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19-4502; Rev 1; 11/09
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KIT ATION EVALU BLE AVAILA
2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
General Description Features
o Efficient DC-DC Converter Powers System Load and Charger o 4MHz Switching for Tiny External Components o Instant On--Works with No Battery or Low Battery o Dual Current-Limiting Input Circuits--AC Adapter or USB Automatic Adapter/USB/Battery Switchover to Support Load Transients 50m System-to-Battery Switch Supports USB Spec o Thermistor Monitor o Integrated Current-Sense Resistor o No External MOSFETS or Diodes o 4.1V to 16V Input Operating Voltage Range
MAX8903B
The MAX8903B is an integrated 1-cell Li+ charger and Smart Power SelectorTM with dual (AC adapter and USB) power inputs. The switch mode charger uses a high switching frequency to eliminate heat and allow for 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 MAX8903B 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 load 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 4.1V to 6.5V range of with up to 8V protection. The MAX8903B 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, taper current detection for charge status, 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 MAX8903B is available in a 4mm x 4mm, 28-pin thin QFN package.
Ordering Information
PART MAX8903BETI+ TEMP RANGE -40C to +85C PIN-PACKAGE 28 Thin QFN-EP (4mm x 4mm)
+Denotes a lead(Pb)-free/RoHS-compliant package. **EP = Exposed pad.
Typical Operating Circuit
AC ADAPTER OR USB
LX DC
CS Q1 SYS LOAD CURRENT CHARGE AND SYS LOAD SWITCH Q3 BAT BATTERY SYSTEM LOAD
Applications
PDA, Palmtop, and Wireless Handhelds Personal Navigation Devices Smart Cell Phones Portable Multimedia Players Mobile Internet Devices
CHARGE CURRENT
PWM STEP-DOWN USB
USB Q2
Smart Power Selector is a trademark of Maxim Integrated Products, Inc.
MAX8903B
GND
Pin Configuration appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
ABSOLUTE MAXIMUM RATINGS
DC, LX to GND .......................................................-0.3V to +20V DCM to GND .............................................-0.3V to (VDC + 0.3V) 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 VL Short-Circuit to GND .............................................Continuous Continuous Power Dissipation (TA = +70C) (derate 28.6 mW/C above +70C) ............................2286mW Operating Temperature Range ...........................-40C to +85C Junction Temperature Range ............................-40C to +150C Storage Temperature Range .............................-65C to +150C Soldering Temperature (Reflow) ......................................+260C
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 = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER DC INPUT DC Operating Range DC Undervoltage Threshold DC Overvoltage Threshold When VDOK goes low, VDC rising, 500mV typical hysteresis No valid USB input Valid USB input 4.15 3.9 4.0 16.5 4.0 4.3 17 2.3 15 1 1 0.10 0.15 0.15 0.31 When SYS regulation and charging stops, VDC falling, 200mV hysteresis VDC = 8V, VBAT = 4V VDC = 5V, VBAT = 3V 0.5 RIDC = 3k VDC = 6V, VSYS = 4V No valid USB input Valid USB input before soft-start RIDC = 6k RIDC = 12k DC Soft-Start Time 1900 950 450 2000 1000 500 1 20 0 15 4 3 2 2100 1050 550 ms s mA 30 2 2 0.25 mV MHz A mA 16 4.1 4.4 17.5 4 V V V CONDITIONS MIN TYP MAX UNITS
When VDOK goes high, VDC rising, 500mV typical hysteresis Charger enabled, no switching, VSYS = 5V Charger enabled, f = 3MHz, VDC = 5V
DC Supply Current
Charger enabled, VCEN = 0V, 100mA USB mode (Note 2) Charger enabled, VCEN = 5V, 100mA USB mode (Note 2) VDCM = 0V, VUSUS = 5V
DC High-Side Resistance DC Low-Side Resistance DC-to-BAT Dropout Resistance DC-to-BAT Dropout Voltage Switching Frequency DC Step-Down Output Current- Limit Step Range DC Step-Down Output Current Limit
2
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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 = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER DC Output Current 500mA USB Mode (Note 3) DC Output Current 100mA USB Mode (Note 2) SYS to DC Reverse Current Blocking USB INPUT USB Operating Range USB Standoff Voltage USB Undervoltage Threshold USB Overvoltage Threshold USB Current Limit When VUOK goes low, VUSB rising, 500mV hysteresis When VUOK goes high, VUSB rising, 500mV hysteresis VIUSB = 0V (100mA setting) VIUSB = 5V (500mA Setting) ISYS = IBAT = 0mA, VCEN = 0V USB Supply Current Minimum USB to BAT Headroom USB to SYS Dropout Resistance USB Soft-Start Time SYS OUTPUT Minimum SYS Regulation Voltage (VSYSMIN) Regulation Voltage Load Regulation CS to SYS Resistance SYS to CS Leakage BAT to SYS Resistance BAT to SYS Reverse Regulation Voltage SYS Undervoltage Threshold BATTERY CHARGER BAT Regulation Voltage (VBATREG) Charger Restart Threshold (VRSTRT) BAT Prequal Threshold Prequal Charge Current IBAT = 0mA TA = +25C TA = -40C to +85C 4.179 4.158 -150 2.4 4.2 4.2 -100 2.5 10 4.221 4.242 -60 2.6 V mV V % ISYS = 1A, VBAT < VSYS_MIN ISYS = 0A ISYS = 0 to 2A VDC = 6V, VDCM = 5V, VSYS = 4V, ICS = 1A VSYS = 5.5V, VDC = VCS = 0V VDC = VUSB = 0V, VBAT = 4.2V, ISYS = 1A VUSB = 5V, VDC = 0V, VIUSB = 0V, ISYS = 200mA SYS falling, 200mV hysteresis (Note 4) 50 1.8 4.265 3.0 4.325 25 0.07 0.01 0.05 75 1.9 0.1 100 2.0 4.395 V V mV/A A mV V VUSB rising VDC falling below DC UVLO to initiate USB soft-start ISYS = IBAT = 0mA, VCEN = 5V VUSUS = 5V (USB suspend mode) 0 3.95 6.8 90 450 4.0 6.9 95 475 1.3 0.8 0.115 15 0.2 1 20 4.1 6.3 8 4.05 7.0 100 500 3 2 0.25 30 0.35 mV ms s mA V V V V mA CONDITIONS VDCM = 0V, VIUSB = 5V MIN 450 TYP 475 MAX 500 UNITS mA
MAX8903B
VDCM = 0V, VIUSB = 0V
90
95
100
mA
VSYS = 5.5V, VDC = 0V
0.01
A
Change in VBAT from DONE to fast-charge VBAT rising, 180mV hysteresis Percentage of fast-charge current set at ISET
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
ELECTRICAL CHARACTERISTICS (continued)
(VDC = VUSB = 5V, VBAT = 4V, circuit of Figure 2, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER RISET = 600 Fast-Charge Current DONE Threshold RISET Resistor Range ISET Output Voltage ISET Current Monitor Gain BAT Leakage Current Charger Soft-Start Time Charger Thermal-Limit Temperature Charger Thermal-Limit Gain CHARGER TIMER Prequalification Time Fast-Charge Time Top-Off Time Timer Accuracy Timer Extend Current Threshold Timer Suspend Current Threshold THERMISTOR MONITOR THM Threshold, Hot THM Threshold, Cold THM Threshold, Disabled THM Threshold DC, USB Enabled THM Input Leakage When charging is suspended, 1% hysteresis When charging is suspended, 1% hysteresis When THM function is disabled below this voltage When power from DC, USB is enabled, THM falling, 50mV hysteresis THM = GND or VL (Note 5) High level Logic Input Thresholds (DCM, CEN, USUS, IUSB) Low level Hysteresis 50 0.27 x VVL 0.73 x VVL 0.0254 x VVL 0.83 x VVL -0.2 1.3 0.4 0.28 x VVL 0.74 x VVL 0.03 x VVL 0.87 x VVL 0.001 0.29 x VVL 0.75 x VVL 0.036 x VVL 0.91 x VVL +0.2 V V V V A V V mV Percentage of fast-charge current below which the timer clock operates at half-speed Percentage of fast-charge current below which timer clock pauses CCT = 0.15F CCT = 0.15F CCT = 0.15F -15 40 16 50 20 33 660 132 +15 60 24 min min min % % % Charge current = 0 at +120C No DC or USB input With valid input power, VCEN = 5V RISET = 1.2k RISET = 2.4k Percentage of fast-charge, IBAT decreasing 0.6 1.5 1.25 0.05 3 1.0 100 5 4 6 CONDITIONS MIN 1800 900 450 TYP 2000 1000 500 10 4.0 MAX 2200 1100 550 % k V mA/A A ms C %/C mA UNITS
THERMAL SHUTDOWN, VL, AND LOGIC I/O: CHG, FLT, DOK, UOK, DCM, CEN, USUS, IUSB
4
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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 = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Logic Input Leakage Current (CEN, USUS, IUSB) Logic Input Leakage Current (DCM) Logic Output Voltage, Low (CHG, FLT, DOK, UOK) Logic Output Leakage Current, High (CHG, FLT, DOK, UOK) VL Output Voltage Thermal Shutdown Temperature Thermal Shutdown Hysteresis CONDITIONS VINPUT = 0V to 5.5V (Note 5) VDCM = 0V to 16V, VDC = 16V Sinking 1mA Sinking 10mA VOUT = 5.5V (Note 5) VDC = VUSB = 6V, IVL = 0 to 10mA 4.6 TA = +25C TA = +85C MIN -0.2 TYP 0.001 0.001 0.01 8 80 0.001 5 160 15 1 5.4 50 MAX +0.2 1 UNITS A A mV A V C C
MAX8903B
Note 1: Limits are 100% production tested at TA = +25C. 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 its high-side switch operates as a linear regulator with a 100mA current limit. The linear regulator's output is connected to LX and its output current flows through the inductor into CS and finally to SYS. Note 3: For the 500mA USB mode, the actual current drawn from USB is less than the output current by the VIN/VOUT ratio 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. Note 5: Limits over the operating temperature range are generated by design only.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
BATTERY CHARGER EFFICIENCY vs. BATTERY VOLTAGE
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 BATTERY VOLTAGE (V) IBATT = 0.15A IBATT = 1.5A VDC = 12V VDC = 8V
MAX8903B toc01
SWITCHING FREQUENCY vs. DC VOLTAGE
MAX8903B toc02
SYS EFFICIENCY vs. SYS OUTPUT CURRENT
90 80
MAX8903B toc03
100 VDC = 5V
4.5 4.0 SWITCHING FREQUENCY (MHz) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 4 6 8 10 VDC (V) 12 14 RISET = 1.2k VCEN = 0V VBAT = 4V VBAT = 3V
100
SYS EFFICIENCY (%)
70 60 50 40 30 20 10 0 VDC = 4.5V 1 10 100 1000 10,000 VDC = 6V VDC = 16V VDC = 11V
16
SYS OUTPUT CURRENT (mA)
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
USB QUIESCENT CURRENT vs. USB VOLTAGE
MAX8903B toc04
USB QUIESCENT CURRENT vs. USB VOLTAGE
MAX8903B toc05
BATTERY LEAKAGE CURRENT vs. BATTERY VOLTAGE
70 60 50 40 30 20 10 0 USB UNCONNECTED 0 1 2 3 4 5 6
MAX8903B toc06
1.6 1.4 USB QUIESCENT CURRENT (mA) 1.2 1.0 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 6 7 USB VOLTAGE (V) CHARGER DISABLED CHARGER ENABLED
140 USB QUIESCENT CURRENT (A) 120 100 80 60 40 USB SUSPEND 20 0 0 1 2 3 4 5 6 7 USB VOLTAGE (V)
80 BATTERY LEAKAGE CURRENT (nA)
BATTERY VOLTAGE (V)
BATTERY LEAKAGE CURRENT vs. AMBIENT TEMPERATURE
MAX8903B toc07
CHARGE CURRENT vs. BATTERY VOLTAGE--USB MODE
MAX8903B toc08
CHARGE CURRENT vs. BATTERY VOLTAGE--DC MODE
900 800 CHARGE CURRENT (mA) 700 600 500 400 300 200 CHARGER ENABLED IBAT SET TO 1A IDC SET TO 1A
MAX8903B toc09
90 BATTERY LEAKAGE CURRENT (nA) 80 70 60 50 40 30 20 10 0 -40 -15 10 35 60
500 450 400 CHARGE CURRENT (mA) 350 300 250 200 150 100 50 0 VIUSB = 0V 0 1 2 3 4 5 VIUSB = VUSB CHARGER ENABLED IBAT SET TO 1A
1000
100 0 0 1 2 3 4 5
85
TEMPERATURE (C)
BATTERY VOLTAGE (V)
BATTERY VOLTAGE (V)
NORMALIZED CHARGE CURRENT vs. AMBIENT TEMPERATURE
MAX8903B toc10
BATTERY REGULATION VOLTAGE vs. AMBIENT TEMPERATURE
MAX8903B toc11
SYS VOLTAGE vs. USB VOLTAGE
4.5 4.0 SYS VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 VUSB RISING VCEN = 5V VBAT = 0V VDC = 0V VUSB FALLING
MAX8903B toc12
1.015 NORMALIZED CHARGE CURRENT 1.010 1.005 1.000 0.995 0.990 0.985 -40
4.205 29ppm/C BATTERY REGULATION VOLTAGE (V) 4.200
5.0
VUSB = 5V, VBATT = 4V
4.195
4.190
4.185
1.0 0.5 RSYS = 1M 0 1 2 3 4 5 6 7
-15
10
35
60
85
4.180 -40
0 -15 10 35 60 85 TEMPERATURE (C) USB VOLTAGE (V)
TEMPERATURE (C)
6
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
SYS OUTPUT CURRENT vs. SYS VOLTAGE
MAX8903B toc13
MAX8903B
SYS VOLTAGE vs. DC VOLTAGE
5.0 4.5 4.0 SYS VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 2 4 6 8 10 12 14 16 18 DC VOLTAGE (V) VCEN = 5V VBAT = 0V VDC = 0V VDC FALLING VDC RISING 1.2
VDC = 5V 1.0 SYS OUTPUT CURRENT (A) 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 SYS VOLTAGE (V)
SYS VOLTAGE vs. SYS OUTPUT CURRENT, DC INPUT
MAX8903B toc15
SYS VOLTAGE vs. SYS OUTPUT CURRENT, USB INPUT
VUSB = 5V 4.335 SYS VOLTAGE (V) 4.330 4.325 4.320 4.315 4.310
MAX8903B toc16
4.40 4.35 4.30 SYS VOLTAGE (V) 4.25 4.20 4.15 4.10 4.05 4.00 3.95 3.90 0 0.5 1.0 USB AND DC UNCONNECTED VBATT = 4V VDC = 5.75V
4.340
1.5
0
100
200
300
400
500
SYS OUTPUT CURRENT (A)
SYS OUTPUT CURRENT (mA)
VL VOLTAGE vs. DC VOLTAGE
MAX8903B toc17
CHARGE PROFILE--1400mAh BATTERY ADAPTER INPUT--1A CHARGE
6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
MAX8903B toc18
6 5 VL VOLTAGE (V) 4
IDC SET TO 1A IBAT SET TO 2A
VBAT
VBAT (V)
MAX8903B toc14
1.2 1.0 0.8 0.6 IBAT (A)
3 2 1 0 0 2 4 6 8 10 12 14 16 18 DC VOLTAGE (V)
IBAT
0.4 0.2 0 120 140
0
20
40
60
80
100
TIME (min)
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
CHARGE PROFILE--1400mAh BATTERY USB INPUT--500mA CHARGE
5.0 4.5 4.0 3.5 VBAT (V) 3.0 2.5 2.0 1.5 1.0 0.5 0 0 IUSB SET TO 500mA IBAT SET TO 2A VBAT IBAT
MAX8903B toc19
DC SWITCHING WAVEFORMS--LIGHT LOAD
0.500 0.450 0.400 0.350 IBAT (A) 0.300 0.250 0.200 0.150 0.100 0.050 200ns/div RSYS = 44 500mA/div 0A 5V/div 0V
MAX8903B toc20
20mV/div AC-COUPLED
0 20 40 60 80 100 120 140 160 180 200 TIME (min)
DC SWITCHING WAVEFORMS--HEAVY LOAD
MAX8903B toc21
DC CONNECT WITH USB CONNECTED (RSYS = 25)
MAX8903B toc22
VOUT
20mV/div AC-COUPLED
3.6V VSYS IDC 347mA
2V/div 500mA/div
VLX RSYS = 5 ILX
5V/div 0V IUSB
475mA -IBAT = CHARGING
500mA/div
500mA/div 0A 200ns/div
IBAT
-355mA
0A 500mA/div
200s/div
DC CONNECT WITH NO USB (RSYS = 25)
3.6V 3.6V 3.44V 3.84V
MAX8903B toc23
DC DISCONNECT WITH NO USB (RSYS = 25)
20V/div 5V/div 3.68V VSYS VBAT 3.6V 3.6V
MAX8903B toc24
VSYS VBAT
2V/div 5V/div
CDC CHARGING IDC IBAT 0A
CSYS CHARGING 850mA
1A/div
IDC
850mA
0A
1A/div
-IBAT = CHARGING 144mA BATTERY CHARGER SOFT-START 400s/div IBAT 1A/div -1A 40s/div -1A 144mA -IBAT = CHARGING 1A/div
8
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.) SYS LOAD TRANSIENT (0A TO 1A)
MAX8903B toc25
MAX8903B
USB CONNECT WITH NO DC (RSYS = 25)
3.6V VSYS 3.75V 3.5V CUSB CHARGING 5V
MAX8903B toc26
2V/div 5V/div
VSYS
50mV/div AC-COUPLED
VUSB 475mA
500mA/div ISYS 500mA/div 0A IUSB IBAT 144mA 500mA/div -330mA
BATTERY CHARGER SOFT-START 400s/div
100s/div
USB DISCONNECT WITH NO DC (RSYS = 25)
3.6V
USB SUSPEND
MAX8903B toc28
MAX8903B toc27
VSYS VUSB
2V/div 5V/div
VUSUS
0V
3V
5V/div 500mA/div
5V 475mA
IUSB VSYS
475mA
0A
IUSB IBAT
500mA/div
3.7V
2V/div
-330mA
144mA
500mA/div
IBAT -475mA
0A
500mA/div
200s/div
100s/div
USB RESUME
MAX8903B toc29
VUSUS 3V CUSB CHARGING IUSB VSYS 0A 3.6V
0V
5V/div 475mA 500mA/div
3.8V
3.6V 2V/div
IBAT
0A
BATTERY CHARGER SOFT-START 200s/div
-475mA
500mA/div
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Pin Description
PIN 1, 2 NAME PG FUNCTION Power Ground for Step-Down Low-Side Synchronous n-channel MOSFET. Both PG pins must be connected together externally. 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 4.7F ceramic capacitor from DC to PG. Current-Limit Mode Setting for the DC Power Input. When logic-high, the DC input current limit is set by the resistance from IDC to GND. When logic-low, the DC input current limit is internally programmed to 500mA or 100mA, as set by the IUSB logic input. There is an internal diode from DCM (anode) to DC (cathode) as shown in Figure 1. High-Side MOSFET Driver Supply. Bypass BST to LX with a 0.1F ceramic capacitor. 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. 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). Logic LDO Output. VL is the output of an LDO that powers the MAX8903B internal circuitry and charges the BST capacitor. Connect a 1F ceramic capacitor from VL to GND. 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. 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. Ground. GND is the low-noise ground connection for the internal circuitry. 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. 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. USB Suspend Input. Drive USUS logic-high to enter USB suspend mode, lowering USB current to 170A, and internally shorting SYS to BAT. Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor 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. USB Power Input. USB is capable of delivering 100mA or 500mA to SYS as set by the IUSB logic input. Connect a 4.7F ceramic capacitor from USB to GND. Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or fast-charge completes. 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). 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.
3, 4
DC
5
DCM
6 7 8 9 10 11 12 13 14 15
BST IUSB DOK VL CT IDC GND ISET CEN USUS
16
THM
17 18 19
USB FLT UOK
20, 21
BAT
10
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
Pin Description (continued)
PIN 22 NAME CHG FUNCTION Charger Status Output. Active-low, open-drain output pulls low when the battery is in fast-charge or prequal. Otherwise, CHG is high impedance. System supply output. SYS connects to BAT through an internal 50m 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 4.325V. When the system load (ISYS) exceeds the DC or USB current limit, SYS is regulated to 50mV below BAT and both the USB input and the battery service SYS. Bypass SYS to GND with a 22F X5R or X7R ceramic capacitor. Both SYS pins must be connected together externally. 25, 26 CS 70m Current-Sense Input. Connect the step-down inductor from LX to CS. When the step-down regulator is on, there is a 70m 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. Inductor Connection. Connect the inductor between LX and CS. Both LX pins must be connected together externally. 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.
MAX8903B
23, 24
SYS
27, 28 --
LX EP
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
PG
LX
BST
CS
AC ADAPTER
DC
DC POWER MANAGEMENT
MAX8903B SYS TO SYSTEM LOAD
PWROK PWM STEP-DOWN REGULATOR
Li+ BATTERY CHARGER AND SYS LOAD SWITCH
ISET
DOK
SET INPUT LIMIT
CHARGER CURRENTVOLTAGE CONTROL
BATTERY CONNECTOR BAT BAT+ + BAT-
USB USB
USB POWER MANAGEMENT
T THERMISTOR MONITOR (SEE FIGURE 7) IC THERMAL REGULATION THM NTC
PWROK UOK
CURRENTLIMITED VOLTAGE REGULATOR
VL
SET INPUT LIMIT DC
CHARGE TERMINATION AND MONITOR
CHG
DCM DC MODE USB LIMIT 500mA 100mA USB SUSPEND USUS IDC DC LIMIT IUSB INPUT AND CHARGER CURRENT-LIMIT SET LOGIC
FLT CHARGE TIMER CT
CEN GND EP
Figure 1. Functional Diagram
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
RPU 4 x 100k TO VL 1 2 CDC 4.7F ADAPTER 3 DC 4 DC 6 CBST 0.1F BST
PG PG MAX8903B FLT UOK DOK CHG 18 19 8 22 RISET FAULT OUTPUT USB PWR-OK DC PWR-OK CHARGE INDICATOR
27 LX ISET 28 LX IDC 25 26 CS CS SYS SYS
13
11
RIDC
24 23 CSYS 22F
TO SYSTEM LOAD
USB VBUS GND
CUSB 4.7F
17
USB
BAT BAT
21 20 CBAT 4.7F 1-CELL LI+
TO DC OFF CHARGE ON 500mA 100mA USB SUSPEND
5
DCM VL CEN 16 9 CVL 1F THM RT 10k
14
7
IUSB
15 10
USUS CT GND 12
NTC 10k
CCT 0.15F
Figure 2. Typical Application Circuit Using a Separate DC and USB Connector
Circuit Description
The MAX8903B 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.
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 MAX8903B also manages load switching from the battery to and from an external power source with an on-chip 50m MOSFET. This switch also helps support load peaks using battery power when the input source is overloaded.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
RPU 4 x 100k TO VL 1 5-PIN USB CONNECTOR CDC 4.7F VBUS DD+ ID GND CBST 0.1F 3 DC 4 DC 6 BST 2
PG PG MAX8903B FLT UOK DOK CHG 18 19 8 22 RISET FAULT OUTPUT USB PWR-OK DC PWR-OK CHARGE INDICATOR
27 LX ISET 28 LX IDC 25 26 CS CS SYS SYS
13
11
RIDC
24 23 CSYS 22F
499k
TO SYSTEM LOAD
17 DC MODE USB ADAPTER
USB
BAT BAT
21 20 CBAT 4.7F 1-CELL LI+
5
DCM VL CEN 16 9 CVL 1F THM RT 10k
OFF CHARGE ON 500mA 100mA USB SUSPEND
14
7
IUSB
15 10
USUS CT GND 12
NTC 10k
CCT 0.15F
Figure 3. Typical Application Circuit Using a Mini 5 Style Connector or Other DC/USB Common Connector
As shown in Figure 1, the IC includes a full-featured charger with thermistor monitor, fault timer, charger status, and fault outputs. The IC also includes 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 system up). The MAX8903B prevents overheating during high ambient temperatures by limiting charging current when the die temperature exceeds +100C.
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 shorts the system voltage to the battery for lowest power dissipation. The step-down regulation point is then controlled by three feedback signals: maximum
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Table 1. External Components List for Figures 2 and 3
COMPONENT (FIGURES 2 AND 3) CDC, CUSB CVL CSYS CBAT CCT RPU (x4) THM RT RIDC RISET VL filter capacitor SYS output bypass capacitor Battery bypass capacitor Charger timing capacitor Logic output pullup resistors Negative TC thermistor THM pullup resistor DC input current limit programming resistor Fast-charge current programming resistor FUNCTION Input filter capacitor PART 4.7F ceramic capacitor 1.0F ceramic capacitor 22F ceramic capacitor 4.7F ceramic capacitor 0.15F low TC ceramic capacitor 100k Phillips NTC thermistor, P/N 2322-640-63103, 0k 5% at +25C 10k 3k 1%, for 2A limit 1.2k 1%, for 1A charging
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 charge current 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 short the system voltage to the battery and the system voltage (V SYS) is slightly above V SYSMIN as shown in Figure 4. The battery charger independently controls the battery charging current. VSYSMIN is set to 3.0V in the MAX8903B. For other V SYSMIN values, please contact the factory. After the battery charges to 50mV above VSYSMIN, the system voltage is shorted 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 and fast-charge current are satisfied.
4.325V 4.2V
VSYS VSYSMIN IBAT x RON
VBAT
VCEN = 0V VDC AND/OR VUSB = 5.0V
Figure 4. SYS Tracking VBAT to the Minimum System Voltage
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. 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, the ripple current in the inductor is always as small as possible to reduce the 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 varies with operating conditions. See the Typical Operating Characteristics.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
DC Mode (DCM) As shown in Table 2, the DC input supports both AC adapters (up to 2A) and USB (up to 500mA). With the DCM logic input set high, the DC input is in adapter mode and the DC input current limit is set by the resistance from IDC to GND (RIDC). Calculate RIDC according to the following equation: RIDC = 6000V/IDC-MAX
With the DCM logic input set low, the DC input current limit is internally programmed to 500mA or 100mA as set by the IUSB logic input. With the IUSB logic input set high, the DC input current limit is 500mA and the DC input delivers current to SYS through the step-down regulator. With the IUSB logic input set low, the DC input current limit is 100mA. In this 100mA mode, the step-down regulator is turned off and its high-side switch operates as a linear regulator with a 100mA current limit. The linear regulator's output is connected to LX and its output current flows through the inductor into CS and finally to SYS. The DCM pin has an internal diode to DC as shown in Figure 1. To prevent current from flowing from DCM through the internal diode and to the DC input, DCM cannot be driven to a voltage higher than DC. The circuit of Figure 3 shows a simple MOSFET and resistor on DCM to prevent any current from flowing from DCM through the internal diode to DC. This circuit of Figure 3 allows a microprocessor to drive the gate of the MOSFET to any state at any time. An alternative to the simple MOSFET and resistor on DCM as shown in Figure 3 is to place a 1M resistor in series with the DCM input to the microprocessor. The microprocessor can then monitor the DOK output and make sure that whenever DOK is high DCM is also low. In the event that DCM is driven to a higher voltage than DC, the 1M series resistance limits the current from DCM through the internal diode to DC to a few A.
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 valid and DOK is driven low when: 4.15V < VDC < 16V. When the USB voltage is also valid, the DC source is 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 +100C, a thermallimiting circuit reduces the input current limit by 5%/C, bringing the charge current to 0mA at +120C. 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 while in this mode. If the junction temperature rises beyond +120C, 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.
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.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Table 2. Input Limiter Control Logic
POWER SOURCE DOK UOK DCM*** IUSB USUS DC STEP-DOWN OUTPUT CURRENT LIMIT 6000V/RIDC USB INPUT CURRENT LIMIT MAXIMUM CHARGE CURRENT** Lesser of 1200V/RISET and 6000V/RIDC USB input off. DC input has priority. Lesser of 1200V/RISET and 100mA Lesser of 1200V/RISET and 500mA 0 100mA Lesser of 1200V/RISET and 100mA Lesser of 1200V/RISET and 500mA 0 0
AC Adapter at DC Input
L
X
H
X
X
L USB Power at DC Input L L H USB Power at USB Input, DC Unconnected
X
L
L
L
100mA
X X L
L L X
H X L
L H L
500mA USB suspend
H H
L L H
X X X
H X X
L H X
No DC input
500mA USB suspend No USB input
DC and USB Unconnected
H
**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. ***There is an internal diode from DCM (anode) to DC (cathode) as shown in Figure 1. If the DCM level needs to be set by a P, use a MOSFET for isolation as shown in Figure 3. X = Don't care.
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 4.325V. 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 50m 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-limiting current. The 50m pMOS also turns on if valid DC input power is removed.
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 4.325V. 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 170A to accommodate USB suspend mode.
USB Input When charging from the USB input, the DC input stepdown regulator is turned 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 shorted to the battery. The USB input then supplies the SYS load and charges the battery with any extra available current, while not
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 MAX8903B smart power selector circuitry independently manages charging and adapter/battery power hand-off. In these situations, CEN may be connected to ground.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
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, the SYS current is ramped from zero current to the set current-limit value in typically 50s. 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 current 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 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.
MONITORING THE BATTERY CHARGE CURRENT WITH VISET
1.5
VISET (V)
0
DISCHARGING
0 BATTERY CHARGING CURRENT (A)
1200V/RISET
Figure 5. Monitoring the Battery Charge Current with the Voltage from ISET to GND
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 top-off period and then enters the DONE state where charging stops. See the Charge Timer section. Note that if 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.
Battery Charger
While a valid input source is present, the battery charger attempts to charge the battery with a fast-charge current determined by the resistance from ISET to GND. Calculate the RISET resistance according to the following equation: RISET = 1200V/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 overload an AC adapter. See Figure 5. When the VBATT is below 2.5V, 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.
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 (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 charge indicator.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
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 0V < VBAT < 2.5V ICHG ICHGMAX/10 VBATT < 2.32V RESET TIMER = 0 VBATT > 2.5V RESET TIMER TIMER > tPREQUAL
TOGGLE CEN OR REMOVE AND RECONNECT THE INPUT SOURCE(S)
FAULT UOK AND/OR DOK = LOW CHG = HIGH IMPEDANCE FLT = LOW ICHG = 0mA TIMER > tFSTCHG (TIMER SLOWED BY 2x IF ICHG < ICHGMAX/2, AND PAUSED IF ICHG < ICHGMAX/5 WHILE VBAT < 4.2V
VBATT < 2.32V RESET TIMER
FAST-CHARGE UOK AND/OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE 2.5V < VBAT < VBATREG ICHG ICHGMAX ICHG > ITERM RESET TIMER ICHG < ITERM AND VBAT = VBATREG AND THERMAL OR INPUT LIMIT NOT EXCEEDED; RESET TIMER
ANY CHARGING STATE THM OK TIMER RESUME THM NOT OK TIMER SUSPEND TOP-OFF UOK AND/OR DOK = LOW CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE VBAT = VBATREG ICHG = ITERM
VBAT < VBATREG + VRSTRT RESET TIMER
TEMPERATURE SUSPEND ICHG = 0mA UOK OR DOK PREVIOUS STATE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE
TIMER > tTOP-OFF
DONE UOK AND/OR DOK = 0V CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE VBATREG + VRSTRT < VBAT < VBATREG ICHG = 0mA
Figure 6. MAX8903B Charger State Flow Chart
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 (P), connect a pullup resistor between FLT and the logic I/O voltage to indicate charge status to the P. 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.
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
CEN MAX8903B THERMISTOR CIRCUITRY VL VL
ALTERNATE THERMISTOR CONNECTION
RTB 0.74 VL THM COLD
THERMISTOR DETECTOR
RTS 0.28 VL RTP RT ENABLE THM RT 0.03 VL ALL COMPARATORS 60mV HYSTERESIS GND HOT
THM OUT OF RANGE DISABLE CHARGER
Figure 7. Thermistor Monitor Circuitry
Table 3. Fault Temperatures for Different Thermistors
THERMISTOR Thermistor (K) RTB (k) (Figure 7) Resistance at +25C (k) Resistance at +50C (k) Resistance at 0C (k) Nominal Hot Trip Temperature (C) Nominal Cold Trip Temperature (C) 3000 10 10 4.59 25.14 55 -3 3250 10 10 4.30 27.15 53 -1 VALUE 3500 10 10 4.03 3750 10 10 3.78 4250 10 10 3316 36.91 46 4.5
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).
tPREQUAL = 33 min x CCT 0.15 F CCT 0.15 F CCT 0.15 F
tFST - CHG = 660 min x t TOP - OFF = 132 min x
29.32 31.66 50 0 49 2
While in fast-charge mode, a large system load or device self-heating may cause the MAX8903B 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).
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
VL Regulator VL is a 5V linear regulator that powers the MAX8903's internal circuitry and charges the BST capacitor. VL is used externally to bias the battery's thermistor. VL takes its input power from USB or DC. When input power is available from both USB and DC, VL takes power from DC. VL is enabled whenever the input voltage at USB or DC is greater than ~1.5V. VL does not turn off when the input voltage is above the overvoltage threshold. Similarly, VL does not turn off when the charger is disabled (CEN = high). Connect a 1F ceramic capacitor from VL to GND.
Table 4 shows the MAX8903B 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. 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 10k thermistor and a 10k pullup to VL, this results in an additional 250A load. This load can be reduced to 25A by instead using a 100k thermistor and 100k pullup resistor.
MAX8903B
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 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 10k (at +25C). Any resistance thermistor can be used as long as the value 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 . 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:
1 1 - T + 273C 298C
Power Dissipation
Table 4. Package Thermal Characteristics
28-PIN 4mm x 4mm THIN QFN SINGLE-LAYER PCB Continuous Power Dissipation JA JC 1666.7mW Derate 20.8mW/C above +70C 48C/W 3C/W MULTILAYER PCB 2286mW Derate 28.6mW/C above +70C 28.6C/W 3C/W
Inductor Selection for Step-Down DC-DC Regulator
The MAX8903B step-down DC-DC regulator implements a control scheme that typically results in a 4MHz nominal switching frequency. When the input voltage decreases to a value near the output voltage, high duty cycle operation occurs and, due to minimum off-time constraints, 4MHz operation is not achievable. The regulator then provides a fixed minimum off-time, peak current regulation. Similarly, when the input voltage is too high to allow 4MHz operation due to minimum on-time constraints, the regulator becomes a fixed minimum ontime valley current regulator.
RT = R25 x e
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
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
For a given maximum output voltage, the minimum ripple current condition occurs at the lowest input voltage provided that the minimum input voltage allows the regulator to maintain 4MHz operation. If the minimum input voltage dictates an off-time less than 100ns, then the minimum ripple condition occurs just before the regulator enters fixed minimum off-time operation. To allow the current-mode regulator to provide a low-jitter, stable duty factor operation, the inductor ripple current should be greater than 200mA in the minimum ripple current condition. The maximum allowed output inductance LOUT_MAX is therefore obtained using the equations (1) and (2) below. VSYS(MAX) TOFF = 100ns if 1 - VDC(MIN) (1)
x 1 100ns, 4MHz
MAX8903B
(4) L OUT _ MIN _ TON =
(VDC(MAX) - VSYS(MIN) ) x TON
K x IDC
where VDC(MAX) is maximum input voltage, VSYS(MIN) is the minimum charger output voltage, and TON is the ontime at high input voltage, as given by the following equation: VSYS(MIN) 1 TON = 70ns if x 70ns, VDC(MAX) 4MHz otherwise, VSYS(MIN) 1 TON = x VDC(MAX) 4MHz (5) The saturation current rating of the inductor must be greater than the maximum step-down output current programmed at the IDC pin plus one-half the maximum ripple current, as given by equation (6). (6) ISAT > IDC + ILRIPPLE _ MAX 2
otherwise, VSYS(MAX) 1 TOFF = 1 - x VDC(MIN) 4MHz where TOFF is the minimum off-time, VSYS(MAX) is maximum charger output voltage, and VDC(MIN) is minimum DC input voltage. (2) L OUT _ MAX = VSYS(MAX) x TOFF 0.2A
where ISAT is the saturation current rating of the output inductor, IDC is the maximum step-down output current programmed at the IDC pin, and ILRIPPLE_MAX is the greater of the ripple currents obtained from (7) and (8). (7) ILRIPPLE _ MIN _ TOFF = VSYS(MAX) x TOFF L OUT
where LOUT_MAX is the maximum allowed inductance. To obtain a small-sized inductor with acceptable core loss, while providing stable, jitter-free operation, the actual output inductance LOUT, is obtained by choosing an appropriate ripple factor K, and picking an available inductor in the range of the two values of inductance yielded by equations (3) and (4) which describe the maximum ripple current conditions in the minimum ontime and minimum off-time modes. The recommended ripple factor ranges from (0.2 K 0.4) for (2A IDC 1A) designs. (3) L OUT _ MIN _ TOFF = VSYS(MAX) x TOFF K x IDC
(8) ILRIPPLE _ MIN _ T
ON
=
(VDC(MAX) - VSYS(MIN) ) x TON
L OUT
where TOFF is the minimum off-time obtained from (1).
Table 5 gives recommended inductors for typical charger applications. Example: VDC(MIN) = 4.5V, VDC(MAX) = 5.5V, VSYS(MIN) = 3V, VSYS(MAX) = 4.2V, RIDC = 3k, K = 0.2, IDC = 2A (maximum step-down output current) From (1): TOFF = 100ns From (2): L OUT _ MAX = 4.2V x 100ns = 2.1H 0.2A
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
From (3): L OUT _ MIN _ TOFF = From (5): TON = 3V 1 x = 136ns 5.5V 4MHz 4.2V x 100ns = 1.05H 0.2 x 2A
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.
MAX8903B
which is greater than the minimum on-time of 70ns. From (4): L OUT _ MIN _ TON = Choose LOUT = 1H. From (7): ILRIPPLE _ MIN _ TOFF = From (8): ILRIPPLE _ MIN _ TON = 4.2V x 100ns = 420mA 1H (5.5V - 3V) x 136ns = 0.85H 0.2 x 2A
(5.5V - 3V) x 136ns = 341mA
1s
UOK BAT BAT
Pin Configuration
USUS 15 14 13 12 CEN ISET GND IDC CT VL DOK 11 10 9 + 1 PG 2 PG 3 DC 4 DC 5 DCM 6 BST 7 IUSB 8 THM 16 USB 17 FLT 18
From (6), the saturation current rating for the inductor: ISAT > 2A + 0.420A , 2 ISAT > 2.21A
TOP VIEW
21 CHG 22 SYS 23 SYS 24 CS 25 CS 26 LX 27 LX 28
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MAX8903B
THIN QFN 4mm x 4mm
Chip Information
PROCESS: BiCMOS
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 28 TQFN-EP PACKAGE CODE T2844-1 DOCUMENT NO. 21-0139
24L QFN THIN.EPS
24
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power
Package Information continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
MAX8903B
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2A, 1-Cell Li+ DC-DC Charger for USB and Adapter Power MAX8903B
Revision History
REVISION NUMBER 0 1 REVISION DATE 3/09 11/09 Initial release Made various corrections DESCRIPTION PAGES CHANGED -- 1-7, 10, 12-21
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.
26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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