MAX1926ETC+T [MAXIM]
Battery Charge Controller, BICMOS, 4 X 4 MM, 0.80 MM HEIGHT, QFN-12;
| 型号： | MAX1926ETC+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Battery Charge Controller, BICMOS, 4 X 4 MM, 0.80 MM HEIGHT, QFN-12 电池 开关 |
| 文件： | 总16页 (文件大小：442K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-2556; Rev 1; 10/02
Switch-Mode 1-Cell Li+ Chargers
General Description
Features
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.
ꢀ Small (4mm ✕ 4mm) Package
ꢀ 4.25V to 12V Input Range (MAX1926)
ꢀ Overvoltage Lockout at 6.1V (MAX1925)
ꢀ ±±.ꢀ5ꢁ ꢂatterꢃ Regulatꢄon Voltage
ꢀ Set Charge Current wꢄth One Resꢄstor
ꢀ Automatꢄc Input Power Sense
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.
ꢀ LED (or Logꢄc-Out) Charge Status and Fault
Indꢄcator
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).
ꢀ Programmable Safetꢃ Tꢄmer
ꢀ Autorestart at Cell = 4V
ꢀ Thermꢄstor Monꢄtor Input
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
INPUT
TEMP
PIN-
CHARGING
RANGE
PART
RANGE
PACKAGE
Applications
12 Thin QFN
4mm x 4mm
MAX1925ETC -40°C to +85°C
MAX1926ETC -40°C to +85°C
4.5V to 6.1V
4.25V to 12V
Digital Cameras
Self-Charging Battery Packs
PDAs
12 Thin QFN
4mm x 4mm
Cradle Chargers
Typical Operating Circuit
INPUT
4.5V TO 12V
Pin Configuration
IN
INP
11
EXT
10
IN
INP
EXT PGND
12
CS
CHG
EN
1
2
3
9
8
7
PGND
GND
LED
BATT
GND
CHG
CT
MAX1925
MAX1926
MAX1925
MAX1926
THRM
BATT
THRM
ON
OFF
EN
ACON
1-CELL
Li+
4
5
6
BATTERY
ACON
CT
CS
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
AꢂSOLUTE MAXIMUM RATINGS
IN, INP, ACON to GND...........................................-0.3V to +14V
Continuous Power Dissipation (T = +70°C)
A
Exposed Paddle Soldered to Board
CHG, EXT to PGND ...................................-0.3V to (V + 0.3V)
INP
(derate 16.9mW/°C above +70°C).............................1349mW
Exposed Paddle Unsoldered
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
(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
= V
= 0, V
= V = V
= 5V, V
= V = V = 4V, THRM = 10kΩ to GND, C = 100nF, T = ±°C to +85°C,
BATT CS EN CT A
PGND
GND
INP
IN
CHG
unless otherwise noted. Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
V
V
, V (MAX1925 does not charge above 6.1V)
4.5
4.30
4.00
4.17
3.90
5.8
12.0
4.78
4.50
4.43
4.40
6.4
V
INP IN
MAX1925
MAX1926
MAX1925
MAX1926
Rising
4.50
4.25
4.30
4.15
, V rising
INP IN
ACON Trip Point
V
V
, V falling
INP IN
INP, IN Shutdown Threshold
MAX1925
V
Falling
5.3
5.9
EN Input Resistance
MAX1926 internally pulled up to 3V
MAX1925
125
-1
300
550
+1
kΩ
µA
V
EN Leakage Current
EN Logic Input High Threshold
EN Logic Input Low Threshold
2
0.8
50
10
10
V
DONE state, V
= 4.1V
25
2
BATT
BATT + CS Input Current
(Total Current into BATT and CS)
µA
EN = GND (Note 1)
= V = V = 4V, shutdown (Note 1)
V
2
BATT
INP
IN
CS Input Current
Charging
EN = GND
39
5
µA
mA
µA
8
10
10
8
V
V
V
= V
= V = 4V, shutdown
2
BATT
BATT
BATT
INP
IN
IN + INP Total Input Current
= 4.1V; charging
= 4.3V; done
mA
5
VOLTAGE LOOP
Voltage Loop Set Point
Voltage Loop Hysteresis
4.1685 4.2000 4.2315
15
V
mV
BATT Prequal1 Voltage Threshold
BATT Prequal2 Voltage Threshold
1.9
2
3
2.1
V
V
2.85
3.15
2
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= 0, V
= V = V
= 5V, V
= V = V = 4V, THRM = 10kΩ to GND, C = 100nF, T = 0°C to +85°C,
BATT CS EN CT A
PGND
GND
INP
IN
CHG
unless otherwise noted. Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Restart Threshold
Charging restarts when BATT falls to this point
3.92
4.00
4.08
V
If BATT exceeds this threshold, EXT is high
(external MOSFET is off) and CHG blinks
BATT Voltage Fault Threshold
CURRENT LOOP
4.275
4.350
4.425
V
V
- V
, average value
132
3
142
30
4
152
6
CS
BATT
CS - BATT Sense Threshold
mV
mA
mV
Rise/fall hysteresis
< 2V
Prequal1 Charge Current
V
BATT
Average value, 2V < V
< 3V (charge current is C/10)
14
12
BATT
Prequal2 CS - BATT Sense
Threshold
Rise/fall hysteresis, 2V < V
< 3V
BATT
Current Threshold for
Full-Battery Indication
I
falling, as percentage of fast charge current
6
12
20
12
%
LOAD
DRIVER FUNCTIONS
EXT Sink/Source Current
EXT On-Resistance
1
5
A
Ω
EXT high or low
Nominal Switching Frequency
TIMER FUNCTIONS
V
= 3.6V, L =10µH
235
kHz
BATT
Full-Time Timeout - t
C
C
= 100nF
= 100nF
3.02
hours
s
FULL
CT
CT
t
FULL/1088
(10s)
Prequal1 Timeout
t
FULL/17
Prequal2 Timeout
Timer Accuracy
C
C
= 100nF
min
CT
(10.67 min)
= 100nF for 3 hours
-15
7
+15
14
%
CT
CHG Output Low Current
V
= 1V
10
mA
CHG
CHG Output High Leakage
Current
V
= 12V
1
µA
CHG
CHG Blink Rate - Fault
ACON High Leakage
Fault state (50% duty cycle), C = 100nF
0.5
Hz
µA
CT
V
V
= 12V
0.01
1.00
ACON
ACON
ACON Sink Current
= 0.4V
2
mA
THERMISTOR MONITOR (Note 2)
THRM Sense Current for Hot
Qualification
344.1
352.9
361.7
µA
THRM Sense Current for Cold
Qualification
47.58
1.386
48.80
1.400
50.02
1.414
µA
V
THRM Sense-Voltage Trip Point
(Note 3)
_______________________________________________________________________________________
3
Switch-Mode 1-Cell Li+ Chargers
ELECTRICAL CHARACTERISTICS
(V
= V
= 0, V
= V = V
= 5V, V
= V = V = 4V, THRM = 10kΩ to GND, C = 100nF, T = -40°C to +85°C,
BATT CS EN CT A
PGND
GND
INP
IN
CHG
unless otherwise noted. Typical values are at T = +25°C.) (Note 4)
A
PARAMETER
CONDITIONS
, V (MAX1925 does not charge above 6.1V)
MIN
4.5
4.30
4.0
4.17
3.9
5.8
5.3
125
-1
TYP
MAX
12.0
4.78
4.5
UNITS
Supply Voltage Range
V
V
V
INP IN
MAX1925
MAX1926
MAX1925
MAX1926
Rising
, V rising
INP IN
ACON Trip point
V
4.43
4.4
V
, V falling
INP IN
6.4
INP, IN Shutdown Threshold
MAX1925
V
Falling
5.9
EN Input Resistance
MAX1926 internally pulled up to 3V
MAX1925
550
+1
kΩ
µA
V
EN Leakage Current
EN Logic Input High Threshold
EN Logic Input Low Threshold
2
0.8
50
10
10
8
V
DONE State, V
= 4.1V
BATT
BATT + CS Input Current
(Total Current into BATT and CS)
µA
EN = GND (Note 2)
= V = V = 4V, shutdown (Note 1)
V
BATT
INP
IN
EN = GND
mA
µA
V
V
V
= V
= V = 4V, shutdown
10
10
8
BATT
BATT
BATT
INP
IN
IN + INP Total Input Current
= 4.1V, charging
= 4.3V, done
mA
VOLTAGE LOOP
Voltage Loop Set Point
4.158
1.9
4.242
2.1
V
V
BATT Prequal1 Voltage Threshold
BATT Prequal2 Voltage Threshold
Restart Threshold
2.85
3.92
3.15
4.08
V
V
V
Charging restarts when BATT falls to this point
If BATT exceeds this threshold, EXT is high (external
MOSFET is off) and CHG blinks
BATT Voltage Fault Threshold
4.275
4.425
CURRENT LOOP
CS - BATT Sense Threshold
Prequal1 Charge Current
V
V
- V
, average value
127
3
157
6
mV
mA
CS
BATT
< 2V
BATT
Current Threshold for Full-Battery
Indication
I
falling, as percentage of fast charge current
4
20
%
LOAD
DRIVER FUNCTIONS
EXT On-Resistance
TIMER FUNCTIONS
Timer Accuracy
EXT high or low
12
Ω
C
V
= 100nF for 3 hours
-16
7
+16
14
%
CT
CHG Output Low Current
= 1V
mA
CHG
4
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
= 0, V
= V = V
= 5V, V
= V = V = 4V, THRM = 10kΩ to GND, C = 100nF, T = -40°C to +85°C,
BATT CS EN CT A
PGND
GND
INP
IN
CHG
unless otherwise noted. Typical values are at T = +25°C.) (Note 4)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
CHG Output High Leakage
Current
V
= 12V
1
1
µA
CHG
ACON High Leakage
ACON Sink Current
V
V
= 12V
µA
ACON
ACON
= 0.4V
2
mA
THERMISTOR MONITOR
THRM Sense Current for Hot
Qualification
342
363
µA
THRM Sense Current for Cold
Qualification
47.3
50.3
µA
V
THRM Sense-Voltage Trip Point
(Note 3)
1.379
1.421
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
lower than 1.4V during the cold test or higher than 1.4V during the hot test. Hot and cold tests
THRM
occur on alternate CT clock transitions.
Note 4: Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
Switch-Mode 1-Cell Li+ Chargers
Typical Operating Characteristics
(Circuit of Figure 1, V
= 5V, V
= 4V, T = +25°C, unless otherwise noted.)
BATT A
SUPPLY
CHARGE-CURRENT ACCURACY
vs. SUPPLY VOLTAGE
CHARGE CURRENT
vs. BATTERY VOLTAGE
FULL-BATTERY VOLTAGE
vs. SUPPLY VOLTAGE
1.2
20
15
10
5
4.210
4.208
4.206
4.204
4.202
4.200
4.198
4.196
4.194
V
= 12V
IN
1.0
0.8
0.6
0.4
0.2
0
V
BATT
= 4V
V
= 10V
IN
V
= 8V
IN
V
= 5V
IN
0
-5
SEE THE DROPOUT
BEHAVIOR SECTION
-10
-15
-20
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
BATTERY VOLTAGE (V)
5
6
7
8
9
10
11
12
4
3.0
5
5
6
7
8
9
10 11 12
V
(V)
V
(V)
SUPPLY
SUPPLY
SHUTDOWN BATTERY CURRENT
vs. BATTERY VOLTAGE
EFFICIENCY vs. BATTERY VOLTAGE
EFFICIENCY vs. SUPPLY VOLTAGE
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
100
95
90
85
80
75
70
100
95
90
85
80
75
70
65
60
V
= 4V
V = 5V
IN
BATT
V
= 8V
IN
V
= 12V
IN
3.0
3.2
3.4
3.6
3.8
4.0
4.2
5
6
7
8
9
10
11
12
3.2
3.4
3.6
3.8
4.0
4.2
V
(V)
V
(V)
BATTERY VOLTAGE (V)
BATT
SUPPLY
SWITCHING FREQUENCY
vs. SUPPLY VOLTAGE
SWITCHING FREQUENCY vs. INDUCTANCE
SWITCHING FREQUENCY vs. R
SENSE
500
450
400
350
300
250
200
150
100
50
1000
100
10
1000
100
10
V
= 12V
IN
V
= 12V
IN
V
= 4V
BATT
V
= 8V
IN
V
= 8V
IN
V
= 5V
IN
V
= 5V
IN
V
= 4V
V
= 4V
BATT
BATT
0
6
7
8
9
10
11
12
1
10
INDUCTANCE (µH)
100
0.01
0.10
(Ω)
1.00
V
(V)
R
SUPPLY
SENSE
6
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
= 5V, V
= 4V, T = +25°C, unless otherwise noted.)
SUPPLY
BATT
A
FREQUENCY vs. BATTERY VOLTAGE
CHARGE CURRENT vs. TIME
TIMER vs. CT CAPACITANCE
500
450
400
350
300
250
200
150
100
50
1.2
1.0
0.8
0.6
0.4
0.2
0
1000
V
= 12V
IN
t
FULLCHG
100
10
V
= 8V
IN
t
PREQUAL2
V
= 5V
IN
1
t
PREQUAL1
0.1
0.01
0
2.5
3.0
3.5
4.0
0
0.5
1.0
1.5
2.0
2.5
3.0
10
100
CT CAPACITANCE (nF)
1000
BATTERY VOLTAGE (V)
TIME (h)
BATTERY VOLTAGE vs. TIME
SWITCHING WAVEFORM
MAX1925/26 toc14
4.5
4.4
4.3
4.2
4.1
4.0
3.9
V
= 5V
IN
1.2A
1A
0.8A
10V
0V
INDUCTOR
CURRENT
V
LX
V
100mV/
div
BATT
3.8
0
4µs/div
0.5
1.0
1.5
2.0
2.5
3.0
TIME (h)
SWITCHING WAVEFORM
CHARGE-ENABLE REPSONSE
MAX1925/26 toc16
MAX1925/26 toc15
1.4A
1.2A
V
= 12V
IN
5V
INDUCTOR
CURRENT
0V
EN
1A
0.8A
10V
0V
V
LX
1A
0A
V
100mV/
div
INDUCTOR
CURRENT
BATT
1µs/div
_______________________________________________________________________________________
7
Switch-Mode 1-Cell Li+ Chargers
Pin Description
PIN
NAME
FUNCTION
Charge Status LED Driver. Open-drain LED driver sinks 10mA when the MAX1925/MAX1926 are charging.
CHG also blinks at a 0.5Hz rate during fault states (see the Timing section). High impedance when charger is
in shutdown. See Tables 1 and 2.
1
CHG
Enable. Drive EN high to enable charger. Logic level input for normal ON/OFF control. In the MAX1926 EN is
internally pulled up to 3V with a 300kΩ resistor.
2
3
4
EN
Thermistor Input. Monitors external thermistor (10kΩ at +25°C). When external temperature is lower than 0°C
or above +50°C, charging stops and the charger enters fault mode. Charging resumes when the temperature
returns to normal. During a temperature fault the MAX1926 blinks the CHG output, while MAX1925 CHG
remains off (high).
THRM
ACON
Power-OK Indicator Output. Open-drain output goes low when AC adapter power is valid. See Table 2 for
ACON states.
Timing Capacitor Connection. Connect timer cap to program full-charge safety timeout interval and
prequalification fault times. Timeouts with C = 100nF are:
CT
5
CT
Full Timer (t ): 3 hours—If FASTCHG is not completed within this time a fault is asserted.
FULLCHG
Prequal2 Timer: Full Timer/17 (10.67 min)
Prequal1 Timer: Full Timer/1088 (10s)
6
7
8
9
CS
Charge-Current Sense Input. 142mV nominal regulation threshold. CS is high impedance during shutdown.
Battery-Sense Input. Also negative side of charge-current sense. BATT is high impedance during shutdown.
Ground
BATT
GND
PGND Power Ground
PMOS Gate-Driver Output. Drives gate of external PMOS switching transistor from IN to GND. When using the
10
EXT
MAX1926, ensure that the MOSFET V rating is greater than V
GS
.
IN
11
12
INP
IN
Supply Voltage Input
Supply-Sense Input. Connect IN to INP.
8
_______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
D1
POWER
SOURCE
C3
10µF
Q1
D2
D3
LED
L1
10µH
CHG
IN
ACON
INP
EXT
4.5V FOR MAX1926
4.25V FOR MAX1925
10mA
ACON
PREQUAL1
4mA
CS
R
BATT > 2V
SET
0.14Ω
6.1V
MAX1925 ONLY
BATT
MAX1925
MAX1926
INP
C2
10µF
HV
DRIVER
REF/8
OSC
PGND
C2
0.1µF
REF/10
I > 12%
REF
ACON
REF
BATT > 2V
BATT > 3V
REF
STATE
MACHINE AND
TIMERS
EN
REF
TEMP FAULT
49µA
REF
BATT > 4.35V
353µA
REF
3V_ANA
3V_DIG
ACON
IN
REGULATOR
THRM
10kΩ
REF
GND
PGND
Figure 1. Functional Diagram
_______________________________________________________________________________________
9
Switch-Mode 1-Cell Li+ Chargers
mode, the charger regulates the peak and valley of the
output ripple.
Detailed Description
The MAX1925/MAX1926 switch-mode battery chargers
form a complete solution for a single-cell Li+ battery. The
devices include battery undervoltage/overvoltage fault
protection. The MAX1925/MAX1926 use EN and THRM
for shutdown, battery detection, and temperature monitor-
ing. The devices provide outputs to indicate charge sta-
tus (CHG) and presence of input power (ACON).
Charge Cycle
The MAX1925/MAX1926 initiate PREQUAL when one of
the following occurs:
• When an external power source is connected
• The cell voltage falls to 4V after charging is finished
• EB is toggled
The MAX1925/MAX1926 include two prequalification
modes that must be passed before the charger enters
the fast-charge state. During fast charge, the charger
operates initially in constant-current mode until the bat-
tery voltage reaches 4.2V. When the battery voltage
has reached 4.2V, the charger operates in constant-
voltage mode. In constant-current mode, the charger
acts as a hysteretic current source, controlling the
inductor’s peak and valley currents. In constant-voltage
• Input power is cycled
Some Li+ cells can be damaged when fast-charged
from a completely dead state. Moreover, an over-dis-
charged cell may indicate a dangerous abnormal cell
condition. As a built-in safety feature, the MAX1925/
MAX1926 use a two-level prequalification charge to
determine if it is safe to charge. When the cell voltage is
less than 2V, the cell is charged from an internal
V
OUTSIDE ACON WINDOW*
IN
RESET
ANY STATE
V
> V
AND V
IN
IN
BATT
V
WITHIN ACON
WINDOW*
(ACON IS LOW)
(INCLUDING FAULT)
IN
EN LOW OR
IN OUTSIDE ACON
WINDOW*
OUTSIDE ACON WINDOW*
EN HIGH AND
IN WITHIN ACON
WINDOW*
TEMP
IN RANGE
V
> 4.35V
BATT
OFF
AND IN WITHIN ACON
TEMP OUT
OF RANGE
(ACON HIGH Z)
WINDOW*
F-TEMP
AND EN HIGH
PREQUAL1
(I = 4mA)
V
> V
V < V
IN BATT
IN
BATT
CHG
(CHG LED ON)
t
TIMES OUT
BATT
PREQUAL1
BEFORE V
F_VB
SHDN
(ACON HIGH Z)
> 2V
V
> 2V
BATT
(DEBOUNCED)
F_PQ1
FAULT
(CHG LED BLINK AT 0.5Hz)
(EXT HIGH FET OFF)
PREQUAL2
(I = C/10)
V
< V
BATT
IN
CHG
(CHG LED ON)
t
TIMES OUT
BATT
PREQUAL2
BEFORE V
> 3V
V
> 3V
BATT
(DEBOUNCED)
AUTOMATIC RESTART
BATT DROPS TO 4V
F_PQ2
F_FULL
FASTCHG
(I = C)
(CHG LED ON)
CHG
t
TIMES OUT
FULLCHG
BEFORE ENTERING
FULL TOP-OFF
STATE
I
< C/8
(DEBOUNCED)
CHG
10-SECOND
TIMER
FULL TOPOFF
(CHG LED OFF)
KELVIN
(CHG LED OFF)
V
BATT
< 4.2V
V
BATT
> 4.2V
*SEE TABLE 2 FOR ACON WINDOW
FOR MAX1925/MAX1926
DONE
(CHG LED OFF)
FULL-CHARGE
TIMER TIMES OUT
Figure 2. MAX1925/MAX1926 State Diagram
10 ______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
CHG LED OFF
FULL TOPOFF
CVM
4V
3V
2V
1V
CCM
FASTCHG
PREQUAL1
PREQUAL2
4mA
C/10
C/8
C
CHARGE CURRENT
CVM
NORMAL VOLTAGE
PROFILE
4V
3V
2V
1V
4.2V
CHG LED OFF
CCM
C
FAULT
FASTCHG
NORMAL
CURRENT
PROFILE
FAULT
C/8
C/10
2mA
t
t
= t/16
PREQUAL2
CHARGE TIME (t
FULLCHG
= 3 HOURS WITH C = 100nF)
CT
t
= t/1024
PREQUAL1
Figure 3. Charging Current and Voltage Timing Diagrams
linear 4mA current source (PREQUAL1). When the cell
voltage exceeds 2V, the cell is charged with 10% of the
charge current drops below 1/8th of I
. The
FASTCHG
charger then enters full topoff mode and the CHG LED
is turned off. In full topoff mode, the controller continues
to operate as in fast-charge mode, except that it
remains in constant-voltage mode (CVM) unless the bat-
programmed fast-charge current (I
) until it
FASTCHG
reaches 3V. When the cell voltage is above 3V, fast
charging occurs at the full set current. If the cell fails to
reach the next prequalification threshold before a set
tery voltage falls. After every t
(see the Timer
PREQUAL1
time (see t
and t
in the Timer
PREQUAL2
Capacitor and Fault Modes section) the charger enters
the Kelvin state (for 2 CT clock cycles, 60ms with C
PREQUAL1
Capacitor and Fault Modes section), charging stops, a
fault alarm is set, and the CHG output blinks.
=
CT
100nF) where charge current is interrupted so that the
battery voltage can be accurately measured.
Figures 2 and 3 show charging behavior typical Li+ cell.
The MAX1925/MAX1926 remain in fast-charge mode
until the battery voltage reaches regulation and the
The MAX1925/MAX1926 do not enter done mode until
t
has been reached. If the battery is removed
FULLCHG
______________________________________________________________________________________ 11
Switch-Mode 1-Cell Li+ Chargers
and a new battery is connected during either fast-charge
or full topoff modes, the charger begins with full charge
current without prequalification unless the part is reset.
Detect battery insertion by connecting THRM to a ther-
mistor on the battery, if a thermistor is used, or to a 10kΩ
resistor linked to a battery door mechanism.
For this reason choose L for an on-time and off-time greater
than 2 ✕ t
IDelay
to minimize error in the charging current.
Constant-Voltage Mode (CVM)
In constant-voltage mode (CVM), the controller regu-
lates the peak and valley of the output ripple. The maxi-
mum cell voltage is regulated to 4.2V. If, for any reason,
the cell voltage exceeds 4.35V, a fault alarm is set, the
CHG output blinks, and the PFET power switch is held
off. The charger can then be restarted only by cycling
input power or the EN input.
Constant-Current Mode (CCM)
When the battery voltage is below 4.2V, the
MAX1925/MAX1926 regulate the charging current by
controlling the peak and valley inductor currents. When
the inductor current exceeds the 158mV/R
, the
SET
Indication of Charge Completion (CHG)
The CHG output is a 10mA current-sink output that indi-
cates the cell’s charging status. Connect an LED from
IN to CHG for a visible indicator. Alternatively, a pullup
resistor (typically 200kΩ) from a logic supply to CHG
provides a logic-level output. Table 1 relates the status
of the LED to the condition of the charger and battery.
MAX1925/MAX1926 turn the external PFET off. When
the inductor current falls below 128mV/R , the
SET
MAX1925/MAX1926 turns the external PFET on, but
only if the battery voltage is below regulation. The maxi-
mum cell charging current is programmed by selecting
the external R
(see Figure 1) resistor connected
SET
between BATT and CS. Select the external resistor
value using RSET = 142mV/I
.
FASTCHG
ACON Output
The accuracy of the charge current is a function of
input voltage, battery voltage, inductance, and com-
parator delay (300ns typ). Determine the charge-cur-
rent error according to the following equation:
The ACON open-drain output indicates when usable
power is applied to IN. In the MAX1926 when V
IN
exceeds ACON threshold (nominally 4.25V with IN ris-
ing—see the Electrical Characteristics table), ACON
goes low. In the MAX1925, ACON goes low when the
input voltage is between 4.5V and 6.1V (see Table 2).
V
−2× V
× t
(
=
)
IN
BATT IDelay
∆I
CHG
2×L
Re-Initiating a Charging Cycle
The MAX1925/MAX1926 feature automatic restart that
resumes charging when the cell voltage drops to 4V and
where ∆I
is the charge-current error, and t
is
CHG
IDelay
the current-sense comparator delay.
t
is completed. By automatically resuming charg-
FULL_CHG
Table 1. CHG Output States
STATE
CONDITION
CHG
High impedance (LED off)
Low (LED on)
OFF
EN low or no battery or input power
PREQUAL1
PREQUAL2
FAST CHARGE
FULL CHARGE
Charge current = 4mA until BATT reaches 2V.
Charge current = C/10 until BATT reaches 3V.
Low (LED on)
Charge current = C = 142mV/R
.
Low (LED on)
SET
Charge current has fallen to C/8.
High impedance (LED off)
FAULT PREQUAL1 BATT does not reach 2V before PREQUAL1 timeout.
FAULT PREQUAL2 BATT does not reach 3V before PREQUAL2 timeout.
Blinking. LED on 50% f
only be cleared by cycling input power,
THRM, or EN.
(0.5Hz). Can
BLINK
Charge current does not drop to C/8 before FULL CHARGE
FAULT FULL
timeout.
FAULT BATT
Battery voltage has exceeded 4.35V.
VOLTAGE
Blinking. LED on 50% f
(0.5Hz).
BLINK
MAX1925—High impedance (LED off)
MAX1926—Blinking (LED on 50% 0.5Hz)
Temperature has risen above +50°C or fallen below 0°C.
Temp fault clears by itself.
FAULT TEMP
Blinking at rapid rate as charger cycles
through RESET, PREQUAL1, and DONE.
NONE
Initial power-up or enable with battery not present.
12 ______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
Table 2. ACON Behavior vs. V
IN
PART
V
ACON
CHARGING
CHG LED
IN
V
V
> V
> V
threshold (4.5V nom) and < 6.1V, and
ON
IN
IN
ACON
LOW
YES
(until charge complete)
BATT
MAX1925
V
> V
threshold and V < V
ACON IN BATT
IN
High Z
High Z
LOW
NO
NO
OFF
OFF
(Note: This state should never occur)
V
< V
threshold
IN
ACON
ON
V
> V
threshold (4.25V nom) and V > V
YES
IN
ACON
IN
BATT
(until charge complete)
MAX1926
V
> V
threshold and V < V
ACON IN BATT
IN
High Z
High Z
NO
NO
OFF
OFF
(Note: This state should never occur)
V
< V Threshold
IN
ACON
ing when the battery voltage drops, the MAX1925/MAX1926
ensure that the cell does not remain partially charged after
use when charger power is available.
Inductor Selection
Because the MAX1925/MAX1926 is hysteretic, the con-
stant-current mode switching frequency is a function of
the inductance, sense resistance, and current-sense
hysteresis (30mV, from the Electrical Characteristics).
To minimize charge-current error:
Charging also restarts if input power is cycled or if the
charger is restarted by the EN or THRM input. If a new
battery is inserted, the charger must be restarted. If the
THRM functionality is used, the charger is automatically
restarted upon battery insertion. When THRM is not
used, toggle EN or connect THRM through a resistor to
be grounded with a battery-door latch switch.
V
− 2 × V × t
BATT Delay
(
)
IN
L >
2 × ∆I
CHG
where ∆I
is the acceptable charge-current error
CHG
Applications Information
and should usually be less than 1/4th the full charge
current. t is the current-sense comparator delay
IDelay
Timer Capacitor and Fault Modes
The on-chip timer checks charge progress and issues
an alarm signal through a blinking CHG output when one
of the safety timers times out (see Table 1). All timers are
set by one external capacitor at CT. A 100nF value sets
(300ns typical). Calculate L for V = V
, V
=
IN
IN,MAX BATT
V
V
, with positive ∆I
BATT,MAX
and V = V
,
IN,MIN
BATT,MIN
CHG
IN
= V
, with negative ∆I
. Use the larg-
BATT
CHG
er calculated value for L.
The resulting switching frequency in CCM is:
the full-charge timer (t
) to 3 hours, the
FULLCHG
t
t
timer to (t
)/1088 (10s), and the
PREQUAL1
PREQUAL2
FULLCHG
I
×L + t
V
HYST
IDelay BATT
timer at (t
)/17 (10.67 minutes).
FULLCHG
f
>
+2× t
+
Switch
IDelay
V
− V
BATT
IN
If the charger enters full-charge state (after the charging
current has fallen below C/8) before the full-charge timer
expires, no fault occurs, but if the timer expires before full
charge is reached, a fault is indicated (see Table 1).
−1
I
×L + t
×(V − V )
IN BATT
HYST
IDelay
V
BATT
A fault is also indicated if the battery voltage exceeds
4.35V. When the cell voltage exceeds 4.35V a fault alarm
is set, the CHG output blinks, and the PFET turns off.
Choose an inductor with an RMS and saturation current
rating according to the following equation:
V
− V
t
(
+
)
V
To restart the charger after a fault occurs, the fault state
must be cleared by toggling EN, or by cycling input power
at IN (see Figure 1). Temperature faults do not need to be
cleared by EN. The MAX1925/MAX1926 resume charging
after the temperature returns to within the set window.
IN
BATT IDelay
L
IPK
I
>
SAT/RMS
R
SET
where V is the peak current-sense threshold (158mV typ).
IPK
Output Capacitor Selection
The ESR of the output capacitor influences the switch-
ing frequency of the charger during voltage regulation
_______________________________________________________________________________________ 13
Switch-Mode 1-Cell Li+ Chargers
mode. To ensure stable transition from CCM to CVM
choose a capacitor with the following ESR:
This results in an average current of 142mV/R
. At
SET
input voltages near dropout (4.6V at IN for the typical
circuit), the inductor current ramp waveform becomes
somewhat flattened as inductor, MOSFET, input diode,
and battery resistance limit inductor current. When the
inductor current waveform flattens, it’s average value
rises with respect to the upper and lower current
thresholds. This creates a slight peak (about 5%) in
charging current at high battery voltages as seen in the
Charging Current vs. Battery Voltage plot in the Typical
Operating Characteristics. Charging current is still con-
trolled in dropout and the charger operates normally.
The dropout current peak can be minimized by reduc-
ing MOSFET and inductor resistance, as well as for-
ward voltage in the input diode.
V
V
VHIST
R
>
×R
SET
ESR
IHIST
where V
IHIST
is the voltage hysteresis (15mV typ) and
VHIST
V
is the current-sense threshold hysteresis (typi-
cally 30mV). Tantalum capacitors are recommended.
However a ceramic capacitor (typically 10µF) with a
series resistor can also be used.
MOSFET Selection
The MAX1925/MAX1926 drive an external P-channel
MOSFET’s gate from IN to GND. Choose a P-channel
MOSFET with a |V
| > V . Since EXT drives from
IN
DS,MAX
rail to rail the MOSFET must also be rated for |V
|
GS,MAX
Thermistor Interface
An external thermistor inhibits charging by setting a
fault flag when the cell is cold (<0°C) or hot (>+50°C).
The THRM time-multiplexes two sense currents to test
for both hot and cold qualification. Connect the thermis-
tor between THRM and GND. If no temperature qualifi-
cation is desired, replace the thermistor with a 10kΩ
resistor connected through the battery-latch mecha-
nism. The thermistor should be 10kΩ at +25°C and
have a negative temperature coefficient, as defined by
the expression below:
> V . At the lower operating frequencies and currents
IN
for typical MAX1925/MAX1926 applications resistive
and diode losses dominate switching losses. For this
reason choose a MOSFET with a low R
. The resis-
DSON
tive losses are:
2
2
P
≅ D ✕ I
CHG
✕ R
DSON
+ I
✕
Resistive_losses
CHG
(R
+ R )
L
SET
where D is the operating duty cycle (V
/V ) and R
L
OUT IN
is the inductor resistance. The MOSFET’s power dissi-
2
pation must exceed D ✕ I
✕ R
.
DSON
CHG
Diode Selection
1
1
298
β
−
In the event of a short-circuited source, the body diode
inherent in the external PFET allows the cell to dis-
charge. To prevent this and to protect against negative
input voltages, add a Schottky or silicon diode between
the power source and IN.
T +273
R =R
T
25°C × e
Table 3 shows nominal fault detection temperatures
that result from a wide range of available thermistor
temperature curves.
The MAX1925/MAX1926 use a diode for catching the
inductor current during the off cycle. Select a Schottky
For a given thermistor characteristic, it is possible to
adjust the fault-detection temperatures by adding a
resistor in series with the thermistor or a parallel resistor
from THRM to GND.
diode with a current rating greater than V /R
and
IPK SET
a voltage rating greater than V .
IN
Dropout Behavior
Chip Information
TRANSISTOR COUNT: 5722
The MAX1925/MAX1926 regulate charging current by
ramping inductor current between upper and lower
thresholds, typically 128mV and 158mV across R
.
SET
PROCESS: BiCMOS
Table 3. Fault Temperature for Different Thermistors
THERMISTOR BETA
3000
10000Ω
4587.78Ω
25140.55Ω
55.14°C
-3.24°C
3250
10000Ω
4299.35Ω
27148.09Ω
52.60°C
-1.26°C
3500
10000Ω
4029.06Ω
29315.94Ω
50.46°C
0.46°C
3750
10000Ω
3775.75Ω
31656.90Ω
48.63°C
1.97°C
Resistance at +25°C
Resistance at +50°C
Resistance at 0°C
Nominal Hot Trip Temperature
Nominal Cold Trip Temperature
14 ______________________________________________________________________________________
Switch-Mode 1-Cell Li+ Chargers
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
______________________________________________________________________________________ 15
Switch-Mode 1-Cell Li+ Chargers
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
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.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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