EVALUATION KIT AVAILABLE
MAX8814
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
General Description
Benefits and Features
The MAX8814 intelligent, stand-alone constant-current,
constant-voltage (CCCV), thermally regulated linear
charger is designed for charging a single-cell lithium-ion
(Li+) battery.
The MAX8814 controls the charging sequence from the
prequalification state through constant-current fastcharge and the final constant voltage charge. The IC
achieves high flexibility by providing an adjustable fastcharge current through an external resistor. It also features a booting assistant circuit that distinguishes input
sources and battery connection, and provides an output signal (ABO) for system booting.
The device operates over the extended temperature
range (-40°C to +85°C), and is available in an 8-pin
thermally enhanced 2mm x 2mm TDFN package
(0.8mm max height).
• Reduces External Components and Total Cost
Applications
Smartphones
Portable Music Players
• Integrated Current-Sensing Circuit, MOSFET Pass
Element, and Thermally Regulation Circuitry
• No Reverse Blocking Diode Required
• Guarantees Safe and Accurate Battery Charging
• Proprietary Die Temperature Regulation Control
(+115°C) Allows Maximum Charging Current
Without Damaging the IC
• 4.25V to 28V Input Voltage Range with OverVoltage Protection Above +7V to Protect Against
Unqualified or Faulty AC Adapters
• Soft-Start Limits Inrush Current
• Integrated System Features for Compact Designs
• Programmable Fast-Charge Current: 1ARMS Max
• Charge-Current Monitor for Fuel Gauging (ISET)
• Input Power-Source Detection Output (POK) and
Charge-Enable Input (EN)
• Output for Autobooting (ABO)
• Reduce Power Dissipation
• Low Dropout Voltage (300mV at 500mA)
Digital Still Cameras
USB Appliances
Charging Cradles and Docks
Bluetooth® Equipment
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX8814ETA+
-40°C to +85°C
8 TDFN
(2mm x 2mm)
TOP
MARK
ABI
+Denotes a lead-free and RoHS-compliant package.
Typical Operating Circuit
BATT
4.25V TO 28V
MAX8814
SYSTEM
SUPPLY
OFF
ON
EN
ABI
ISET
GND
Bluetooth is a registered trademark of Bluetooth SIG.
Pin Configuration appears at end of data sheet.
19-0994; Rev 3; 5/15
+
2.2µF
IN
POK
EP
ABO
Li+
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 = +70°C)
8-Pin TDFN (derate 11.9mW/°C above +70°C)
(multilayer PCB) ........................................................953.5mW
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
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 = 1MΩ to BATT, EN = 0V, RISET = 2.8kΩ to GND, CBATT = 2.2µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
Input Voltage Range
Input Operating Voltage Range
UNITS
0
28
V
4.25
6.80
V
40
30
Overvoltage-Lockout Trip
Threshold
VIN rising, 100mV hysteresis (typ)
6.8
7.5
Constant-current charging mode (IBATT = 0A)
0.8
1.35
IC disabled (VEN = 5V)
0.23
0.50
TA = +25°C
0.021
0.065
TA = +85°C
0.021
VIN = 0 to 4V,
VBATT = 4.2V
1
IC disabled
3
IBATT = 0A
4.179
4.200
4.221
TA = -40°C to +85°C
4.158
4.200
4.242
2.2
524
570
616
TA = -40°C to +85°C
485
570
656
TA = 0°C to +85°C
89
107
125
TA = -40°C to +85°C
80
107
134
Percentage of the fast-charge current, VBATT = 2.2V,
TA = 0°C to +85°C
4
10
15
Fast-Charge Current
VBATT = 3.5V,
RISET = 14kΩ
Die Temperature Regulation
Threshold
+115
VBATT Prequalification Threshold
Voltage
VBATT rising, 100mV hysteresis (typ)
Current-Sense Amplifier Gain
(IBATT to IISET)
IBATT = 570mA
2.3
2.5
877.2
V
mA
µA
V
µF
TA = 0°C to +85°C
VBATT = 3.5V
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10
TA = 0°C to +85°C
Minimum BATT Bypass
Capacitance
Prequalification Charge Current
mV
7
VIN = 4V,
VBATT = 4.2V
Battery Regulation Voltage
MAX
VIN falling
VIN - VBATT,
10mV hysteresis (typ)
BATT Input Current
TYP
VIN rising
Power-OK Threshold
IN Input Current
MIN
mA
%
°C
2.7
V
µA/A
Maxim Integrated | 2
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
Electrical Characteristics (continued)
(VIN = 5V, VBATT = 4V, R POK = 1MΩ to BATT, EN = 0V, RISET = 2.8kΩ to GND, CBATT = 2.2µF, TA = -40°C to +85°C, unless otherPARAMETER
CONDITIONS
Regulator Dropout Voltage
(VIN - VBATT )
VBATT = 4.1V, IBATT = 425mA
EN Logic-Input Low Voltage
4.25V < VIN < 6.5V
EN Logic-Input High Voltage
4.25V < VIN < 6.5V
MIN
MAX
UNITS
240
500
mV
0.4
1.3
EN and ABI Internal Pulldown
Resistance
100
ABI Logic-Input Low Voltage
VIN = 0V
ABI Logic-Input High Voltage
VIN = 0V
ABO Output Low Voltage
IABO (SINK) = 1mA
ABO Output High Voltage
IABO (SOURCE) = 1mA
POK Output Low Voltage
I POK = 5mA
POK Output High Leakage
Current
TYP
200
400
0.4
1.3
kΩ
V
V
0.4
VBATT 0.4V
V
V
0.4
V POK = 5.5V
V
V
TA = +25°C
0.001
TA = +85°C
0.002
1
V
µA
Note 1: Specifications are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by
design and characterization.
Typical Operating Characteristics
(VIN = 5V, VBATT = 4V, R POK = 1MΩ to BATT, EN = 0V, RISET = 2.8kΩ to GND, CBATT = 2.2µF, TA = -40°C to +85°C, unless otherSUPPLY CURRENT
vs. VOLTAGE
0.7
0.6
0.5
0.4
0.3
600
500
400
300
200
0.2
0.1
100
0
0
0
4
8
12
16
20
INPUT VOLTAGE (V)
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24
28
1000
MAX8814 toc03
700
SUPPLY CURRENT (μA)
SUPPLY CURRENT (mA)
0.8
VEN = 5V
900
800
CHARGE CURRENT (mA)
0.9
800
MAX8814 toc02
EN = 0V
MAX8814 toc01
1.0
CHARGE CURRENT
vs. BATTERY VOLTAGE
DISABLED MODE SUPPLY CURRENT
vs. INPUT VOLTAGE
700
600
500
400
300
200
100
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
BATTERY VOLTAGE (V)
Maxim Integrated | 3
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
Package Information (continued)
(VIN = 5V, VBATT = 4V, R POK = 1MΩ to BATT, EN = 0V, RISET = 2.8kΩ to GND, CBATT = 2.2µF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
CHARGE CURRENT vs. INPUT
VOLTAGE HEADROOM
CHARGE CURRENT
vs. INPUT VOLTAGE
900
800
CHARGE CURRENT (mA)
700
600
500
400
300
VIN
100mA/div
0A
5V/div
0V
VEN
5V/div
IBATT
700
600
500
400
300
0V
200
200
100
100
0
0
4
8
12
16
20
24
VBATT = 4V
VIN RISING
28
0
100
INPUT VOLTAGE (V)
200
300
400
5V/div
0V
VPOK
500
40μs/div
VIN - VBATT (mV)
BATTERY REGULATION VOLTAGE
ACCURACY vs. AMBIENT TEMPERATURE
IBATT
500mA/div
0A
5V/div
VIN
0V
5V/div
VEN
0V
5V/div
0V
VPOK
1.0
IBATT = 0A
0.8
0.6
0.4
0.2
0
-0.2
-0.4
100
10
-0.6
-0.8
1
-1.0
-40
100μs/div
CHARGE CURRENT vs. RISET
1000
CHARGE CURRENT (mA)
MAX8814 toc07
BATTERY REGULATION VOLTAGE ACCURACY (%)
SHUTDOWN
(FAST-CHARGE TO SHUTDOWN)
MAX8814 toc09
0
CHARGE CURRENT vs. AMBIENT
TEMPERATURE
-15
10
35
60
85
1
10
100
RISET (kΩ)
AUTOBOOT ENABLED
BY ABI SIGNAL
AUTOBOOT ENABLED
BY INPUT SUPPLY
600
MAX8814 toc10
VBATT = 4V
VBATT = 3.2V
5V/div
VABI
0V
5V/div
5V/div
400
VIN
10,000
MAX8814 toc12
5V/div
0V
VABI
500
1000
TEMPERATURE (°C)
MAX8814 toc11
700
CHARGE CURRENT (mA)
VBATT = 2V
MAX8814 toc08
CHARGE CURRENT (mA)
800
MAX8814 toc06
MAX8814 toc05
900
STARTUP INTO PRECHARGE
1000
MAX8814 toc04
1000
0V
VIN
0V
300
VBATT
5V/div
200
VBATT
5V/div
0V
100
0V
VABO
-15
10
35
60
5V/div
5V/div
RISET = 2.8kΩ
0
-40
0V
85
4μs/div
0V
VABO
4μs/div
TEMPERATURE (°C)
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Maxim Integrated | 4
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
Pin Description
PIN
NAME
FUNCTION
1
IN
Input Supply Voltage. Bypass IN to GND with a 1µF or larger ceramic capacitor to minimize line noise
and maximize input transient rejection.
2
GND
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.
3
ISET
Charge-Current Program and Fast-Charge Current Monitor. Output current from ISET is 877.2µA 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.
4
ABI
Autobooting External Input. See the Autobooting Assistant section and Table 1 for autobooting
conditions. ABI is pulled to GND through an internal 200kΩ resistor.
5
ABO
Autobooting Logic Output. See the Autobooting Assistant section and Table 1 for autobooting
conditions.
6
EN
7
POK
Input-Voltage Status Indicator. Connect a 1MΩ 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.
8
BATT
Battery Connection. Bypass BATT to GND with a minimum of 2.2µF of capacitor.
—
EP
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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.
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.
Maxim Integrated | 5
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
4.25V TO 28V
BATT
IN
C1
1μF
C3
2.2μF
Li+
+115°C
OUTPUT DRIVER,
CURRENT SENSE,
AND LOGIC
TEMPERATURE
SENSOR
ISET
R2
2.8kΩ
VI/O
IN
VREF
VREF
R3
1MΩ
POK
VIN
OVLO
VL
REGULATOR
BATT
BATT
VL
VL
UVLO
ABO
REF
VREF
ABI
REFOK
POK
200kΩ
LOGIC
EN
MAX8814
200kΩ
GND
EP
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
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ISET to GND. As the battery voltage approaches 4.2V,
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 +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 IC.
Maxim Integrated | 6
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
SHUTDOWN
CHARGER = DISABLED
VBATT < 2.5V
(VIN - VBATT) < 30mV
PRECHARGE
10% CHARGE CURRENT
VIN < 7V, AND
(VIN - VBATT) ≥ 40mV, AND
IC ENABLED
ASYNCHRONOUS
FROM ANYWHERE
VIN > 7V, OR
(VIN - VBATT) < 30mV, OR
IC DISABLED
VIN > 7V, OR
(VIN - VBATT) < 30mV, OR
IC DISABLED
VBATT < 2.4V
VBATT ≥ 2.5V
FAST-CHARGE
CONSTANT-CURRENT CHARGE
100% CHARGE CURRENT
VBATT ≥ 4.2V
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 200kΩ pull-down
resistor.
Table 1. ABO and POK States
ABI
BATT
POK
CHARGER STATE
Low
Present
Hi-Z
Shutdown
Low
High
Present
Hi-Z
Shutdown
High
X
Not present
Low
Fast-charge/voltage
regulation
High
X
Present
Low
Fast-charge/voltage
regulation
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 (1MΩ typ) to an
external power supply. POK is high impedance when
VBATT ≥ (VIN - 40mV).
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
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ABO
X = Don’t care.
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 200kΩ 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 250µs to the full charging current.
This reduces the inrush current on the input supply.
Maxim Integrated | 7
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
FACTORY TEST
FIXTURE
OR
AC ADAPTER
C1
1μF
BATT
IN
C3
2.2μF
Li+
SYSTEM
R1
10kΩ
MAX8814
VI/O
ABI
C2
0.1μF
GND
R3
1MΩ
POK
GPIO
EN
GPIO
ABO
GND
EP
ISET
R4
10kΩ
ADC
R2
2.8kΩ
C4
0.1μF
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
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 877.2µA per
ampere of charging current. The output voltage at ISET
is proportional to the charging current:
I
× 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.
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Capacitor Selection
Connect a ceramic capacitor from BATT to GND for
proper stability. Use a 2.2µF X5R ceramic capacitor for
most applications. Connect a 1µF 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.
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.
Maxim Integrated | 8
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
VBUS
C1
1μF
BATT
IN
+
C3
2.2μF
Li+
SYSTEM
USB PORT
MAX8814
VI/O
ABI
GND
R3
1MΩ
GPIO
POK
ABO
GPIO
EN
GND
EP
R4
10kΩ
ISET
ADC
R5
4.99kΩ
R2
15.8kΩ
C4
0.1μF
N
GPIO
POWER
SUPPLY
ON
Figure 4. USB Battery Charger
Application Circuits
Layout and Bypassing
Microprocessor-Interfaced Charger
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.
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.
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Chip Information
PROCESS: BiCMOS
Maxim Integrated | 9
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
Pin Configuration
Package Information
TOP VIEW
BATT
POK
EN
ABO
8
7
6
5
MAX8814
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
8 TDFN
T822+2
21-0168
EXPOSED PADDLE
+
1
2
3
4
IN
GND
ISET
ABI
TDFN
2mm x 2mm
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Maxim Integrated | 10
28V Linear Li+ Battery Charger
with Smart Autoboot Assistant
MAX8814
Revision History
REVISION
NUMBER
REVISION
DATE
0
10/07
1
PAGES
CHANGED
DESCRIPTION
Initial release
—
2/08
Changed OVP (min) to 6.8V from 6.5V with 6 sigma without silicon
change
2
2
3/08
Changed Input Operating Voltage maximum range from 6.8V to
6.5V.
1
3
5/15
Revised General Description and Benefits and Features section
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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