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19-4405; Rev 0; 3/09
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output
General Description
The MAX8845Z/MAX8845Y are intelligent, stand-alone constant-current, constant-voltage (CCCV), thermally regulated linear chargers designed for charging a single-cell lithium-ion (Li+) battery. The MAX8845Z/ MAX8845Y integrate a current-sense circuit, MOSFET pass element, thermal-regulation circuitry, and eliminates the external reverse-blocking Schottky diode to create the simplest and smallest charging solutions for handheld equipment. The ICs control the charging sequence from the prequalification state through constant current fast-charge, top-off charge, and full-charge indication. Proprietary thermal-regulation circuitry limits the die temperature during fast-charging or when the ICs are exposed to high ambient temperatures, allowing maximum charging current without damaging the ICs. The MAX8845Z/MAX8845Y achieve high flexibility by providing adjustable fast-charge currents (SETI) and an adjustable top-off current threshold (MIN) through external resistors. The MAX8845Z/ MAX8845Y feature a booting assistant circuit that distinguishes input sources and battery connection and provides an enable signal (ABO--MAX8845Z and ABO--MAX8845Y) for system booting. The MAX8845Z/MAX8845Y also integrate an overvoltage-protected output (SAFEOUT) for low voltage-rated USB or charger inputs in system, and a battery-pack detection circuit (DETBAT) that disables the charger when the battery pack is absent. Other features include an active-low control input (EN), an active-low input power source detection output (POK), and a fully charged top-off threshold detection output (CHG). The MAX8845Z/MAX8845Y accept an input supply range from 4.25V to 28V, but disables charging if the supply voltage exceeds +7.5V to protect against unqualified or faulty AC adapters. The IC's operate over the extended temperature range (-40C to +85C) and are available in a compact 12-pin, thermally enhanced thin QFN, 3mm x 3mm package (0.8mm max height).
Features
CCCV, Thermally Regulated Linear 1-Cell Li+ Battery Charger No External MOSFET, Reverse Blocking Diode, or Current-Sense Resistor Programmable Fast-Charge Currents (1ARMS max) Programmable Top-Off Current Threshold (MIN) Input Overvoltage Protected 4.7V Output (SAFEOUT) Proprietary Die Temperature Regulation Control (+115C) 4.25V to 28V Input Voltage Range with Input Overvoltage Protection Above +7.5V Low-Dropout Voltage (300mV at 500mA) Input Power-Source Detection Output (POK), Charge Status Output (CHG), Charge-Enable Input (EN) Output for Autobooting (ABO--MAX8845Z, ABO--MAX8845Y) Tiny, 3mm x 3mm 12-Pin Thin QFN Package, 0.8mm Height (max)
MAX8845Z/MAX8845Y
Ordering Information
PART MAX8845ZETC+ MAX8845YETC+ PIN-PACKAGE 12 Thin QFN-EP* 12 Thin QFN-EP* TOP MARK ABL ABM ABO ACTIVE STATE Active high Active low
Note: All devices are specified over the -40C to +85C operating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
Applications
Cellular and Cordless Phones Smart Phones and PDAs Digital Still Cameras MP3 Players USB Appliances Charging Cradles and Docks Bluetooth(R) Equipment
Bluetooth is a registered trademark of Bluetooth SIG.
Typical Operating Circuit and Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
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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 Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +30V ABI, BATT, EN, POK, ABO, ABO, CHG, DETBAT, SETI, MIN, SAFEOUT to GND ................................................-0.3V to +6V IN to BATT Continuous Current .........................................1ARMS Continuous Power Dissipation (TA = +70C) 12-Thin QFN (derate 14.7mW/C above +70C) (multilayer PCB) ......................................................1176.5mW 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, RPOK = 1M to BATT, EN = unconnected, RSETI = 2.8k to GND, VDETBAT = 0, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Input Supply Voltage Range Input Supply Operating Voltage Range Overvoltage Lockout Trip Threshold VIN rising, 100mV hysteresis (typ) Constant current charging IIN - IBATT, IBATT = 0 Input Current Constant current charging IIN - IBATT, IBATT = 500mA IC disabled, VEN = 5V VIN = 4V, VBATT = 4.2V BATT, CHG, POK Minimum BATT Bypass Capacitance VBATT Prequalification Threshold Voltage Battery Regulation Voltage Regulator Dropout Voltage (VIN - VBATT) BATT Input Current Current-Sense Amplifier Gain (IBATT to ISETI) VBATT rising, 100mV hysteresis (typ) IBATT = 0 TA = -40C to +85C 2.3 4.175 4.158 2.2 2.5 4.200 4.200 260 5 3 1016 TA = 0C to +85C TA = -40C to +85C TA = 0C to +85C 460 425 85 500 500 100 106 38 4.0 6.2 10.7 540 575 115 mA mA ms mA A/A 10 2.7 4.225 4.242 F V V mV A TA = +25C TA = +85C CONDITIONS MIN 0 4.25 7.0 7.5 0.22 1 0.20 0.02 0.03 0.50 TYP MAX 28 7.00 8.0 0.50 UNITS V V V
mA
VBATT = 4.1V, IBATT = 425mA VIN = 0 to 4V, VBATT = 4.2V IC disabled IBATT = 500mA VBATT = 3.5V, RSETI = 2.8k
Fast-Charge Current VBATT = 3.5V, RSETI = 14k CHG Top-Off Threshold CHG Hysteresis CHG Detection Delay
IBATT falling, battery is charged RMIN = 1.75k IBATT rising after top-off is detected, RMIN = 1.75k IBATT falls below top-off threshold
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 5V, VBATT = 4V, RPOK = 1M to BATT, EN = unconnected, RSETI = 2.8k to GND, VDETBAT = 0, CBATT = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Prequalification Charge Current CHG, POK Output Low Threshold CHG, POK Output High Leakage Current POK Threshold DETBAT, SAFEOUT DETBAT Logic-Input Low Threshold DETBAT Logic-Input High Threshold DETBAT Pullup Resistor Minimum SAFEOUT Bypass Capacitance SAFEOUT Regulated Output SAFEOUT Current Limit EN, ABI, ABO, ABO EN, ABI Internal Pulldown Resistor EN Logic-Input Low Threshold EN Logic-Input High Threshold ABI Logic-Input Low Threshold ABI Logic-Input High Threshold ABO Output Low Threshold (MAX8845Y) ABO Output High Threshold (MAX8845Y) ABO Output Low Threshold (MAX8845Z) ABO Output High Threshold (MAX8845Z) THERMAL Die Temperature Regulation Threshold 115 C 4.25V VIN 7V 4.25V VIN 7V VBATT = 4V, VIN = 0 VBATT = 4V, VIN = 0 Open drain, IABO(SINK) = 1mA Open drain, 100k pullup to BATT IABO(SINK) = 1mA IABO(SOURCE) = 1mA VBATT 0.4V VBATT 0.4V 0.4 1.3 0.4 1.3 0.4 100 200 400 0.4 k V V V V V V V V ISAFEOUT = 30mA, VIN = 5V, TA = 0C to +85C 4.5 DETBAT to VL = 3V 1.3 470 1 4.7 100 4.9 CONDITIONS Percentage of the fastcharge current, VBATT = 2.2V TA = 0C to +85C MIN 5 TYP 10 MAX 15 0.4 1 0.01 40 30 0.4 UNITS % V A mV
MAX8845Z/MAX8845Y
IPOK = 5mA , ICHG = 5mA VPOK = 5.5V, V CHG = 5.5V VIN - VBATT TA = +25C TA = +85C VIN rising VIN falling
V k F V mA
Note 1: Specifications are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design and characterization.
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Typical Operating Characteristics
(VIN = 5V, VBATT = 4V, RPOK = RCHG = 200k to 5V, EN = unconnected, RSETI = 2.8k to GND, RMIN = 1.74k to GND, RDETBAT = 4.7k to GND, CBATT = 2.2F, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. INPUT VOLTAGE
MAX8845Z/Y toc01
DISABLED MODE SUPPLY CURRENT vs. INPUT VOLTAGE
VEN = 5V 0.5 SUPPLY CURRENT (A) 0.4 0.3 0.2 0.1 0
MAX8845Z/Y toc02
CHARGE CURRENT vs. BATTERY VOLTAGE
900 800 CHARGE CURRENT (mA) 700 600 500 400 300 200 100 0
MAX8845Z/Y 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
VEN = 0, IBATT = 0 VIN RISING
0.6
1000
20
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)
CHARGE CURRENT vs. INPUT VOLTAGE
MAX8845Z/Y toc04
CHARGE CURRENT vs. INPUT VOLTAGE HEADROOM
MAX8845Z/Y toc05
SAFEOUT OUTPUT VOLTAGE vs. INPUT VOLTAGE
4.5 4.0 SAFEOUT VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 ISAFEOUT = 1mA
MAX8845Z/Y toc06
600 500 CHARGE CURRENT (mA) 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
5.0
28
0
100
200
300
400
500
600
0
4
8
12
16
20
24
28
INPUT VOLTAGE (V)
VIN - VBATT (mV)
INPUT VOLTAGE (V)
SAFEOUT OUTPUT VOLTAGE vs. LOAD CURRENT
4.5 4.0 SAFEOUT VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 20 40 60 80 100 VPOK
MAX8845Z/Y toc07
STARTUP INTO PRECHARGE
MAX8845Z/Y toc08
SHUTDOWN (FAST-CHARGE TO SHUTDOWN)
MAX8845Z/Y toc09
5.0
IBATT VIN VEN
I 100mA/div BATT 0 5V/div 0 5V/div 0 5V/div 0 40s/div VPOK 40s/div VIN VEN
500mA/div 0 5V/div 0 5V/div 0 5V/div 0
LOAD CURRENT (mA)
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output
Typical Operating Characteristics (continued)
(VIN = 5V, VBATT = 4V, RPOK = RCHG = 200k to 5V, EN = unconnected, RSETI = 2.8k to GND, RMIN = 1.74k to GND, RDETBAT = 4.7k to GND, CBATT = 2.2F, TA = +25C, unless otherwise noted.)
BATTERY REGULATION ACCURACY vs. AMBIENT TEMPERATURE
MAX8845Z/Y toc10
MAX8845Z/MAX8845Y
FAST-CHARGE CURRENT vs. RSETI
MAX8845Z/Y toc11
TOP-OFF CURRENT THRESHOLD vs. 1/RMIN (k)
TOP-OFF CURRENT THRESHOLD (mA) 550 500 450 400 350 300 250 200 150 100 50 TOP-OFF CURRENT FALLING TOP-OFF CURRENT RISING
MAX8845Z/Y toc12
1.0 BATTERY REGULATION ACCURACY (%) 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 = 0
1000
600
FAST-CHARGE CURRENT (mA)
100
10
1 85 1 10 100 RSETI (k) 1000 10,000 AMBIENT TEMPERATURE (C)
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 1/RMIN (k)
CHARGE CURRENT vs. AMBIENT TEMPERATURE
VBATT = 4V
MAX8845Z/Y toc13
AUTOBOOT ENABLED BY ABI SIGNAL (MAX8845Z)
MAX8845Z/Y toc14
700 600 CHARGE CURRENT (mA) 500 400 300 VBATT = 3.2V
5V/div VABI 0 5V/div VIN 0 5V/div
200 100 RSETI = 2.8k 0 -40 -20 0 20 40 60 80 100 AMBIENT TEMPERATURE (C)
VBATT
0 5V/div 0 4s/div
VABO
AUTOBOOT ENABLED BY INPUT VOLTAGE (MAX8845Z)
MAX8845Z/Y toc15
AUTOBOOT ENABLED BY ABI SIGNAL (MAX8845Y)
MAX8845Z/Y toc16
5V/div VABI 0 5V/div VIN 0 5V/div VBATT VABO 20s/div 0 5V/div 0 VABO 4s/div VBATT VIN VABI
5V/div 0 5V/div 0 5V/div 0 5V/div 0
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Pin Description
PIN MAX8845Z MAX8845Y NAME FUNCTION Charge-Current Program and Fast-Charge Current Monitor. Output current from SETI is 1016A per ampere of battery charging current. Set the charging current by connecting a resistor (RSETI in Figure 3) from SETI to GND. IFAST-CHARGE = 1400V/RSETI. To configure the MAX8845Z/MAX8845Y as a USB charger, see Figure 5. Battery Pack ID Resistor Detection Input. If DETBAT is pulled low through a pulldown resistor less than 51k the charger is enabled. If DETBAT is left unconnected, the charger is disabled. Autobooting External Input. See the Autobooting Assistant section and Table 1 for autobooting conditions. ABI is pulled to GND through an internal 200k resistor. Active-Low, 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. Ground. Connect GND and the exposed pad to a large copper ground plane for maximum power dissipation. Connect GND to the exposed pad directly under the IC. Active-Low, Input Voltage Status Indicator. POK is an open-drain output that asserts low when 2.35V < VIN < 7V and (VIN - VBATT) > 40mV. If VIN > +7.5V or VBATT > VIN the IC is shut down and POK becomes high impedance. Connect a pullup resistor to the microprocessor's I/O voltage when interfacing with a microprocessor logic input. Active-High, Autobooting Logic Output. See the Autobooting Assistant section and Table 1 for autobooting conditions. Active-Low, Open-Drain Logic Output. See the Autobooting Assistant section and Table 1 for autobooting conditions. Li+ Battery Connection. Bypass BATT to GND with a 2.2F ceramic capacitor. Top-Off Current Threshold Programmable Input. IMIN (mA) falling = 148V/RMIN (k) + 22 (mA). Active-Low, Charging Indicator. CHG is an open-drain output that is pulled low once charging begins. CHG is high impedance when the battery current drops below MIN, or when the IC is disabled. Connect a pullup resistor to the microprocessor's I/O voltage when interfacing with a microprocessor logic input. Input Supply Voltage. Bypass IN to GND with a 1F or larger ceramic capacitor to improve line noise and input transient rejection. 4.7V Regulated LDO Output with Input Overvoltage Protection. Bypass SAFEOUT to GND with a 1F or larger ceramic capacitor. SAFEOUT can be used to supply low voltage-rated USB systems. Exposed Pad. Connect the exposed pad to a large ground plane for maximum power dissipation. Connect GND to the exposed pad directly under the IC.
1
1
SETI
2
2
DETBAT
3
3
ABI
4
4
EN
5
5
GND
6
6
POK
7 -- 8 9
-- 7 8 9
ABO ABO BATT MIN
10
10
CHG
11
11
IN
12
12
SAFEOUT
--
--
EP
6
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
LINEAR REGULATOR WITH OVP
SAFEOUT
IN
BATT 4.2V Li+ OUTPUT DRIVER, CURRENT SENSE, AND LOGIC +115C
TEMPERATURE SENSOR
DETBAT
SETI
VREF IMINREF MIN IN
VREF VI/O
CHG
VIN OVLO BATT
VL REGULATOR
POK
VL VL UVLO DETBAT REFOK REF LOGIC VREF
POK
BATT
ABO (MAX8845Z ONLY)
ABI ABO (MAX8845Y ONLY) 200k
MAX8845Z MAX8845Y
200k EP
EN
GND
Figure 1. MAX8845Z/MAX8845Y Functional Diagram
Detailed Description
The MAX8845Z/MAX8845Y chargers use 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 MAX8845Z/MAX8845Y chargers enter a prequalification stage where it precharges that cell with 10% of the
user-programmed fast-charge current (Figure 2). The CHG indicator is driven low to indicate entry into the prequalification state. When the battery voltage exceeds 2.5V, the charger soft-starts as it enters the fast-charge stage. The fast-charge current level is programmed through a resistor from SETI to GND. As the battery voltage approaches 4.2V, the charging current
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
SHUTDOWN CHARGER = DISABLED CHG = HIGH-Z VIN > 7V, OR (VIN - VBATT) < 30mV, OR IC DISABLED ASYNCHRONOUS FROM ANYWHERE VIN > 7.5V, OR (VIN - VBATT) < 30mV, OR THERMAL SHUTDOWN, OR IC DISABLED
VBATT < 2.5V
(VIN - VBATT) < 30mV
PRECHARGE 10% OF IFAST-CHARGE CHG = LOW
VIN < 7.5V, AND (VIN - VBATT) 40mV, AND IC ENABLED
VBATT < 2.4V VBATT 2.5V
ANY CHARGING STATE
DIE TEMPERATURE > +115C
CHARGING CURRENT REDUCTION CHARGING CURRENT IS REDUCED AS NECESSARY
DIE TEMPERATURE +115C IBATT > 295V/RMIN (k) - 24mA FAST-CHARGE CONSTANT-CURRENT CHARGE 100% OF IFAST-CHARGE CHG = LOW TOP-OFF 4.2 VOLTAGE REGULATION CHG = HIGH-Z IBATT IMIN FOR 6.2ms (typ) OR LONGER RETURN TO CHARGING STATE
Figure 2. Charge-State Diagram
is reduced. If the battery current drops to less than the top-off current threshold set by R MIN , the charger enters top-off mode and the CHG indicator goes high impedance signaling that the battery is fully charged.
Autobooting Assistant
The MAX8845Z/MAX8845Y contain autobooting assistant circuits that generate an enable signal for system booting (ABO--MAX8845Z, ABO--MAX8845Y). For the MAX8845Z, the booting assistant functions as an internal OR gate (Figure 1). The first input is dependant on the input voltage (VIN) and DETBAT while the second input is an external signal applied to ABI. The first input (POK) is driven high once DETBAT is pulled low through a resistor less than 51k, 2.35V VIN 7V, and (VIN - VBATT) 40mV (typ VIN rising). The second input signal (ABI) is driven by an external source (Table 1). ABI enables an autoboot signal 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. ABI is pulled to GND through an internal 200k resistor. If ABI is supplied from an outside exposed pin, a RC filter (Figure 4) 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. For the MAX8845Y, the output ABO is only dependent on the state of ABI (Table 1).
Overvoltage-Protected Output (SAFEOUT)
SAFEOUT is a linear regulator that provides an output voltage of 4.7V and can be used to supply low voltagerated USB systems. The SAFEOUT linear regulator turns on when VIN 4.25V regardless of EN and is disabled when VIN is greater than the overvoltage threshold (7.5V typ).
Battery-Pack Detection Input (DETBAT)
DETBAT is a battery-pack ID resistor detector that enables the battery charger if pulled low through a resistor that is less than 51k. If DETBAT is left unconnected or the pulldown resistor is 51k or greater the battery charger is disabled. If DETBAT is not used connect DETBAT to GND for normal operation. The open-drain POK output asserts low when 2.35V VIN 7V, (VIN - VBATT) 40mV (typ VIN rising), and DETBET is pulled low through a resistor that is less than 51k. POK is high impedance during shutdown. When interfacing with a microprocessor logic input, a pullup resistor to the microprocessor's I/O voltage may be required.
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POK Output
CHG Charge Indicator Output
CHG is an open-drain output that indicates charge status. Table 2 describes the state of CHG during different stages of operation. CHG is suitable for driving a charge indication LED. If the MAX8845Z/MAX8845Y are
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Table 1. Autobooting Output States
ABI Low High Low Low High BATT Present Present Not present Present Present POK High-Z High-Z Low Low Low CHARGER STATE Shutdown Shutdown CC/CV mode Fast-charge/top-off Fast-charge/top-off ABO (MAX8845Z) Low High High High High ABO (MAX8845Y) High-Z Low High-Z High-Z Low
Note: Present indicates that VBATT 2V and Not Present indicates that the battery is not connected.
Table 2. CHG States
EN High Low Low Low Low VIN X > 7.5V X 4.25V VIN 7.5V 4.25V VIN 7.5V 4.25V VIN 7.5V VBATT X X > VIN - 30mV < 2.4V 2.5V 4.2V IBATT 0 0 10% of IFAST-CHARGE* 100% of IFAST-CHARGE* < IMIN CHG High-Z High-Z Low Low High-Z STATE Disabled Shutdown Precharge Fast-charge Top-off
X = Don't care.
*IFAST-CHARGE is reduced as necessary to prevent the die temperature from exceeding +115C.
used in conjunction with a microprocessor, a pullup resistor to the logic I/O voltage allows CHG to indicate charge status to the microprocessor instead of driving an LED.
Applications Information
Fast Charge-Current Setting
The maximum charging current is programmed by an external resistor connected from SETI to GND (RSETI). Use the following equation to determine the fast-charge current (IFAST_CHARGE): IFAST _ CHARGE = 1400V RSETI
Thermal Regulation
The thermal-regulation loop limits the MAX8845Z/ MAX8845Y 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 system.
Charger Enable Input
The MAX8845Z/MAX8845Y contain active-low logic input (EN) used to enable the chargers. Drive EN low, leave unconnected, or connect to GND to enable the charge-control circuitry. Drive EN high to disable the charger-control circuitry. EN has an internal 200k pulldown resistor.
where IFAST_CHARGE is in amps and RSETI is in ohms. RSETI must always be 1.4k or higher due to the continuous charging current limit of 1ARMS.
Top-Off Current Threshold Setting
The top-off current threshold is programmed by an external resistor connected from MIN to GND (RMIN). Use the following equation to determine the top-off current (IMIN): IMIN (falling) = 148V/RMIN (k) + 22mA IMIN (rising) = 295V/RMIN (k) - 24mA where IMIN is in mA and RMIN is in k. Use RMIN 2.2k.
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Soft-Start
The soft-start algorithm activates when entering fastcharge mode. When the prequalification state is complete (V BATT exceeds +2.5V), the charging current ramps up in 250s to the full charging current. This reduces the inrush current demand on the input supply.
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Capacitor Selection
Connect a ceramic capacitor from BATT to GND for proper stability. Use a 2.2F ceramic capacitor for most applications. Connect a 1F ceramic capacitor from IN to GND. A larger input capacitor can be used for high charging current to reduce input voltage ripple. Connect a 1F ceramic capacitor from SAFEOUT to GND. A larger bypass capacitor for SAFEOUT can be used for optimum noise immunity. Ceramic capacitors with X5R or X7R dielectric are highly recommended due to their small size, low ESR, and small temperature coefficients.
Factory System Interface Connector Application Figure 4 shows the MAX8845Z as an autoboot assistor with the factory system interface connector. The MAX8845Z detects the ABI input even though there is no input voltage available and generates an ABO signal to turn on power supplies to boot up the system. The configuration in Figure 4 is used for system development, testing, and calibrations in production or design stage. 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 MAX8845Z/MAX8845Y can be configured to charge batteries at the highest current possible from the host port. Figure 5 shows the MAX8845Z 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 450mA to avoid exceeding the 500mA USB specification through GPIO control. The MAX8845Z/MAX8845Y also provide an overvoltageprotected SAFEOUT to the system.
Thermal Considerations
The MAX8845Z/MAX8845Y are available in thermally enhanced Thin QFN packages with exposed pads. Connect the exposed pad to a large copper ground plane to provide a thermal contact between the device and the circuit board for increased power dissipation. The exposed pad transfers heat away from the device, allowing the IC to charge the battery with maximum current, while minimizing the increase in die temperature.
DC Input Sources
The MAX8845Z/MAX8845Y operate from well-regulated DC sources. The full charging input voltage range is 4.25V to 7.5V. The device can withstand up to 28V on the input without damage to the IC. If VIN is greater than 7.5V, the internal overvoltage-protection circuitry disables charging until the input falls below 7.5V. An appropriate power supply must provide at least 4.25V at the desired peak charging current and stay below 7V when unloaded.
Recommended PCB Layout and Routing
Place all bypass capacitors for IN, BATT, and SAFEOUT as close as possible to the device. Connect the battery to BATT as close as possible to the device to provide accurate battery voltage sensing. Provide a large copper ground plane to allow the exposed pad to sink heat away from the device. Make all high-current traces short and wide to minimize voltage drops. A sample layout is available in the MAX8845Z Evaluation Kit to speed designs.
Typical Application Circuits
AC Adapter Application Figure 3 shows the MAX8845Z as a Li+ battery charger with an AC adapter. The MAX8845Z detects the presence of an input supply and DETBET, resulting in POK pulled low. Once POK is pulled low, the autobooting assistant drives ABO high (MAX8845Z) and enables the power supplies of the system to boot up. The MAX8845Z begins charging the battery when EN is low or unconnected. By monitoring CHG, the system can detect the top-off threshold and terminate the charge through EN. The MAX8845Z/MAX8845Y also provide an overvoltage-protected SAFEOUT to the system.
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28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
IN AC ADAPTER GND CIN 1F
4.2V Li+ BATT CBATT 2.2F SYSTEM
MAX8845Z
DETBAT ABI SAFEOUT CSAFEOUT 1F RCHG 1M ABO SETI RSETI 2.8k MIN RMIN 1.75k GND EP POK EN CHG RPOK 1M GPIO GPIO GPIO VI/O VBUS
POWER SUPPLY ON
Figure 3. AC Adapter Application
______________________________________________________________________________________
11
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
IN CIN 1F 4.2V INTERFACE CONNECTOR GND
BATT CBATT 2.2F SYSTEM
RABI 10k ABI CABI 1F
MAX8845Z
DETBAT SAFEOUT CSAFEOUT 1F RCHG 1M ABO SETI CHG RPOK 1M POK MIN RMIN 1.75k GND EP EN GPIO GPIO GPIO VI/O VBUS
RSETI 2.8k
POWER SUPPLY ON
IF THE POWER SUPPLY IS ACTIVE-LOW ENABLED, USE THE MAX8845Y.
Figure 4. Factory System Interface Connector Application
12
______________________________________________________________________________________
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
IN MINI-USB CONNECTOR GND CIN 1F 4.2V Li+ BATT CBATT 2.2F SYSTEM
MAX8845Z
DETBAT SAFEOUT CSAFEOUT 1F RCHG 1M ABO SETI RSETIA 15.4k RSETI 3.42k MIN RMIN 3.09k GND EP POK EN CHG RPOK 1M GPIO GPIO GPIO VI/O
ABI
VBUS
GPIO
POWER SUPPLY ON
Figure 5. Mini USB Battery Charger
______________________________________________________________________________________
13
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
OVP POK VIN VPOK
OVP
VEN
VCHG
VSAFEOUT = 4.7V
VSAFEOUT TIME
Figure 6. Timing Diagram
14
______________________________________________________________________________________
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output
Typical Operating Circuit
MAX8845Z/MAX8845Y
4.25V TO 28V IN CIN 1F
DETBAT BATT CBATT 2.2F ABI 4.2V Li+
MAX8845Z MAX8845Y
SYSTEM SUPPLY
OFF ON EN
MIN RMIN 1.75k CHG SETI RSET 2.80k POK (MAX8845Z, ABO) (MAX8845Y, ABO) SAFEOUT GND EP VSAFEOUT 1F
______________________________________________________________________________________
15
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Pin Configurations
TOP VIEW BATT ABO MIN TOP VIEW BATT 8 ABO 7 MIN 9 6 POK GND EN
9
8
7
CHG 10
IN SAFEOUT 11 12
CHG 10
IN SAFEOUT 11 12
6
POK GND EN
MAX8845Z
5 4
MAX8845Y
5 4
*EXPOSED PAD
*EXPOSED PAD
+
1 SETI
2 DETBAT
3 ABI
+
1 SETI
2 DETBAT
3 ABI
Chip Information
PROCESS: BiCMOS
16
______________________________________________________________________________________
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 12 Thin QFN-EP (3mm x 3mm) PACKAGE CODE T1233-4 DOCUMENT NO. 21-0136
MAX8845Z/MAX8845Y
MARKING
E E/2
(ND - 1) X e
(NE - 1) X e
D2/2
D/2 D
AAAA
e
C L
D2
b k
0.10 M C A B
E2/2
C L
L
E2
0.10 C
0.08 C A A2 A1 L
C L
C L
L
e
e
PACKAGE OUTLINE, 12L THIN QFN, 3X3X0.75mm
21-0136 custom eng
1 2
______________________________________________________________________________________
THIN QFN.EPS
17
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage Protected Output MAX8845Z/MAX8845Y
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
PKG
12L 3x3 PKG. CODES T1233-1 T1233-3 T1233-4
EXPOSED PAD VARIATIONS
D2 MIN. 0.95 0.95 0.95 NOM. 1.10 1.10 1.10 MAX. 1.25 1.25 1.25 MIN. 0.95 0.95 0.95 E2 NOM. MAX. 1.10 1.10 1.10 1.25 1.25 1.25 PIN ID
0.35 x 45 0.35 x 45 0.35 x 45
REF. MIN. NOM. MAX. A b D E e L N ND NE A1 A2 k 0 0.70 2.90 0.75 3.00 0.80 3.10
JEDEC WEED-1 WEED-1 WEED-1
0.20 0.25 0.30 2.90 3.00 3.10 0.50 BSC. 0.45 0.55 12 3 3 0.02 0.05 0.20 REF 0.25 0.65
NOTES: 1. 2. 3. 4. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. N IS THE TOTAL NUMBER OF TERMINALS. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. DRAWING CONFORMS TO JEDEC MO220 REVISION C. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. WARPAGE NOT TO EXCEED 0.10mm.
5. 6. 7. 8. 9. 10. 11. 12.
PACKAGE OUTLINE, 12L THIN QFN, 3X3X0.75mm
21-0136 custom eng
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.
18 ____________________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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