19-1545; Rev 0; 9/99
KIT
ATION
EVALU
BLE
AVAILA
Single-Cell Li+ Battery Charger
for Current-Limited Supply
General Description
Features
o
Simple Stand-Alone Application Circuit
o
Lowest Power Dissipation
o
8-Pin µMAX Package Saves Space
o
No Inductor Required
o
0.75% Overall System Accuracy
o
Continuous Voltage and Temperature Protection
o
Safely Precharges Near-Dead Cells
o
Programmable Safety Timeout
o
Top-Off Charging to Achieve Full Battery Capacity
o
Automatic Power-Down when Power Source is
Removed
MAX1679
The MAX1679 battery charger for a single lithium-ion (Li+)
cell comes in a space-saving 8-pin µMAX package. This
simple device, in conjunction with a current-limited wall
cube and a PMOS transistor, allows safe and fast charg-
ing of a single Li+ cell.
The MAX1679 initiates charging in one of three ways:
battery insertion, charger power-up, or external manip-
ulation of the THERM pin. Charging terminates when
the average charging current falls to approximately 1%
of the fast-charge current, or when the on-chip counter
times out.
Key safety features include continuous voltage and
temperature monitoring, a programmable charger time-
out, and a 5mA precharge current mode to charge
near-dead cells. Automatic detection of input power
removal shuts down the device, minimizing current
drain from the battery. An overall system accuracy of
0.75% ensures that the cell capacity is fully utilized
without cycle life degradation.
The MAX1679 evaluation kit (MAX1679EVKIT) is avail-
able to help reduce design time.
Ordering Information
PART
MAX1679EUA
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
8 µMAX
Applications
Single-Cell Li+ Portable Applications
Self-Charging Battery Packs
PDAs
Cell Phones
Cradle Chargers
CURRENT-
LIMITED
VOLTAGE
SOURCE
LED
IN
GATE
BATT
BATTERY
IN
GATE
CHG
TSEL
1
2
3
4
8
BATT
THERM
GND
ADJ
THERMISTOR
7
6
5
TIMER
RANGE
SELECT
PFET
Typical Operating Circuit
Pin Configuration
TOP VIEW
CHG
MAX1679
TSEL
THERM
GND
ADJ
MAX1679
µMAX
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Single-Cell Li+ Battery Charger
for Current-Limited Supply
MAX1679
ABSOLUTE MAXIMUM RATINGS
IN,
CHG,
GATE to GND ........................................ -0.3V to +26V
BATT, TSEL, THERM, ADJ to GND ........................ -0.3V to +6V
GATE to IN................................................................-6V to +0.3V
THERM, ADJ to BATT...............................................-6V to +0.3V
GATE Continuous Current ................................................ -10mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C) ........... 330mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range ............................ -65°C to +150°C
Lead Temperature (soldering, 10sec) ............................ +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
(V
IN
= V
CHG
= +10V, V
BATT
= +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND,
T
A
= 0°C
to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage (Note 1)
Input Voltage for Removable
Battery (Note 1)
Undervoltage Lockout Trip Point
Undervoltage Lockout Trip-Point
Hysteresis
Fast-Charge Qualification
Threshold
Fast-Charge Restart Threshold
Precharge Source Current
BATT Regulation Voltage
BATT Regulation Adjust Range
ADJ Source Impedance
ADJ Output Voltage
Battery Removal Detection
Threshold
Battery Removal Detection
Threshold Hysteresis
BATT Input Current (Note 2)
BATT Input Current, Fast-
Charge State
BATT Input Current, Done State
IN Input Current, Fast-Charge
State
IN Input Current, Done State
Timer Accuracy
CHG
Output Leakage Current
I
BATT
I
BATT
I
IN
I
IN
No load on ADJ
V
BATT
rising
V
BATT
falling
V
IN
≤
V
BATT
-0.3V
V
BATT
= 4V
V
BATT
= 4.25V
V
BATT
= 4V, V
IN
= 4V
V
BATT
= 4.25V, V
IN
= 22V
See Table 3
V
CHG
= 22V,
CHG
= high
-10
-1
SYMBOL
V
IN
V
IN
CONDITIONS
External PMOS FET off
External PMOS FET off
V
BATT
rising
V
BATT
falling
V
BATT
rising, transition from precharge to full
current
V
BATT
falling, transition from DONE to
PREQUAL state (Figure 2)
V
BATT
= 2V
2.425
3.783
4
4.1685
4.0
9.8
1.393
4.875
10
1.400
5.0
125
0.1
900
500
30
250
1
1500
1000
100
600
+10
+1
MIN
5
6
2.1
2.2
60
2.500
3.89
5
4.2000
2.575
4.00
6
4.2315
4.2
10.2
1.407
5.125
TYP
MAX
22
22
2.3
UNITS
V
V
V
mV
V
V
mA
V
V
kΩ
V
V
%
mV
µA
µA
µA
µA
µA
%
µA
2
_______________________________________________________________________________________
Single-Cell Li+ Battery Charger
for Current-Limited Supply
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CHG
= +10V, V
BATT
= +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND,
T
A
= 0°C
to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CHG
Output Sink Current
THERM Sense Current (for hot
qualification)
THERM Sense Current (for cold
qualification)
THERM Sense Voltage Trip
Point
GATE Source/Sink Current
GATE Drive Current at Battery
Removal
V
IN
= 10V, V
GATE
= 8V
V
BATT
= 5.1V, gate driven high
SYMBOL
CONDITIONS
V
CHG
= 1V,
CHG
= low
MIN
4
346
47.8
1.379
75
20
TYP
5
352.9
48.8
1.40
105
40
MAX
6
360
49.8
1.421
130
60
UNITS
mA
µA
µA
V
%
µA
mA
MAX1679
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CHG
= +10V, V
BATT
= +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND,
T
A
= -40°C
to +85°C,
unless otherwise noted.)
PARAMETER
Input Voltage (Note 1)
Input Voltage for Removable
Battery (Note 1)
Undervoltage Lockout Trip Point
Fast-Charge Qualification
Threshold
Fast-Charge Restart Threshold
Precharge Source Current
BATT Regulation Voltage
BATT Regulation Adjust Range
ADJ Source Impedance
ADJ Output Voltage
Battery Removal Detection
Threshold
BATT Input Current (Note 2)
BATT Input Current, Fast-
Charge State
BATT Input Current, Done State
IN Input Current, Fast-Charge
State
I
BATT
I
BATT
I
IN
No load on ADJ
V
BATT
rising
V
IN
≤
V
BATT
- 0.3V
V
BATT
= 4.0V
V
BATT
= 4.25V
V
BATT
= 4.0V, V
IN
= 4.0V
SYMBOL
V
IN
V
IN
CONDITIONS
External PMOS FET off
External PMOS FET off
V
BATT
rising
V
BATT
rising, transition from precharge to full
current
V
BATT
falling, transition from DONE to
PREQUAL state, Figure 2
V
BATT
= 2V
MIN
5
6
2.05
2.35
3.74
3
4.137
4.0
9.8
1.386
4.850
MAX
22
22
2.35
2.65
4.04
7
4.263
4.2
10.2
1.414
5.150
1
1500
1000
100
UNITS
V
V
V
V
V
mA
V
V
kΩ
V
V
µA
µA
µA
µA
_______________________________________________________________________________________
3
Single-Cell Li+ Battery Charger
for Current-Limited Supply
MAX1679
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CHG
= +10V, V
BATT
= +4.2V, TSEL = GND, GATE = unconnected, ADJ = unconnected, THERM = 10kΩ to GND,
T
A
= -40°C
to +85°C,
unless otherwise noted.)
PARAMETER
IN Input Current, Done State
Timer Accuracy
CHG
Output Leakage Current
CHG
Output Sink Current
THERM Sense Current (for hot
qualification)
THERM Sense Current (for cold
qualification)
THERM Sense Voltage Trip
Point
GATE Source/Sink Current
GATE Drive Current at Battery
Removal
V
IN
= 10V, V
GATE
= 8V
V
BATT
= 5.1V, gate driven high
SYMBOL
I
IN
See Table 3
V
CHG
= 22V,
CHG
= high
V
CHG
= 1.0V,
CHG
= low
CONDITIONS
V
BATT
= 4.25V, V
IN
= 22V
-15
-1
4
342
47.3
1.358
60
20
MIN
MAX
700
+15
+1
6
363
50.3
1.442
140
90
UNITS
µA
%
µA
mA
µA
µA
V
µA
mA
Note 1:
The input voltage range is specified with the external PFET off. When charging, the PFET turns on and the input voltage
(the output voltage of the constant-current power source) drops to very near the battery voltage. When the PFET is on, V
IN
may be as low as 2.5V.
Note 2:
BATT Input Current is the supply current to the device. When V
IN
is removed, the MAX1679 shuts down and the input current
is less than 1µA, even if there is an external R
ADJ
resistor (ADJ to GND).
4
_______________________________________________________________________________________
Single-Cell Li+ Battery Charger
for Current-Limited Supply
Typical Operating Characteristics
(VIN = V
CHG
= +10V, VBATT = +4.2V, THERM = 10kΩ to GND, TA = +25°C, unless otherwise noted.)
MAX1679
TIMER PERIOD vs.
AMBIENT TEMPERATURE
MAX1679 toc01
NORMALIZED BATT REGULATION VOLTAGE
vs. TEMPERATURE
MAX1679 toc02
PRECHARGE CURRENT
vs. INPUT VOLTAGE
5.8
PRECHARGE CURRENT (mA)
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
V
BATT
= 4.1V
V
BATT
= 2V
V
BATT
= 0V
MAX1679 toc03
1.0200
NORMALIZED TO +25°C
1.0150
TIMER PERIOD
1.0100
1.0050
1.0000
0.9950
0.9900
-40
1.0015
1.0010
BATT REGULATION VOLTAGE
1.0005
1.0000
0.9995
0.9990
0.9985
0.9980
0.9975
-40
-20
0
20
40
60
80
NORMALIZED TO +25°C
6.0
-20
0
20
40
60
80
100
100
5
10
TEMPERATURE (°C)
TEMPERATURE (°C)
15
V
IN
(V)
20
25
Pin Description
PIN
1
2
NAME
IN
GATE
FUNCTION
Input Voltage from Current-Limited Voltage Source (+22V max). Bypass to GND with a 0.1µF capacitor. The
cell charging current is set by the current limit of the external power supply.
Gate Drive for External PMOS Pass Element. The PMOS device should have a V
GS
threshold of 2.5V or
less. See
Selecting External Components.
Charge Status Indication.
CHG
is an open-drain, current-limited N-channel MOSFET suitable for directly dri-
ving an LED. Connect a pull-up resistor to BATT to generate a logic-level signal. See Table 2 for
CHG
out-
put states.
Maximum Total Charge-Time Selection. See Table 3 for timer options.
Battery Regulation Voltage Adjustment. Bypass to GND with a 1000pF capacitor. Connect a resistor from
ADJ to GND to reduce the nominal +4.200V regulation setpoint. See
Adjusting the Battery Regulation
Voltage.
Ground. See
Layout Guidelines
for information on system grounding. Connect the battery’s negative termi-
nal to GND.
Thermistor Temperature-Sensor Input. Connect a thermistor from THERM to GND to prequalify the cell tem-
perature for fast-charge. Drive THERM high (> +1.4V) during Done or Fault states to reset the MAX1679 and
reinitiate the charging sequence. Replace the thermistor with a 10kΩ resistor if temperature sensing is not
required.
Cell Voltage Monitor Input, Trickle-Charge Output, and MAX1679 Power Source. Connect BATT to the posi-
tive terminal of a single Li+ cell. Bypass BATT with a capacitor to ground (1.5µF per amp of charge current).
3
4
5
CHG
TSEL
ADJ
6
GND
7
THERM
8
BATT
_______________________________________________________________________________________
5
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