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MAX8845XETC+-MAX8845YETC+
28V Linear Li+ Battery Chargers with Battery Detection and Overvoltage-Protected Output
General DescriptionThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W are
intelligent, stand-alone constant-current, constant-volt-
age (CCCV), thermally regulated linear chargers
designed for charging a single-cell lithium-ion (Li+) bat-
tery. The MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
integrate a current-sense circuit, MOSFET pass element,
thermal-regulation circuitry, and eliminate 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 pre-
qualification 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 charg-
ing current without damaging the ICs.
The MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
achieve high flexibility by providing adjustable fast-
charge currents (SETI) and an adjustable top-off cur-
rent threshold (MIN) through external resistors. The
MAX8845Z/MAX8845Y/MAX8845X/MAX8845Wfeature
a booting assistant circuit that distinguishes input
sources and battery connection and provides an
enable signal (ABO—MAX8845Z and ABO—
MAX8845Y/MAX8845X/MAX8845W) for system booting.
The MAX8845Z/MAX8845Y/MAX8845X/MAX8845W 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/MAX8845X/MAX8845W
accept an input supply range from 4.25V (4.4V for
MAX8845W only) to 28V, but disable charging if the
supply voltage exceeds +7.5V (+8.0V for MAX8845X
only) to protect against unqualified or faulty AC
adapters. The ICs operate over the extended tempera-
ture range (-40°C to +85°C) and are available in a com-
pact 12-pin, thermally enhanced thin QFN, 3mm x 3mm
package (0.8mm max height).
ApplicationsCellular and Cordless Phones
Smart Phones and PDAs
Digital Still Cameras
MP3 Players
USB Appliances
Charging Cradles and Docks®
FeaturesCCCV, Thermally Regulated Linear 1-Cell Li+
Battery ChargerNo External MOSFET, Reverse Blocking Diode, or
Current-Sense ResistorProgrammable Fast-Charge Currents (1ARMSmax)Programmable Top-Off Current Threshold (MIN)Input Overvoltage Protected 4.7V Output
(MAX8845Z/MAX8845Y/MAX8845W) or 4.85V
(MAX8845X) (SAFEOUT)Proprietary Die Temperature Regulation Control
(+115°C)4.25V (4.4V for MAX8845W only) to 28V Input
Voltage Range with Input Overvoltage Protection
Above +7.5V (+8.0V for MAX8845X only)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/MAX8845X/MAX8845W)
Tiny, 3mm x 3mm 12-Pin Thin QFN Package,
0.8mm Height (max)
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output19-4340; Rev 1; 9/09
EVALUATION KIT
AVAILABLE
Ordering Information
PARTPIN-PACKAGETOP
MARK
ABO
ACTIVE
STATE
MAX8845ZETC+12 Thin QFN-EP*ABLActive high
MAX8845YETC+12 Thin QFN-EP*ABMActive low
MAX8845XETC+12 Thin QFN-EP*ABQActive low
MAX8845WETC+12 Thin QFN-EP*ABRActive low
Note:All devices are specified over the -40°C to +85°C oper-
ating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Bluetooth is a registered trademark of Bluetooth SIG.
Typical Operating Circuit and Pin Configurations appear at
end of data sheet.
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VIN= 5V, VBATT= 4V, RPOK= 1MΩto BATT, EN= unconnected, RSETI= 2.8kΩto GND, VDETBAT= 0, CBATT= 2.2µF, TA= -40°C to
+85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
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.
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= +70°C)
12-Thin QFN (derate 14.7mW/°C above +70°C)
(multilayer PCB)......................................................1176.5mW
BATT Short-Circuit Duration.......................................Continuous
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERCONDITIONSMINTYPMAXUNITSInput Supply Voltage Range028V
4.257.00Input Supply Operating Voltage RangeMAX8845W only4.407.00V
VIN rising, 100mV hysteresis (typ)7.07.58.0Overvoltage Lockout Trip ThresholdMAX8845X only7.58.08.5V
Constant current charging
IIN - IBATT, IBATT = 00.220.50
Constant current charging
IIN - IBATT, IBATT = 500mA1
IC disabled, VEN = 5V0.200.50
TA = +25°C0.02
Input Current
VIN = 4V,
VBATT = 4.2V (4.35V for
MAX8845W only)TA = +85°C0.03
BATT, CHG, POKMinimum BATT Bypass Capacitance2.2µF
VBATT Prequalification Threshold VoltageVBATT rising, 100mV hysteresis (typ)2.32.52.7V
4.1754.2004.225IBATT = 0TA = -40°C to +85°C4.1584.2004.242
4.3244.3504.376Battery Regulation Voltage
MAX8845W only4.3064.3504.394
Regulator Dropout Voltage (VIN - VBATT)VBATT = 4.1V, IBATT = 425mA260mV
VIN = 0 to 4V,
VBATT = 4.2V (4.35V for MAX8845W only)510BATT Input Current
IC disabled3
Current-Sense Amplifier Gain (IBATT to ISETI)IBATT = 500mA1016µA/A
TA = 0°C to +85°C460500540VBATT = 3.5V,
RSETI = 2.8kΩTA = -40°C to +85°C425500575Fast-Charge Current
VBATT = 3.5V,
RSETI = 14kΩTA = 0°C to +85°C85100115
CHG Top-Off ThresholdIBATT falling, battery is charged
RMIN = 1.75kΩ106mA
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
PARAMETERCONDITIONSMINTYPMAXUNITSCHG HysteresisIBATT rising after top-off is detected,
RMIN = 1.75kΩ38mA
CHG Detection DelayIBATT falls below top-off threshold4.06.210.7ms
Prequalification Charge Current
Percentage of the fast-
charge current, VBATT
= 2.2V
TA = 0°C to +85°C51015%
CHG, POK Output Low ThresholdIPOK = 5mA , ICHG = 5mA0.4V
TA = +25°C1CHG, POK Output High Leakage CurrentVPOK = 5.5V,
V CHG = 5.5VTA = +85°C0.01µA
VIN rising40POK ThresholdVIN - VBATTVIN falling30mV
DETBAT, SAFEOUTDETBAT Logic-Input Low Threshold0.4
DETBAT Logic-Input High Threshold1.3V
DETBAT Pullup ResistorDETBAT to VL = 3V470kΩ
Minimum SAFEOUT Bypass Capacitance1µF
ISAFEOUT = 30mA, VIN = 5V, TA = 0°C to
+85°C (MAX8845Z/MAX8845Y/MAX8845W)4.54.74.9
SAFEOUT Regulated OutputISAFEOUT = 20mA, VIN = 5V, TA = 0°C to
+85°C (MAX8845X)4.754.855.0
SAFEOUT Current Limit100mA
EN, ABI, ABO, ABO
EN, ABI Internal Pulldown Resistor100200400kΩ
EN Logic-Input Low Threshold4.25V (4.4V for MAX8845W only) ≤ VIN ≤ 7V0.4V
EN Logic-Input High Threshold4.25V (4.4V for MAX8845W only) ≤ VIN ≤ 7V1.3V
ABI Logic-Input Low ThresholdVBATT = 4V, VIN = 00.4V
ABI Logic-Input High ThresholdVBATT = 4V, VIN = 01.3V
ABO Output Low Threshold (MAX8845Y/
MAX8845X/MAX8845W)Open drain, IABO(SINK) = 1mA0.4V
ABO Output High Threshold (MAX8845Y/
MAX8845X/MAX8845W)Open drain, 100kΩ pullup to BATTVBATT -
0.4VV
ABO Output Low Threshold
(MAX8845Z)IABO(SINK) = 1mA0.4V
ABO Output High Threshold (MAX8845Z)IABO(SOURCE) = 1mAVBATT -
0.4VV
THERMALDie Temperature Regulation Threshold115°C
ELECTRICAL CHARACTERISTICS (continued)(VIN= 5V, VBATT= 4V, RPOK= 1MΩto BATT, EN= unconnected, RSETI= 2.8kΩto GND, VDETBAT= 0, CBATT= 2.2µF, TA= -40°C to
+85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
Note 1:Specifications are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by
design and characterization.
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
Typical Operating Characteristics(VIN= 5V, VBATT= 4V, RPOK= RCHG= 200kΩto 5V, EN= unconnected, RSETI= 2.8kΩto GND, RMIN= 1.74kΩto GND, RDETBAT=
4.7kΩto GND, CBATT= 2.2µF, TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX8845Z/Y/X/W toc01
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
VEN = 0,
IBATT = 0
VIN RISING
DISABLED MODE SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX8845Z/Y/X/W toc02
INPUT VOLTAGE (V)
SUPPLY CURRENT (
VEN = 5V
CHARGE CURRENT
vs. BATTERY VOLTAGE
MAX8845Z/Y/X/W toc03
BATTERY VOLTAGE (V)
CHARGE CURRENT (mA)
CHARGE CURRENT
vs. INPUT VOLTAGE
MAX8845Z/Y/X/W toc04
INPUT VOLTAGE (V)
CHARGE CURRENT (mA)
CHARGE CURRENT
vs. INPUT VOLTAGE HEADROOM
MAX8845Z/Y/X/W toc05
VIN - VBATT (mV)
CHARGE CURRENT (mA)
VBATT = 4V,
VIN RISING
SAFEOUT OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX8845Z/Y/X/W toc06
INPUT VOLTAGE (V)
SAFEOUT VOLTAGE (V)
ISAFEOUT = 1mA
SAFEOUT OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX8845Z/Y/X/W toc07
LOAD CURRENT (mA)
SAFEOUT VOLTAGE (V)
40μs/div
STARTUP INTO PRECHARGEIBATT
VIN
100mA/div
5V/div
5V/div
5V/div
MAX8845Z/Y/X/W toc08
VEN
VPOK
40μs/div
SHUTDOWN
(FAST-CHARGE TO SHUTDOWN)IBATT
VIN
500mA/div
5V/div
5V/div
5V/div
MAX8845Z/Y/X/W toc09
VEN
VPOK
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
Typical Operating Characteristics (continued)(VIN= 5V, VBATT= 4V, RPOK= RCHG= 200kΩto 5V, EN= unconnected, RSETI= 2.8kΩto GND, RMIN= 1.74kΩto GND, RDETBAT=
4.7kΩto GND, CBATT= 2.2µF, TA= +25°C, unless otherwise noted.)
BATTERY REGULATION ACCURACY
vs. AMBIENT TEMPERATURE
MAX8845Z/Y/X/W toc10
AMBIENT TEMPERATURE (°C)
BATTERY REGULATION ACCURACY (%)
IBATT = 0
FAST-CHARGE CURRENT
vs. RSETIMAX8845Z/Y/X/W toc11
RSETI (kΩ)
FAST-CHARGE CURRENT (mA)
100010,000
TOP-OFF CURRENT THRESHOLD
vs. 1/RMIN (kΩ)MAX8845Z/Y/X/W toc12
1/RMIN (kΩ)
TOP-OFF CURRENT THRESHOLD (mA)
TOP-OFF CURRENT RISING
TOP-OFF CURRENT FALLING
CHARGE CURRENT
vs. AMBIENT TEMPERATURE
MAX8845Z/Y/X/W toc13
AMBIENT TEMPERATURE (°C)
CHARGE CURRENT (mA)
VBATT = 4V
VBATT = 3.2V
RSETI = 2.8kΩ
4μs/div
AUTOBOOT ENABLED BY ABI SIGNAL
(MAX8845Z)VABI
VIN
5V/div
5V/div
5V/div
5V/div
MAX8845Z/Y/X/W toc14
VBATT
VABO
20μs/div
AUTOBOOT ENABLED BY INPUT VOLTAGE
(MAX8845Z)VABI
VIN
5V/div
5V/div
5V/div
5V/div
MAX8845Z/Y/X/W toc15
VBATT
VABO
4μs/div
AUTOBOOT ENABLED BY ABI SIGNAL
(MAX8845Y/MAX8845X/MAX8845W)VABI
VIN
5V/div
5V/div
5V/div
5V/div
MAX8845Z/Y/X/W toc16
VBATT
VABO
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
Pin Description
PIN
MAX8845Z
MAX8845Y/
MAX8845X/
MAX8845W
NAMEFUNCTION1SETI
Charge-Current Program and Fast-Charge Current Monitor. Output current from SETI is
1016µA 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/MAX8845X/MAX8845W as a USB charger, see
Figure 5.2DETBAT
Battery Pack ID Resistor Detection Input. If DETBAT is pulled low through a pulldown
resistor less than 51kΩ the charger is enabled. If DETBAT is left unconnected, the
charger is disabled.3ABIAutobooting External Input. See the Autobooting Assistant section and Table 1 for
autobooting conditions. ABI is pulled to GND through an internal 200kΩ resistor.ENActive-Low, Logic-Level Enable Input. Drive EN high to disable charger. Drive EN low or
leave unconnected for normal operation. EN has an internal 200kΩ pulldown resistor.5GNDGround. 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.POK
Active-Low, Input Voltage Status Indicator. POK is an open-drain output that asserts low
when 2.35V < VIN < 7V (7.5V for MAX8845X only) and (VIN - VBATT) > 40mV. If VIN >
+7.5V (+8.0V for MAX8845X only) 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.—ABOActive-High, Autobooting Logic Output. See the Autobooting Assistant section and Table
1 for autobooting conditions.ABOActive-Low, Open-Drain Logic Output. See the Autobooting Assistant section and Table
1 for autobooting conditions.8BATTLi+ Battery Connection. Bypass BATT to GND with a 2.2µF ceramic capacitor.MINTop - O ff C ur r ent Thr eshol d P r og r am m ab l e Inp ut. IM IN ( m A) fal l i ng = 148V /RM IN ( kΩ ) + 22m A) .10CHG
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.11INInput Supply Voltage. Bypass IN to GND with a 1µF or larger ceramic capacitor to
improve line noise and input transient rejection.12SAFEOUT
4.7V (MAX8845Z/MAX8845Y/MAX8845W) or 4.85V (MAX8845X) Regulated LDO Output
with Input Overvoltage Protection. Bypass SAFEOUT to GND with a 1µF or larger
ceramic capacitor. SAFEOUT can be used to supply low voltage-rated USB systems.EPExposed Pad. Connect the exposed pad to a large ground plane for maximum power
dissipation. Connect GND to the exposed pad directly under the IC.
Detailed DescriptionThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
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/MAX8845X/
MAX8845W chargers enter a prequalification stage
where it precharges that cell with 10% of the user-pro-
grammed fast-charge current (Figure 2). The CHGindi-
cator is driven low to indicate entry into the prequalifi-
cation 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 is
reduced. If the battery current drops to less than the
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected OutputOUTPUT DRIVER,
CURRENT SENSE,
AND LOGICTEMPERATURE
SENSOR
REGULATOR
REF
REFOK
VIN
OVLO
UVLO
VREFVREF
LOGIC
BATT
DETBAT
ABI
ABO (MAX8845Z ONLY)
ABO (MAX8845Y/MAX8845X/MAX8845W)
POK
BATT
BATT
POK
200kΩ
GNDEP
+115°C
4.2V Li+
(4.35V FOR
MAX8845W ONLY)
VI/O
200kΩ
CHG
MAX8845Z
MAX8845Y
MAX8845X
MAX8845W
VREF
IMINREF
DETBAT
LINEAR
REGULATOR
WITH OVP
SETI
MIN
SAFEOUT
Figure 1. MAX8845Z/MAX8845Y/MAX8845X/MAX8845W Functional Diagram
MAX8845Z/MAX8845Y/MAX8845X/MAX8845Wtop-off current threshold set by RMIN, the charger
enters top-off mode and the CHGindicator goes high
impedance signaling that the battery is fully charged.
Overvoltage-Protected Output (SAFEOUT)SAFEOUT is a linear regulator that provides an output
voltage of 4.7V (MAX8845Z/MAX8845Y/MAX8845W) or
4.85V (MAX8845X) and can be used to supply low volt-
age- rated USB systems. The SAFEOUT linear regulator
turns on when VIN≥4.25V regardless of ENand is dis-
abled when VINis greater than the overvoltage thresh-
old (7.5V typ) (8.0V typ for MAX8845X only).
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 51kΩ. If DETBAT is left uncon-
nected or the pulldown resistor is 51kΩor greater the
battery charger is disabled. If DETBAT is not used con-
nect DETBAT to GND for normal operation.
POKOutputThe open-drain POKoutput asserts low when 2.35V ≤
VIN≤7V (7.5V for MAX8845X only) and (VIN- VBATT) ≥
40mV (typ VINrising). POKis high impedance during
shutdown. When interfacing with a microprocessor
logic input, a pullup resistor to the microprocessor’s I/O
voltage may be required.
Autobooting AssistantThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W con-
tain autobooting assistant circuits that generate an
enable signal for system booting (ABO—MAX8845Z,
ABO—MAX8845Y/MAX8845X/MAX8845W). 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 51kΩ, 2.35V ≤VIN≤7V (7.5V for only
MAX8845X), and (VIN - VBATT) ≥40mV (typ VINrising).
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 POKis pulled low, the booting assistant always
drives ABO high regardless of ABI. ABI is pulled to GND
through an internal 200kΩresistor. 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/MAX8845X/
MAX8845W, the output ABOis only dependent on the
state of ABI (Table 1).
CHGCharge Indicator OutputCHGis an open-drain output that indicates charge sta-
tus. Table 2 describes the state of CHGduring different
stages of operation. CHGis suitable for driving a charge
indication LED. If the MAX8845Z/MAX8845Y/MAX8845X/
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected OutputVBATT < 2.5V
PRECHARGE10% OF IFAST-CHARGE
CHG = LOW
FAST-CHARGECONSTANT-CURRENT CHARGE
100% OF IFAST-CHARGE
CHG = LOW
TOP-OFF4.2 VOLTAGE REGULATION
CHG = HIGH-Z
(MAX8845Z/MAX8845Y/MAX8845X)
4.35 VOLTAGE REGULATION (MAX8845W)
(VIN - VBATT) < 30mV
VBATT < 2.4V
VBATT ≥ 2.5V
VIN < OVP, AND
(VIN - VBATT) ≥ 40mV, AND
IC ENABLED
SHUTDOWNCHARGER = DISABLED
CHG = HIGH-Z
VIN > OVP, OR
(VIN - VBATT) < 30mV, OR
IC DISABLED
ASYNCHRONOUS
FROM ANYWHERE
VIN > OVP, OR
(VIN - VBATT) < 30mV, OR
THERMAL SHUTDOWN, OR
IC DISABLED
IBATT > 295V/RMIN (kΩ) - 24mA
IBATT ≤ IMIN
FOR 6.2ms (typ) OR LONGER
CHARGING CURRENT REDUCTIONCHARGING CURRENT IS REDUCED
AS NECESSARY
DIE TEMPERATURE > +115°CANY CHARGING STATE
RETURN TO
CHARGING STATE
DIE TEMPERATURE ≤ +115°C
Figure 2. Charge-State Diagram
MAX8845W are used in conjunction with a microproces-
sor, a pullup resistor to the logic I/O voltage allows CHG
to indicate charge status to the microprocessor instead
of driving an LED.
Thermal RegulationThe thermal-regulation loop limits the MAX8845Z/
MAX8845Y/MAX8845X/MAX8845W die temperature to
+115°C 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 InputThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
contain active-low logic input (EN) used to enable the
chargers. Drive ENlow, leave unconnected, or connect
to GND to enable the charge-control circuitry. Drive EN
high to disable the charger-control circuitry. ENhas an
internal 200kΩpulldown resistor.
Soft-StartThe soft-start algorithm activates when entering fast-
charge mode. When the prequalification state is com-
plete (VBATTexceeds +2.5V), the charging current
ramps up in 250µs to the full charging current. This
Applications Information
Fast Charge-Current SettingThe 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):
where IFAST_CHARGEis in amps and RSETIis in ohms.
RSETImust always be 1.4kΩor higher due to the con-
tinuous charging current limit of 1ARMS.
Top-Off Current Threshold SettingThe 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 cur-
rent (IMIN):
IMIN(falling) = 148V/RMIN (kΩ) + 22mA
IMIN(rising) = 295V/RMIN (kΩ) - 24mA
where IMINis in mA and RMINis in kΩ. Use RMIN≤
2.2kΩ.VFASTCHARGESETI_=1400
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
ABIBATTPOK
CHARGER STATEABO
(MAX8845Z)ABO
(MAX8845Y/
MAX8845X/MAX8845W)LowPresentHigh-ZShutdownLowHigh-Z
HighPresentHigh-ZShutdownHighLow
LowNot presentLowCC/CV modeHighHigh-Z
LowPresentLowFast-charge/top-offHighHigh-Z
HighPresentLowFast-charge/top-offHighLow
Table 1. Autobooting Output StatesVINVBATTIBATTCHG
STATEHighXX0High-ZDisabled
> 7.5VXLowX> VIN - 30mV0High-ZShutdown
Low4.25V (4.4V for MAX8845W only) ≤ VIN ≤ 7.5V< 2.4V10% of IFAST-CHARGE*LowPrecharge
Low4.25V (4.4V for MAX8845W only) ≤ VIN ≤ 7.5V≥ 2.5V100% of IFAST-CHARGE*LowFast-charge
Low4.25V (4.4V for MAX8845W only) ≤ VIN ≤ 7.5V4.2V (4.35V for
MAX8845W only)< IMINHigh-ZTop-off
Table 2. CHGStatesX = Don’t care.
*IFAST-CHARGEis reduced as necessary to prevent the die temperature from exceeding +115°C.
Note:Present indicates that VBATT≥2V and Not Present indicates that the battery is not connected.
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
Capacitor SelectionConnect a ceramic capacitor from BATT to GND for
proper stability. Use a 2.2µF ceramic capacitor for most
applications. Connect a 1µF ceramic capacitor from IN
to GND. A larger input capacitor can be used for high
charging current to reduce input voltage ripple.
Connect a 1µF 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.
Thermal ConsiderationsThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W 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 SourcesThe MAX8845Z/MAX8845Y/MAX8845X/MAX8845W
operate from well-regulated DC sources. The full charg-
ing input voltage range is 4.25V (4.4V for MAX8845W
only) to 7.5V (8V for MAX8845X only). The device can
withstand up to 28V on the input without damage to the
IC. If VINis greater than 7.5V (8V for MAX8845X only),
the internal overvoltage-protection circuitry disables
charging until the input falls below 7.5V (8V for
MAX8845X only). An appropriate power supply must
provide at least 4.25V at the desired peak charging
current and stay below 7V when unloaded.
Typical Application Circuits
AC Adapter ApplicationFigure 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 POKpulled
low. Once POKis 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 ENis low or unconnected. By
monitoring CHG, the system can detect the top-off thresh-
old and terminate the charge through EN. The
MAX8845Z/MAX8845Y/MAX8845X/MAX8845W also pro-
vide an overvoltage-protected SAFEOUT to the system.
Factory System Interface Connector ApplicationFigure 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 con-
figuration in Figure 4 is used for system development,
testing, and calibrations in production or design stage.
USB-Powered Li-Ion ChargerThe universal serial bus (USB) provides a high-speed
serial communication port as well as power for the
remote device. The MAX8845Z/MAX8845Y/MAX8845X/
MAX8845W 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 charg-
ing 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/MAX8845X/
MAX8845W also provide an overvoltage-protected
SAFEOUT to the system.
Recommended PCB Layout and RoutingPlace 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.
28V Linear Li+ Battery Chargers with Battery
Detection and Overvoltage Protected Output
