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19-0994; Rev 0; 10/07
KIT ATION EVALU BLE AVAILA
28V Linear Li+ Battery Charger with Smart Autoboot Assistant
General Description Features
o CCCV, Thermally Regulated Linear 1-Cell Li+ Battery Charger o No External MOSFET, Reverse Blocking Diode, or Current-Sense Resistor o Programmable Fast-Charge Current (1ARMS max) o Proprietary Die Temperature Regulation Control (+115C) o 4.25V to 28V Input Voltage Range with Input OVP Above +7V o Charge-Current Monitor for Fuel Gauging (ISET) o Low Dropout Voltage (300mV at 500mA) o Input Power-Source Detection Output (POK), Charge-Enable Input (EN) o Soft-Start Limits Inrush Current o Output for Autobooting (ABO) o Tiny 2mm x 2mm, 8-Pin TDFN Package, 0.8mm Height (max)
MAX8814
The MAX8814 intelligent, stand-alone constant-current, constant-voltage (CCCV), thermally regulated linear charger is designed for charging a single-cell lithiumion (Li+) battery. The MAX8814 integrates the currentsense circuit, MOSFET pass element, thermalregulation circuitry, and eliminates the reverse-blocking Schottky diode to create the simplest and smallest charging solution for handheld equipment. The IC controls the charging sequence from the prequalification state through constant-current fast-charge and the final constant voltage charge. Proprietary thermal-regulation circuitry limits the die temperature during fast-charging or when the IC is exposed to high ambient temperatures, allowing maximum charging current without damaging the IC. The MAX8814 achieves high flexibility by providing an adjustable fast-charge current through an external resistor. Other features include an active-low control input (EN) and an active-low input power-source detection output (POK). The IC also features a booting assistant circuit that distinguishes input sources and battery connection and provides an output signal (ABO) for system booting. The MAX8814 accepts an input supply range from 4.25V to 28V, but disables charging if the input voltage exceeds +7V to protect against unqualified or faulty AC adapters. The IC operates over the extended temperature range (-40C to +85C) and is available in a compact 8-pin thermally enhanced TDFN 2mm x 2mm package (0.8mm max height).
Ordering Information
PART MAX8814ETA+ TEMP RANGE -40C to +85C PINPACKAGE 8 TDFN 2mm x 2mm PKG CODE T822+2 TOP MARK ABI
Applications
Cellular and Cordless Phones Smartphones and PDAs MP3 Players Digital Still Cameras USB Appliances Charging Cradles and Docks Bluetooth(R) Equipment
+Denotes a lead-free and RoHS-compliant package.
Typical Operating Circuit
4.25V TO 28V IN BATT 2.2F
+
Li+
MAX8814
OFF ON EN ABI ISET GND
SYSTEM SUPPLY
POK EP ABO
Bluetooth is a registered trademark of Bluetooth SIG. 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.
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +30V ABI, BATT, EN, POK to GND....................................-0.3V to +6V ABO to GND............................................-0.3V to (VBATT + 0.3V) ISET to GND .............................................................-0.3V to +4V IN to BATT Continuous Current .........................................1ARMS Continuous Power Dissipation (TA = +70C) 8-Pin TDFN (derate 11.9mW/C above +70C) (multilayer PCB) ........................................................953.5mW BATT Short-Circuit Duration .......................................Continuous Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+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
(VIN = 5V, VBATT = 4V, R POK = 1M to BATT, EN = 0V, RISET = 2.8k to GND, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Input Voltage Range Input Operating Voltage Range Power-OK Threshold Overvoltage-Lockout Trip Threshold VIN - VBATT, 10mV hysteresis (typ) VIN rising VIN falling 6.5 CONDITIONS MIN 0 4.25 40 30 7 0.8 0.23 TA = +25C TA = +85C 0.021 0.021 1 3 TA = 0C to +85C TA = -40C to +85C 4.179 4.158 4.200 4.200 2.2 VBATT = 3.5V Fast-Charge Current VBATT = 3.5V, RISET = 14k Prequalification Charge Current Die Temperature Regulation Threshold VBATT Prequalification Threshold Voltage Current-Sense Amplifier Gain (IBATT to IISET) VBATT rising, 100mV hysteresis (typ) IBATT = 570mA 2.3 TA = 0C to +85C TA = -40C to +85C TA = 0C to +85C TA = -40C to +85C 524 485 89 80 4 570 570 107 107 10 +115 2.5 877.2 2.7 616 656 125 134 15 % C V A/A mA 4.221 4.242 V F 10 A 7.5 1.35 0.50 0.065 mA TYP MAX 28 6.50 UNITS V V mV V
VIN rising, 100mV hysteresis (typ) Constant-current charging mode (IBATT = 0A)
IN Input Current
IC disabled (VEN = 5V) VIN = 4V, VBATT = 4.2V
BATT Input Current
VIN = 0 to 4V, VBATT = 4.2V IC disabled
Battery Regulation Voltage Minimum BATT Bypass Capacitance
IBATT = 0A
Percentage of the fast-charge current, VBATT = 2.2V, TA = 0C to +85C
2
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28V Linear Li+ Battery Charger with Smart Autoboot Assistant
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 5V, VBATT = 4V, R POK = 1M to BATT, EN = 0V, RISET = 2.8k to GND, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Regulator Dropout Voltage (VIN - VBATT ) EN Logic-Input Low Voltage EN Logic-Input High Voltage EN and ABI Internal Pulldown Resistance ABI Logic-Input Low Voltage ABI Logic-Input High Voltage ABO Output Low Voltage ABO Output High Voltage POK Output Low Voltage POK Output High Leakage Current VIN = 0V VIN = 0V IABO (SINK) = 1mA IABO (SOURCE) = 1mA I POK = 5mA V POK = 5.5V TA = +25C TA = +85C 0.001 0.002 VBATT 0.4V 0.4 1 1.3 0.4 CONDITIONS VBATT = 4.1V, IBATT = 425mA 4.25V < VIN < 6.5V 4.25V < VIN < 6.5V 1.3 100 200 400 0.4 MIN TYP 240 MAX 500 0.4 UNITS mV V V k V V V V V A
MAX8814
Note 1: Specifications are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design and characterization.
Typical Operating Characteristics
(VIN = 5V, VBATT = 4V, R POK = 1M to BATT, EN = 0V, RISET = 2.8k to GND, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
SUPPLY CURRENT vs. VOLTAGE
MAX8814 toc01
DISABLED MODE SUPPLY CURRENT vs. INPUT VOLTAGE
EN = 0V VEN = 5V 700 SUPPLY CURRENT (A) 600 500 400 300 200 100 0
MAX8814 toc02
CHARGE CURRENT vs. BATTERY VOLTAGE
900 800 CHARGE CURRENT (mA) 700 600 500 400 300 200 100 0
MAX8814 toc03
1.0 0.9 0.8 SUPPLY CURRENT (mA) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 4 8 12 16 20
800
1000
24
28
0
5
10
15
20
25
30
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 BATTERY VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
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3
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
Typical Operating Characteristics (continued)
(VIN = 5V, VBATT = 4V, R POK = 1M to BATT, EN = 0V, RISET = 2.8k to GND, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
CHARGE CURRENT vs. INPUT VOLTAGE
MAX8814 toc04
CHARGE CURRENT vs. INPUT VOLTAGE HEADROOM
MAX8814 toc05
STARTUP INTO PRECHARGE
VBATT = 2V IBATT VIN
1000 900 800 700 600 500 400 300 200 100 0 0 4 8 12 16 20 24
1000 900 800 CHARGE CURRENT (mA) 700 600 500 400 300 200 100 0 VBATT = 4V VIN RISING 0 100 200 300 400
MAX8814 toc06
CHARGE CURRENT (mA)
100mA/div 0A 5V/div 0V
VEN
5V/div 0V 5V/div 0V 40s/div
28
500
VPOK
INPUT VOLTAGE (V)
VIN - VBATT (mV)
SHUTDOWN (FAST-CHARGE TO SHUTDOWN)
BATTERY REGULATION VOLTAGE ACCURACY (%)
MAX8814 toc07
BATTERY REGULATION VOLTAGE ACCURACY vs. AMBIENT TEMPERATURE
MAX8814 toc08
CHARGE CURRENT vs. RISET
MAX8814 toc09
1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -40 -15 10 35 60 IBATT = 0A
1000
IBATT
500mA/div 0A
CHARGE CURRENT (mA) 85
VIN
5V/div 0V 5V/div
100
10
VEN
0V 5V/div
VPOK 100s/div
0V
1 1 10 100 RISET (k) 1000 10,000 TEMPERATURE (C)
CHARGE CURRENT vs. AMBIENT TEMPERATURE
VBATT = 4V 600 CHARGE CURRENT (mA) 500 VBATT = 3.2V 400 VIN 300 VBATT 200 100 RISET = 2.8k 0 -40 -15 10 35 60 85 TEMPERATURE (C) VABO
MAX8814 toc10
AUTOBOOT ENABLED BY ABI SIGNAL
MAX8814 toc11
AUTOBOOT ENABLED BY INPUT SUPPLY
MAX8814 toc12
700
VABI
5V/div 0V 5V/div 0V 5V/div 0V 5V/div 0V 4s/div
5V/div VABI 0V 5V/div VIN VBATT 0V 5V/div 0V 5V/div VABO 4s/div 0V
4
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28V Linear Li+ Battery Charger with Smart Autoboot Assistant
Pin Description
PIN 1 2 NAME IN GND FUNCTION Input Supply Voltage. Bypass IN to GND with a 1F or larger ceramic capacitor to minimize line noise and maximize input transient rejection. Ground. Connect GND and the exposed paddle to a large copper ground plane for maximum power dissipation. Connect GND to the exposed paddle directly under the IC. Charge-Current Program and Fast-Charge Current Monitor. Output current from ISET is 877.2A per ampere of battery charging current. Set the charging current by connecting a resistor (R2 in Figure 3) from ISET to GND. IFAST-CHARGE = 1596V / RISET. To configure the MAX8814 as a USB charger, see Figure 4. Autobooting External Input. See the Autobooting Assistant section and Table 1 for autobooting conditions. ABI is pulled to GND through an internal 200k resistor. Autobooting Logic Output. See the Autobooting Assistant section and Table 1 for autobooting conditions. Logic-Level Enable Input. Drive EN high to disable charger. Drive EN low or leave unconnected for normal operation. EN has an internal 200k pulldown resistor. Input-Voltage Status Indicator. Connect a 1M pullup resistor from POK to an external system supply. POK is an open-drain output that asserts low when VIN > 4.25V and (VIN - VBATT) 40mV. If VBATT (VIN - 40mV), the IC is shut down and POK becomes high impedance. Battery Connection. Bypass BATT to GND with a minimum of 2.2F of capacitor. Exposed Paddle. Connect the exposed paddle to a large ground plane for maximum power dissipation. Connect GND to the exposed paddle directly under the IC.
MAX8814
3
ISET
4 5 6
ABI ABO EN
7 8 --
POK BATT EP
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5
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
4.25V TO 28V C1 1F OUTPUT DRIVER, CURRENT SENSE, AND LOGIC +115C IN BATT C3 2.2F
Li+
TEMPERATURE SENSOR
ISET
R2 2.8k
IN
VI/O VREF VREF R3 1M POK
VIN OVLO BATT VL
VL REGULATOR BATT
VL UVLO
REF VREF REFOK POK LOGIC 200k
ABO
ABI
MAX8814
200k EP
EN
GND
Figure 1. Functional Diagram
Detailed Description
The MAX8814 charger uses voltage, current, and thermal-control loops to charge a single Li+ cell and protect the battery (Figure 1). When a Li+ battery with a cell voltage below 2.5V is inserted, the MAX8814 charger enters the prequalification stage where it precharges that cell with 10% of the user-programmed fast-charge current (Figure 2). When the battery voltage exceeds 2.5V, the charger soft-starts as it enters the fast-charge stage. In the MAX8814, the fast-charge current level is programmed through a resistor from ISET to GND. As the battery voltage approaches 4.2V,
6
the charging current is reduced. Once the battery voltage reaches 4.2V, the IC then enters a constant voltage regulation mode to maintain the battery at full charge.
Thermal Regulation
The thermal-regulation loop limits the MAX8814 die temperature to +115C by reducing the charge current as necessary. This feature not only protects the IC from overheating, but also allows a higher charge current without risking damage to the IC.
_______________________________________________________________________________________
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
SHUTDOWN CHARGER = DISABLED VBATT < 2.5V (VIN - VBATT) < 30mV ASYNCHRONOUS FROM ANYWHERE VIN > 7V, OR (VIN - VBATT) < 30mV, OR IC DISABLED
PRECHARGE 10% CHARGE CURRENT
VIN < 7V, AND (VIN - VBATT) 40mV, AND IC ENABLED
VIN > 7V, OR (VIN - VBATT) < 30mV, OR IC DISABLED
VBATT < 2.4V VBATT 2.5V VBATT 4.2V
FAST-CHARGE CONSTANT-CURRENT CHARGE 100% CHARGE CURRENT
VOLTAGE REGULATION CONSTANT VOLTAGE CHARGE REGULATED 4.2V AT BATT
VBATT < 4.2V
Figure 2. Charge-State Diagram
Charger Enable Input
The MAX8814 contains an active-low logic input (EN) used to enable the charger. Drive EN low, leave unconnected, or connect to GND to enable the chargercontrol circuitry. Drive EN high to disable the chargercontrol circuitry. EN has an internal 200k pull-down resistor.
Table 1. ABO and POK States
ABI Low High X X BATT Present Present Not present Present POK Hi-Z Hi-Z Low Low CHARGER STATE Shutdown Shutdown Fast-charge/voltage regulation Fast-charge/voltage regulation ABO Low High High High
POK Output
The open-drain POK output asserts low when VIN 4.25V and (VIN - VBATT) 40mV (typ, VIN rising). POK requires an external pullup resistor (1M typ) to an external power supply. POK is high impedance when VBATT (VIN - 40mV).
X = Don't care.
Autobooting Assistant
The MAX8814 contains an autobooting assistant circuit that generates an enable signal for system booting (ABO). The booting assistant functions as an internal "OR" gate (Figure 1). The first input is dependent on the input voltage (V IN), and the second input is an external signal applied to ABI. The first input (POK) is driven high once VIN 4.25V and (VIN - VBATT) 40mV (typ, VIN rising). The second input signal (ABI) is driven by an external source. ABI enables an autoboot signal (ABO high) when a battery is connected at BATT and is independent of POK. If POK is pulled low, the booting assistant always drives ABO high, regardless of ABI (see Table 1). ABI is pulled to GND through an internal 200k resistor.
If ABI is driven externally, a RC filter (R1 and C2 of Figure 3) is required for ESD protection and noise filtering. If ABI is supplied by a system's internal GPIO, or logic, the RC filter is not required.
Soft-Start
The soft-start algorithm activates when entering fastcharge mode. In the MAX8814, when the prequalification state is complete (V BATT 2.5V), the charging current ramps up in 250s to the full charging current. This reduces the inrush current on the input supply.
_______________________________________________________________________________________
7
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
C1 1F R1 10k ABI GND C2 0.1F POK ABO EN GND EP ISET R4 10k ADC R2 2.8k C4 0.1F GPIO IN BATT C3 2.2F Li+ SYSTEM
FACTORY TEST FIXTURE OR AC ADAPTER
MAX8814
VI/O
R3 1M GPIO
POWER SUPPLY ON
Figure 3. Microprocessor-Interfaced Li+ Battery Charger
Applications Information
Charge-Current Selection
The maximum charging current is programmed by an external resistor connected from ISET to GND (RISET). Calculate RISET as follows: R ISET = 1596V I FAST-CHARGE
Capacitor Selection
Connect a ceramic capacitor from BATT to GND for proper stability. Use a 2.2F X5R ceramic capacitor for most applications. Connect a 1F ceramic capacitor from IN to GND. Use a larger input bypass capacitor for high charging currents to reduce supply noise.
Thermal Considerations
The MAX8814 is available in a thermally enhanced TDFN package with an exposed paddle. Connect the exposed paddle to a large copper ground plane to provide a thermal contact between the device and the circuit board for increased power dissipation. The exposed paddle transfers heat away from the device, allowing the IC to charge the battery with maximum current, while minimizing the increase in die temperature.
where I FAST-CHARGE is in amperes and R ISET is in ohms. ISET can be used to monitor the fast-charge current level. The output current from ISET is 877.2A per ampere of charging current. The output voltage at ISET is proportional to the charging current: I x R ISET V ISET = CHARGE 1140 The voltage at ISET is nominally 1.4V at the selected fast-charge current and falls with charging current as the cell becomes fully charged or as the thermal-regulation circuitry activates.
DC Input Sources
The MAX8814 operates from a well-regulated DC source. The full charging input voltage range is 4.25V to 7V. The device can withstand up to 28V on the input without damage to the IC. If VIN is greater than 7V, the internal overvoltage-protection circuitry disables charging until the input falls below 7V. An appropriate power supply must provide at least 4.25V at the desired peak charging current.
8
_______________________________________________________________________________________
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
VBUS C1 1F IN BATT C3 2.2F + Li+ SYSTEM
USB PORT
ABI GND
MAX8814
VI/O R3 1M POK GPIO GPIO R4 10k ADC R5 4.99k N C4 0.1F
ABO EN GND EP ISET
R2 15.8k
GPIO
POWER SUPPLY ON
Figure 4. USB Battery Charger
Application Circuits
Microprocessor-Interfaced Charger Figure 3 shows the MAX8814 as a microprocessorcooperated Li+ battery charger. The MAX8814 begins charging the battery when EN is low. The microprocessor can drive EN high to disable the charger. The MAX8814 generates a POK signal to indicate the presence of an input supply. By monitoring VISET, the system can measure the charging current and decide when to terminate the charge. USB-Powered Li-Ion Charger The universal serial bus (USB) provides a high-speed serial communication port as well as power for the remote device. The MAX8814 can be configured to charge a battery at the highest current possible from the host port. Figure 4 shows the MAX8814 as a USB battery charger. To make the circuit compatible with either 100mA or 500mA USB ports, the circuit initializes at 100mA charging current. The microprocessor then enumerates the host to determine its current capability. If the host port is capable, the charging current is increased to 425mA to avoid exceeding the 500mA USB specification.
Layout and Bypassing
Place the input and output capacitors as close as possible to the IC. Provide a large copper ground plane to allow the exposed paddle to sink heat away from the IC. Connect the battery to BATT as close as possible to the IC to provide accurate battery voltage sensing. Make all high-current traces short and wide to minimize voltage drops. A sample layout is available in the MAX8814 Evaluation Kit to speed designs.
Chip Information
PROCESS: BiCMOS
_______________________________________________________________________________________
9
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
Pin Configuration
TOP VIEW
BATT 8 POK 7 EN 6 ABO 5
MAX8814
EXPOSED PADDLE + 1 IN 2 GND 3 ISET 4 ABI
TDFN 2mm x 2mm
10
______________________________________________________________________________________
28V Linear Li+ Battery Charger with Smart Autoboot Assistant
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
8L TDFN EXPOSED PADS.EPS
MAX8814
PACKAGE OUTLINE 6 & 8L TDFN EXPOSED PAD, 2x2x0.80mm
21-0168
D
1 2
______________________________________________________________________________________
11
28V Linear Li+ Battery Charger with Smart Autoboot Assistant MAX8814
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 1.90 1.90 0.00 0.20 MAX. 0.80 2.10 2.10 0.05 0.40
0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T622-1 T822-1 T822-2 N 6 8 8 D2 0.900.10 0.700.10 0.800.10 E2 1.600.10 1.300.10 1.200.10 e 0.65 TYP. 0.50 TYP. 0.50 TYP. b 0.300.05 0.250.05 0.250.05 r 0.150 0.125 0.125 [(N/2)-1] x e 1.30 REF 1.50 REF 1.50 REF
PACKAGE OUTLINE 6 & 8L TDFN EXPOSED PAD, 2x2x0.80mm
21-0168
D
2 2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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