General Description
The MAX1908/MAX8724 highly integrated, multichemistry
battery-charger control ICs simplify the construction of
accurate and efficient chargers. These devices use ana-
log inputs to control charge current and voltage, and can
be programmed by the host or hardwired. The MAX1908/
MAX8724 achieve high efficiency using a buck topology
with synchronous rectification.
The MAX1908/MAX8724 feature input current limiting.
This feature reduces battery charge current when the
input current limit is reached to avoid overloading the AC
adapter when supplying the load and the battery charger
simultaneously. The MAX1908/MAX8724 provide outputs
to monitor current drawn from the AC adapter (DC input
source), battery-charging current, and the presence of
an AC adapter. The MAX1908's conditioning charge fea-
ture provides 300mA to safely charge deeply discharged
lithium-ion (Li+) battery packs.
The MAX1908 includes a conditioning charge feature
while the MAX8724 does not.
The MAX1908/MAX8724 charge two to four series Li+
cells, providing more than 5A, and are available in a
space-saving 28-pin thin QFN package (5mm
5mm).
An evaluation kit is available to speed designs.
Applications
Notebook and Subnotebook Computers
Personal Digital Assistants
Hand-Held Terminals
Features
0.5% Output Voltage Accuracy Using Internal
Reference (0C to +85C)
4% Accurate Input Current Limiting
5% Accurate Charge Current
Analog Inputs Control Charge Current and
Charge Voltage
Outputs for Monitoring
Current Drawn from AC Adapter
Charging Current
AC Adapter Presence
Up to 17.6V Battery-Voltage Set Point
Maximum 28V Input Voltage
>95% Efficiency
Shutdown Control Input
Charges Any Battery Chemistry
Li+, NiCd, NiMH, Lead Acid, etc.
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
________________________________________________________________ Maxim Integrated Products
1
28
27
26
25
24
23
22
IINP
CSSP
CSSN
DHI
BST
LX
DLOV
8
9
10
11
12
13
14
SHDN
ICHG
ACIN
ACOK
REFIN
ICTL
GND
15
16
17
18
19
20
21
VCTL
BATT
CELLS
CSIN
CSIP
PGND
DLO
7
6
5
4
3
2
1
CCV
CCI
CCS
REF
CLS
LDO
DCIN
MAX1908
MAX8724
THIN QFN
TOP VIEW
Pin Configuration
Ordering Information
MAX1908
MAX8724
AC ADAPTER
INPUT
TO EXTERNAL
LOAD
LDO
FROM HOST
P
10
H
0.015
BATT+
DCIN
REFIN
VCTL
ICTL
ACIN
ACOK
SHDN
ICHG
IINP
CCV
CCI
CCS
CELLS
LDO
BST
DLOV
DHI
LX
DLO
PGND
CSIP
CSIN
BATT
REF
CLS
GND
CSSP
CSSN
0.01
Minimum Operating Circuit
19-2764; Rev 2; 7/04
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.
EVALUATION KIT
AVAILABLE
PART
TEMP RANGE
PIN-PACKAGE
MAX1908ETI
-40C to +85C
28 Thin QFN
MAX8724ETI
-40C to +85C
28 Thin QFN
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
DCIN
= V
CSSP
= V
CSSN
= 18V, V
BATT
= V
CSIP
= V
CSIN
= 12V, V
REFIN
= 3V, V
VCTL
= V
ICTL
= 0.75 x V
REFIN
, CELLS = float, CLS =
REF, V
BST
- V
LX
= 4.5V, ACIN = GND = PGND = 0, C
LDO
= 1F, LDO = DLOV, C
REF
= 1F; CCI, CCS, and CCV are compensated
per Figure 1a; T
A
= 0C to +85C, unless otherwise noted. Typical values are at T
A
= +25C.)
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.
DCIN, CSSP, CSSN, ACOK to GND.......................-0.3V to +30V
BST to GND ............................................................-0.3V to +36V
BST to LX..................................................................-0.3V to +6V
DHI to LX ...................................................-0.3V to (V
BST
+ 0.3V)
LX to GND .................................................................-6V to +30V
BATT, CSIP, CSIN to GND .....................................-0.3V to +20V
CSIP to CSIN or CSSP to CSSN or PGND
to GND...............................................................-0.3V to +0.3V
CCI, CCS, CCV, DLO, ICHG,
IINP, ACIN, REF to GND...........................-0.3V to (V
LDO
+ 0.3V)
DLOV, VCTL, ICTL, REFIN, CELLS, CLS,
LDO, SHDN to GND .................................................-0.3V to +6V
DLOV to LDO.........................................................-0.3V to +0.3V
DLO to PGND .........................................-0.3V to (V
DLOV
+ 0.3V)
LDO Short-Circuit Current...................................................50mA
Continuous Power Dissipation (T
A
= +70C)
28-Pin Thin QFN (5mm
5mm)
(derate 20.8mW/C above +70C) .........................1666.7mW
Operating Temperature Range ..........................-40C to +85C
Junction Temperature ......................................................+150C
Storage Temperature Range .............................-60C to +150C
Lead Temperature (soldering, 10s) .................................+300C
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CHARGE VOLTAGE REGULATION
V
VCTL
= V
REFIN
(2, 3, or 4 cells)
-0.5
+0.5
V
VCTL
= V
REFIN
/ 20 (2, 3, or 4 cells)
-0.5
+0.5
Battery Regulation Voltage
Accuracy
V
VCTL
= V
LDO
(2, 3, or 4 cells)
-0.5
+0.5
%
VCTL Default Threshold
V
VCTL
rising
4.0
4.1
4.2
V
REFIN Range
(Note 1)
2.5
3.6
V
REFIN Undervoltage Lockout
V
REFIN
falling
1.20
1.92
V
CHARGE CURRENT REGULATION
CSIP-to-CSIN Full-Scale Current-
Sense Voltage
V
ICTL
= V
REFIN
71.25
75
78.75
mV
V
ICTL
= V
REFIN
-5
+5
V
ICTL
= V
REFIN
x 0.6
-5
+5
V
ICTL
= V
LDO
-6
+6
Charging Current Accuracy
MAX8724 only: V
ICTL
= V
REFIN
x 0.058
-33
+33
%
ICTL Default Threshold
V
ICTL
rising
4.0
4.1
4.2
V
BATT/CSIP/CSIN Input Voltage
Range
0
19
V
V
DCIN
= 0 or V
ICTL
= 0 or SHDN = 0
1
CSIP/CSIN Input Current
Charging
400
650
A
Cycle-by-Cycle Maximum Current
Limit
I
MAX
RS2 = 0.015
6.0
6.8
7.5
A
ICTL Power-Down Mode
Threshold Voltage
V
ICTL
rising
REFIN /
100
REFIN /
55
REFIN /
33
V
V
VCTL
= V
ICTL
= 0 or 3V
-1
+1
ICTL, VCTL Input Bias Current
V
DCIN
= 0, V
VCTL
= V
ICTL
= V
REFIN
= 5V
-1
+1
A
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
CSSP
= V
CSSN
= 18V, V
BATT
= V
CSIP
= V
CSIN
= 12V, V
REFIN
= 3V, V
VCTL
= V
ICTL
= 0.75 x V
REFIN
, CELLS = float, CLS =
REF, V
BST
- V
LX
= 4.5V, ACIN = GND = PGND = 0, C
LDO
= 1F, LDO = DLOV, C
REF
= 1F; CCI, CCS, and CCV are compensated
per Figure 1a; T
A
= 0C to +85C, unless otherwise noted. Typical values are at T
A
= +25C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
DCIN
= 5V, V
REFIN
= 3V
-1
+1
REFIN Input Bias Current
V
REFIN
= 5V
-1
+1
A
ICHG Transconductance
G
ICHG
V
CSIP
- V
CSIN
= 45mV
2.7
3
3.3
A/mV
V
CSIP
- V
CSIN
= 75mV
-6
+6
V
CSIP
- V
CSIN
= 45mV
-5
+5
ICHG Accuracy
V
CSIP
- V
CSIN
= 5mV
-40
+40
%
ICHG Output Current
V
CSIP
- V
CSIN
= 150mV, V
ICHG
= 0
350
A
ICHG Output Voltage
V
CSIP
- V
CSIN
= 150mV, ICHG
= float
3.5
V
INPUT CURRENT REGULATION
CSSP-to-CSSN Full-Scale
Current-Sense Voltage
72
75
78
mV
V
CLS
= V
REF
-4
+4
Input Current-Limit Accuracy
V
CLS
= V
REF
/ 2
-7.5
+7.5
%
CSSP, CSSN Input Voltage
Range
8
28
V
V
DCIN
= 0
0.1
1
CSSP, CSSN Input Current
V
CSSP
= V
CSSN
= V
DCIN
> 8V
350
600
A
CLS Input Range
1.6
REF
V
CLS Input Bias Current
V
CLS
= 2V
-1
+1
A
IINP Transconductance
G
IINP
V
CSSP
- V
CSSN
= 75mV
2.7
3
3.3
A/mV
V
CSSP
- V
CSSN
= 75mV
-5
+5
IINP Accuracy
V
CSSP
- V
CSSN
= 37.5mV
-7.5
+7.5
%
IINP Output Current
V
CSSP
- V
CSSN
= 150mV, V
IINP
= 0
350
A
IINP Output Voltage
V
CSSP
- V
CSSN
= 150mV,V
IINP
= float
3.5
V
SUPPLY AND LDO REGULATOR
DCIN Input Voltage Range
V
DCIN
8
28
V
V
DCIN
falling
7
7.4
DCIN Undervoltage-Lockout Trip
Point
V
DCIN
rising
7.5
7.85
V
DCIN Quiescent Current
I
DCIN
8.0V < V
DCIN
< 28V
3.2
6
mA
V
BATT
= 19V, V
DCIN
= 0
1
BATT Input Current
I
BATT
V
BATT
= 2V to 19V, V
DCIN
= 19.3V
200
500
A
LDO Output Voltage
8V < V
DCIN
< 28V, no load
5.25
5.4
5.55
V
LDO Load Regulation
0 < I
LDO
< 10mA
34
100
mV
LDO Undervoltage-Lockout Trip
Point
V
DCIN
= 8V
3.20
4
5.15
V
REFERENCE
REF Output Voltage
0 < I
REF
< 500A
4.072
4.096
4.120
V
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
4
_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
CSSP
= V
CSSN
= 18V, V
BATT
= V
CSIP
= V
CSIN
= 12V, V
REFIN
= 3V, V
VCTL
= V
ICTL
= 0.75 x V
REFIN
, CELLS = float, CLS =
REF, V
BST
- V
LX
= 4.5V, ACIN = GND = PGND = 0, C
LDO
= 1F, LDO = DLOV, C
REF
= 1F; CCI, CCS, and CCV are compensated
per Figure 1a; T
A
= 0C to +85C, unless otherwise noted. Typical values are at T
A
= +25C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
REF Undervoltage-Lockout Trip
Point
V
REF
falling
3.1
3.9
V
TRIP POINTS
BATT Power-Fail Threshold
V
DCIN
falling, referred to V
CSIN
50
100
150
mV
BATT Power-Fail Threshold
Hysteresis
200
mV
ACIN Threshold
ACIN rising
2.007
2.048
2.089
V
ACIN Threshold Hysteresis
0.5% of REF
20
mV
ACIN Input Bias Current
V
ACIN
= 2.048V
-1
+1
A
SWITCHING REGULATOR
DHI Off-Time
V
BATT
= 16V, V
DCIN
= 19V,
V
CELLS
= V
REFIN
0.36
0.4
0.44
s
DHI Minimum Off-Time
V
BATT
= 16V, V
DCIN
= 17V,
V
CELLS
= V
REFIN
0.24
0.28
0.33
s
DHI Maximum On-Time
2.5
5
7.5
ms
DLOV Supply Current
I
DLOV
DLO low
5
10
A
BST Supply Current
I
BST
DHI high
6
15
A
BST Input Quiescent Current
V
DCIN
= 0, V
BST
= 24.5V,
V
BATT
= V
LX
= 20V
0.3
1
A
LX Input Bias Current
V
DCIN
= 28V, V
BATT
= V
LX
= 20V
150
500
A
LX Input Quiescent Current
V
DCIN
= 0, V
BATT
= V
LX
= 20V
0.3
1
A
DHI Maximum Duty Cycle
99
99.9
%
Minimum Discontinuous-Mode
Ripple Current
0.5
A
Battery Undervoltage Charge
Current
V
BATT
= 3V per cell (RS2 = 15m
),
MAX1908 only, V
BATT
rising
150
300
450
mA
CELLS = GND, MAX1908 only, V
BATT
rising
6.1
6.2
6.3
CELLS = float, MAX1908 only, V
BATT
rising
9.15
9.3
9.45
Battery Undervoltage Current
Threshold
CELLS = V
REFIN
, MAX1908 only, V
BATT
rising
12.2
12.4
12.6
V
DHI On-Resistance High
V
BST
- V
LX
= 4.5V, I
DHI
= +100mA
4
7
DHI On-Resistance Low
V
BST
- V
LX
= 4.5V, I
DHI
= -100mA
1
3.5
DLO On-Resistance High
V
DLOV
= 4.5V, I
DLO
= +100mA
4
7
DLO On-Resistance Low
V
DLOV
= 4.5V, I
DLO
= -100mA
1
3.5
ERROR AMPLIFIERS
GMV Amplifier Transconductance
GMV
V
V C T L
= V
LD O
, V
BAT T
= 16.8V ,
C E LLS = V
RE F IN
0.0625
0.125
0.2500
A/mV
GMI Amplifier Transconductance
GMI
V
ICTL
= V
RE F IN
, V
CSIP
- V
CSIN
= 75mV
0.5
1
2.0
A/mV
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
_______________________________________________________________________________________
5
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
CSSP
= V
CSSN
= 18V, V
BATT
= V
CSIP
= V
CSIN
= 12V, V
REFIN
= 3V, V
VCTL
= V
ICTL
= 0.75 x V
REFIN
, CELLS = float, CLS =
REF, V
BST
- V
LX
= 4.5V, ACIN = GND = PGND = 0, C
LDO
= 1F, LDO = DLOV, C
REF
= 1F; CCI, CCS, and CCV are compensated
per Figure 1a; T
A
= 0C to +85C, unless otherwise noted. Typical values are at T
A
= +25C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GMS Amplifier Transconductance
GMS
V
CLS
= V
REF
, V
CSSP
- V
CSSN
= 75mV
0.5
1
2.0
A/mV
CCI, CCS, CCV Clamp Voltage
0.25V < V
CCV,CCS,CCI
< 2V
150
300
600
mV
LOGIC LEVELS
CELLS Input Low Voltage
0.4
V
CELLS Input Float Voltage
CELLS = float
(V
REFIN
/ 2) -
0.2V
V
REFIN
/ 2
( V
R E F IN
/ 2) +
0.2V
V
CELLS Input High Voltage
V
REFIN
- 0.4V
V
CELLS Input Bias Current
CELLS = 0 or V
REFIN
-2
+2
A
ACOK AND SHDN
ACOK Input Voltage Range
0
28
V
ACOK Sink Current
V
ACOK
= 0.4V, V
ACIN
= 3V
1
mA
ACOK Leakage Current
V
ACOK
= 28V, V
ACIN
= 0
1
A
SHDN Input Voltage Range
0
LDO
V
V
SHDN
= 0 or V
LDO
-1
+1
SHDN Input Bias Current
V
DCIN
= 0, V
SHDN
= 5V
-1
+1
A
SHDN Threshold
V
SHDN
falling
22
23.5
25
% of
V
REFIN
SHDN Threshold Hysteresis
1
% of
V
REFIN
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