19-2556; Rev 1; 10/02
IT
TION K
VALUA
E
BLE
AVAILA
Switch-Mode 1-Cell Li+ Chargers
General Description
Features
o
Small (4mm
✕
4mm) Package
o
4.25V to 12V Input Range (MAX1926)
o
Overvoltage Lockout at 6.1V (MAX1925)
o
±0.75% Battery Regulation Voltage
o
Set Charge Current with One Resistor
o
Automatic Input Power Sense
o
LED (or Logic-Out) Charge Status and Fault
Indicator
o
Programmable Safety Timer
o
Autorestart at Cell = 4V
o
Thermistor Monitor Input
MAX1925/MAX1926
The MAX1925/MAX1926 single-cell lithium-ion (Li+)
switch-mode battery chargers use an external PMOS
pass element step-down configuration. Charge current
is programmable, and an external capacitor sets the
maximum charge time.
Additional features include automatic input power
detection (ACON output), logic-controlled enable, and
temperature monitoring with an external thermistor. The
MAX1925 disables charging for inputs greater than
6.1V, while the MAX1926 charges for inputs between
4.25V and 12V.
The MAX1925/MAX1926 feature two precondition levels
to restore near-dead cells. The devices source 4mA to
a cell that is below 2V while sourcing C/10 to a cell
between 2V and 3V. Full charge current is then applied
above 3V. A
CHG
output drives an LED to indicate
charging (LED on) and fault conditions (LED blinking).
The MAX1925/MAX1926 are available in a 12-pin
4mm
✕
4mm thin QFN package and are specified over
the extended temperature range (-40°C to +85°C). An
evaluation kit is available to speed design.
Ordering Information
PART
TEMP
RANGE
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
12 Thin QFN
4mm
x
4mm
12 Thin QFN
4mm
x
4mm
INPUT
CHARGING
RANGE
4.5V to 6.1V
4.25V to 12V
Applications
Digital Cameras
Self-Charging Battery Packs
PDAs
Cradle Chargers
MAX1925ETC
MAX1926ETC
Typical Operating Circuit
Pin Configuration
IN
12
INP
11
EXT
10
IN
INP
EXT
PGND
CS
INPUT
4.5V TO 12V
CHG
EN
THRM
1
2
3
9
PGND
GND
BATT
LED
CHG
BATT
CT
MAX1925
MAX1926
8
7
MAX1925
MAX1926
GND
THRM
4
ACON
5
CT
6
CS
ON
OFF
EN
ACON
1-CELL
Li+
BATTERY
THIN QFN
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Switch-Mode 1-Cell Li+ Chargers
MAX1925/MAX1926
ABSOLUTE MAXIMUM RATINGS
IN, INP,
ACON
to GND...........................................-0.3V to +14V
CHG,
EXT to PGND ...................................-0.3V to (V
INP
+ 0.3V)
CS, BATT, EN, THRM to GND ..................................-0.3V to +6V
CT to GND ................................................................-0.3V to +4V
EN, THRM, CT to IN................................................-14V to +0.3V
INP to IN ................................................................-0.3V to +0.3V
PGND to GND .......................................................-0.3V to +0.3V
CS to BATT ............................................................-0.3V to +0.3V
EXT Continuous RMS Current.........................................±100mA
Continuous Power Dissipation (T
A
= +70°C)
Exposed Paddle Soldered to Board
(derate 16.9mW/°C above +70°C) .............................1349mW
Exposed Paddle Unsoldered
(derate 9mW/°C above +70°C) ....................................721mW
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
(V
PGND
= V
GND
= 0, V
INP
= V
IN
= V
CHG
= 5V, V
BATT
= V
CS
= V
EN
= 4V, THRM = 10kΩ to GND, C
CT
= 100nF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Supply Voltage Range
CONDITIONS
V
INP
, V
IN
(MAX1925 does not charge above 6.1V)
V
INP
, V
IN
rising
ACON
Trip Point
V
INP
, V
IN
falling
INP, IN Shutdown Threshold
EN Input Resistance
EN Leakage Current
EN Logic Input High Threshold
EN Logic Input Low Threshold
BATT + CS Input Current
(Total Current into BATT and CS)
CS Input Current
DONE state, V
BATT
= 4.1V
EN = GND (Note 1)
V
BATT
= V
INP
= V
IN
= 4V, shutdown (Note 1)
Charging
EN = GND
IN + INP Total Input Current
V
BATT
= V
INP
= V
IN
= 4V, shutdown
V
BATT
= 4.1V; charging
V
BATT
= 4.3V; done
VOLTAGE LOOP
Voltage Loop Set Point
Voltage Loop Hysteresis
BATT Prequal1 Voltage Threshold
BATT Prequal2 Voltage Threshold
1.9
2.85
4.1685
4.2000
15
2
3
2.1
3.15
4.2315
V
mV
V
V
5
25
2
2
39
5
2
8
10
10
8
MAX1925
MAX1925
MAX1926
MAX1925
MAX1926
Rising
Falling
MIN
4.5
4.30
4.00
4.17
3.90
5.8
5.3
125
-1
2
0.8
50
10
10
µA
mA
µA
mA
µA
300
4.50
4.25
4.30
4.15
TYP
MAX
12.0
4.78
4.50
4.43
4.40
6.4
5.9
550
+1
V
kΩ
µA
V
V
V
UNITS
V
MAX1926 internally pulled up to 3V
MAX1925
2
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
PGND
= V
GND
= 0, V
INP
= V
IN
= V
CHG
= 5V, V
BATT
= V
CS
= V
EN
= 4V, THRM = 10kΩ to GND, C
CT
= 100nF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Restart Threshold
BATT Voltage Fault Threshold
CURRENT LOOP
CS - BATT Sense Threshold
Prequal1 Charge Current
Prequal2 CS - BATT Sense
Threshold
Current Threshold for
Full-Battery Indication
DRIVER FUNCTIONS
EXT Sink/Source Current
EXT On-Resistance
Nominal Switching Frequency
TIMER FUNCTIONS
Full-Time Timeout - t
FULL
Prequal1 Timeout
Prequal2 Timeout
Timer Accuracy
CHG
Output Low Current
CHG
Output High Leakage
Current
CHG
Blink Rate - Fault
ACON
High Leakage
ACON
Sink Current
THERMISTOR MONITOR
(Note 2)
THRM Sense Current for Hot
Qualification
THRM Sense Current for Cold
Qualification
THRM Sense-Voltage Trip Point
(Note 3)
344.1
47.58
1.386
352.9
48.80
1.400
361.7
50.02
1.414
µA
µA
V
C
CT
= 100nF
C
CT
= 100nF
C
CT
= 100nF
C
CT
= 100nF for 3 hours
V
CHG
= 1V
V
CHG
= 12V
Fault state (50% duty cycle), C
CT
= 100nF
V
ACON
= 12V
V
ACON
= 0.4V
2
0.5
0.01
1.00
-15
7
10
3.02
t
FULL/1088
(10s)
t
FULL/17
(10.67 min)
+15
14
1
hours
s
min
%
mA
µA
Hz
µA
mA
EXT high or low
V
BATT
= 3.6V, L =10µH
1
5
235
12
A
Ω
kHz
V
CS
- V
BATT
, average value
Rise/fall hysteresis
V
BATT
< 2V
Average value, 2V < V
BATT
< 3V (charge current is C/10)
Rise/fall hysteresis, 2V < V
BATT
< 3V
I
LOAD
falling, as percentage of fast charge current
6
3
132
142
30
4
14
12
12
20
6
152
mV
mA
mV
%
CONDITIONS
Charging restarts when BATT falls to this point
If BATT exceeds this threshold, EXT is high
(external MOSFET is off) and
CHG
blinks
MIN
3.92
4.275
TYP
4.00
4.350
MAX
4.08
4.425
UNITS
V
V
MAX1925/MAX1926
_______________________________________________________________________________________
3
Switch-Mode 1-Cell Li+ Chargers
MAX1925/MAX1926
ELECTRICAL CHARACTERISTICS
(V
PGND
= V
GND
= 0, V
INP
= V
IN
= V
CHG
= 5V, V
BATT
= V
CS
= V
EN
= 4V, THRM = 10kΩ to GND, C
CT
= 100nF,
T
A
= -40°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 4)
PARAMETER
Supply Voltage Range
CONDITIONS
V
INP
, V
IN
(MAX1925 does not charge above 6.1V)
V
INP
, V
IN
rising
ACON
Trip point
V
INP
, V
IN
falling
INP, IN Shutdown Threshold
EN Input Resistance
EN Leakage Current
EN Logic Input High Threshold
EN Logic Input Low Threshold
BATT + CS Input Current
(Total Current into BATT and CS)
DONE State, V
BATT
= 4.1V
EN = GND (Note 2)
V
BATT
= V
INP
= V
IN
= 4V, shutdown (Note 1)
EN = GND
IN + INP Total Input Current
V
BATT
= V
INP
= V
IN
= 4V, shutdown
V
BATT
= 4.1V, charging
V
BATT
= 4.3V, done
VOLTAGE LOOP
Voltage Loop Set Point
BATT Prequal1 Voltage Threshold
BATT Prequal2 Voltage Threshold
Restart Threshold
BATT Voltage Fault Threshold
CURRENT LOOP
CS - BATT Sense Threshold
Prequal1 Charge Current
Current Threshold for Full-Battery
Indication
DRIVER FUNCTIONS
EXT On-Resistance
TIMER FUNCTIONS
Timer Accuracy
CHG
Output Low Current
C
CT
= 100nF for 3 hours
V
CHG
= 1V
-16
7
+16
14
%
mA
EXT high or low
12
Ω
V
CS
- V
BATT
, average value
V
BATT
< 2V
I
LOAD
falling, as percentage of fast charge current
127
3
4
157
6
20
mV
mA
%
Charging restarts when BATT falls to this point
If BATT exceeds this threshold, EXT is high (external
MOSFET is off) and
CHG
blinks
4.158
1.9
2.85
3.92
4.275
4.242
2.1
3.15
4.08
4.425
V
V
V
V
V
MAX1925
MAX1925
MAX1926
MAX1925
MAX1926
Rising
Falling
MIN
4.5
4.30
4.0
4.17
3.9
5.8
5.3
125
-1
2
0.8
50
10
10
8
10
10
8
mA
µA
mA
µA
TYP
MAX
12.0
4.78
4.5
4.43
4.4
6.4
5.9
550
+1
V
kΩ
µA
V
V
V
UNITS
V
MAX1926 internally pulled up to 3V
MAX1925
4
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
PGND
= V
GND
= 0, V
INP
= V
IN
= V
CHG
= 5V, V
BATT
= V
CS
= V
EN
= 4V, THRM = 10kΩ to GND, C
CT
= 100nF,
T
A
= -40°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 4)
PARAMETER
CHG
Output High Leakage
Current
ACON
High Leakage
ACON
Sink Current
THERMISTOR MONITOR
THRM Sense Current for Hot
Qualification
THRM Sense Current for Cold
Qualification
THRM Sense-Voltage Trip Point
(Note 3)
342
47.3
1.379
363
50.3
1.421
µA
µA
V
V
CHG
= 12V
V
ACON
= 12V
V
ACON
= 0.4V
2
CONDITIONS
MIN
TYP
MAX
1
1
UNITS
µA
µA
mA
MAX1925/MAX1926
Note 1:
When the AC adapter is unplugged or if the charger is shut down, BATT drain is less than 10µA.
Note 2:
These specifications guarantee the thermistor interface detects a fault at the correct temperature (0°C to +5°C cold temper-
ature and 45°C to +50°C hot temperature) with Philips NTC Thermistor Series 640-6, 2322-640-63103, 10.0K at +25°C, ±5%
(or equivalent).
Note 3:
A fault is generated if V
THRM
lower than 1.4V during the cold test or higher than 1.4V during the hot test. Hot and cold tests
occur on alternate CT clock transitions.
Note 4:
Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
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