBST - VLX = 4.5V, VFBSA = VFBSB = VCSIP = VCSIN = 16.8V, BATSEL = GND = PGND = 0, CLDO = 1µF, VCC = LDO, CREF = 1µF, CDAC = 0.1µF , VDD = 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per Figure 1; TA = -40°C to +85°C, unless otherwise noted.) (Note 2) SMB TIMING SPECIFICATION (VDD = 2.7V to 5.
Typical Operating Characteristics (Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C, unless otherwise noted.) TYPICAL 0 -2 MINIMUM INPUT CURRENT LIMIT = 3.584A 0.2 0 INPUT CURRENT LIMIT = 4.096A -0.2 1.0 2 4 6 8 10 INPUT CURRENT-LIMIT SETTING (A) 0 1 2 3 SYSTEM CURRENT (A) -0.6 VBATT = 8.4V -0.2 8 6 NOT SWITCHING 4 1.5 VBATT = 16.8V VBATT = 8.4V 1.0 -0.4 0 -2 TYPICAL -8 INPUT CURRENT LIMIT = 3.
SMBus Level 2 Battery Charger with Remote Sense (Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C, unless otherwise noted.) CHARGE-VOLTAGE ERROR vs. CHARGE-VOLTAGE SETTING BATTERY-VOLTAGE ERROR vs. CHARGE CURRENT 0.2 0.0 -0.2 -0.4 MAX8731A toc11 0.4 0.3 BATTERY-VOLTAGE ERROR (%) MAX8731A toc10 CHARGE-VOLTAGE ERROR (%) 0.6 0.2 0.1 2 CELLS 0 4 CELLS -0.1 -0.2 3 CELLS -0.6 -0.
Typical Operating Characteristics (continued) (Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C, unless otherwise noted.) REF LOAD REGULATION NOT SWITCHING 0.15 0.3 MAX8731A toc18 MAX8731A toc16 -1 REF ERROR vs. TEMPERATURE 0.20 MAX8731A toc17 LDO LINE REGULATION 0 0.2 REF ERROR (%) -2 -3 -4 REF ERROR (%) 0.10 LDO ERROR (mV) 0.05 0 -0.05 0.1 0 -0.1 -0.10 -0.2 -0.15 -6 -0.20 13 18 VDCIN (V) 23 -0.3 0 0.2 0.
SMBus Level 2 Battery Charger with Remote Sense PIN NAME FUNCTION 1, 12 GND Analog Ground. Connect directly to the paddle. 2 ACIN AC Adapter Detect Input. ACIN is the input to an uncommitted comparator. 3 REF 4.096V Voltage Reference. Bypass REF with a 1µF capacitor to GND. 4 CCS Input Current Regulation Loop-Compensation Point. Connect 0.01µF from CCS to GND. 5 CCI Output Current Regulation Loop-Compensation Point. Connect 0.01µF from CCI to GND.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ADAPTER INPUT R2 100kΩ R1 150kΩ R13 100kΩ D1 CSSP RS1 10mΩ DCIN C1 1μF ACIN CSSN VCC R3 49.9kΩ N R12 33Ω D2 ACOK INPUT BST VDD VDD KBC LDO C11 1μF LDO R4 10kΩ N1 DHI R6 10kΩ C2 0.1μF DHI SCL LX SDA C9 220pF N3 PGND RS2 10mΩ CSIP C3 0.1μF L1 4.3μH L1: SUMIDA CEP125-4R3MC-U IINP R7 10kΩ N2 R11 1Ω DLO SDA N1, N2,: SI4800BDY N3: SI4810BDY C10 0.
SMBus Level 2 Battery Charger with Remote Sense the set point. A third loop (CCS) takes control and reduces the charge current when the adapter current exceeds the input current limit set by the InputCurrent() command. A functional diagram is shown in Figure 2.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense Setting Charge Voltage To set the output voltage, use the SMBus to write a 16-bit ChargeVoltage() command using the data format listed in Table 1. The ChargeVoltage() command uses the WriteWord protocol (see Figure 3). The command code for ChargeVoltage() is 0x15 (0b00010101). The MAX8731A provides a 1.024V to 19.200V charge voltage range, with 16mV resolution. Set ChargeVoltage() below 1.024V to terminate charging.
SMBus Level 2 Battery Charger with Remote Sense Setting Input-Current Limit System current normally fluctuates as portions of the system are powered up or put to sleep. By using the input-current-limit circuit, the output-current requirement of the AC wall adapter can be lowered, reducing system cost. The total input current, from a wall cube or other DC source, is the sum of the system supply current and the current required by the charger.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense ⎡ (ICHARGE × VBATTERY ) ⎤ IINPUT = ILOAD + ⎢ ⎥ + IBIAS (VIN × η) ⎢⎣ ⎥⎦ where η is the efficiency of the DC-DC converter (typically 85% to 95%). To set the input current limit, use the SMBus to write a 16-bit InputCurrent() command using the data format listed in Table 3. The InputCurrent() command uses the Write-Word protocol (see Figure 3). The command code for InputCurrent() is 0x3F (0b00111111).
SMBus Level 2 Battery Charger with Remote Sense The MAX8731A includes a safety feature, which limits the charge voltage when FBS_ or the selector is disconnected. The MAX8731A guarantees that CSIN does not regulate more than 250mV above the selected charging voltage. This also limits the extent to which remote sense can cancel charge-path impedance. Input Current Measurement Use IINP to monitor the system-input current sensed across CSSP and CSSN.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense SMBus Interface The MAX8731A receives control inputs from the SMBus interface. The MAX8731A uses a simplified subset of the commands documented in System Management Bus Specification V1.1, which can be downloaded from www.smbus.org. The MAX8731A uses the SMBus Read-Word and Write-Word protocols (Figure 3) to communicate with the smart battery.
SMBus Level 2 Battery Charger with Remote Sense tLOW B tHIGH C E D F G I H J K L MAX8731A A M SMBCLK SMBDATA tSU:STA tHD:STA tSU:DAT A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW tHD:DAT tHD:DAT tSU:STO tBUF J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION F = ACKNOWLEDGE BIT CLOCKED INTO M
MAX8731A SMBus Level 2 Battery Charger with Remote Sense Table 4.
SMBus Level 2 Battery Charger with Remote Sense Continuous-Conduction Mode With sufficient charge current, the MAX8731A’s inductor current never crosses zero, which is defined as continuous-conduction mode. The regulator switches at 400kHz (nominal) if VCSIN < 0.88 x VCSSP. The controller starts a new cycle by turning on the high-side MOSFET and turning off the low-side MOSFET.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense Compensation The charge-voltage and charge-current regulation loops are independent and compensated separately at the CCV, CCI, and CCS. CCV Loop Compensation The simplified schematic in Figure 7 is sufficient to describe the operation of the MAX8731A when the voltage loop (CCV) is in control. The required compensation network is a pole-zero pair formed with CCV and RCV.
SMBus Level 2 Battery Charger with Remote Sense 1 RL ⋅ ≅ (1+ sCOUT × RL ) sCOUT If RESR is small enough, its associated output zero has a negligible effect near crossover and the loop-transfer function can be simplified as follows: RCV LTF = GMOUT × GMV sCOUT Setting LTF = 1 to solve for the unity-gain frequency yields: fCO _ CV = GMOUT × GMV × RCV 2π × COUT For stability, choose a crossover frequency lower than 1/10 the switching frequency.
The loop-transfer function is given by: LTF = GMOUT × A CSI × RS2 × GMI ROGMI 1+ sROGMI × CCI This describes a single-pole system. Since: 1 GMOUT = A CSI × RS2 the loop-transfer function simplifies to: LTF = GMI ROGMI 1+ sROGMI × CCI The crossover frequency is given by: GMI fCO _ CI = 2πCCI CCS Loop Compensation The simplified schematic in Figure 11 is sufficient to describe the operation of the MAX8731A when the input current-limit loop (CCS) is in control.
SMBus Level 2 Battery Charger with Remote Sense fCO _ CS = the device). Unlike the DLO output, the DHI output uses a 50ns (typ) delay time to prevent the low-side MOSFET from turning on until DHI is fully off. The same considerations should be used for routing the DHI signal to the high-side MOSFET.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense where tTRANS is the driver’s transition time and can be calculated as follows: ⎛ 1 1 ⎞ 2QG t TRANS = ⎜ + , and fSW ≈ 400kHz ⎟× ⎝ IGsrc IGsnk ⎠ IGATE IGATE is the peak gate-drive current.
SMBus Level 2 Battery Charger with Remote Sense ⎛ V ⎞ BATT ( VDCIN − VBATT ) ⎟ IRMS = ICHG ⎜ ⎜ ⎟ VDCIN ⎝ ⎠ The input capacitors should be sized so that the temperature rise due to ripple current in continuous conduction does not exceed approximately +10°C. The maximum ripple current occurs at 50% duty factor or VDCIN = 2 x VBATT, which equates to 0.5 x ICHG. If the application of interest does not achieve the maximum value, size the input capacitors according to the worst-case conditions.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense Good PCB layout is required to achieve specified noise immunity, efficiency, and stable performance. The PCB layout artist must be given explicit instructions—preferably, a sketch showing the placement of the powerswitching components and high-current routing. Refer to the PCB layout in the MAX8731A evaluation kit for examples. A ground plane is essential for optimum performance.
SMBus Level 2 Battery Charger with Remote Sense QFN THIN.EPS PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm 21-0140 K 1 2 ______________________________________________________________________________________ 31 MAX8731A 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.
MAX8731A SMBus Level 2 Battery Charger with Remote Sense Package Information (continued) (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.) PACKAGE OUTLINE, 16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm 21-0140 K 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.
