View MAX8903A_4556152.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

19-4410; Rev 0; 12/08
KIT ATION EVALU LE B AVAILA
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power
General Description Features
Efficient DC-DC Converter Eliminates Heat 4MHz Switching for Tiny External Components Instant On--Works with No Battery or Low Battery Dual Current-Limiting Input Circuits--AC Adapter or USB Automatic Adapter/USB/Battery Switchover to Support Load Transients 50m System-to-Battery Switch Supports USB Spec Thermistor Monitor Integrated Current-Sense Resistor No External MOSFETS or Diodes 4.1V to 16V Input Operating Voltage Range
MAX8903A
The MAX8903A 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 tiny external components. It can operate with either separate inputs for USB and AC adapter power, or from a single input that accepts both. All power switches for charging and switching the load between battery and external power are included on-chip. No external MOSFETs, blocking diodes, or current-sense resistors are required. The MAX8903A features optimized smart power control to make the best use of limited USB or adapter power. Battery charge current and SYS output current limit are independently set. Power not used by the system charges the battery. Charge current and SYS output current limit can be set up to 2A while USB input current can be set to 100mA or 500mA. Automatic input selection switches the system from battery to external power. The DC input operates from 4.15V to 16V with up to 20V protection, while the USB input has a range of 4.1V to 6.3V with up to 8V protection. The MAX8903A internally blocks current from the battery and system back to the DC and USB inputs when no input supply is present. Other features include prequal charging and timer, fast charge timer, overvoltage protection, charge status and fault outputs, power-OK monitors, and a battery thermistor monitor. In addition, on-chip thermal limiting reduces battery charge rate and AC adapter current to prevent charger overheating. The MAX8903A is available in a 4mm x 4mm, 28-pin thin QFN package.
Ordering Information
PART MAX8903AETI+ TEMP RANGE -40C to +85C PIN-PACKAGE 28 Thin QFN-EP**
+Denotes a lead(Pb)-free/RoHS-compliant package. **EP = Exposed pad.
Typical Operating Circuit
AC ADAPTER OR USB
Applications
PDAs, Palmtops, and Wireless Handhelds Personal Navigation Devices Smart Cell Phones Portable Multimedia Players Mobile Internet Devices Ultra Mobile PCs
LX DC
CS SYS LOAD CURRENT CHARGE AND SYS LOAD SWITCH SYSTEM LOAD
CHARGE CURRENT
PWM STEP-DOWN USB
USB
BAT
BATTERY
*Protected by US Patent #6,507,172. Smart Power Selector is a trademark of Maxim Integrated Products, Inc.
MAX8903A
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.
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
ABSOLUTE MAXIMUM RATINGS
DC, LX, DCM to GND .............................................-0.3V to +20V DC to SYS .................................................................-6V to +20V BST to GND ...........................................................-0.3V to +26V BST TO LX ................................................................-0.3V to +6V USB to GND .............................................................-0.3V to +9V USB to SYS..................................................................-6V to +9V VL to GND ................................................................-0.3V to +6V THM, IDC, ISET, CT to GND .........................-0.3V to (VL + 0.3V) DOK, FLT, CEN, UOK, CHG, USUS, BAT, SYS, IUSB, CS to GND ................................-0.3V to +6V SYS to BAT ...............................................................-0.3V to +6V PG, EP (exposed pad) to GND .............................-0.3V to +0.3V DC Continuous Current (total in two pins)......................2.4ARMS USB Continuous Current.......................................................1.6A LX Continuous Current (total in two pins).......................2.4ARMS CS Continuous Current (total in two pins) ......................2.4ARMS SYS Continuous Current (total in two pins) .......................3ARMS BAT Continuous Current (total in two pins) .......................3ARMS Continuous Power Dissipation (TA = +70C) 28-Pin Thin QFN-EP Multilayer (derate 28.6mW/C above +70C) ..........2286mW 28-Pin Thin QFN-EP Single-Layer (derate 20.8mW/C above +70C)...1666.7mW Operating Temperature Range ...........................-40C to +85C Junction Temperature Range ............................-40C to +150C 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 = 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 CurrentLimit Step Range DC Step-Down Output Current Limit
2
_______________________________________________________________________________________
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 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 Charger Restart Threshold BAT Prequal Threshold Prequal Charge Current IBAT = 0mA TA = +25C TA = -40C to +85C 4.179 4.158 -150 2.9 4.2 4.2 -100 3 10 4.221 4.242 -60 3.1 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 4.3 3.0 4.4 40 0.07 0.01 0.05 75 1.9 0.1 100 2.0 4.5 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
MAX8903A
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
_______________________________________________________________________________________
3
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
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 Timer Accuracy Timer Extend Current Threshold Timer Suspend Current Threshold Charge Done Delay Time THERMISTOR MONITOR THM Threshold, Hot THM Threshold, Cold THM Threshold, Disabled THM Input Leakage When charging is suspended, 1% hysteresis When charging is suspended, 1% hysteresis THM function is disabled below this voltage THM = GND or VL; TA = +25C THM = GND or VL; TA = +85C High level Logic-Input Thresholds (DCM, CEN, USUS, IUSB) Logic-Input Leakage Current (DCM, CEN, USUS, IUSB) Low level Hysteresis VINPUT = 0 to 5.5V TA = +25C TA = +85C 50 0.001 0.01 1 1.3 0.4 0.27 x VVL 0.73 x VVL 0.0254 x VVL -0.1 0.28 x VVL 0.74 x VVL 0.03 x VVL +0.001 0.01 0.29 x VVL 0.75 x VVL 0.036 x VVL +0.2 V V V A Percentage of fast-charge current below which the timer clock operates at half-speed Percentage of fast-charge current below which timer clock pauses From done threshold detection until charger turns off and CHG goes high CCT = 0.15F CCT = 0.15F -15 40 16 50 20 15 33 660 +15 60 24 min min % % % s 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 1 1.0 100 5 4 6 CONDITIONS MIN 1800 900 450 TYP 2000 1000 500 10 2.4 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 V mV A
4
_______________________________________________________________________________________
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 Output Voltage, Low (CHG, FLT, DOK, UOK) Sinking 1mA Sinking 10mA TA = +25C TA = +85C 4.6 CONDITIONS MIN TYP 8 80 0.001 0.01 5 3.2 160 15 5.4 1 MAX 50 UNITS mV A V V C C
MAX8903A
Open-Drain Output Leakage VOUT = 5.5V Current, High (CHG, FLT, DOK, UOK) VL Output Voltage VL UVLO Threshold Thermal Shutdown Temperature Thermal Shutdown Hysteresis VVL falling; 200mV hysteresis
VDC = VUSB = 6V, IVL = 0 to 1mA
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 a low-dropout linear regulator is connected from DC to SYS. Note 3: For the 500mA USB mode, the actual current drawn from USB is less than the output current due to the input/output current ratio of the DC-DC converter. Note 4: For short-circuit protection, SYS sources 25mA below VSYS = 400mV, and 50mA for VSYS between 400mV and 2V.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
BATTERY CHARGER EFFICIENCY vs. BATTERY VOLTAGE
MAX8903A toc01
SWITCHING FREQUENCY vs. VDC
MAX8903A toc02
SYS EFFICIENCY vs. DC VOLTAGE
90 80 SYS EFFICIENCY (%) 70 60 50 40 30 20 VDC = 6V VDC = 16V VDC = 11V
MAX8903A toc03
100 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 IBATT = 0.15A IBATT = 1.5A IBATT = 1.5A VDC = 12V VDC = 8V VDC = 5V
4.5 4.0 SWITCHING FREQUENCY (MHz) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 RISET = 1.2k CEN = 0V 4 6 8 10 12 14 VBAT = 4V VBAT = 3V
100
10 0 16 1 10
VDC = 4.5V 100 1000 10,000
5.0
BATTERY VOLTAGE (V)
DC VOLTAGE (V)
SYS OUTPUT CURRENT (mA)
_______________________________________________________________________________________
5
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
USB QUIESCENT CURRENT vs. USB VOLTAGE
MAX8903A toc04
USB QUIESCENT CURRENT vs. USB VOLTAGE
MAX8903A toc05
BATTERY LEAKAGE CURRENT vs. BATTERY VOLTAGE
70 60 50 40 30 20 10 0 7 USB UNCONNECTED 0 1 2 3 4 5 6
MAX8903A 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 20 USB SUSPEND 0 0 1 2 3 4 5 6 USB VOLTAGE (V)
80 BATTERY LEAKAGE CURRENT (nA)
BATTERY VOLTAGE (V)
BATTERY LEAKAGE CURRENT vs. AMBIENT TEMPERATURE
MAX8903A toc07
CHARGE CURRENT vs. BATTERY VOLTAGE--USB
450 400 CHARGE CURRENT (mA) 350 300 250 200 150 100 50 0 VIUSB = 0V VIUSB = VUSB CHARGER ENABLED IBAT SET TO 1.5A
MAX8903A toc08
CHARGE CURRENT vs. BATTERY VOLTAGE--DC MODE
900 800 CHARGE CURRENT (mA) 700 600 500 400 300 200 100 0 CHARGER ENABLED IBAT SET TO 1.5A IDC SET TO 1A
MAX8903A toc09
90 BATTERY LEAKAGE CURRENT (nA) 80 70 60 50 40 30 20 10 0 -40 -15 10 35 60
500
1000
85
0
1
2
3
4
5
0
1
2
3
4
5
TEMPERATURE (C)
BATTERY VOLTAGE (V)
BATTERY VOLTAGE (V)
NORMALIZED CHARGE CURRENT vs. AMBIENT TEMPERATURE
VUSB = 5V, VBATT = 4V
MAX8903A toc10
BATTERY REGULATION VOLTAGE vs. AMBIENT TEMPERATURE
MAX8903A 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 VUSB FALLING
MAX8903A toc12
1.015 NORMALIZED CHARGE CURRENT 1.010 1.005 1.000 0.995 0.990 0.985 -40
4.205 BATTERY REGULATION VOLTAGE (V)
5.0
4.200
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
_______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
SYS VOLTAGE vs. DC VOLTAGE
MAX8903A toc13
MAX8903A
SYS VOLTAGE vs. SYS OUTPUT CURRENT, DC INPUT
MAX8903A toc14
SYS VOLTAGE vs. SYS OUTPUT CURRENT, USB INPUT
4.395 4.390 SYS VOLTAGE (V) 4.385 4.380 4.375 4.370 4.365 VUSB = 5V
MAX8903A toc15
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 VDC FALLING VDC RISING
4.50 4.40 SYS VOLTAGE (V) 4.30 4.20 4.10 4.00 3.90 3.80 USB AND DC UNCONNECTED VBATT = 4V VDC = 5.75V
4.400
4.360 4.355 0 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 0 50 100 150 200 250 300 350 400 450 500 SYS OUTPUT CURRENT (mA) SYS OUTPUT CURRENT (A)
18
DC VOLTAGE (V)
VL VOLTAGE vs. DC VOLTAGE
MAX8903A toc16
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 0 20 40
MAX8903A toc17
CHARGE PROFILE--1400mAh BATTERY USB INPUT--500mA CHARGE
1.2 1.0 0.8 VBAT (V) IBAT (A) 0.6 5.0 4.5
MAX8903A toc18
6 5 VL VOLTAGE (V) 4
IDC SET TO 1A IBAT SET TO 2A
0.500 0.450 0.400 0.350
VBAT
4.0 3.5 3.0 2.5 2.0 VBAT IBAT
VBAT (V)
3 2 1 0 0 2 4 6 8 10 12 14 16 18 DC VOLTAGE (V)
0.250 0.200 0.150 0.100
IBAT
0.4 0.2 0.0 120 140
1.5 1.0 0.5 0 0 IUSB SET TO 500mA IBAT SET TO 2A
0.050
60
80
100
0 20 40 60 80 100 120 140 160 180 200 TIME (min)
TIME (min)
DC SWITCHING WAVEFORMS--LIGHT LOAD
MAX8903A toc19
DC SWITCHING WAVEFORMS--HEAVY LOAD
MAX8903A toc20
VOUT
20mV/div AC-COUPLED
VOUT
20mV/div AC-COUPLED
VLX
5V/div 0V VLX
5V/div 0V
ILX RSYS = 44 200ns/div
500mA/div 0A
ILX RSYS = 5
500mA/div 0A 200ns/div
_______________________________________________________________________________________
7
IBAT (A)
0.300
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.) DC CONNECT WITH USB CONNECTED (RSYS = 25)
MAX8903A toc21
DC CONNECT WITH NO USB (RSYS = 25)
3.6V 3.6V 3.44V 3.84V
MAX8903A toc22
DC DISCONNECT WITH NO USB (RSYS = 25)
2V/div 5V/div 3.68V VSYS VBAT 3.6V 3.6V
MAX8903A toc23
3.6V VSYS IDC 347mA
2V/div 500mA/div
VSYS VBAT
2V/div 5V/div
CDC CHARGING IDC IBAT 0A
CSYS CHARGING 850mA
1A/div
IUSB
475mA -IBAT = CHARGING
500mA/div
IDC
850mA
0A
1A/div
-IBAT = CHARGING 144mA BATTERY CHARGER SOFT-START 400s/div IBAT 1A/div -1A -1A 144mA -IBAT = CHARGING 40s/div 1A/div
IBAT
-335mA
0A 500mA/div
200s/div
SYS LOAD TRANSIENT (0 TO 1A)
MAX8903A toc24
USB CONNECT WITH NO DC (RSYS = 25)
3.6V VSYS 3.75V 3.5V CUSB CHARGING 5V
MAX8903A toc25
USB DISCONNECT WITH NO DC (RSYS = 25)
2V/div 5V/div 3.6V
MAX8903A toc26
VSYS VUSB
2V/div 5V/div
VSYS
50mV/div AC COUPLED
VUSB 475mA
5V 475mA
500mA/div ISYS 500mA/div 0A IUSB IBAT 144mA 500mA/div -330mA
IUSB IBAT
500mA/div
BATTERY CHARGER SOFT-START 400s/div
-330mA
144mA
500mA/div
100s/div
100s/div
USB SUSPEND
MAX8903A toc27
USB RESUME
MAX8903A toc28
VUSUS
0V
3V
5V/div 500mA/div
VUSUS
3V CUSB CHARGING 0A 3.6V
0V
5V/div 475mA 500mA/div
IUSB VSYS
475mA
0A
IUSB 2V/div VSYS
3.8V
3.6V 2V/div
3.7V
IBAT -475mA
0A
IBAT 500mA/div
0A
BATTERY CHARGER SOFT-START 200s/div
-475mA
500mA/div
200s/div
8
_______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power
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 resistor at IDC. When logic-low, the DC input current limit is internally programmed to 500mA or 100mA, as set by the IUSB pin. 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 MAX8903A 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 115A, 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.
MAX8903A
3, 4
DC
5 6 7 8 9 10 11 12 13 14 15
DCM BST IUSB DOK VL CT IDC GND ISET CEN USUS
16
THM
17 18 19
USB FLT UOK
20, 21
BAT
_______________________________________________________________________________________
9
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
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 4.4V. When the system load (ISYS) exceeds the DC or USB current limit, SYS is regulated to 50mV below BAT, and both the powered input and the battery service SYS. Bypass SYS to GND with a 10F X5R or X7R ceramic capacitor. Both SYS pins must be connected together externally. 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.
23, 24
SYS
25, 26
CS
27, 28 --
LX EP
10
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
PG
LX
BST
CS
AC ADAPTER
DC
DC POWER MANAGEMENT
MAX8903A SYS TO SYSTEM LOAD
PWR OK 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
PWR OK UOK
CURRENTLIMITED VOLTAGE REGULATOR
VL
SET INPUT LIMIT
CHARGE TERMINATION AND MONITOR
CHG
DCM DC MODE USB LIMIT 500mA 100mA USB SUSPEND USUS IDC CEN DC LIMIT EP GND IUSB INPUT AND CHARGER CURRENT-LIMIT SET LOGIC FLT CHARGE TIMER CT
Figure 1. Functional Block Diagram
______________________________________________________________________________________
11
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
RPU 4 x 100k TO VL 1 2 CDC 4.7F ADAPTER 3 DC 4 DC 6 CBST 0.1F BST
PG PG MAX8903A FLT UOK DOK CHG 18 19 8 22 RISET FAULT OUTPUT USB PWR OK DC PWR OK CHARGE INDICATOR
27 LX ISET 28 LX
13
L1 1H
IDC 25 26 CS CS SYS SYS
11
RIDC
24 23 CSYS 10F
TO SYSTEM LOAD
USB VBUS GND 17 CUSB 4.7F USB BAT BAT 21 20 CBAT 10F 1-CELL LI+
TO VL OFF CHARGE ON 500mA 100mA USB SUSPEND
5
DCM VL CEN 16 9 RT 10k THM
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 MAX8903A is a dual input charger with a 16V input for a wide range of DC sources and USB inputs. The IC includes a high-voltage (16V) input DC-DC step-down converter that reduces charger power dissipation while also supplying power to the system load. The stepdown converter supplies up to 2A to the system, the battery, or a combination of both.
A USB charge input can charge the battery and power the system from a USB power source. When powered from USB or the DC input, system load current peaks that exceed what can be supplied by the input are supplemented by the battery. The MAX8903A also manages load switching from the battery to and from an external power source with an on-chip 50m MOSFET. This switch also helps support load peaks using battery power when the input source is overloaded.
12
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
RPU 4 x 100k TO VL 1 SERIES MINI-B CDC 4.7F VBUS DD+ ID GND CBST 0.1F 3 DC 4 DC 6 BST 2
PG PG MAX8903A FLT UOK DOK CHG 18 19 8 22 RISET FAULT OUTPUT USB PWR OK DC PWR OK CHARGE INDICATOR
27 LX ISET 28 LX
13
L1 1H
IDC 25 26 CS CS SYS SYS
11
RIDC
24 23 CSYS 10F
TO SYSTEM LOAD
17
USB
BAT BAT
21 20 CBAT 10F 1-CELL LI+
TO SYSTEM LOGIC 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 3. Typical Application Circuit Using a Mini 5 Style Connector or Other DC/USB Common Connector
The IC includes a full-featured charger with thermistor monitor, fault timer, charger status, and fault outputs. Also included are power-OK signals for both USB and DC. Flexibility is maintained with adjustable charge current, input current limit, and a minimum system voltage (when charging is scaled back to hold the system voltage up). The MAX8903A prevents overheating during high ambient temperatures by limiting charging current when the die temperature exceeds +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 connects the system voltage to the battery for lowest power dissipation. The step-down regulation point is then controlled by three feedback signals: maximum
______________________________________________________________________________________
13
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
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 L1 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 DC input step-down inductor FUNCTION Input filter capacitor PART 4.7F ceramic capacitor 1.0F ceramic capacitor 10F ceramic capacitor 10F 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 1H inductor with ISAT > 2A
step-down output current programmed at IDC, maximum charger current programmed at ISET, and maximum die temperature. The feedback signal requiring the smallest current controls the average output current in the inductor. This scheme minimizes total power dissipation for battery charging and allows the battery to absorb any load transients with minimum system voltage disturbance. If the battery voltage is below VSYSMIN, the charger does not directly connect the system voltage to the battery. VSYS pin is held at a fixed point slightly above VSYSMIN, and does not track the battery. The battery charger independently controls the battery charging current. VSYSMIN is set to 3.0V in the MAX8903A, for other VSYSMIN values, please contact the factory. After the battery charges to 50mV above VSYSMIN, the system voltage is connected to the battery. The battery fast-charge current then controls the step-down converter to set the average inductor current so that both the programmed input current limit and fast-charge current limit are satisfied.
4.4V 4.2V
VSYS VSYSMIN IBAT x RON
VBAT
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.
14
Similarly, when the input voltage is too high to allow 4MHz operation due to the minimum on-time, the controller becomes a minimum on-time, valley current regulator. In this way, ripple current in the inductor is always as small as possible to reduce ripple voltage on SYS for a given capacitance. The ripple current is made to vary with input voltage and output voltage in a way that reduces frequency variation. However, the frequency still varies somewhat with operating conditions. See the Typical Operating Characteristics.
DC Input--USB mode When powering from DC with DCM set to logic-low, the DC input is set to USB mode. The input current limit from DC is then internally set to 500mA max if IUSB is high and 100mA max if IUSB is low. For the 500mA case, the DC input continues to operate as a step-down regulator to minimize thermal heating. For the 100mA case, the
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power
step-down regulator is turned off and a low-dropout linear regulator is connected between DC and SYS.
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. DOK is an open-drain, active-low output that indicates the DC input power status. With no source at the USB pin, the source at DC is considered valid and DOK is driven low when: 4.15V < VDC < 16V. When the USB voltage is also valid, the DC source is considered valid and DOK is driven low when: 4.45V < VDC < 16V. The higher minimum DC voltage with USB present helps guarantee cleaner transitions between input supplies. If the DC power-OK output feature is not required, connect DOK to ground. UOK is an open-drain, active-low output that indicates the USB input power status. UOK is low when a valid source is connected at USB. The source at USB is valid when 4.1V < VUSB < 6.6V. If the USB power-OK output feature is not required, connect UOK to ground. Both the UOK and the DOK circuitry remain active in thermal overload, USB suspend, and when the charger is disabled. DOK and UOK can also be wire-ORed together to generate a single power-OK (POK) output.
Power Monitor Outputs (UOK, DOK)
to the battery. Current is provided to both SYS and the battery, up to the maximum program value. The stepdown output current sense and the charger current sense provide feedback to ensure the current loop demanding the lower input current is satisfied. The advantage of this approach when powering from DC is that power dissipation is dominated by the step-down regulator efficiency, since there is only a small voltage drop from SYS to BAT. Also, load transients can be absorbed by the battery while minimizing the voltage disturbance on SYS. If both the DC and USB inputs are valid, the DC input takes priority and delivers the input current, while the USB input is off. After the battery is done charging, the charger is turned off and the SYS load current is supplied from the DC input. The SYS voltage is regulated to 4.4V. The charger turns on again after the battery drops to the restart threshold. If the load current exceeds the input limiter, SYS drops down to the battery voltage and the 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 current limit. The 50m PMOS also turns on if valid DC input power is removed.
MAX8903A
Thermal Limiting
When the die temperature exceeds +100C, a thermal limiting 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 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.
USB Input When charging from the USB input, the DC input stepdown regulator turns off and a linear regulator from USB to SYS powers the system and charges the battery. If the battery is greater than the minimum system voltage, the SYS voltage is connected to the battery. The USB input then supplies the SYS load and charges the battery with any extra available current, while not exceeding the maximum-allowed USB current. Load transients can be absorbed by the battery while minimizing the voltage disturbance on SYS. When battery charging is completed, or the charger is disabled, SYS is regulated to 4.4V. If both USB and DC inputs are valid, power is only taken from the DC input. USB Suspend Driving USUS high turns off charging as well as the SYS output and reduces input current to 170A to accommodate USB suspend mode.
When CEN is low, the charger is on. When CEN is high, the charger turns off. CEN does not affect the SYS output. In many systems, there is no need for the system controller (typically a microprocessor) to disable the charger, because the MAX8903A smart power selector circuitry independently manages charging and adapter/battery power hand-off. In these situations, CEN may be connected to ground.
Charge Enable (CEN)
System Voltage Switching
DC Input When charging from the DC input, if the battery is above the minimum system voltage, SYS is connected
______________________________________________________________________________________
15
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
Table 2. Input Limiter Control Logic
POWER SOURCE DOK UOK DCM IUSB USUS DC STEP-DOWN OUTPUT CURRENT LIMIT USB INPUT CURRENT LIMIT MAXIMUM CHARGE CURRENT** Lesser of 1200/RISET and 6000/RIDC Lesser of 1200/RISET and 100mA Lesser of 1200/RISET and 500mA 0 100mA Lesser of 1200/RISET and 100mA Lesser of 1200/RISET and 500mA 0 0
AC Adapter at DC Input
L
X
H
X
X
6000/RIDC
L USB Power at DC Input L L H USB Power at USB Input, DC Unconnected H H DC and USB Unconnected H
X
L
L
L
100mA
USB input off. DC input has priority.
X X L
L L X
H X L
L H L
500mA USB suspend
L L H
X X X
H X X
L H X
No DC input
500mA USB suspend No USB input
**Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load exceeds the input current limit.
X = Don't care.
Soft-Start
To prevent input transients that can cause instability in the USB or AC adapter power source, the rate of change of the input current and charge current is limited. When an input source is valid, SYS current is ramped from zero to the set current-limit value in typically 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 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.
Battery Charger
While a valid input source is present, the battery charger can attempt to charge the battery with a fast-charge current determined by the resistance at the ISET pin: RISET = 1200/ICHG-MAX
Monitoring Charge Current The voltage from ISET to GND is a representation of the battery charge current and can be used to monitor the current charging the battery. A voltage of 1.5V represents the maximum fast-charge current. If necessary, the charge current is reduced automatically to prevent the SYS voltage from dropping. Therefore, a battery never charges at a rate beyond the capabilities of a 100mA or 500mA USB input, or overloads an AC adapter. See Figure 5.
16
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power
When VBATT is below 3V, the charger enters prequal mode and the battery charges at 10% of the maximum fast-charge rate until the voltage of the deeply discharged battery recovers. When the battery voltage reaches 4.2V and the charge current drops to 10% of the maximum fast-charge current, the charger enters the DONE state. The charger restarts a fast-charge cycle if the battery voltage drops by 100mV.
MAX8903A
MONITORING THE BATTERY CHARGE CURRENT WITH VISET
1.5
Charge Termination
When the charge current falls to the termination threshold (ITERM) and the charger is in voltage mode, charging is complete. Charging continues for a brief 15s top-off period and then enters the DONE state where charging stops. Note that if charge current falls to ITERM as a result of the input or thermal limiter, the charger does not enter DONE. For the charger to enter DONE, charge current must be less than ITERM, the charger must be in voltage mode, and the input or thermal limiter must not be reducing charge current.
VISET (V)
0
DISCHARGING
0 BATTERY CHARGING CURRENT (A)
1200/RISET
Figure 5. Monitoring the Battery Charge Current with the Voltage from ISET to GND
Charge Status Outputs
Charge Output (CHG) CHG is an open-drain, active-low output that indicates charger status. CHG is low when the battery charger is in its prequalification and fast-charge states. CHG goes high impedance if the thermistor causes the charger to go into temperature suspend mode. When used in conjunction with a microprocessor (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. 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. 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 0.15F CCT tFST -CHG = 660 min x 0.15F t TOP-OFF = 15s
While in fast-charge mode, a large system load or device self-heating may cause the MAX8903A to reduce charge current. Under these circumstances, the fast-charge timer is slowed by 2x if the charge current drops below 50% of the programmed fast-charge level, and suspended if the charge current drops below 20% of the programmed level. The fast-charge timer is not affected at any current if the charger is regulating the BAT voltage at 4.2V (i.e., the charger is in voltage mode).
Thermistor Input (THM)
The THM input connects to an external negative temperature coefficient (NTC) thermistor to monitor battery or system temperature. Charging is suspended when the thermistor temperature is out of range. The charge timers are suspended and hold their state but no fault is indicated. When the thermistor comes back into range,
______________________________________________________________________________________
17
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
NOT READY UOK AND DOK = HIGH IMPEDANCE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE ICHG = 0mA CEN = HI OR REMOVE AND RECONNECT THE INPUT SOURCE(S) ANY STATE
UOK AND/OR DOK = LOW CEN = 0 RESET TIMER PREQUALIFICATION UOK AND/OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE 0 < VBAT < 3V ICHG ICHGMAX/10 VBATT < 2.82V RESET TIMER = 0 VBATT > 3.0V 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 < 2.8V RESET TIMER
FAST-CHARGE UOK AND/OR DOK = LOW CHG = LOW FLT = HIGH IMPEDANCE 3V < VBAT < 4.2V ICHG ICHGMAX ICHG > ITERM RESET TIMER ICHG < ITERM AND VBAT = 4.2V 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 = 4.2V ICHG = ITERM TIMER > 15s
VBAT < 4.1V RESET TIMER
TEMPERATURE SUSPEND ICHG = 0mA UOK OR DOK PREVIOUS STATE CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE
DONE UOK AND/OR DOK = 0 CHG = HIGH IMPEDANCE FLT = HIGH IMPEDANCE 4.1V < VBAT < 4.2V ICHG = 0mA
Figure 6. MAX8903A Charger State Flow Chart
charging resumes and the charge timer continues from where it left off. Connecting THM to GND disables the thermistor monitoring function. Table 4 lists the fault temperature of different thermistors. Since the thermistor monitoring circuit employs an external bias resistor from THM to VL (RTB, Figure 7), the thermistor is not limited only to 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
18
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
CEN THERMISTOR CIRCUITRY VL VL MAX8903A
ALTERNATE THERMISTOR CONNECTION
RTB 0.74 VL THM COLD
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 (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 3500 10 10 4.03 3750 10 10 3.78 4250 10 10 3316 36.91 46 4.5
1 1 - T+273 298 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 Table 4 shows the MAX8903A THM temperature limits for different thermistor material constants. Some designs might prefer other thermistor temperature limits. Threshold adjustment can be accommodated by changing RTB, connecting a resistor in series and/or in parallel with the thermistor, or using a thermistor with different . 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
19
29.32 31.66 50 0 49 2
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:
______________________________________________________________________________________
2A 1-Cell Li+ DC-DC Charger for USB* and Adapter Power MAX8903A
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.
Pin Configuration
USUS 15 14 13 12 CEN ISET GND IDC CT VL DOK 11 10 *EP 9 8 2 PG 3 DC 4 DC 5 DCM 6 BST 7 IUSB THM 16 UOK USB 17 BAT BAT FLT 18
TOP VIEW
21 CHG 22 SYS 23 SYS 24 CS 25
20
19
Power Dissipation
MAX8903A
CS 26 LX 27 LX 28
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 35C/W 3C/W
+
1 PG
THIN QFN 4mm x 4mm
*EXPOSED PAD
Chip Information
PCB Layout and Routing
PROCESS: BiCMOS
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.
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 28 TQFN-EP PACKAGE CODE T2844-1 DOCUMENT NO. 21-0139
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

▲Up To Search▲

Price & Availability of MAX8903A

	To Download MAX8903A Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .