19-0781; Rev 0; 4/07 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector The MAX8677C is an integrated 1-cell Li+ charger and Smart Power SelectorTM with dual (DC and USB) power inputs. 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 are required. The MAX8677C features a Smart Power Selector to make the best use of limited USB or adapter power. The battery charge current and input current limit are independently set up to 1.5A and 2A, respectively. Input power not used by the system charges the battery. USB input current can be set to 100mA or 500mA. Automatic input selection switches the system load from battery to external power. Other features include overvoltage protection (OVP), charge status and fault outputs, power-OK monitors, charge timer, and battery thermistor monitor. Additionally, on-chip thermal limiting reduces the battery charge rate to prevent overheating. The MAX8677C is available in a 4mm x 4mm, 24-pin TQFN-EP package. Applications Features o Complete Charger and Smart Power Selector o No External MOSFETs Required o Common or Separate USB and Adapter Inputs o System Operates with Discharged or No Battery o Automatic Adapter/USB/Battery Switchover o Load Peaks Over Adapter Rating Are Supported by Battery o Input Overvoltage Protection to 16V o 40m System-to-Battery Switch o Thermal Regulation Prevents Overheating o PREQ, CHG, DOK, UOK, and FLT Indicators o 4.35V (typ) SYS Regulation Voltage Ordering Information PART TEMP RANGE PINPACKAGE MAX8677CETG+ -40C to +85C 24 TQFN-EP** (4mm x 4mm) Smart Cell Phones Portable Media/MP3 Players Pin Configuration Typical Operating Circuit Q2 Q3 USB USB TSET USUS 13 CHG 19 12 THM SYS 20 11 ISET SYS 21 10 CT MAX8677C DOK 22 SYSTEM LOAD UOK 23 8 VL FLT 24 7 PSET 1 BAT CHARGE AND SYS LOAD SWITCH BATTERY 9 GND 2 3 4 5 6 PEN2 USB 14 PEN1 LOAD CURRENT 15 CEN CHARGE CURRENT 16 DC USB SYS 17 DC Q1 18 PREQ DC BAT Digital Cameras BAT GPS Navigation MAX8677C T2444-4 +Denotes a lead-free package. **EP = Exposed paddle. PDAs, Palmtops, and Wireless Handhelds AC ADAPTER PKG CODE TQFN (4mm x 4mm x 0.8mm) GND Smart Power Selector is a trademark of Maxim Integrated Products, Inc. *Protected by U.S. Patent #6,507,172. ________________________________________________________________ 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 MAX8677C General Description MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector ABSOLUTE MAXIMUM RATINGS DC, PEN1 to GND .................................................-0.3V to +16V USB to GND .............................................................-0.3V to +9V VL to GND ................................................................-0.3V to +4V BAT, SYS, CEN, USUS, PEN2, TSET to GND...........-0.3V to +6V THM, PSET, ISET, CT to GND .........................-0.3V to VL + 0.3V PREQ, CHG, DOK, UOK, FLT to GND .....................-0.3V to +6V EP (exposed paddle) to GND ...............................-0.3V to +0.3V DC Continuous Current (total in 2 pins) .........................2.4ARMS SYS Continuous Current (total in 2 pins) ........................2.4ARMS USB Continuous Current (total in 2 pins) .......................2.0ARMS BAT Continuous Current (total in 2 pins)........................2.4ARMS Continuous Power Dissipation (TA = +70C) (derate 27.8mW/C above +70C) ........................... 2222mW Operating Temperature Range ...........................-40C to +85C Junction Temperature Range ............................-40C to +125C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C 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 = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS DC-TO-SYS PREREGULATOR DC Operating Range 4.1 DC Standoff Voltage VBAT = VSYS = 0V DC Undervoltage Threshold When V DOK goes low, VDC rising, 500mV typical hysteresis 3.95 DC Overvoltage Threshold When V DOK goes high, VDC rising, 360mV typical hysteresis 6.8 6.6 V 14 V 4.0 4.05 V V 6.9 7.0 ISYS = IBAT = 0mA, V CEN = 0V 1 2 ISYS = IBAT = 0mA, V CEN = 5V 0.8 1.5 DC Shutdown Current VDC = V CEN = USUS = 5V, VPEN1 = 0V 195 333 A DC-to-SYS On-Resistance ISYS = 400mA, V CEN = 5V 0.2 0.35 DC-to-BAT Dropout Voltage When SYS regulation and charging stops, VDC falling, 150mV hysteresis 10 50 90 mV RPSET= 1.5k 1800 2000 2200 RPSET = 3k 900 1000 1100 RPSET = 6.3k 450 475 500 VPEN1 = 0V, VPEN2 = 5V (500mA USB mode) 450 475 500 VPEN1 = 0V, VPEN2 = 0V (100mA USB mode) 80 95 100 4.35 4.40 DC Supply Current DC Current Limit (See Table 2 for Input Source Control) VDC = 6V, VSYS = 5V, TA = +25C PSET Resistance Range SYS Regulation Voltage Input Current Soft-Start Time 1.5 VDC = 6V, ISYS = 1mA to 1.75A, V CEN = 5V 6.3 mA k V Connecting DC when no USB present 1.5 ms Connecting DC with USB present 50 s +100 C Thermal-Limit Temperature Die temperature at which charging and input current limits are reduced Thermal-Limit Gain ISYS reduction/die temperature (above +100C) VL Voltage IVL = 0 to 10mA 2 4.29 mA 5 3.0 3.3 _______________________________________________________________________________________ %/C 3.6 V 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector (VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS USB-TO-SYS PREREGULATOR USB Operating Range 4.1 USB Standoff Voltage VBAT = VSYS = 0V USB Undervoltage Threshold When V UOK goes low, VUSB rising, 500mV hysteresis 3.95 USB Overvoltage Threshold When V UOK goes high, VUSB rising, 100mV hysteresis 6.8 6.6 V 8 V 4.0 4.05 V V 6.9 7.0 ISYS = IBAT = 0mA, V CEN = 0V, VPEN2 = 0V 1 2 ISYS = IBAT = 0mA, V CEN = 5V, VPEN2 = 0V 0.9 1.5 USB Shutdown Current DC = unconnected, VUSB = V CEN = VUSUS = 5V 190 333 A USB-to-SYS On-Resistance DC = unconnected, VUSB = V CEN = 5V, ISYS = 400mA 0.2 0.31 USB-to-BAT Drop-Out Voltage When SYS regulation and charging stops, VUSB falling, 250mV hysteresis 10 50 90 mV USB Current Limit (See Table 2 for Input Source Control) DC = unconnected, VUSB = 5V, TA = +25C VPEN1 = 0V, VPEN2 = 5V 450 475 500 VPEN1 = 0V, VPEN2 = 0V 80 95 100 SYS Regulation Voltage DC = unconnected, VUSB = 6V; ISYS = 1mA to 400mA, V CEN = 5V 4.29 4.35 4.40 Input Limiter Soft-Start Time Input current ramp time USB Supply Current mA Thermal-Limit Start Temperature Thermal-Limit Gain ISYS reduction/die temperature (above +100C) VL Voltage DC = unconnected, VUSB = 5V; IVL = 0 to 10mA mA 50 s +100 C 5 3.0 V %/C 3.3 3.6 V 0.04 0.08 68 90 mV CHARGER BAT-to-SYS On-Resistance VDC = 0V, VBAT = 4.2V, ISYS = 1A BAT-to-SYS Reverse Regulation Voltage VPEN1 = VPEN2 = 0V, ISYS = 200mA BAT Regulation Voltage IBAT = 0mA BAT Recharge Threshold Change in VBAT from DONE to fast-charge BAT Charge-Current Set Range RISET = 10k to 2k (Note 2) BAT Charge-Current Accuracy, Charger Loop in Control VSYS = 5.5V, TA = 0C to +85C 40 TA = +25C 4.179 4.2 4.221 TA = 0C to +85C 4.158 4.2 4.242 -135 -95 -45 mV 1.5 A 0.3 RISET = 2.4k 1125 1250 1375 RISET = 4k 675 750 825 RISET = 10k 270 300 330 RISET = 4k, VBAT = 2.5V (prequal mode) 50 75.0 100 RISET = 6.2k, VBAT = 2.5V (prequal mode) 23 48 73 RISET = 10k, VBAT = 2.5V (prequal mode) V mA 30 _______________________________________________________________________________________ 3 MAX8677C ELECTRICAL CHARACTERISTICS (continued) MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector ELECTRICAL CHARACTERISTICS (continued) (VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS ISET Voltage RISET = 4k, IBAT = 500mA (VISET = 1.5V at full charge current) 0.9 1.0 1.1 V Charger Soft-Start Time Charge-current ramp time BAT Prequal Threshold VBAT rising, 180mV hysteresis BAT Leakage Current VBAT = 4.2V DONE Threshold as a Percentage of Fast-Charge IBAT decreasing 1.5 2.9 ms 3 3.1 No DC or USB power connected 3 6 DC or USB connected, V CEN = 5V 3 6 VTSET = 0 5 VTSET = open 10 VTSET = VL 15 V A % Maximum Prequal Time From V CEN falling to end of prequal charge, VBAT = 2.5V, CT = 0.068F 30 Min Maximum Fast-Charge Time From V CEN falling to VFLT falling, CT = 0.068F 300 Min Timer Accuracy CT = 0.068F Timer Extend Threshold Percentage of fast-charge current below which timer clock operates at half speed -20 +20 % 50 % Timer Suspend Threshold Percentage of fast-charge current below which timer clock pauses 20 % THM THM Threshold, Cold When charging is suspended, 2% hysteresis 72 74 76 % of VL THM Threshold, Hot When charging is suspended, 2% hysteresis 26 28 30 % of VL THM Threshold, Disabled When THM function is disabled THM Input Leakage 3 THM = GND or VL; TA = +25C -0.1 THM = GND or VL; TA = +85C 0.001 % of VL +0.2 0.01 A LOGIC I/O: CHG, FLT, PREQ, DOK, UOK, PEN1, PEN2, CEN, TSET, USUS High level Logic Input Thresholds 1.3 Low level 0.4 Hysteresis 50 High level TSET Input Threshold Midlevel 1.2 VL - 1.2 Logic Output Voltage, Low Sinking 1mA Logic Output-Leakage Current, High -20 TSET = VL VINPUT = 0 to 5.5V VOUT = 5.5V V 0.3 TSET = GND Logic Input-Leakage Current mV VL - 0.3 Low level TSET Input-Bias Current V -6 6 20 TA = +25C 0.001 1 TA = +85C 0.01 25 100 TA = +25C 0.001 1 TA = +85C 0.01 A A mV A Note 1: Limits are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design. Note 2: Guaranteed by design. 4 _______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 0.7 0.6 VUSB RISING VUSB FALLING 0.5 0.4 0.3 0.2 ENTERING OVLO 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 0 6 7 8 2 3 4 5 6 7 PEN1 = X, PEN2 = 1 0.30 0.25 0.20 0.15 0.10 0.05 0 0 8 1 2 3 4 5 6 7 8 USB VOLTAGE (V) USB VOLTAGE (V) BATTERY LEAKAGE CURRENT vs. BATTERY VOLTAGE (USB DISCONNECTED) BATTERY LEAKAGE CURRENT vs. TEMPERATURE BATTERY LEAKAGE CURRENT vs. BATTERY VOLTAGE (USB CONNECTED) 2.5 2.0 1.5 1.0 3.58 3.56 3.54 3.52 3.50 7 1 2 3 4 -40 5 10 35 60 0 85 1 2 3 4 CHARGE CURRENT vs. BATTERY VOLTAGE (500mA USB) CHARGE CURRENT vs. BATTERY VOLTAGE (1ADC) 400 CHARGE CURRENT (mA) VUSB = 5V PEN1 = X , PEN2 = 1 VBAT RISING VBAT FALLING 30 VBAT RISING VBAT FALLING 350 300 250 200 150 20 100 10 50 0 VUSB = 5V PEN1 = X, PEN2 = 1 450 2 3 BATTERY VOLTAGE (V) 4 5 VDC = 5V PEN1 = 1 , PEN2 = X 1.0 VBAT RISING VBAT FALLING 0.8 0.6 0.4 0.2 0 0 1 1.2 CHARGE CURRENT (A) MAX8677C toc07 500 5 MAX8677C toc09 CHARGE CURRENT vs. BATTERY VOLTAGE (100mA USB) 70 0 2 BATTERY VOLTAGE (V) 80 40 3 TEMPERATURE (C) 90 50 4 BATTERY VOLTAGE (V) 100 60 -15 MAX8677C toc08 0 5 0 3.46 0 VUSB = 5V USUS = 1 CEN = 1 6 1 3.48 0.5 MAX8677C toc06 VBAT = 4V BATTERY LEAKAGE CURRENT (A) 3.0 MAX8677C toc05 3.5 3.60 BATTERY LEAKAGE CURRENT (A) MAX8677C toc04 USB = OPEN BATTERY LEAKAGE CURRENT (A) 1 0 0.35 USB VOLTAGE (V) 4.0 CHARGE CURRENT (mA) VBAT = 4.2, USUS = 1 ENTERING OVLO EXITING UVLO 0.1 EXITING UVLO VUSB RISING VUSB FALLING CEN = 1 ISYS = 0V PEN1 = X, PEN2 = 1 1.0 0.40 MAX8677C toc03 0.8 VBAT = 4.2, VUSUS = 0V MAX8677C toc02 CHARGER IN DONE MODE ISYS = 0V PEN1 = X, PEN2 = 1 1.2 USB QUIESCENT CURRENT (mA) VBAT = 4.2, VUSUS = 0V 0.9 USB QUIESCENT CURRENT (mA) MAX8677C toc01 1.0 USB QUIESCENT CURRENT vs. USB VOLTAGE (SUSPEND) USB QUIESCENT CURRENT vs. USB VOLTAGE (CHARGER DISABLED) USB QUIESCENT CURRENT (mA) USB QUIESCENT CURRENT vs. USB VOLTAGE (CHARGER ENABLED) 0 1 2 3 BATTERY VOLTAGE (V) 4 5 0 1 2 3 4 5 BATTERY VOLTAGE (V) _______________________________________________________________________________________ 5 MAX8677C Typical Operating Characteristics (TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) 1.0050 1.0025 1.0000 0.9975 0.9950 4.200 MAX8677C toc12 4.40 VBAT = 4V NO SYS LOAD 4.35 4.30 4.195 VSYS (V) 1.0075 BATTERY REGULATION VOLTAGE (V) VUSB = 5V, VBAT = 4V MAX8677C toc11 4.205 MAX8677C toc10 NORMALIZED CHARGE CURRENT 1.0100 SYS OUTPUT VOLTAGE vs. USB VOLTAGE BATTERY REGULATION VOLTAGE vs. TEMPERATURE NORMALIZED CHARGE CURRENT vs. AMBIENT TEMPERATURE (LOW IC POWER DISSIPATION) 4.190 4.25 4.20 4.15 4.10 4.185 4.05 0.9925 40ppm/C 4.00 -15 10 35 60 -40 85 -15 VBAT = 4V NO SYS LOAD 4.35 60 VBAT = 4V 4 5 7 THE SLOPE OF THIS LINE SHOWS THAT THE BAT-TO-SYS RESISTANCE IS 40m 4.1 4.0 VBAT = 4V PEN1 = 1, PEN2 = X CEN = 1 5.1 8 4.7 4.3 3.9 4.10 3.8 4.05 3.9 3.7 3.6 4.00 0 2 4 6 8 10 12 3.5 0 14 0.5 VDC (V) 1.0 1.5 2.0 1.0 4.7 2.0 VL OUTPUT VOLTAGE vs. DC VOLTAGE 3.5 MAX8677C toc17 VBAT = 4V VUSB = 5V PEN1 = X CEN = 1 4.9 1.5 ISYS (A) MAX8677C toc16 5.1 3.0 2.5 4.5 VVL (V) VSYS (V) 0.5 0 ISYS (A) SYS OUTPUT VOLTAGE vs. SYS OUTPUT CURRENT 4.3 500mA USB IVL = 10mA 2.0 IVL = 0mA 1.5 4.1 1.0 3.9 0.5 100mA 3.7 0 3.5 0 0.5 1.0 1.5 ISYS (A) 6 6 5.5 VSYS (V) VSYS (V) 4.15 3 SYS OUTPUT VOLTAGE vs. SYS OUTPUT CURRENT (DC) 4.2 4.20 2 SYS OUTPUT VOLTAGE vs. SYS OUTPUT CURRENT (USB AND DC DISCONNECTED) 4.3 4.25 1 VUSB (V) 4.4 4.30 0 85 4.5 MAX8677C toc13 4.40 35 TEMPERATURE (C) AMBIENT TEMPERATURE (C) SYS OUTPUT VOLTAGE vs. DC VOLTAGE 10 MAX8677C toc14 -40 MAX8677C toc15 4.180 0.9900 VSYS (V) MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 2.0 2.5 3.0 0 2 4 6 8 10 12 VDC (V) _______________________________________________________________________________________ 14 2.5 3.0 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector MAX8677C toc18 1.0 0.6 2.5 2.0 1.5 0.4 0.2 1.0 0.5 0 0 50 100 0.40 IBAT 3.5 VBAT (V) IBAT 3.0 0.30 2.5 0.25 2.0 0.20 1.5 0.15 1.0 0.10 0.5 0.05 0 0 0 20 40 60 80 100 120 140 TIME (min) TIME (min) DC CONNECT WITH USB CONNECTED (RSYS = 25) DC CONNECT WITH NO USB (RSYS = 25) 3.6V IDC VBAT 3.68V CDC CHARGING 2V/div VSYS 3.6V 180 500mA/div 4.35V 3.6V CDC CSYS CHARGING CHARGING CSYS CHARGING 500mA 0A 160 MAX8677C toc21 MAX8677C toc20 VSYS 0.35 3.0 150 4.35V 1.2A IDC 0A IUSB 0A 500mA NEGATIVE BATTERY CURRENT FLOWS INTO THE BATTERY (CHARGING) 0A IBAT BATTERY -335mA CHARGER 500mA/div 500mA/div NEGATIVE BATTERY CURRENT FLOWS INTO THE BATTERY (CHARGING) 120mA IBAT BATTERY CHARGER SOFT-START 500mA/div -330mA SOFT-START 200s/div 400s/div DC DISCONNECT WITH NO USB (RSYS = 25) USB CONNECT WITH NO DC (RSYS = 20) 4.35V MAX8677C toc23 VUSB 3.6V 1.2A IDC IUSB 500mA/div 0A VSYS VUOK 0.2A 500mA/div IBAT -1A NEGATIVE BATTERY CURRENT FLOWS INTO THE BATTERY (CHARGING) 20s/div 500mA/div -1A MAX8677C toc22 VSYS 0.50 0.45 4.0 0.8 0 VBAT 4.5 VBAT 5.0 4.5 4.0 3.5 MAX8677C toc19 5.0 1.2 IBAT (A) VBAT (V) 6.0 5.5 CHARGE PROFILE --1400mAh BATTERY USB INPUT--500mA CHARGE IBAT (A) CHARGE PROFILE --1400mAh BATTERY ADAPTER INPUT--1A CHARGE VCHG IBAT 0V 5V CUSB CHARGING 10V/div CSYS CHARGING 500mA/div 500mA 0A 3.6V 4.35V 4.3V 3V 0V 5V/div 3V 0V 5V/div 155mA -300mA 500mA/div BATTERY CHARGER SOFT-START 200s/div _______________________________________________________________________________________ 7 MAX8677C Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) USB DISCONNECT WITH NO DC (RSYS = 20) USB SUSPEND MAX8677C toc24 VUSB MAX8677C toc25 5V 0V VUSUS 10V/div 475mA IUSB VSYS 3.7V IBAT 5V/div 3V 0V -300mA 500mA IUSB 3.7V VSYS 3.6V 0V VUOK VCHG 500mA/div 0A VCHG 120mA IBAT 1A/div 5V/div 0A 500mA/div 3.6V 0V 3V 5V/div -500mA 0A 500mA/div 5V/div 3V 3V 200s/div 200s/div USB RESUME MAX8677C toc26 VUSUS 0V IUSB 0A VSYS 3.6V VCHG IBAT 5V/div 3V CUSB CHARGING 500mA 4.35V 3V 500mA/div 3.7V 5V/div 0V 0A BATTERY CHARGER SOFT-START -500mA 500mA/div 200s/div Pin Description 8 PIN NAME FUNCTION 1 PREQ 2, 3 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 with PEN1, PEN2, USUS, and RPSET. See Table 2. Both DC pins must be connected together externally. 4 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 with a logic signal to disable battery charging. 5 PEN1 DC Input Limit Control. If PEN1 is high, the DC input current limit is 3000/RPSET. If PEN1 is low, the DC limit is set by PEN2 and USUS. See Table 2. Charge Prequal Output. Active-low, open-drain output pulls low when the charger enters the prequal state. See Figure 5. _______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector PIN NAME FUNCTION 6 PEN2 USB High/Low Control. PEN2 sets the DC or USB current limit to 100mA (PEN2 low) or 500mA (PEN2 high). PEN2 controls both DC and USB current limits when PEN1 is low. See Table 2. 7 PSET DC Input Current-Limit Set. Connect a resistor to ground to program the DC current limit to 3000/RPSET. 8 VL 9 GND 10 CT 11 ISET Charge Current Set Input. A resistor (RISET) from ISET to GND programs the maximum charge current up to 1.5A. The prequal charge current is 10% of the set maximum charge current. 12 THM Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor that has good thermal contact with the battery from THM to GND. Connect a resistor equal to the thermistor +25C 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. 13 USUS USB Suspend Input. With PEN1 low, driving USUS high turns off both the USB and DC inputs. With PEN1 high, driving USUS high turns off only the USB input. See Table 2. 14 TSET Termination Current Set Pin. Connect to GND, leave open, or connect to VL for a 5%, 10%, or 15% (of ICHGMAX) termination current (ITERM) threshold. 15, 16 USB USB Power Input. USB is capable of delivering up to 0.5A to SYS. The USB current limit is set with PEN2 and USUS. See Table 2. Both USB pins must be connected together externally. 17, 18 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. 19 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. Logic LDO Output. VL is the output of an LDO that powers the MAX8667C internal circuitry. VL also provides 3.3V at up to 10mA to power external circuitry. Connect a 0.1F capacitor from VL to GND. Ground Charge Timer Program Pin. A capacitor from CT to GND sets the fast-charge (tFSTCHG) and prequal (tPREQUAL) fault timers. Connect to GND to disable the timer. System Supply Output. SYS is connected to BAT through an internal 40m system load switch when DC or USB is invalid, or when the SYS load is greater than the input current limit. 20, 21 SYS When a valid voltage is present at DC or USB, SYS is limited to 4.35V. When the system load (ISYS) exceeds the DC or USB current limit, SYS is regulated to 68mV below BAT, and both the USB input and the battery service SYS. 22 DOK Bypass SYS to GND with a 10F X5R or X7R ceramic capacitor. Both SYS pins must be connected together externally. DC Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at DC. 23 UOK USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB. 24 FLT Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or fast-charge complete. -- EP Exposed Paddle. Connect the exposed paddle to GND. Connecting the exposed paddle does not remove the requirement for proper ground connections to the appropriate pins. _______________________________________________________________________________________ 9 MAX8677C Pin Description (continued) MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector AC ADAPTER DC DC POWER MANAGEMENT PWR OK DOK MAX8677C SYS CURRENTLIMITED VOLTAGE REGULATOR Li+ BATTERY CHARGER AND SYS LOAD SWITCH CHARGER CURRENTVOLTAGE CONTROL SET INPUT LIMIT TO SYSTEM LOAD ISET BAT BAT+ BATT USB USB USB POWER MANAGEMENT THERMISTOR MONITOR (SEE FIGURE 7) THM NTC VL PWR OK UOK CURRENTLIMITED VOLTAGE REGULATOR IC THERMAL REGULATION CHARGE TERMINATION AND MONITOR CHG PREQ VL = 15% TSET SET INPUT LIMIT DC MODE 500mA USB 100mA LIMIT 5% FLT CHARGE TIMER CT PEN1 PEN2 USB SUSPEND N.C. = 10% USUS PSET CEN INPUT AND CHARGER CURRENT LIMIT SET LOGIC GND EP DC LIMIT Figure 1. Block Diagram Circuit Description The MAX8677C contains an Li+ battery charger, as well as power MOSFETs and control circuitry to manage power flow in portable devices. See Figure 1. The 10 charger has two power inputs, DC and USB. These can be separately connected to an AC adapter output and a USB port, or the DC input can be a single power input that connects to either an adapter or USB. Logic inputs, PEN1 and PEN2, select the correct current limits ______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector MAX8677C RPU 3X 560k TO VL RPU 560k PREQUAL ADAPTER CDC 4.7F OFF 1 PREQ 2 DC 3 DC 4 CHARGE ON 5 MAX8677C CEN PEN1 FLT UOK DOK SYS SYS 24 FAULT OUTPUT 23 USB PWR OK 22 DC PWR OK 21 20 TO SYSTEM LOAD CSYS 10F 560k TO VL 500mA 6 100mA 7 PEN2 PSET CHG BAT 19 18 RPSET 8 CL 0.1F CT 0.068F VL BAT 17 USB 16 1-CELL Li+ CBAT 4.7F USB 9 10 11 GND CT ISET USB 15 12 THM VBUS CUSB 4.7F GND TSET 14 RISET 10k CHARGE INDICATOR USUS 13 TO VL: ITERM = 15% OPEN: ITERM = 10% GND: ITERM = 5% NTC 10k +25C USB SUSPEND Figure 2. Typical Application Circuit Using Separate DC and USB Connectors for two-input or single-input operation. Figure 2 is the typical application circuit using separate DC and USB connectors. Figure 3 is the typical application circuit using a Mini 5-style connector or other DC/USB common connector. In addition to charging the battery, the MAX8677C also supplies power to the system through the SYS output. The charging current is also provided from SYS so that the set input current limit controls the total SYS current, which is the sum of the system load current and the battery-charging current. SYS is powered from either the DC input pin or the USB input pin. If both the DC and USB are connected, DC takes precedence. ______________________________________________________________________________________ 11 MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 3X 560k TO VL 560k MINI 5-STYLE CONNECTOR VBUS DD+ ID GND PREQUAL 1 2 3 CDC 4.7F 1 PREQ 2 DC 3 DC 4 5 OFF CHARGE ON 4 HI = DC DC-USB ID LO = USB 5 500mA 6 CEN PEN1 MAX8677C FLT UOK DOK SYS SYS 24 FAULT OUTPUT 23 USB PWR OK 22 DC PWR OK 21 20 560k TO VL 100mA 7 PEN2 PSET CHG BAT 19 8 CL 0.1F CT 0.068F 9 10 11 VL GND CT BAT 17 USB 16 USB 15 ISET TSET THM USUS CHARGE INDICATOR 18 RPSET 12 1-CELL Li+ CBAT 4.7F 14 RISET 10k TO SYSTEM LOAD CSYS 10F TO VL: ITERM = 15% 13 OPEN: ITERM = 10% GND: ITERM = 5% NTC 10k +25C USB SUSPEND Figure 3. Typical Application Circuit Using Mini 5-Style Connector or Other DC/USB Common Connector In some instances, there may not be enough adapter current or USB current to supply peak system loads. The MAX8677C Smart Power Selector circuitry offers flexible power distribution from an AC adapter or USB source to the battery and system load. The battery is charged with any available power not used by the system load. If a system load peak exceeds the input 12 current limit, supplemental current is taken from the battery. Thermal limiting prevents overheating by reducing power drawn from the input source. In the past, it might have been necessary to reduce system functionality to limit current drain when a USB source is connected. However, in the MAX8677C, this is no longer the case. When the DC or USB source hits its limit, the battery supplies supplemental current to maintain the load. ______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector COMPONENT (FIGURES 2, 3) FUNCTION Input filter capacitor 4.7F ceramic capacitor CL VL filter capacitor 0.1F ceramic capacitor CSYS SYS output bypass capacitors 10F ceramic capacitor CBAT Battery bypass capacitor 4.7F ceramic capacitor CT Charger timing capacitor 0.068F low TC ceramic capacitor Logic output pullup resistors 560k THM RT Negative TC thermistor Phillips NTC thermistor, P/N 2322-640-63103, 10k 5% at +25C THM pullup resistor 10k 1% RPSET Input current-limit programming resistor 1.5k 1% for 2A limit RISET Fast-charge current programming resistor 3k 1% for 1A charging The MAX8677C features OVP. Part of this protection is a 4.35V voltage limiter at SYS. If the DC or USB input exceeds 4.35V, SYS still limits at 4.35V. The MAX8677C has numerous other charging and power-management features, which are detailed in the following sections. Smart Power Selector The MAX8677C Smart Power Selector seamlessly distributes power between the external inputs, the battery, and the system load (Figure 4). The basic functions performed are: * With both an external power supply (USB or adapter) and battery connected: When the system load requirements are less than the input current limit, the battery is charged with residual power from the input. When the system load requirements exceed the input current limit, the battery supplies supplemental current to the load. * * PART CIN RPU (x 4) MAX8677C Table 1. External Components List for Figures 2 and 3 System Load Switch An internal 40m MOSFET connects SYS to BAT (Q3, Figure 4) when no voltage source is available at DC or USB. When an external source is detected at DC or USB, this switch is opened and SYS is powered from the valid input source through the input limiter. The SYS-BAT switch also holds up SYS when the system load exceeds the input current limit. If that should happen, the SYS-BAT switch turns on so that the battery supplies additional SYS load current. If the system load continuously exceeds the input current limit, the battery does not charge, even though external power is connected. This is not expected to occur in most cases, since high loads usually occur only in short peaks. During these peaks, battery energy is used, but at all other times the battery charges. AC ADAPTER Q1 When the battery is connected and there is no external power input, the system is powered from the battery. When an external power input is connected and there is no battery, the system is powered from the external power input. A thermal-limiting circuit reduces the battery charge rate and external power-source current to prevent the MAX8677C from overheating. DC USB MAX8677C SYS CHARGE CURRENT LOAD CURRENT USB Q2 Q3 SYSTEM LOAD BAT CHARGE AND SYS LOAD SWITCH BATTER GND Figure 4. Smart Power Selector Block Diagram ______________________________________________________________________________________ 13 MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector Input Limiter The input voltage limiter is essentially an LDO regulator. While in dropout, the regulator dissipates a small I2R loss through the 0.2 MOSFET (Q1, Figure 4) between DC and SYS. With an AC adapter or USB source connected, the input limiter distributes power from the external power source to the system load and battery charger. In addition to the input limiter's primary function of passing power to the system and charger loads at SYS, it performs several additional functions to optimize use of available power: * Input Voltage Limiting. If an input voltage is above the overvoltage threshold (6.9V typ), the MAX8677C enters overvoltage lockout (OVLO). OVLO protects the MAX8677C and downstream circuitry from highvoltage stress up to 14V at DC and 8V at USB. In OVLO, VL remains on, the input switch that sees overvoltage (Q1, Q3, Figure 4) opens, and the appropriate power-monitor output (DOK, UOK) is high impedance, and CHG is high impedance. * Thermal Limiting. The MAX8677C reduces input limiter current by 5%/C when its die temperature exceeds +100C. The system load (SYS) has priority over the charger current, so input current is first reduced by lowering charge current. If the junction temperature still reaches +120C in spite of chargecurrent reduction, no input (DC or USB) current is drawn, the battery supplies the entire system load, and SYS is regulated at 68mV below BAT. Note that this on-chip thermal-limiting circuitry is not related to and operates independently from the thermistor input. * Adaptive Battery Charging. While the system is powered from DC, the charger draws power from SYS to charge the battery. If the charger load plus system load exceeds the input current limit, an adaptive charger control loop reduces charge current to prevent the SYS voltage from collapsing. Maintaining a higher SYS voltage improves efficiency and reduces power dissipation in the input limiter. The total current through the switch (Q1 or Q2 in Figure 4) is the sum of the load current at SYS and the battery charging current. The limiter clamps at 4.35V, so input voltages greater than 4.35V can increase power dissipation in the limiter. The limiter power loss is (VDC - 4.35) x I, but not less than I2 x 0.2. Also note that the MAX8677C turns off any input that exceeds 6.9V (nominal). If both DC and USB see overvoltage, both input switches (Q1 and Q2, Figure 4) open and the charger turns off. The BAT-SYS switch (Q3, Figure 4) closes, allowing the battery to power SYS. An input is also invalid if it is less than BAT, or less than the DC undervoltage threshold of 3.5V (falling). With an invalid input voltage, SYS connects to BAT through a 40m switch (Q3, Figure 4). Input Overcurrent Protection. The current at DC and USB is limited to prevent input overload. This current limit can be selected to match the capabilities of the source, whether it is a 100mA or 500mA USB source, or an AC adapter. When the load exceeds the input current limit, SYS drops to 68mV below BAT and the battery supplies supplemental load current. * DC and USB Connections and Current-Limit Options Input Current Limit The input and charger current limits are set as shown in Table 2. It is often preferable to change the input current limit as the input power source is changed. The MAX8677C facilitates this by allowing different input current limits for DC and USB as shown in Table 2. Table 2. Input Limiter Control Logic POWER SOURCE AC adapter at DC input USB power at DC input DOK UOK PEN1 PEN2 USUS DC INPUT CURRENT LIMIT L X H X X 3000/RPSET L X L L L 100mA L X L H L 500mA USB suspend L X L X H H L X L L USB power at USB input; DC unconnected H L X H L H L X X H DC and USB unconnected H H X X X USB INPUT CURRENT LIMIT 3000/RISET USB input off; DC input has priority 100mA 500mA 0 100mA No DC input MAXIMUM CHARGE CURRENT* 500mA 3000/RISET USB suspend 0 No USB input 0 *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. 14 ______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector Separate Adapter and USB Connectors When the AC adapter and USB have separate connectors, the adapter output connects to DC and the USB source connects to USB. PEN1 is permanently tied high (to DC or VL). The DC current limit is set by RPSET, while the USB current limit is set by PEN2 and USUS. Single Common Connector for USB or Adapter When a single connector is used for both AC adapter and USB sources, the DC input is used for both input sources. When an AC adapter is connected at DC, PEN1 should be pulled high to select the current limit set by RPSET. When a USB source is connected, PEN1 should be low to select 500mA, 100mA, or USB suspend (further selected by PEN2 and USUS). PEN1 can be pulled up by the AC adapter power to implement hardware adapter/USB selection. USB Suspend Driving USUS high when PEN1 is low turns off charging, as well as the SYS output and reduces input current to 190A to accommodate USB suspend mode. Power Monitor Outputs (UOK, DOK) DOK is an open-drain output that pulls low when the DC input has valid power. UOK is an open-drain output that pulls low when the USB input sees valid power. A valid input for DC or USB is between 4.1V and 6.6V. If a single power-OK output is preferred, DOK and UOK can be wire-ORed together. The combined output then pulls low if either USB or DC sees a valid input. Soft-Start To prevent input transients that can cause instability in the USB or AC adapter power source, the rate of change of input current and charge current is limited. When a valid DC or USB input is connected, the input current limit is ramped from zero to the set current-limit value (as shown in Table 2). If DC is connected with no USB power present, input current ramps in 1.5ms. If DC is connected with USB already present, input current ramps in 50s. When USB is connected with no DC present, input current also ramps in 50s. If USB is connected with DC already present, the USB input is ignored. If an adapter is plugged into DC while USB is already powered, the input current limit reramps from zero back up to the DC current limit so that the AC adapter does not see a load step. During this transition, if the input current limit is below the SYS load current, the battery supplies the additional current needed to support the load. Additionally, capacitance can be added to SYS to support the load during input power transitions. When the charger is turned on, charge current ramps from zero to the ISET current value in typically 1.5ms. Charge current also ramps when transitioning to fastcharge from prequal and when changing the USB charge current from 100mA to 500mA with PEN2. There is no dI/dt limiting, however, if ISET is changed suddenly using a switch at RISET. Battery Charger The battery charger state diagram is illustrated in Figure 5. With a valid DC or USB input, the battery charger initiates a charge cycle when the charger is enabled. It first detects the battery voltage. If the battery voltage is less than the BAT prequal threshold (3.0V), the charger enters prequal mode in which the battery charges at 10% of the maximum fast-charge current. This reduced charge rate ensures that the battery is not damaged by the fast-charge current while deeply discharged. Once the battery voltage rises to 3.0V, the charger transitions to fast-charge mode and applies the maximum charge current. As charging continues, the battery voltage rises until it approaches the battery regulation voltage (4.2V) where charge current starts tapering down. When charge current decreases to 5%, 10%, or 15% (as set by TSET) of the fast-charge current, the charger enters a brief 15s top-off, and then charging stops. If the battery voltage subsequently drops below the 4.1V recharge threshold, charging restarts and the timers reset. ______________________________________________________________________________________ 15 MAX8677C When the input current limit is reached, the first action taken by the MAX8677C is to reduce the battery charge current. This allows the regulator to stay in dropout, or at 4.35V, during heavy loads, thus reducing power dissipation. If, after the charge current is reduced to 0mA, the load at SYS still exceeds the input current limit, SYS begins to fall. When the SYS voltage drops to BAT, the SYS-BAT switch turns on, using battery power to support the system load during the load peak. The MAX8677C features flexible input connections (at the DC and USB input pins) and current-limit settings (set by PEN1, PEN2, PSET, and ISET) to accommodate nearly any input power configuration. However, it is expected that most systems use one of two external power schemes: separate connections for USB and an AC adapter, or a single connector that accepts either USB or AC adapter output. Input and charger current limit are controlled by PEN1, PEN2, RPSET, and RISET, as shown in Table 2. MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector NOT READY UOK AND DOK = HIGH IMPEDANCE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE PREQ = HIGH IMPEDANCE ICHG = 0mA UOK OR DOK = LOW CEN = 0 RESET TIMER CEN = HI OR REMOVE AND RECONNECT THE INPUT SOURCE(S). ANY STATE TOGGLE CEN OR REMOVE AND RECONNECT THE INPUT SOURCE(S). PREQUAL UOK OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE PREQ = LOW 0V VBATT 3V ICHG = ICHGMAX/10 VBATT < 2.82V, RESET TIMER VBATT > 3V, RESET TIMER FAST CHARGE VBATT < 2.8V RESET TIMER UOK OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE PREQ = HIGH IMPEDANCE 3V < VBATT < 4.2V ICHG ICHGMAX 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 THM NOT OK TIMER SUSPEND TEMPERATURE SUSPEND ICHG = 0mA UOK OR DOK = PREVIOUS STATE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE PREQ = PREVIOUS STATE TIMER > tPREQUAL FAULT UOK OR DOK = LOW CHG = HIGH IMPEDANCE FLT = LOW PREQ = PREVIOUS STATE ICHG = 0mA TIMER > tFSTCHG (TIMER SLOWED BY 2X IF ICHG < ICHGMAX/2, AND PAUSED IF ICHG < ICHGMAX/5 WHILE BAT < 4.2V) TOP-OFF UOK OR DOK = LOW CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE PREQ = HIGH IMPEDANCE BATT = 4.2V ICHG < ITERM VBAT < 4.1V RESET TIMER TIMER > 15s DONE UOK OR DOK = 0V CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE PREQ = HIGH IMPEDANCE 4.1 < VBATT < 4.2V ICHG = 0mA Figure 5. MAX8677C Charger State Flowchart 16 ______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector MONITORING THE BATTERY CHARGE CURRENT WITH VISET VISET = RISET 2000 x ICHG 1.5 VISET (V) Setting the Charge Current MAX8677C 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 MAX8677C Smart Power Selector circuitry independently manages charging and adapter/battery power hand-off. In these situations, CEN can be connected to ground. ISET adjusts charge current to match the capacity of the battery. A resistor from ISET to ground sets the maximum fast-charge current: ICHGMAX = 2000 x 1.5V/RISET = 3000/RISET Determine the ICHGMAX value by considering the characteristics of the battery. It is not necessary to limit the charge current based on the capabilities of the expected AC adapter/USB charging input, the system load, or thermal limitations of the PCB. The MAX8677C automatically adjusts the charging algorithm to accommodate these factors. Monitoring the Charge Current In addition to setting the charge current, ISET can also be used to monitor the actual current charging the battery. The ISET output voltage is: VISET = ICHG x 1.5V/ICHGMAX = ICHG x RISET/2000 where ICHGMAX is the set fast-charge current and ICHG is the actual battery charge current. A 1.5V output indicates the battery is being charged at the maximum set fast-charge current; 0V indicates no charging. This voltage is also used by the charger control circuitry to set and monitor the battery current. Avoid adding more than 10pF capacitance directly to the ISET pin. If filtering of the charge-current monitor is necessary, add a resistor of 100k or more between ISET and the filter capacitor to preserve charger stability. See Figure 6. Note that the actual charge current can be less than the set fast-charge current when the charger enters voltage mode or when charge current is reduced by the input current limiter or thermal limiter. This prevents the charger from overloading the input source or overheating the system. Charge Termination When the charge current falls to the termination threshold 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 in which charging stops. The termination current threshold (ITERM) is set by TSET to a percentage of the fast-charge current: Connect TSET to GND for ITERM = ICHGMAX x 5% 0 DISCHARGING 0 2000 (1.5V / RISET) BATTERY CHARGING CURRENT (A) Figure 6. Monitoring the Charge Current with the ISET Voltage Leave TSET open for ITERM = ICHGMAX x 10% Connect TSET to VL for ITERM = ICHGMAX x 15% 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, the charge current must be less than ITERM, the charger must be in voltage mode, and the input or thermal limiter must not be reducing the charge current. The charger exits the DONE state, and fast charge resumes if the battery voltage subsequently drops 100mV or if CEN is cycled. Charge Status Outputs Charge Output (CHG) CHG is an open-drain, active-low output that is low during charging. CHG is low when the battery charger is in its prequalification and fast-charge states. When charge current falls to the charge termination threshold and the charger is in voltage mode, CHG goes high impedance. CHG goes high impedance if the thermistor causes the charger to enter temperature suspend mode. When the MAX8677C is used with a microprocessor (P), connect a pullup resistor between CHG and the logic I/O voltage to indicate charge status to the P. Alternatively, CHG can sink up to 20mA for an LED indicator. Prequal Output PREQ PREQ is an open-drain, active-low output that goes low when the charger is in prequal state. ______________________________________________________________________________________ 17 MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector When the MAX8677C is used in conjunction with a P, connect a pullup resistor between PREQ and the logic I/O voltage to indicate charge status to the P. Alternatively, PREQ can sink up to 20mA for an LED indicator. Fault Output (FLT) and Charge Timer FLT is an open-drain, active-low output that goes low during a battery fault. The fault state occurs when either the prequal or fast-charge timer expires. The prequal and fast-charge fault timers are set by CCT: CCT tPREQUAL = 30 min x 0.068F tFSTCHG = 300 min x CCT 0.068F While in fast-charge mode, a large system load or device self-heating can cause the MAX8677C to reduce charge current. Under these circumstances, the fast-charge timer adjusts to ensure that adequate charge time is still allowed. Consequently, the fastcharge timer is slowed by 2x if charge current is reduced below 50% of the programmed fast-charge level. If charge current is reduced to below 20% of the programmed level, the fast-charge timer is paused. The fast-charge timer is not adjusted if the charger is in voltage mode where charge current reduces due to current tapering under normal charging. To exit a fault state, toggle CEN or remove and reconnect the input source(s). Note also that thermistor outof-range or on-chip thermal-limit conditions are not considered faults. When the MAX8677C is used in conjunction with a P, connect a pullup resistor between FLT and the logic I/O voltage to indicate fault status to the P. Alternatively, FLT can sink up to 20mA for an LED indicator. 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, charging resumes and the charge timer continues from where it left off. Connecting THM to GND disables the thermistor monitoring function. Table 3 lists fault temperatures for 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 10k (at +25C). Any resistance thermistor can be used as long as the value of RTB is equivalent to the thermistor's +25C resistance. For example, with a 10k at +25C thermistor, use 10k at RTB, and with a 100k at +25C thermistor, use 100k. CEN VL MAX8677C VL THERMISTOR CIRCUITRY RTB ALTERNATE THERMISTOR CONNECTION 0.74 VL COLD THM RTS 0.28 VL HOT THM OK RTP RT BYPASS THM 0.03 VL RT ALL COMPARATORS 60mV HYSTERESIS GND Figure 7. Thermistor Monitor Circuitry 18 ______________________________________________________________________________________ DISABLE CHARGER 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 1 1 RT = R25 x e T +273 - 298 Power Dissipation It is important to ensure that the heat generated by the MAX8677C is dissipated into the PCB. The package's exposed paddle must be soldered to the PCB with multiple vias tightly packed under the exposed paddle to ensure optimum thermal contact to the ground plane. This minimizes heat rise in the IC and ensures that maximum charging current is maintained over the widest range of external conditions. Table 4 shows the thermal characteristics of the MAX8677C package. Table 4. Package Thermal Characteristics where: RT = The resistance in of the thermistor at temperature T in Celsius R25 = The resistance in of the thermistor at +25C = The material constant of the thermistor, which typically ranges from 3000K to 5000K T = The temperature of the thermistor in C Table 3 shows the MAX8677C 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 . For example, a +45C hot threshold and 0C cold threshold can be realized by using a thermistor with a of 4250 and connecting 120k in parallel. Since the thermistor resistance near 0C is much higher than it is near +50C, a large parallel resistance lowers the cold threshold, while only slightly lowering the hot threshold. Conversely, a small series resistance 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. SINGLE-LAYER PCB MULTILAYER PCB Continuous Power Dissipation 1666.7mW Derate 20.8mW/C above +70C 2222.2mW Derate 27.8mW/C above +70C JA 48C/W 36C/W JC 2.7C/W 2.7C/W PCB Layout and Routing Good design minimizes ground bounce and voltage gradients in the ground plane, which can result in instability or regulation errors. GND 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. Connect GND to the exposed paddle directly under the IC. Use multiple tightly spaced vias to the ground plane under the exposed paddle to help cool the IC. Position input capacitors from DC, SYS, BAT, and USB to the powerground plane as close as possible to the IC. Keep highcurrent traces, such as those to DC, SYS, and BAT, as short and wide as possible. Refer to the MAX8677C evaluation kit for a suitable PCB layout example. Table 3. Fault Temperatures for Different Thermistors Thermistor (K) RTB (k) (Figure 7) 3000 3250 3500 3750 4250 10 10 10 10 10 Resistance at +25C (k) 10 10 10 10 10 Resistance at +50C (k) 4.59 4.30 4.03 3.78 3.32 Resistance at 0C (k) 25.14 27.15 29.32 31.66 36.91 Nominal Hot-Trip Temperature (C) 55 53 51 49 46 Nominal Cold-Trip Temperature (C) -3 -1 0 2 4.5 Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 19 MAX8677C For a typical 10k (at +25C) thermistor and a 10k RTB resistor, the charger enters a temperature suspend state when the thermistor resistance falls below 3.97k (too hot) or rises above 28.7k (too cold). This corresponds to a 0C to +50C range when using a 10k NTC thermistor with a beta of 3500. The general relation of thermistor resistance to temperature is defined by the following equation: 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.) 24L QFN THIN.EPS MAX8677C 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 20 ______________________________________________________________________________________ 1.5A Dual-Input USB/AC Adapter Charger and Smart Power Selector 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. MAX8677C 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.) Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX8677CETG+ MAX8677CETG+T MAX8677CETG/V+ MAX8677CETG/V+T MAX8677CETG+B4H