19-4410; Rev 0; 12/08 KIT ATION EVALU E L B AVAILA 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power The MAX8903A is an integrated 1-cell Li+ charger and Smart Power Selector™ with dual (AC adapter and USB) power inputs. The switch mode charger uses a high switching frequency to eliminate heat and allow tiny external components. It can operate with either separate inputs for USB and AC adapter power, or from a single input that accepts both. All power switches for charging and switching the load between battery and external power are included on-chip. No external MOSFETs, blocking diodes, or current-sense resistors are required. The MAX8903A features optimized smart power control to make the best use of limited USB or adapter power. Battery charge current and SYS output current limit are independently set. Power not used by the system charges the battery. Charge current and SYS output current limit can be set up to 2A while USB input current can be set to 100mA or 500mA. Automatic input selection switches the system from battery to external power. The DC input operates from 4.15V to 16V with up to 20V protection, while the USB input has a range of 4.1V to 6.3V with up to 8V protection. The MAX8903A internally blocks current from the battery and system back to the DC and USB inputs when no input supply is present. Other features include prequal charging and timer, fast charge timer, overvoltage protection, charge status and fault outputs, power-OK monitors, and a battery thermistor monitor. In addition, on-chip thermal limiting reduces battery charge rate and AC adapter current to prevent charger overheating. The MAX8903A is available in a 4mm x 4mm, 28-pin thin QFN package. Applications PDAs, Palmtops, and Wireless Handhelds Features ♦ Efficient DC-DC Converter Eliminates Heat ♦ 4MHz Switching for Tiny External Components ♦ Instant On—Works with No Battery or Low Battery ♦ Dual Current-Limiting Input Circuits—AC Adapter or USB Automatic Adapter/USB/Battery Switchover to Support Load Transients 50mΩ System-to-Battery Switch Supports USB Spec ♦ Thermistor Monitor ♦ Integrated Current-Sense Resistor ♦ No External MOSFETS or Diodes ♦ 4.1V to 16V Input Operating Voltage Range Ordering Information PART MAX8903AETI+ TEMP RANGE PIN-PACKAGE -40°C to +85°C 28 Thin QFN-EP** +Denotes a lead(Pb)-free/RoHS-compliant package. **EP = Exposed pad. Typical Operating Circuit AC ADAPTER OR USB LX CS SYS DC Personal Navigation Devices Smart Cell Phones CHARGE CURRENT Portable Multimedia Players Mobile Internet Devices PWM STEP-DOWN Ultra Mobile PCs USB *Protected by US Patent #6,507,172. Smart Power Selector is a trademark of Maxim Integrated Products, Inc. LOAD CURRENT CHARGE AND SYS LOAD SWITCH BAT USB MAX8903A SYSTEM LOAD BATTERY GND Pin Configuration appears at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX8903A General Description MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power ABSOLUTE MAXIMUM RATINGS DC, LX, DCM to GND .............................................-0.3V to +20V DC to SYS .................................................................-6V to +20V BST to GND ...........................................................-0.3V to +26V BST TO LX ................................................................-0.3V to +6V USB to GND .............................................................-0.3V to +9V USB to SYS..................................................................-6V to +9V VL to GND ................................................................-0.3V to +6V THM, IDC, ISET, CT to GND .........................-0.3V to (VL + 0.3V) DOK, FLT, CEN, UOK, CHG, USUS, BAT, SYS, IUSB, CS to GND ................................-0.3V to +6V SYS to BAT ...............................................................-0.3V to +6V PG, EP (exposed pad) to GND .............................-0.3V to +0.3V DC Continuous Current (total in two pins)......................2.4ARMS USB Continuous Current.......................................................1.6A LX Continuous Current (total in two pins).......................2.4ARMS CS Continuous Current (total in two pins) ......................2.4ARMS SYS Continuous Current (total in two pins) .......................3ARMS BAT Continuous Current (total in two pins) .......................3ARMS Continuous Power Dissipation (TA = +70°C) 28-Pin Thin QFN-EP Multilayer (derate 28.6mW/°C above +70°C) ..........2286mW 28-Pin Thin QFN-EP Single-Layer (derate 20.8mW/°C above +70°C)...1666.7mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature Range ............................-40°C to +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 (VDC = VUSB = 5V, VBAT = 4V, circuit of Figure 2, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS 16 V DC INPUT DC Operating Range 4.15 No valid USB input 3.9 4.0 4.1 Valid USB input 4.0 4.3 4.4 16.5 17 17.5 Charger enabled, no switching, VSYS = 5V 2.3 4 Charger enabled, f = 3MHz, VDC = 5V 15 Charger enabled, VCEN = 0V, 100mA USB mode (Note 2) 1 2 Charger enabled, VCEN = 5V, 100mA USB mode (Note 2) 1 2 0.10 0.25 DC Undervoltage Threshold When VDOK goes low, VDC rising, 500mV typical hysteresis DC Overvoltage Threshold When VDOK goes high, VDC rising, 500mV typical hysteresis DC Supply Current VDCM = 0V, VUSUS = 5V V V mA DC High-Side Resistance 0.15 Ω DC Low-Side Resistance 0.15 Ω 0.31 Ω DC-to-BAT Dropout Resistance DC-to-BAT Dropout Voltage Switching Frequency When SYS regulation and charging stops, VDC falling, 200mV hysteresis DC Soft-Start Time 2 15 VDC = 8V, VBAT = 4V 4 VDC = 5V, VBAT = 3V 3 DC Step-Down Output CurrentLimit Step Range DC Step-Down Output Current Limit 0 0.5 VDC = 6V, VSYS = 4V 30 mV MHz 2 RIDC = 3kΩ 1900 2000 2100 RIDC = 6kΩ 950 1000 1050 RIDC = 12kΩ 450 500 550 A mA No valid USB input 1 ms Valid USB input before soft-start 20 µs _______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power (VDC = VUSB = 5V, VBAT = 4V, circuit of Figure 2, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER MIN TYP MAX UNITS VDCM = 0V, VIUSB = 5V 450 475 500 mA DC Output Current 100mA USB Mode (Note 2) VDCM = 0V, VIUSB = 0V 90 95 100 mA SYS to DC Reverse Current Blocking VSYS = 5.5V, VDC = 0V DC Output Current 500mA USB Mode (Note 3) CONDITIONS 0.01 µA USB INPUT USB Operating Range 4.1 USB Standoff Voltage 6.3 V 8 V USB Undervoltage Threshold When VUOK goes low, VUSB rising, 500mV hysteresis 3.95 4.0 4.05 V USB Overvoltage Threshold When VUOK goes high, VUSB rising, 500mV hysteresis 6.8 6.9 7.0 V USB Current Limit USB Supply Current VIUSB = 0V (100mA setting) 90 95 100 VIUSB = 5V (500mA setting) 450 475 500 ISYS = IBAT = 0mA, VCEN = 0V 1.3 3 ISYS = IBAT = 0mA, VCEN = 5V 0.8 2 0.115 0.25 VUSUS = 5V (USB suspend mode) Minimum USB to BAT Headroom 0 USB to SYS Dropout Resistance 15 30 0.2 0.35 mA mA mV Ω VUSB rising 1 ms VDC falling below DC UVLO to initiate USB soft-start 20 µs Minimum SYS Regulation Voltage ISYS = 1A, VBAT < VSYS_MIN 3.0 V Regulation Voltage ISYS = 0A Load Regulation ISYS = 0 to 2A CS to SYS Resistance VDC = 6V, VDCM = 5V, VSYS = 4V, ICS = 1A SYS to CS Leakage VSYS = 5.5V, VDC = VCS = 0V 0.01 BAT to SYS Resistance VDC = VUSB = 0V, VBAT = 4.2V, ISYS = 1A 0.05 0.1 Ω BAT to SYS Reverse Regulation Voltage VUSB = 5V, VDC = 0V, VIUSB = 0V, ISYS = 200mA 50 75 100 mV SYS Undervoltage Threshold SYS falling, 200mV hysteresis (Note 4) 1.8 1.9 2.0 V TA = +25°C 4.179 4.2 4.221 TA = -40°C to +85°C 4.158 4.2 4.242 -150 -100 -60 3 3.1 USB Soft-Start Time SYS OUTPUT 4.3 4.4 4.5 V 40 mV/A 0.07 Ω µA BATTERY CHARGER BAT Regulation Voltage IBAT = 0mA Charger Restart Threshold Change in VBAT from DONE to fast-charge BAT Prequal Threshold VBAT rising, 180mV hysteresis Prequal Charge Current Percentage of fast-charge current set at ISET 2.9 10 V mV V % _______________________________________________________________________________________ 3 MAX8903A ELECTRICAL CHARACTERISTICS (continued) MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power ELECTRICAL CHARACTERISTICS (continued) (VDC = VUSB = 5V, VBAT = 4V, circuit of Figure 2, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER Fast-Charge Current DONE Threshold MIN TYP MAX RISET = 600Ω CONDITIONS 1800 2000 2200 RISET = 1.2kΩ 900 1000 1100 RISET = 2.4kΩ 450 500 550 Percentage of fast-charge, IBAT decreasing 10 RISET Resistor Range 0.6 UNITS mA % 2.4 kΩ ISET Output Voltage 1.5 V ISET Current Monitor Gain 1.25 mA/A BAT Leakage Current No DC or USB input With valid input power, VCEN = 5V 0.05 4 1 6 µA Charger Soft-Start Time 1.0 ms Charger Thermal Limit Temperature 100 °C 5 %/°C Charger Thermal Limit Gain Charge current = 0 at +120°C CHARGER TIMER Prequalification Time CCT = 0.15µF 33 min Fast-Charge Time CCT = 0.15µF 660 min Timer Accuracy -15 Timer Extend Current Threshold Percentage of fast-charge current below which the timer clock operates at half-speed 40 Timer Suspend Current Threshold Percentage of fast-charge current below which timer clock pauses 16 Charge Done Delay Time From done threshold detection until charger turns off and CHG goes high +15 % 50 60 % 20 24 % 15 s THERMISTOR MONITOR THM Threshold, Hot When charging is suspended, 1% hysteresis 0.27 x VVL 0.28 x VVL 0.29 x VVL V THM Threshold, Cold When charging is suspended, 1% hysteresis 0.73 x VVL 0.74 x VVL 0.75 x VVL V THM Threshold, Disabled THM function is disabled below this voltage 0.0254 x VVL 0.03 x VVL 0.036 x VVL V -0.1 +0.001 +0.2 THM Input Leakage THM = GND or VL; TA = +25°C THM = GND or VL; TA = +85°C 0.01 µA THERMAL SHUTDOWN, VL, AND LOGIC I/O: CHG, FLT, DOK, UOK, DCM, CEN, USUS, IUSB High level Logic-Input Thresholds (DCM, CEN, USUS, IUSB) 1.3 Low level 0.4 Hysteresis Logic-Input Leakage Current (DCM, CEN, USUS, IUSB) 4 VINPUT = 0 to 5.5V 50 TA = +25°C 0.001 TA = +85°C 0.01 _______________________________________________________________________________________ V mV 1 µA 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power (VDC = VUSB = 5V, VBAT = 4V, circuit of Figure 2, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS Logic Output Voltage, Low (CHG, FLT, DOK, UOK) TYP MAX Sinking 1mA 8 50 Sinking 10mA 80 Open-Drain Output Leakage VOUT = 5.5V Current, High (CHG, FLT, DOK, UOK) MIN TA = +25°C 0.001 TA = +85°C 0.01 VL Output Voltage VDC = VUSB = 6V, IVL = 0 to 1mA VL UVLO Threshold VVL falling; 200mV hysteresis 4.6 UNITS mV 1 5 µA 5.4 V 3.2 V Thermal Shutdown Temperature 160 °C Thermal Shutdown Hysteresis 15 °C Note 1: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 2: For the 100mA USB mode using the DC input, the step-down regulator is turned off and a low-dropout linear regulator is connected from DC to SYS. Note 3: For the 500mA USB mode, the actual current drawn from USB is less than the output current due to the input/output current ratio of the DC-DC converter. Note 4: For short-circuit protection, SYS sources 25mA below VSYS = 400mV, and 50mA for VSYS between 400mV and 2V. Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) SWITCHING FREQUENCY vs. VDC VDC = 8V 60 50 VDC = 12V 40 30 IBATT = 0.15A 20 IBATT = 1.5A 10 4.0 3.5 VBAT = 3V 3.0 2.5 VBAT = 4V 2.0 1.5 1.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 BATTERY VOLTAGE (V) 4.5 5.0 70 60 VDC = 16V 50 VDC = 11V 40 VDC = 6V 30 VDC = 4.5V 10 0.0 0 80 20 RISET = 1.2kΩ CEN = 0V 0.5 IBATT = 1.5A 90 SYS EFFICIENCY (%) EFFICIENCY (%) 70 SYS EFFICIENCY vs. DC VOLTAGE 100 MAX8903A toc02 VDC = 5V 80 4.5 SWITCHING FREQUENCY (MHz) 90 MAX8903A toc01 100 MAX8903A toc03 BATTERY CHARGER EFFICIENCY vs. BATTERY VOLTAGE 0 4 6 8 10 12 DC VOLTAGE (V) 14 16 1 10 100 1000 10,000 SYS OUTPUT CURRENT (mA) _______________________________________________________________________________________ 5 MAX8903A ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) 1.0 0.8 0.6 CHARGER DISABLED 0.4 80 60 40 20 0 0 2 3 4 5 6 60 50 40 30 20 1 2 3 4 5 6 7 0 2 3 4 BATTERY VOLTAGE (V) BATTERY LEAKAGE CURRENT vs. AMBIENT TEMPERATURE CHARGE CURRENT vs. BATTERY VOLTAGE—USB CHARGE CURRENT vs. BATTERY VOLTAGE—DC MODE 40 30 VIUSB = VUSB 300 250 200 800 VIUSB = 0V 150 700 600 500 400 300 20 100 200 10 50 100 0 0 -15 10 35 60 0 0 85 1 2 3 4 NORMALIZED CHARGE CURRENT vs. AMBIENT TEMPERATURE BATTERY REGULATION VOLTAGE vs. AMBIENT TEMPERATURE 1.000 0.995 0.990 2 3 4 SYS VOLTAGE vs. USB VOLTAGE 4.200 4.5 4.0 4.195 4.190 3.5 VUSB FALLING 3.0 2.5 2.0 VUSB RISING 1.5 1.0 4.185 0.5 0.985 -15 10 35 TEMPERATURE (°C) 6 60 85 4.180 -40 5 5.0 SYS VOLTAGE (V) 1.005 4.205 MAX8903A toc11 MAX8903A toc10 BATTERY VOLTAGE (V) 1.010 1 BATTERY VOLTAGE (V) TEMPERATURE (°C) VUSB = 5V, VBATT = 4V 0 5 MAX8903A toc12 50 350 CHARGER ENABLED IBAT SET TO 1.5A IDC SET TO 1A 900 CHARGE CURRENT (mA) 400 MAX8903A toc09 450 CHARGE CURRENT (mA) 60 CHARGER ENABLED IBAT SET TO 1.5A 6 1000 MAX8903A toc08 500 MAX8903A toc07 70 -40 5 USB VOLTAGE (V) 80 1.015 1 USB VOLTAGE (V) 90 -40 USB UNCONNECTED 0 0 7 70 10 USB SUSPEND 1 MAX8903A toc06 MAX8903A toc05 100 0.2 0 BATTERY LEAKAGE CURRENT (nA) 120 80 BATTERY LEAKAGE CURRENT (nA) 1.2 USB QUIESCENT CURRENT (μA) CHARGER ENABLED 140 BATTERY REGULATION VOLTAGE (V) USB QUIESCENT CURRENT (mA) MAX8903A toc04 1.6 1.4 BATTERY LEAKAGE CURRENT vs. BATTERY VOLTAGE USB QUIESCENT CURRENT vs. USB VOLTAGE USB QUIESCENT CURRENT vs. USB VOLTAGE NORMALIZED CHARGE CURRENT MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power RSYS = 1MΩ 0 -15 10 35 TEMPERATURE (°C) 60 85 0 1 2 3 4 USB VOLTAGE (V) _______________________________________________________________________________________ 5 6 7 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) SYS VOLTAGE vs. SYS OUTPUT CURRENT, DC INPUT VDC RISING 3.0 2.5 2.0 VDC FALLING 1.5 4.40 SYS VOLTAGE (V) 3.5 VDC = 5.75V 4.30 4.20 4.10 USB AND DC UNCONNECTED VBATT = 4V 4.00 4.390 4.385 4.380 4.375 4.370 4.365 1.0 3.90 4.360 3.80 0 2 4 6 8 10 12 14 16 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 0 50 100 150 200 250 300 350 400 450 500 DC VOLTAGE (V) SYS OUTPUT CURRENT (A) SYS OUTPUT CURRENT (mA) VL VOLTAGE vs. DC VOLTAGE CHARGE PROFILE—1400mAh BATTERY ADAPTER INPUT—1A CHARGE CHARGE PROFILE—1400mAh BATTERY USB INPUT—500mA CHARGE VBAT (V) 4 3 2 1 0 2 4 6 8 10 12 14 16 18 IDC SET TO 1A IBAT SET TO 2A 5.5 5.0 4.5 4.0 3.5 VBAT 1.0 0.6 IBAT 0.4 0.2 0.450 4.0 0.400 0.350 VBAT 3.0 0 20 40 DC VOLTAGE (V) 60 80 100 IBAT 0.200 1.5 0.150 0.100 1.0 IUSB SET TO 500mA IBAT SET TO 2A 0 0 0 20 40 60 80 100 120 140 160 180 200 DC SWITCHING WAVEFORMS—HEAVY LOAD MAX8903A toc19 MAX8903A toc20 20mV/div AC-COUPLED 20mV/div AC-COUPLED VOUT 5V/div 0V ILX RSYS = 44Ω 200ns/div 0.050 TIME (min) DC SWITCHING WAVEFORMS—LIGHT LOAD VLX 0.250 2.0 TIME (min) VOUT 0.300 2.5 0.5 0.0 120 140 0.500 4.5 3.5 0.8 3.0 2.5 2.0 1.5 1.0 0.5 0 MAX8903A toc18 5.0 1.2 IBAT (A) 5 MAX8903A toc17 6.0 MAX8903A toc16 6 0 4.355 0 18 VBAT (V) 0 500mA/div 0A 5V/div 0V VLX ILX 500mA/div RSYS = 5Ω 0A 200ns/div _______________________________________________________________________________________ 7 IBAT (A) 0.5 VL VOLTAGE (V) VUSB = 5V 4.395 SYS VOLTAGE (V) 4.0 4.400 MAX8903A toc14 4.5 SYS VOLTAGE (V) 4.50 MAX8903A toc13 5.0 SYS VOLTAGE vs. SYS OUTPUT CURRENT, USB INPUT MAX8903A toc15 SYS VOLTAGE vs. DC VOLTAGE MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) DC CONNECT WITH USB CONNECTED (RSYS = 25Ω) DC CONNECT WITH NO USB (RSYS = 25Ω) MAX8903A toc21 3.6V 2V/div VSYS IDC IUSB 500mA/div 347mA 475mA 500mA/div -IBAT = CHARGING IBAT 3.84V 3.6V VSYS 3.6V VBAT IDC 0A 500mA/div MAX8903A toc23 3.68V 2V/div 5V/div CSYS CHARGING 850mA 3.6V VSYS 3.44V CDC CHARGING IBAT -335mA DC DISCONNECT WITH NO USB (RSYS = 25Ω) MAX8903A toc22 3.6V VBAT 1A/div IDC 0A 2V/div 5V/div 1A/div 0A 850mA -IBAT = CHARGING IBAT 144mA BATTERY CHARGER SOFT-START 144mA -1A 1A/div 1A/div -IBAT = CHARGING -1A 400μs/div 40μs/div USB CONNECT WITH NO DC (RSYS = 25Ω) USB DISCONNECT WITH NO DC (RSYS = 25Ω) 200μs/div SYS LOAD TRANSIENT (0 TO 1A) 3.6V 3.75V VSYS 50mV/div AC COUPLED VSYS MAX8903A toc26 MAX8903A toc25 MAX8903A toc24 3.5V 2V/div 5V/div VUSB CUSB CHARGING VUSB 500mA/div IUSB 0A IBAT 144mA BATTERY CHARGER SOFT-START 5V/div 475mA 500mA/div 500mA/div IUSB IBAT -330mA 144mA -330mA 100μs/div 400μs/div 100µs/div USB SUSPEND USB RESUME MAX8903A toc27 VUSUS IUSB VSYS 0V 475mA 3V MAX8903A toc28 5V/div 0A 0A 200μs/div VUSUS 500mA/div IUSB 2V/div 3.7V IBAT -475mA 8 2V/div 5V 475mA 500mA/div ISYS 3.6V VSYS 5V 3V 5V/div CUSB CHARGING 475mA 0A 3.6V VSYS IBAT 500mA/div 0V 3.8V 500mA/div 3.6V 2V/div 0A BATTERY CHARGER SOFT-START -475mA 200μs/div _______________________________________________________________________________________ 500mA/div 500mA/div 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power PIN NAME FUNCTION 1, 2 PG Power Ground for Step-Down Low-Side Synchronous n-Channel MOSFET. Both PG pins must be connected together externally. 3, 4 DC DC Power Input. DC is capable of delivering up to 2A to SYS. DC supports both AC adapter and USB inputs. The DC current limit is set through DCM, IUSB, or IDC depending on the input source used. See Table 2. Both DC pins must be connected together externally. Connect at least a 4.7µF ceramic capacitor from DC to PG. 5 DCM Current-Limit Mode Setting for the DC Power Input. When logic-high, the DC input current limit is set by the resistor at IDC. When logic-low, the DC input current limit is internally programmed to 500mA or 100mA, as set by the IUSB pin. 6 BST High-Side MOSFET Driver Supply. Bypass BST to LX with a 0.1µF ceramic capacitor. 7 IUSB USB Current-Limit Set Input. Drive IUSB logic-low to set the USB current limit to 100mA. Drive IUSB logichigh to set the USB current limit to 500mA. 8 DOK DC Power-OK Output. Active-low open-drain output pulls low when a valid input is detected at DC. DOK is still valid when the charger is disabled (CEN high). 9 VL Logic LDO Output. VL is the output of an LDO that powers the MAX8903A internal circuitry and charges the BST capacitor. Connect a 1µF ceramic capacitor from VL to GND. 10 CT Charge Timer Set Input. A capacitor (CCT) from CT to GND sets the fast-charge and prequal fault timers. Connect to GND to disable the timer. 11 IDC DC Current-Limit Set Input. Connect a resistor (RIDC) from IDC to GND to program the current limit of the step-down regulator from 0.5A to 2A when DCM is logic-high. 12 GND Ground. GND is the low-noise ground connection for the internal circuitry. 13 ISET Charge Current Set Input. A resistor (RISET) from ISET to GND programs the fast-charge current up to 2A. The prequal charge current is 10% of the fast-charge current. 14 CEN Charger Enable Input. Connect CEN to GND to enable battery charging when a valid source is connected at DC or USB. Connect to VL, or drive high to disable battery charging. 15 USUS USB Suspend Input. Drive USUS logic-high to enter USB suspend mode, lowering USB current to 115µA, and internally shorting SYS to BAT. 16 THM Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor from THM to GND. Connect a resistor equal to the thermistor +25°C resistance from THM to VL. Charging is suspended when the thermistor is outside the hot and cold limits. Connect THM to GND to disable the thermistor temperature sensor. 17 USB USB Power Input. USB is capable of delivering 100mA or 500mA to SYS as set by the IUSB logic input. Connect a 4.7µF ceramic capacitor from USB to GND. 18 FLT Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or fast-charge completes. 19 UOK USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB. UOK is still valid when the charger is disabled (CEN high). 20, 21 BAT Battery Connection. Connect to a single-cell Li+ battery. The battery charges from SYS when a valid source is present at DC or USB. BAT powers SYS when neither DC nor USB power is present, or when the SYS load exceeds the input current limit. Both BAT pins must be connected together externally. _______________________________________________________________________________________ 9 MAX8903A Pin Description MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power Pin Description (continued) PIN NAME FUNCTION CHG Charger Status Output. Active-low, open-drain output pulls low when the battery is in fast-charge or prequal. Otherwise, CHG is high impedance. 23, 24 SYS System Supply Output. SYS connects to BAT through an internal 50mΩ system load switch when DC or USB are invalid, or when the SYS load is greater than the input current limit. When a valid voltage is present at DC or USB, SYS is limited to 4.4V. When the system load (ISYS) exceeds the DC or USB current limit, SYS is regulated to 50mV below BAT, and both the powered input and the battery service SYS. Bypass SYS to GND with a 10µF X5R or X7R ceramic capacitor. Both SYS pins must be connected together externally. 25, 26 CS 70mΩ Current-Sense Input. Connect the step-down inductor from LX to CS. When the step-down regulator is on, there is a 70mΩ current-sense MOSFET from CS to SYS. When the step-down regulator is off, the internal CS MOSFET turns off to block current from SYS back to DC. 27, 28 LX Inductor Connection. Connect the inductor between LX and CS. Both LX pins must be connected together externally. — EP Exposed Pad. Connect the exposed pad to GND. Connecting the exposed pad does not remove the requirement for proper ground connections to the appropriate pins. 22 10 ______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power AC ADAPTER DC LX BST CS DC POWER MANAGEMENT MAX8903A SYS PWR OK Li+ BATTERY CHARGER AND SYS LOAD SWITCH PWM STEP-DOWN REGULATOR DOK MAX8903A PG CHARGER CURRENTVOLTAGE CONTROL SET INPUT LIMIT TO SYSTEM LOAD ISET BATTERY CONNECTOR BAT BAT+ + BAT- USB POWER MANAGEMENT USB USB PWR OK T THERMISTOR MONITOR (SEE FIGURE 7) CURRENTLIMITED VOLTAGE REGULATOR UOK IC THERMAL REGULATION NTC VL CHARGE TERMINATION AND MONITOR SET INPUT LIMIT THM CHG DCM DC MODE USB LIMIT 500mA IUSB 100mA USB SUSPEND USUS FLT INPUT AND CHARGER CURRENT-LIMIT SET LOGIC CHARGE TIMER CT IDC CEN DC LIMIT GND EP Figure 1. Functional Block Diagram ______________________________________________________________________________________ 11 MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power RPU 4 x 100kΩ TO VL 1 2 PG PG MAX8903A CDC 4.7μF 3 DC ADAPTER 4 DC 6 CBST 0.1μF BST FLT UOK DOK CHG 27 LX 18 FAULT OUTPUT 19 USB PWR OK 8 DC PWR OK 22 CHARGE INDICATOR 13 RISET 11 RIDC ISET 28 LX IDC L1 1μH 25 CS 26 CS SYS 24 SYS 23 BAT 21 BAT 20 CSYS 10μF TO SYSTEM LOAD USB 17 VBUS USB CUSB 4.7μF GND TO VL 5 OFF CHARGE ON 14 500mA 100mA 7 USB SUSPEND 15 10 CCT 0.15μF CBAT 10μF 1-CELL LI+ DCM VL 9 CEN IUSB RT 10kΩ THM 16 NTC 10kΩ USUS CT GND 12 Figure 2. Typical Application Circuit Using a Separate DC and USB Connector Circuit Description The MAX8903A is a dual input charger with a 16V input for a wide range of DC sources and USB inputs. The IC includes a high-voltage (16V) input DC-DC step-down converter that reduces charger power dissipation while also supplying power to the system load. The stepdown converter supplies up to 2A to the system, the battery, or a combination of both. 12 A USB charge input can charge the battery and power the system from a USB power source. When powered from USB or the DC input, system load current peaks that exceed what can be supplied by the input are supplemented by the battery. The MAX8903A also manages load switching from the battery to and from an external power source with an on-chip 50mΩ MOSFET. This switch also helps support load peaks using battery power when the input source is overloaded. ______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A RPU 4 x 100kΩ TO VL 1 2 SERIES MINI-B PG PG MAX8903A CDC 4.7μF 3 DC VBUS 4 DC DD+ ID GND 6 CBST 0.1μF BST FLT UOK DOK CHG 27 LX 18 FAULT OUTPUT 19 USB PWR OK 8 DC PWR OK 22 CHARGE INDICATOR 13 RISET 11 RIDC ISET 28 LX L1 1μH IDC 25 CS 26 CS 17 TO SYSTEM LOGIC 5 OFF CHARGE ON 14 500mA 100mA 7 USB SUSPEND 15 10 CCT 0.15μF USB SYS 24 SYS 23 BAT 21 BAT 20 TO SYSTEM LOAD CSYS 10μF CBAT 10μF 1-CELL LI+ DCM VL 9 CVL 1μF CEN IUSB THM 16 NTC 10kΩ USUS CT RT 10kΩ GND 12 Figure 3. Typical Application Circuit Using a Mini 5 Style Connector or Other DC/USB Common Connector The IC includes a full-featured charger with thermistor monitor, fault timer, charger status, and fault outputs. Also included are power-OK signals for both USB and DC. Flexibility is maintained with adjustable charge current, input current limit, and a minimum system voltage (when charging is scaled back to hold the system voltage up). The MAX8903A prevents overheating during high ambient temperatures by limiting charging current when the die temperature exceeds +100°C. DC Input—Fast Hysteretic Step-Down Regulator If a valid DC input is present, the USB power path is turned off and power for SYS and battery charging is supplied by the high-frequency step-down regulator from DC. If the battery voltage is above the minimum system voltage (VSYSMIN, Figure 4), the battery charger connects the system voltage to the battery for lowest power dissipation. The step-down regulation point is then controlled by three feedback signals: maximum ______________________________________________________________________________________ 13 MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power Table 1. External Components List for Figures 2 and 3 COMPONENT (FIGURES 2 AND 3) CDC, CUSB CVL FUNCTION Input filter capacitor 4.7µF ceramic capacitor VL filter capacitor 1.0µF ceramic capacitor CSYS SYS output bypass capacitor 10µF ceramic capacitor CBAT Battery bypass capacitor 10µF ceramic capacitor CCT Charger timing capacitor 0.15µF low TC ceramic capacitor Logic output pullup resistors 100kΩ Negative TC thermistor Phillips NTC thermistor, P/N 2322-640-63103, 0kΩ ±5% at +25°C THM pullup resistor 10kΩ RIDC DC input current-limit programming resistor 3kΩ ±1%, for 2A limit RISET Fast-charge current programming resistor 1.2kΩ ±1%, for 1A charging DC input step-down inductor 1µH inductor with ISAT > 2A RPU (X4) THM RT L1 step-down output current programmed at IDC, maximum charger current programmed at ISET, and maximum die temperature. The feedback signal requiring the smallest current controls the average output current in the inductor. This scheme minimizes total power dissipation for battery charging and allows the battery to absorb any load transients with minimum system voltage disturbance. If the battery voltage is below VSYSMIN, the charger does not directly connect the system voltage to the battery. VSYS pin is held at a fixed point slightly above VSYSMIN, and does not track the battery. The battery charger independently controls the battery charging current. VSYSMIN is set to 3.0V in the MAX8903A, for other VSYSMIN values, please contact the factory. After the battery charges to 50mV above VSYSMIN, the system voltage is connected to the battery. The battery fast-charge current then controls the step-down converter to set the average inductor current so that both the programmed input current limit and fast-charge current limit are satisfied. DC-DC Step-Down Control Scheme A proprietary hysteretic current PWM control scheme ensures fast switching and physically tiny external components. The feedback control signal that requires the smallest input current controls the center of the peak and valley currents in the inductor. The ripple current is internally set to provide 4MHz operation. When the input voltage decreases near the output voltage, very high duty cycle occurs and, due to minimum off-time, 4MHz operation is not achievable. The controller then provides minimum off-time, peak current regulation. 14 PART 4.4V 4.2V VSYS IBAT x RON VSYSMIN VBAT Figure 4. SYS Tracking VBAT to the Minimum System Voltage Similarly, when the input voltage is too high to allow 4MHz operation due to the minimum on-time, the controller becomes a minimum on-time, valley current regulator. In this way, ripple current in the inductor is always as small as possible to reduce ripple voltage on SYS for a given capacitance. The ripple current is made to vary with input voltage and output voltage in a way that reduces frequency variation. However, the frequency still varies somewhat with operating conditions. See the Typical Operating Characteristics. DC Input—USB mode When powering from DC with DCM set to logic-low, the DC input is set to USB mode. The input current limit from DC is then internally set to 500mA max if IUSB is high and 100mA max if IUSB is low. For the 500mA case, the DC input continues to operate as a step-down regulator to minimize thermal heating. For the 100mA case, the ______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power USB Input—Linear Regulator If a valid USB input is present with no valid DC input, current for SYS and battery charging is supplied by a low-dropout linear regulator connected from USB to SYS. The SYS regulation voltage shows the same characteristic as when powering from the DC input (see Figure 4). The battery charger operates from SYS with any extra available current, while not exceeding the maximum-allowed USB current. If both USB and DC inputs are valid, power is only taken from the DC input. The maximum USB input current is set by the logic state of the IUSB input to either 100mA or 500mA. Power Monitor Outputs (UOK, DOK) DOK is an open-drain, active-low output that indicates the DC input power status. With no source at the USB pin, the source at DC is considered valid and DOK is driven low when: 4.15V < VDC < 16V. When the USB voltage is also valid, the DC source is considered valid and DOK is driven low when: 4.45V < VDC < 16V. The higher minimum DC voltage with USB present helps guarantee cleaner transitions between input supplies. If the DC power-OK output feature is not required, connect DOK to ground. UOK is an open-drain, active-low output that indicates the USB input power status. UOK is low when a valid source is connected at USB. The source at USB is valid when 4.1V < VUSB < 6.6V. If the USB power-OK output feature is not required, connect UOK to ground. Both the UOK and the DOK circuitry remain active in thermal overload, USB suspend, and when the charger is disabled. DOK and UOK can also be wire-ORed together to generate a single power-OK (POK) output. Thermal Limiting When the die temperature exceeds +100°C, a thermal limiting circuit reduces the input current limit by 5%/°C, bringing the charge current to 0mA at +120°C. Since the system load gets priority over battery charging, the battery charge current is reduced to 0mA before the input limiter drops the load voltage at SYS. To avoid false charge termination, the charge termination detect function is disabled in this mode. If the junction temperature rises beyond +120°C, no current is drawn from DC or USB, and VSYS regulates at 50mV below VBAT. System Voltage Switching DC Input When charging from the DC input, if the battery is above the minimum system voltage, SYS is connected to the battery. Current is provided to both SYS and the battery, up to the maximum program value. The stepdown output current sense and the charger current sense provide feedback to ensure the current loop demanding the lower input current is satisfied. The advantage of this approach when powering from DC is that power dissipation is dominated by the step-down regulator efficiency, since there is only a small voltage drop from SYS to BAT. Also, load transients can be absorbed by the battery while minimizing the voltage disturbance on SYS. If both the DC and USB inputs are valid, the DC input takes priority and delivers the input current, while the USB input is off. After the battery is done charging, the charger is turned off and the SYS load current is supplied from the DC input. The SYS voltage is regulated to 4.4V. The charger turns on again after the battery drops to the restart threshold. If the load current exceeds the input limiter, SYS drops down to the battery voltage and the 50mΩ SYS-to-BAT PMOS switch turns on to supply the extra load current. The SYS-to-BAT switch turns off again once the load is below the input current limit. The 50mΩ PMOS also turns on if valid DC input power is removed. USB Input When charging from the USB input, the DC input stepdown regulator turns off and a linear regulator from USB to SYS powers the system and charges the battery. If the battery is greater than the minimum system voltage, the SYS voltage is connected to the battery. The USB input then supplies the SYS load and charges the battery with any extra available current, while not exceeding the maximum-allowed USB current. Load transients can be absorbed by the battery while minimizing the voltage disturbance on SYS. When battery charging is completed, or the charger is disabled, SYS is regulated to 4.4V. If both USB and DC inputs are valid, power is only taken from the DC input. USB Suspend Driving USUS high turns off charging as well as the SYS output and reduces input current to 170µA to accommodate USB suspend mode. Charge Enable (CEN) When CEN is low, the charger is on. When CEN is high, the charger turns off. CEN does not affect the SYS output. In many systems, there is no need for the system controller (typically a microprocessor) to disable the charger, because the MAX8903A smart power selector circuitry independently manages charging and adapter/battery power hand-off. In these situations, CEN may be connected to ground. ______________________________________________________________________________________ 15 MAX8903A step-down regulator is turned off and a low-dropout linear regulator is connected between DC and SYS. MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power Table 2. Input Limiter Control Logic POWER SOURCE AC Adapter at DC Input UOK DCM IUSB USUS DC STEP-DOWN OUTPUT CURRENT LIMIT L X H X X 6000/RIDC L X L L L 100mA L X L H L 500mA Lesser of 1200/RISET and 500mA L X L X H USB suspend 0 H L X L L H L X H L USB INPUT CURRENT LIMIT Lesser of 1200/RISET and 6000/RIDC USB input off. DC input has priority. USB Power at DC Input USB Power at USB Input, DC Unconnected DC and USB Unconnected MAXIMUM CHARGE CURRENT** DOK Lesser of 1200/RISET and 100mA Lesser of 1200/RISET and 100mA 100mA H L X X H USB suspend Lesser of 1200/RISET and 500mA 0 H H X X X No USB input 0 No DC input 500mA **Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load exceeds the input current limit. X = Don’t care. Soft-Start To prevent input transients that can cause instability in the USB or AC adapter power source, the rate of change of the input current and charge current is limited. When an input source is valid, SYS current is ramped from zero to the set current-limit value in typically 50µs. This also means that if DC becomes valid after USB, the SYS current limit is ramped down to zero before switching from the USB to DC input. At some point, SYS is no longer able to support the load and may switch over to BAT. The switchover to BAT occurs when VSYS < VBATT. This threshold is a function of the SYS capacitor size and SYS load. The SYS current limit then ramps from zero to the set current level and SYS supports the load again as long as the SYS load current is less than the set current limit. When the charger is turned on, the charge current ramps from 0A to the ISET current value in typically 1.0ms. Charge current also soft-starts when transitioning to fastcharge from prequal, when the input power source is switched between USB and DC, and when changing the 16 USB charge current from 100mA to 500mA with the IUSB logic input. There is no di/dt limiting, however, if RISET is changed suddenly using a switch. Battery Charger While a valid input source is present, the battery charger can attempt to charge the battery with a fast-charge current determined by the resistance at the ISET pin: RISET = 1200/ICHG-MAX Monitoring Charge Current The voltage from ISET to GND is a representation of the battery charge current and can be used to monitor the current charging the battery. A voltage of 1.5V represents the maximum fast-charge current. If necessary, the charge current is reduced automatically to prevent the SYS voltage from dropping. Therefore, a battery never charges at a rate beyond the capabilities of a 100mA or 500mA USB input, or overloads an AC adapter. See Figure 5. ______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power Charge Termination When the charge current falls to the termination threshold (ITERM) and the charger is in voltage mode, charging is complete. Charging continues for a brief 15s top-off period and then enters the DONE state where charging stops. Note that if charge current falls to ITERM as a result of the input or thermal limiter, the charger does not enter DONE. For the charger to enter DONE, charge current must be less than ITERM, the charger must be in voltage mode, and the input or thermal limiter must not be reducing charge current. MAX8903A When VBATT is below 3V, the charger enters prequal mode and the battery charges at 10% of the maximum fast-charge rate until the voltage of the deeply discharged battery recovers. When the battery voltage reaches 4.2V and the charge current drops to 10% of the maximum fast-charge current, the charger enters the DONE state. The charger restarts a fast-charge cycle if the battery voltage drops by 100mV. MONITORING THE BATTERY CHARGE CURRENT WITH VISET 1.5 VISET (V) 0 DISCHARGING 0 1200/RISET BATTERY CHARGING CURRENT (A) Figure 5. Monitoring the Battery Charge Current with the Voltage from ISET to GND Charge Status Outputs Charge Output (CHG) CHG is an open-drain, active-low output that indicates charger status. CHG is low when the battery charger is in its prequalification and fast-charge states. CHG goes high impedance if the thermistor causes the charger to go into temperature suspend mode. When used in conjunction with a microprocessor (µP), connect a pullup resistor between CHG and the logic I/O voltage to indicate charge status to the µP. Alternatively, CHG can sink up to 20mA for an LED charge indicator. Charge Timer A fault timer prevents the battery from charging indefinitely. The fault prequal and fast-charge timers are controlled by the capacitance at CT (CCT). Fault Output (FLT) FLT is an open-drain, active-low output that indicates charger status. FLT is low when the battery charger has entered a fault state when the charge timer expires. This can occur when the charger remains in its prequal state for more than 33 minutes or if the charger remains in fast-charge state for more than 660 minutes (see Figure 6). To exit this fault state, toggle CEN or remove and reconnect the input source. When used in conjunction with a microprocessor (µP), connect a pullup resistor between FLT and the logic I/O voltage to indicate charge status to the µP. Alternatively, FLT can sink up to 20mA for an LED fault indicator. If the FLT output is not required, connect FLT to ground or leave unconnected. While in fast-charge mode, a large system load or device self-heating may cause the MAX8903A to reduce charge current. Under these circumstances, the fast-charge timer is slowed by 2x if the charge current drops below 50% of the programmed fast-charge level, and suspended if the charge current drops below 20% of the programmed level. The fast-charge timer is not affected at any current if the charger is regulating the BAT voltage at 4.2V (i.e., the charger is in voltage mode). CCT 0.15μF CCT tFST −CHG = 660 min × 0.15μF t TOP−OFF = 15s tPREQUAL = 33 min × Thermistor Input (THM) The THM input connects to an external negative temperature coefficient (NTC) thermistor to monitor battery or system temperature. Charging is suspended when the thermistor temperature is out of range. The charge timers are suspended and hold their state but no fault is indicated. When the thermistor comes back into range, ______________________________________________________________________________________ 17 MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power NOT READY UOK AND DOK = HIGH IMPEDANCE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE ICHG = 0mA CEN = HI OR REMOVE AND RECONNECT THE INPUT SOURCE(S) ANY STATE UOK AND/OR DOK = LOW CEN = 0 RESET TIMER PREQUALIFICATION UOK AND/OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE 0 < VBAT < 3V ICHG ≤ ICHGMAX/10 VBATT < 2.82V RESET TIMER = 0 TIMER > tPREQUAL FAULT UOK AND/OR DOK = LOW CHG = HIGH IMPEDANCE FLT = LOW ICHG = 0mA VBATT > 3.0V RESET TIMER TIMER > tFSTCHG (TIMER SLOWED BY 2x IF ICHG < ICHGMAX/2, AND PAUSED IF ICHG < ICHGMAX/5 WHILE VBAT < 4.2V) FAST-CHARGE UOK AND/OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE 3V < VBAT < 4.2V ICHG ≤ ICHGMAX VBATT < 2.8V RESET TIMER ICHG < ITERM AND VBAT = 4.2V AND THERMAL OR INPUT LIMIT NOT EXCEEDED; RESET TIMER ICHG > ITERM RESET TIMER ANY CHARGING STATE THM OK TIMER RESUME TOGGLE CEN OR REMOVE AND RECONNECT THE INPUT SOURCE(S) THM NOT OK TIMER SUSPEND TEMPERATURE SUSPEND ICHG = 0mA UOK OR DOK PREVIOUS STATE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE TOP-OFF UOK AND/OR DOK = LOW CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE VBAT = 4.2V ICHG = ITERM VBAT < 4.1V RESET TIMER TIMER > 15s DONE UOK AND/OR DOK = 0 CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE 4.1V < VBAT < 4.2V ICHG = 0mA Figure 6. MAX8903A Charger State Flow Chart charging resumes and the charge timer continues from where it left off. Connecting THM to GND disables the thermistor monitoring function. Table 4 lists the fault temperature of different thermistors. Since the thermistor monitoring circuit employs an external bias resistor from THM to VL (RTB, Figure 7), the thermistor is not limited only to 10kΩ (at +25°C). 18 Any resistance thermistor can be used as long as the value is equivalent to the thermistor’s +25°C resistance. For example, with a 10kΩ at +25°C thermistor, use 10kΩ at RTB, and with a 100kΩ at +25°C thermistor, use 100kΩ . For a typical 10kΩ (at +25°C) thermistor and a 10kΩ RTB resistor, the charger enters a temperature suspend ______________________________________________________________________________________ 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A CEN VL THERMISTOR CIRCUITRY VL MAX8903A ALTERNATE THERMISTOR CONNECTION RTB 0.74 VL COLD THM RTS 0.28 VL RTP HOT RT ENABLE THM 0.03 VL RT THM OUT OF RANGE DISABLE CHARGER ALL COMPARATORS 60mV HYSTERESIS GND Figure 7. Thermistor Monitor Circuitry Table 3. Fault Temperatures for Different Thermistors Thermistor ß (K) 3000 3250 3500 3750 4250 RTB (kΩ) (Figure 7) 10 10 10 10 10 Resistance at +25°C (kΩ) 10 10 10 10 10 Resistance at +50°C (kΩ) 4.59 4.30 4.03 3.78 3316 Resistance at 0°C (kΩ) 25.14 27.15 29.32 31.66 36.91 Nominal Hot Trip Temperature (°C) 55 53 50 49 46 Nominal Cold Trip Temperature (°C) -3 -1 0 2 4.5 state when the thermistor resistance falls below 3.97kΩ (too hot) or rises above 28.7kΩ (too cold). This corresponds to a 0°C to +50°C range when using a 10kΩ NTC thermistor with a beta of 3500. The general relation of thermistor resistance to temperature is defined by the following equation: ⎧ ⎛ 1 1 ⎞⎫ − ⎟⎬ ⎨β⎜ ⎝ ⎠⎭ 273 298 T + RT = R25 × e ⎩ where: RT = The resistance in Ω of the thermistor at temperature T in Celsius R25 = The resistance in Ω of the thermistor at +25°C ß = The material constant of the thermistor, which typically ranges from 3000K to 5000K T = The temperature of the thermistor in °C Table 4 shows the MAX8903A THM temperature limits for different thermistor material constants. Some designs might prefer other thermistor temperature limits. Threshold adjustment can be accommodated by changing RTB, connecting a resistor in series and/or in parallel with the thermistor, or using a thermistor with different ß. For example, a +45°C hot threshold and 0°C cold threshold can be realized by using a thermistor with a ß of 4250 and connecting 120kΩ in parallel. Since the thermistor resistance near 0°C is much higher than it is near +50°C, a large parallel resistance lowers the cold threshold, while only slightly lowering the hot threshold. Conversely, a small series resistance ______________________________________________________________________________________ 19 Table 4. Package Thermal Characteristics THM USUS 19 18 17 16 15 CHG 22 14 CEN SYS 23 13 ISET SYS 24 12 GND 11 IDC 10 CT CS 25 Power Dissipation USB 20 UOK 21 FLT TOP VIEW BAT Pin Configuration BAT raises the cold threshold, while only slightly raising the hot threshold. Raising RTB lowers both the hot and cold thresholds, while lowering RTB raises both thresholds. Note that since VL is active whenever valid input power is connected at DC or USB, thermistor bias current flows at all times, even when charging is disabled (CEN = high). When using a 10kΩ thermistor and a 10kΩ pullup to VL, this results in an additional 250µA load. This load can be reduced to 25µA by instead using a 100kΩ thermistor and 100kΩ pullup resistor. MAX8903A CS 26 LX 27 LX 28 *EP + 9 VL 8 DOK Derate 28.6mW/°C above +70°C θJA 48°C/W 35°C/W θJC 3°C/W 3°C/W 4 5 6 7 IUSB Derate 20.8mW/°C above +70°C 3 BST 2286mW 2 DCM 1666.7mW Continuous Power Dissipation 1 DC MULTILAYER PCB DC SINGLE-LAYER PCB PG 28-PIN 4mm x 4mm THIN QFN PG MAX8903A 2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power THIN QFN 4mm x 4mm *EXPOSED PAD Chip Information PCB Layout and Routing Good design minimizes ground bounce and voltage gradients in the ground plane, which can result in instability or regulation errors. The GND and PGs should connect to the power-ground plane at only one point to minimize the effects of power-ground currents. Battery ground should connect directly to the power-ground plane. The ISET and IDC current-setting resistors should connect directly to GND to avoid current errors. Connect GND to the exposed pad directly under the IC. Use multiple tightly spaced vias to the ground plane under the exposed pad to help cool the IC. Position input capacitors from DC, SYS, BAT, and USB to the power-ground plane as close as possible to the IC. Keep high current traces such as those to DC, SYS, and BAT as short and wide as possible. Refer to the MAX8903A Evaluation Kit for a suitable PCB layout example. PROCESS: BiCMOS Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 28 TQFN-EP T2844-1 21-0139 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. 20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.