MAX8765AETI+T [MAXIM]
Power Management Circuit, BICMOS, PQCC28,;
| 型号： | MAX8765AETI+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Power Management Circuit, BICMOS, PQCC28, 信息通信管理 |
| 文件： | 总30页 (文件大小：863K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
EVALUATION KIT AVAILABLE
MAX1908/MAX8724/
MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
General Description
Features
The MAX1908/MAX8724/MAX8765/MAX8765A highly
integrated, multichemistry battery-charger control ICs
simplify the construction of accurate and efficient charg-
ers. These devices use analog inputs to control charge
current and voltage, and can be programmed by the host
or hardwired. The MAX1908/MAX8724/MAX8765/
MAX8765A achieve high efficiency using a buck topology
with synchronous rectification.
o
0.5% Output Voltage Accuracy Using Internal
Reference ( 0.4% for MAX8765A, 2-/3-Cell Only)
4% Accurate Input Current Limiting
5% Accurate Charge Current
o
o
o Analog Inputs Control Charge Current and
Charge Voltage
o Outputs for Monitoring
Current Drawn from AC Adapter
Charging Current
The MAX1908/MAX8724/MAX8765/MAX8765A 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/MAX8765/MAX8765A provide out-
puts to monitor current drawn from the AC adapter (DC
input source), battery-charging current, and the pres-
ence of an AC adapter. The MAX1908’s conditioning
charge feature provides 300mA to safely charge deeply
discharged lithium-ion (Li+) battery packs.
AC Adapter Presence
o Up to 17.6V Battery-Voltage Set Point
o Maximum 28V Input Voltage
o > 95% Efficiency
o Shutdown Control Input
o Charge Any Battery Chemistry
The MAX1908 includes a conditioning charge feature
while the MAX8724/MAX8765/MAX8765A do not.
Li+, NiCd, NiMH, Lead Acid, etc.
Ordering Information
The MAX1908/MAX8724/MAX8765/MAX8765A 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.
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 Thin QFN-EP*
28 Thin QFN-EP*
28 Thin QFN-EP*
28 Thin QFN-EP*
MAX1908ETI+
MAX8724ETI+
MAX8765ETI+
MAX8765AETI+
Applications
Notebook and Subnotebook Computers
Personal Digital Assistants
Handheld Terminals
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Minimum Operating Circuit
Pin Configuration
AC ADAPTER
INPUT
TO EXTERNAL
LOAD
0.01Ω
TOP VIEW
CSSP
DCIN
CSSN
CELLS
LDO
REFIN
VCTL
ICTL
21 20 19 18 17 16 15
BST
LDO
DLOV
22
14
13
DLOV
GND
ICTL
ACIN
ACOK
23
LX
MAX1908
MAX8724
MAX8765
DHI
LX
24
25
26
27
28
BST
12 REFIN
11
10 ACIN
FROM HOST µP
SHDN MAX8765A
MAX1908
MAX8724
MAX8765
MAX8765A
DHI
CSSN
CSSP
IINP
ACOK
DLO
PGND
ICHG
IINP
CCV
CCI
10µH
9
8
ICHG
CSIP
SHDN
0.015Ω
CSIN
BATT
CCS
+
1
2
3
4
5
6
7
BATT+
REF
CLS
GND
THIN QFN
For pricing, delivery, and ordering information, please contact Maxim Direct
19-2764; Rev 5; 11/09
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ABSOLUTE MAXIMUM RATINGS
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
LDO Short-Circuit Current...................................................50mA
DCIN, CSSP, CSSN, ACOK to GND.......................-0.3V to +30V
BST to GND............................................................-0.3V to +36V
BST to LX..................................................................-0.3V to +6V
+ 0.3V)
DHI to LX...................................................-0.3V to (V
+ 0.3V)
DLOV
BST
LX to GND .................................................................-6V to +30V
BATT, CSIP, CSIN to GND .....................................-0.3V to +20V
CSIP to CSIN or CSSP to CSSN or
Continuous Power Dissipation (T = +70°C)
A
28-Pin Thin QFN (5mm × 5mm)
(derate 20.8mW/°C above +70°C) .........................1666.7mW
Operating Temperature Range ..........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-60°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
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
%
CHARGE-VOLTAGE REGULATION
Battery-Regulation Voltage
Accuracy
(MAX1908/MAX8724/MAX8765
(2, 3, or 4 Cells) and MAX8765A
(4 Cells Only))
V
V
= V
= V
-0.5
-0.5
+0.5
+0.5
VCTL
VCTL
REFIN
/20
REFIN
V
= V
-0.5
+0.5
VCTL
LDO
V
V
V
V
= V
= V
= V
-0.4
-0.4
-0.4
4.0
+0.4
+0.4
+0.4
VCTL
VCTL
VCTL
VCTL
REFIN
REFIN
LDO
Battery-Regulation Voltage
Accuracy (MAX8765A, 2 or 3
Cells Only)
/20
%
VCTL Default Threshold
REFIN Range
rising
4.1
4.2
3.6
V
V
V
(Note 1)
2.5
REFIN Undervoltage Lockout
CHARGE-CURRENT REGULATION
V
falling
1.20
1.92
REFIN
CSIP-to-CSIN Full-Scale Current-
Sense Voltage
V
= V
71.25
75
78.75
mV
%
ICTL
REFIN
V
V
V
= V
= V
= V
-5
-5
-6
+5
+5
+6
ICTL
ICTL
ICTL
REFIN
REFIN
LDO
x 0.6
Charging-Current Accuracy
MAX8765/MAX8765A only; V
0.036
= V
x
REFIN
ICTL
-45
-33
-2
+45
+33
+2
MAX8724 only; V
= V
x 0.058
REFIN
ICTL
Charge-Current Gain Error
(MAX8765/MAX8765A Only)
%
Charge-Current Offset
(MAX8765/MAX8765A Only)
-2
4.0
0
+2
4.2
19
mV
V
ICTL Default Threshold
V
rising
4.1
ICTL
BATT/CSIPN Input Voltage
Range
V
2
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
= 0V or V = 0V or V
MIN
TYP
MAX
1
UNITS
V
= 0V
DCIN
ICTL
SHDN
CSIP/CSIN Input Current
µA
650
Charging
400
6.8
Cycle-by-Cycle Maximum Current
Limit
RS2 = 0.015mΩ
6.0
7.5
A
V
ICTL Power-Down Mode
Threshold Voltage
(MAX1908/MAX8724 Only)
REFIN/ REFIN/ REFIN/
100
V
rising
VCTL
55
33
V
V
V
V
= V
= 0 or 3V
-1
-1
-1
-1
+1
+1
+1
+1
VCTL
DCIN
DCIN
REFIN
ICTL
ICTL, VCTL Input Bias Current
REFIN Input Bias Current
µA
= 0V, V
= 5V, V
= 5V
= V
= V
= 5V
REFIN
VCTL
ICTL
= 3V
REFIN
µA
µA/mV
µA/mV
%
ICHG Transconductance
(MAX1908/MAX8724 Only)
G
G
V
V
- V
= 45mV
= 45mV
2.7
2.85
-5
3
3
3.3
3.15
+5
ICHG
ICHG
CSIP
CSIP
CSIN
CSIN
ICHG Transconductance
(MAX8765/MAX8765A Only)
- V
ICHG Transconductance Error
(MAX8765/MAX8765A Only)
ICHG Transconductance Offset
(MAX8765/MAX8765A Only)
-5
+5
µA
V
V
V
V
V
- V
- V
- V
- V
- V
= 75mV
= 45mV
= 5mV
-6
-5
+6
+5
CSIP
CSIP
CSIP
CSIP
CSIP
CSIN
CSIN
CSIN
CSIN
CSIN
ICHG Accuracy
%
-40
350
3.5
+40
ICHG Output Current
= 150mV, V
= 0V
µA
V
ICHG
ICHG Output Voltage
= 150mV, ICHG = open
INPUT-CURRENT REGULATION
CSSP-to-CSSN Full-Scale
Current-Sense Voltage
72
75
78
mV
%
V
V
V
= V
= V
-4
+4
CLS
CLS
CLS
REF
Input Current-Limit Accuracy
/2
-7.5
-10
+7.5
+10
REF
= 1.1V (MAX8765/MAX8765A only)
Input Current-Limit Gain Error
(MAX8765/MAX8765A Only)
-2
-2
8
+2
+2
28
%
mV
V
Input Current-Limit Offset
(MAX8765/MAX8765A Only)
CSSP, CSSN Input Voltage
Range
V
V
= 0V
0.1
350
0.1
1
DCIN
CSSP
CSSP, CSSN Input Current
(MAX1908/MAX8724 Only)
µA
µA
= V
= V
> 8V
DCIN
600
1
CSSN
V
V
= 0V
DCIN
DCIN
CSSP Input Current
(MAX8765/8765A Only)
V
= V
= 28V
CSSP
CSSN
= 28V
400
650
Maxim Integrated
3
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
0.1
MAX
UNITS
V
= 0V
1
1
DCIN
DCIN
CSSN Input Current
(MAX8765/MAX8765A Only)
V
= V
= 28V
CSSN
µA
CSSP
V
= 28V
0.1
CLS Input Range
(MAX1908/MAX8724 Only)
1.6
REF
V
CLS Input Range
(MAX8765/MAX8765A Only)
1.1
-1
REF
+1
V
CLS Input Bias Current
V
V
= 2V
µA
CLS
IINP Transconductance
(MAX1908/MAX8724 Only)
G
G
- V = 75mV
CSSN
2.7
3
3
3.3
µA/mV
IINP
IINP
CSSP
V
V
- V
- V
= 75mV
-5
+5
CSSP
CSSP
CSSN
IINP Accuracy
%
µA/mV
%
= 37.5mV
-7.5
+7.5
CSSN
IINP Transconductance
(MAX8765/MAX8765A Only)
V
- V
= 75mV
2.82
-6
3.18
+6
CSSP
CCSN
IINP Transconductance Error
(MAX8765/MAX8765A Only)
IINP Transconductance Offset
(MAX8765/MAX8765A Only)
-10
+10
µA
IINP Output Current
V
V
- V
- V
= 150mV, V
= 150mV, V
= 0V
350
3.5
µA
V
CSSP
CSSP
CSSN
IINP
IINP Output Voltage
= open
CSSN
IINP
SUPPLY AND LDO REGULATOR
DCIN Input Voltage Range
V
8
7
28
V
V
DCIN
V
V
falling
rising
7.4
7.5
3.2
DCIN
DCIN
DCIN Undervoltage-Lockout Trip
Point
7.85
6
DCIN Quiescent Current
I
I
8.0V < V
< 28V
DCIN
mA
µA
DCIN
V
V
= 19V, V
= 0V
1
BATT
BATT
DCIN
BATT Input Current
BATT
= 2V to 19V, V
= 19.3V
200
5.4
34
500
5.55
100
DCIN
LDO Output Voltage
LDO Load Regulation
8V < V
< 28V, no load
5.25
3.20
V
DCIN
0 < I
< 10mA
mV
LDO
LDO Undervoltage-Lockout Trip
Point
V
= 8V
4
5.15
V
DCIN
REFERENCE
REF Output Voltage
0 < I
< 500µA
4.072
4.096
3.1
4.120
3.9
V
V
REF
REF Undervoltage-Lockout Trip
Point
V
falling
REF
4
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
TRIP POINTS
V
falling, referred to V
CSIN
DCIN
50
50
100
100
200
150
150
(MAX1908/MAX8724 only)
BATT Power-Fail Threshold
mV
V
falling, referred to V
CSSP
CSIN
(MAX8765/MAX8765A only)
BATT Power-Fail Threshold
Hysteresis
mV
V
ACIN rising (MAX8765/MAX8765A only)
ACIN rising (MAX1908/MAX8724 only)
0.5% of REF
2.028
2.007
2.048
2.048
20
2.068
2.089
ACIN Threshold
ACIN Threshold Hysteresis
ACIN Input Bias Current
SWITCHING REGULATOR
mV
µA
V
= 2.048V
-1
+1
ACIN
V
V
= 16V, V
= 19V,
= 17V,
BATT
DCIN
DHI Off-Time
0.36
0.4
0.44
0.33
µs
µs
= V
CELLS
REFIN
V
V
= 16V, V
BATT
DCIN
DHI Minimum Off-Time
0.24
2.5
0.28
= V
CELLS
REFIN
DHI Maximum On-Time
DLOV Supply Current
BST Supply Current
5
5
6
7.5
10
15
ms
µA
µA
DLO low
DHI high
V
V
= 0V, V
= 24.5V,
BST
DCIN
BATT
BST Input Quiescent Current
0.3
1
µA
= V = 20V
LX
LX Input Bias Current
V
V
= 28V, V
= V = 20V
150
0.3
500
1
µA
µA
%
DCIN
DCIN
BATT
LX
LX Input Quiescent Current
DHI Maximum Duty Cycle
= 0V, V
= V = 20V
BATT LX
99
99.9
Minimum Discontinuous-Mode
Ripple Current
0.5
A
Battery Undervoltage Charge
Current
V
= 3V per cell (RS2 = 15mΩ),
BATT
150
300
450
mA
MAX1908 only, V
rising
BATT
CELLS = GND, MAX1908 only, V
CELLS = open, MAX1908 only, V
rising
rising
6.1
6.2
9.3
12.4
4
6.3
9.45
12.6
7
BATT
Battery Undervoltage Current
Threshold
9.15
12.2
V
BATT
CELLS = V
, MAX1908 only, V
rising
BATT
REFIN
DHI On-Resistance High
DHI On-Resistance Low
DLO On-Resistance High
DLO On-Resistance Low
V
V
V
V
- V = 4.5V, I
= +100mA
= -100mA
Ω
Ω
Ω
Ω
BST
LX
DHI
DHI
- V = 4.5V, I
1
3.5
7
BST
LX
= 4.5V, I
= 4.5V, I
= +100mA
= -100mA
4
DLOV
DLOV
DLO
DLO
1
3.5
Maxim Integrated
5
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ERROR AMPLIFIERS
V
= V
, V
REFIN
= 16.8V,
VCTL
LDO BATT
GMV Amplifier Transconductance
GMI Amplifier Transconductance
GMS Amplifier Transconductance
GMV
GMI
0.0625
0.5
0.125 0.2500 µA/mV
CELLS = V
V
V
= V
, V
- V
= 75mV
= 75mV
1
1
2.0
2.0
µA/mV
µA/mV
ICTL
CLS
REFIN CSIP
CSIN
GMS
= V
, V
- V
0.5
REF CSSP
CSSN
CCI, CCS, CCV Clamp Voltage
0.25V < V
< 2V
150
300
600
mV
CCV,CCS,CCI
LOGIC LEVELS
CELLS Input Low Voltage
0.4
V
V
(V
/2) -
0.2V
(V
REFIN
REFIN
/2) +
0.2V
V
/
REFIN
2
CELLS Input Open Voltage
CELLS = open
V
REFIN
CELLS Input High Voltage
CELLS Input Bias Current
V
- 0.4V
CELLS = 0V or V
-2
+2
28
µA
REFIN
ACOK AND SHDN
ACOK Input Voltage Range
ACOK Sink Current
0
1
V
mA
µA
V
V
V
= 0.4V, V
= 3V
= 0V
A COK
A COK
ACIN
ACOK Leakage Current
SHDN Input Voltage Range
= 28V, V
1
ACIN
0
LDO
V
V
= 0V OR V
= 0V OR V
-1
+1
+1
SHDN
SHDN
LDO
SHDN Input Bias Current
µA
= 5V
-1
SHDN
% of
SHDN Threshold
V
falling
22
23.5
1
25
S HDN
V
REFIN
% of
SHDN Threshold Hysteresis
V
REFIN
6
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = -40°C to +85°C, unless otherwise noted.) (Note 2)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CHARGE-VOLTAGE REGULATION
V
V
V
= V
= V
= V
-0.6
-0.6
-0.6
2.5
+0.6
+0.6
+0.6
3.6
VCTL
VCTL
VCTL
REFIN
REFIN
LDO
Battery Regulation Voltage
Accuracy (2, 3, or 4 Cells)
/20
%
REFIN Range
(Note 1)
V
V
REFIN Undervoltage Lockout
CHARGE CURRENT REGULATION
V
falling
1.92
REFIN
CSIP-to-CSIN Full-Scale Current-
Sense Voltage
V
= V
70.5
79.5
mV
ICTL
REFIN
V
V
V
= V
= V
= V
-6
+6
ICTL
ICTL
ICTL
REFIN
REFIN
LDO
x 0.6
-7.5
-7.5
+7.5
+7.5
Charging-Current Accuracy
%
MAX8765/MAX8765A only; V
0.036
= V
x
REFIN
ICTL
-50
-33
-2
+50
+33
+2
MAX8724 only;
V
= V
x 0.058
REFIN
ICTL
Charge-Current Gain Error
(MAX8765/MAX8765A Only)
%
mV
V
Charge-Current Offset
(MAX8765/MAX8765A Only)
-2
+2
BATT/CSIP/CSIN Input Voltage
Range
0
19
V
= 0V or V
= 0V or V = 0V
SHDN
1
DCIN
ICTL
CSIP/CSIN Input Current
µA
A
Charging
650
Cycle-by-Cycle Maximum Current
Limit
I
RS2 = 0.015Ω
6.0
7.5
MAX
ICTL Power-Down Mode
Threshold Voltage
(MAX1908/MAX8724 Only)
REFIN/
100
REFIN/
33
V
rising
V
ICTL
ICHG Transconductance
(MAX1908/MAX8724 Only)
G
G
V
V
- V
- V
= 45mV
= 45mV
2.7
2.785
-7.5
3.3
3.225
+7.5
+6.5
µA/mV
µA/mV
%
ICHG
ICHG
CSIP
CSIP
CSIN
ICHG Transconductance
(MAX8765/MAX8765A Only)
CSIN
ICHG Transconductance Error
(MAX8765/MAX8765A Only)
ICHG Transconductance Offset
(MAX8765/MAX8765A Only)
-6.5
µA
Maxim Integrated
7
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = -40°C to +85°C, unless otherwise noted.) (Note 2)
A
PARAMETER
SYMBOL
CONDITIONS
= 75mV
MIN
-7.5
-7.5
-40
TYP
MAX
+7.5
+7.5
+40
UNITS
V
V
V
- V
- V
- V
CSIP
CSIP
CSIP
CSIN
CSIN
CSIN
ICHG Accuracy
%
= 45mV
= 5mV
INPUT-CURRENT REGULATION
CSSP-to-CSSN Full-Scale
Current-Sense Voltage
71.25
78.75
mV
%
V
V
V
= V
= V
-5
+5
CLS
CLS
CLS
REF
Input Current-Limit Accuracy
/2
-7.5
-10
+7.5
+10
REF
= 1.1V (MAX8765/MAX8765A only)
Input Current-Limit Gain Error
(MAX8765/MAX8765A Only)
-2
-2
8
+2
+2
28
%
mV
V
Input Current-Limit Offset
(MAX8765/MAX8765A Only)
CSSP, CSSN Input Voltage
Range
V
V
= 0V
1
600
1
DCIN
CSSP
CSSP, CSSN Input Current
(MAX1908/MAX8724 Only)
µA
= V
= V
> 8V
DCIN
CSSN
V
= 0V
DCIN
DCIN
DCIN
DCIN
CSSP Input Current
(MAX8765/MAX8765A Only)
V
V
= V
= 28V
= 28V
µA
CSSP
CSSP
CSSN
V
V
V
= 28V
= 0V
650
1
CSSN Input Current
(MAX8765/MAX8765A Only)
= V
µA
CSSN
= 28V
1
CLS Input Range
(MAX1908/MAX8724 Only)
1.6
1.1
REF
REF
3.3
V
CLS Input Range
(MAX8765/MAX8765A Only)
V
IINP Transconductance
(MAX1908/MAX8724 Only)
G
G
V
V
- V
- V
= 75mV
= 75mV
2.7
µA/mV
µA/mV
%
IINP
IINP
CSSP
CSSP
CSSN
IINP Transconductance
(MAX8765/MAX8765A Only)
2.785
-7.5
-12
3.225
+7.5
+12
CCSN
IINP Transconductance Error
(MAX8765/MAX8765A Only)
IINP Transconductance Offset
(MAX8765/MAX8765A Only)
µA
V
V
- V
- V
= 75mV
-7.5
-7.5
+7.5
+7.5
CSSP
CSSP
CSSN
IINP Accuracy
%
= 37.5mV
CSSN
8
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
REFIN
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = -40°C to +85°C, unless otherwise noted.) (Note 2)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SUPPLY AND LDO REGULATOR
DCIN Input Voltage Range
DCIN Quiescent Current
V
8
28
6
V
DCIN
I
8.0V < V
< 28V
mA
DCIN
DCIN
V
V
= 19V, V
= 0V
1
BATT
BATT
DCIN
BATT Input Current
I
µA
BATT
= 2V to 19V, V
= 19.3V
500
5.55
100
DCIN
LDO Output Voltage
LDO Load Regulation
REFERENCE
8V < V
< 28V, no load
5.25
V
DCIN
0 < I
< 10mA
mV
LDO
REF
REF Output Voltage
TRIP POINTS
0 < I
< 500µA
4.065
4.120
V
V
falling, referred to V
DCIN
CSIN
50
50
150
150
(MAX1908/MAX8724 only)
BATT Power-Fail Threshold
mV
V
V
falling, referred to V
CSSP
CSIN
(MAX8765/MAX8765A only)
ACIN rising (
only)
2.028
2.007
2.068
2.089
MAX8765/MAX8765A
ACIN Threshold
ACIN rising (MAX1908/MAX8724 only)
SWITCHING REGULATOR
DHI Off-Time
V
V
= 16V, V
= 19V,
= 17V,
BATT
DCIN
0.35
0.24
0.45
µs
µs
= V
CELLS
REFIN
V
V
= 16V, V
BATT
DCIN
DHI Minimum Off-Time
0.33
7.5
= V
CELLS
REFIN
DHI Maximum On-Time
2.5
99
ms
%
DHI Maximum Duty Cycle
Battery Undervoltage Charge
Current
V
= 3V per cell (RS2 = 15mΩ),
BATT
150
450
mA
MAX1908 only, V
rising
BATT
CELLS = GND, MAX1908 only, V
CELLS = open, MAX1908 only, V
rising
rising
6.09
9.12
6.30
9.45
12.60
7
BATT
Battery Undervoltage Current
Threshold
V
BATT
CELLS = V
, MAX1908 only, V
rising 12.18
BATT
REFIN
DHI On-Resistance High
DHI On-Resistance Low
DLO On-Resistance High
DLO On-Resistance Low
V
V
V
V
- V = 4.5V, I
= +100mA
= -100mA
Ω
Ω
Ω
Ω
BST
LX
DHI
DHI
- V = 4.5V, I
3.5
7
BST
LX
= 4.5V, I
= 4.5V, I
= +100mA
= -100mA
DLOV
DLOV
DLO
DLO
3.5
Maxim Integrated
9
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
ELECTRICAL CHARACTERISTICS (continued)
(V
= V
BST
= V
= 18V, V
= V
= V
= 12V, V
= 3V, V
= V
= 0.75 x V
, CELLS = open, CLS =
DCIN
CSSP
CSSN
BATT
CSIP
CSIN
REFIN
VCTL
ICTL
REFIN
REF, V
- V = 4.5V, ACIN = GND = PGND = 0, C
= 1µF, LDO = DLOV, C
= 1µF; CCI, CCS, and CCV are compensated
LX
LDO
REF
per Figure 1a; T = -40°C to +85°C, unless otherwise noted.) (Note 2)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ERROR AMPLIFIERS
V
= V
, V
REFIN
= 16.8V,
VCTL
LDO BATT
GMV Amplifier Transconductance
GMV
0.0625
0.250
µA/mV
CELLS = V
GMI Amplifier Transconductance
GMS Amplifier Transconductance
CCI, CCS, CCV Clamp Voltage
LOGIC LEVELS
GMI
V
V
= V
, V
- V
= 75mV
= 75mV
0.5
0.5
150
2.0
2.0
600
µA/mV
µA/mV
mV
ICTL
CLS
REFIN CSIP
CSIN
GMS
= V
, V
- V
REF CSSP CSSN
0.25V < V
< 2V
CCV,CCS,CCI
CELLS Input Low Voltage
0.4
V
V
(V
/2) -
0.2V
(V
REFIN
REFIN
/2) +
0.2V
CELLS Input Open Voltage
CELLS = open
V
REFIN
CELLS Input High Voltage
V
- 0.4V
ACOK AND SHDN
ACOK Input Voltage Range
ACOK Sink Current
0
1
0
28
V
mA
V
V
V
= 0.4V, V
falling
= 3V
ACIN
ACOK
SHDN
SHDN Input Voltage Range
LDO
25
% of
SHDN Threshold
22
V
REFIN
Note 1: If both ICTL and VCTL use default mode (connected to LDO), REFIN is not used and can be connected to LDO.
Note 2: Specifications to T = -40°C are guaranteed by design and not production tested.
A
Typical Operating Characteristics
(Circuit of Figure 1, V
= 20V, T = +25°C, unless otherwise noted.)
A
DCIN
LOAD-TRANSIENT RESPONSE
(STEP IN-LOAD CURRENT)
LOAD-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
(STEP IN-LOAD CURRENT)
(BATTERY INSERTION AND REMOVAL)
MAX1908 toc01
MAX1908 toc03
MAX1908 toc02
ADAPTER
CURRENT
5A/div
LOAD
CURRENT
5A/div
I
BATT
2A/div
LOAD
CURRENT
5A/div
0
0
0
0
ADAPTER
CURRENT
5A/div
0
V
BATT
5V/div
V
BATT
16.8V
CCV
CCI
2V/div
CHARGE
CURRENT
2A/div
CCS
CCI
V
CCI
V
CCI
500mV/div
CCI
500mV/div
V
CCS
V
CCV
V
BATT
CCS
500mV/div
500mV/div
2V/div
1ms/div
CHARGING CURRENT = 3A
1ms/div
1ms/div
CHARGING CURRENT = 3A
ICTL = LDO
ICTL = LDO
ICTL = LDO
VCTL = LDO
V
BATT
= 16.8V
V
= 16.8V
BATT
LOAD STEP = 0 TO 4A
LIMIT = 5A
LOAD STEP = 0 TO 4A
I LIMIT = 5A
SOURCE
I
SOURCE
10
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
= 20V, T = +25°C, unless otherwise noted.)
A
DCIN
LINE-TRANSIENT RESPONSE
LDO LOAD REGULATION
LDO LINE REGULATION
MAX1908 toc04
0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-1.0
0.05
0.04
0.03
0.02
0.01
0
V
DCIN
I
V
= 0
LDO
10V/div
= 5.4V
LDO
V
BATT
500mV/div
-0.01
-0.02
-0.03
-0.04
-0.05
INDUCTOR
CURRENT
500mA/div
V
= 5.4V
LDO
1
10ms/div
0
2
3
4
5
6
7
8
9
10
8
10 12 14 16 18 20 22 24 26 28
(V)
ICTL = LDO
VCTL = LDO
LDO CURRENT (mA)
V
IN
I
= 3A
CHARGE
LINE STEP 18.5V TO 27.5V
REF VOLTAGE LOAD REGULATION
REF VOLTAGE ERROR vs. TEMPERATURE
EFFICIENCY vs. CHARGE CURRENT
0
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
-0.09
-0.10
0.10
0.08
0.06
0.04
0.02
0
100
90
80
V
= 16V
BATT
70
60
V
= 12V
BATT
50
40
V
= 8V
BATT
-0.02
-0.04
-0.06
-0.08
-0.10
30
20
10
0
0
100
200
300
400
500
-40
-15
10
35
60
85
0.01
0.1
1
10
REF CURRENT (µA)
TEMPERATURE (°C)
CHARGE CURRENT (A)
FREQUENCY vs. V - V
BATT VOLTAGE ERROR vs. VCTL
OUTPUT V/I CHARACTERISTICS
IN
BATT
0.5
0.4
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
500
450
400
350
300
250
200
150
100
50
2 CELLS
3 CELLS
3 CELLS
0.3
0.2
4 CELLS
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
4 CELLS
I
= 3A
CHARGE
4 CELLS
REFIN = 3.3V
NO LOAD
VCTL = ICTL = LDO
0
0
2
4
6
8
10 12 14 16 18 20 22
0
1
2
3
4
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
VCTL/REFIN (%)
1.0
(V - V ) (V)
BATT CURRENT (A)
IN
BATT
Maxim Integrated
11
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
= 20V, T = +25°C, unless otherwise noted.)
A
DCIN
ICHG ERROR vs. CHARGE CURRENT
CURRENT-SETTING ERROR vs. ICTL
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
5
4
3
2
1
0
V = 3.3V
REFIN
V
= 3.3V
REFIN
V
= 16V
BATT
V
V
= 12V
= 8V
BATT
BATT
-1
0
0
0.5
1.0
1.5
(A)
2.0
2.5
3.0
0.5
1.0
(V)
1.5
2.0
I
V
BATT
ICTL
IINP ERROR vs. SYSTEM LOAD CURRENT
IINP ERROR vs. INPUT CURRENT
40
30
80
60
20
40
ERROR DUE TO SWITCHING NOISE
I
= 0
BATT
10
20
0
0
-10
-20
-30
-40
-20
-40
-60
-80
SYSTEM LOAD = 0
0
1
2
3
4
0
0.5
1.0
1.5
2.0
SYSTEM LOAD CURRENT (A)
INPUT CURRENT (A)
12
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Pin Description
PIN
1
NAME
DCIN
LDO
CLS
FUNCTION
Charging Voltage Input. Bypass DCIN with a 1µF capacitor to PGND.
2
Device Power Supply. Output of the 5.4V linear regulator supplied from DCIN. Bypass with a 1µF capacitor to GND.
Source Current-Limit Input. Voltage input for setting the current limit of the input source.
4.096V Voltage Reference. Bypass REF with a 1µF capacitor to GND.
3
4
REF
5
CCS
CCI
Input-Current Regulation Loop-Compensation Point. Connect a 0.01µF capacitor to GND.
Output-Current Regulation Loop-Compensation Point. Connect a 0.01µF capacitor to GND.
Voltage Regulation Loop-Compensation Point. Connect 1kΩ in series with a 0.1µF capacitor to GND.
6
7
CCV
Shutdown Control Input. Drive SHDN logic low to shut down the MAX1908/MAX8724/MAX8765 MAX8765A.
Use with a thermistor to detect a hot battery and suspend charging.
8
9
SHDN
Charge-Current Monitor Output. ICHG is a scaled-down replica of the charger output current. Use ICHG to
monitor the charging current and detect when the chip changes from constant-current mode to constant-
voltage mode. The transconductance of (CSIP - CSIN) to ICHG is 3µA/mV.
ICHG
ACIN
10
11
12
AC Detect Input. Input to an uncommitted comparator. ACIN can be used to detect AC-adapter presence.
ACOK AC Detect Output. High-voltage open-drain output is high impedance when V
is less than V
/2.
REF
ACIN
REFIN Reference Input. Allows the ICTL and VCTL inputs to have ratiometric ranges for increased accuracy.
Output Current-Limit Set Input. ICTL input voltage range is V /32 to V . The MAX1908/MAX8724 shut
REFIN
REFIN
13
ICTL
down if ICTL is forced below V /100 while the MAX8765/MAX8765A does not. When ICTL is equal to
REFIN
LDO, the set point for CSIP - CSIN is 45mV.
14
15
GND
VCTL
BATT
Analog Ground
Output Voltage-Limit Set Input. VCTL input voltage range is 0 to V
point is (4.2 x CELLS)V.
. When VCTL is equal to LDO, the set
REFIN
16
17
18
19
20
21
22
23
24
25
26
27
Battery Voltage Input
CELLS Cell Count Input. Tri-level input for setting number of cells. GND = 2 cells, open = 3 cells, REFIN = 4 cells.
CSIN
CSIP
Output Current-Sense Negative Input
Output Current-Sense Positive Input. Connect a current-sense resistor from CSIP to CSIN.
PGND Power Ground
DLO
DLOV
LX
Low-Side Power MOSFET Driver Output. Connect to low-side nMOS gate.
Low-Side Driver Supply. Bypass DLOV with a 1µF capacitor to GND.
High-Side Power MOSFET Driver Power-Return Connection. Connect to the source of the high-side nMOS.
High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1µF capacitor from LX to BST.
High-Side Power MOSFET Driver Output. Connect to high-side nMOS gate.
Input Current-Sense Negative Input
BST
DHI
CSSN
CSSP
Input Current-Sense Positive Input. Connect a current-sense resistor from CSSP to CSSN.
Input-Current Monitor Output. IINP is a scaled-down replica of the input current. IINP monitors the total
system current. The transconductance of (CSSP - CSSN) to IINP is 3µA/mV.
28
IINP
Maxim Integrated
13
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
voltage. By limiting the adjust range to 10% of the regu-
Detailed Description
lation voltage, the external resistor mismatch error is
The MAX1908/MAX8724/MAX8765/MAX8765A include
reduced from 1% to 0.05% of the regulation voltage.
all the functions necessary to charge Li+ batteries. A
Therefore, an overall voltage accuracy of better than
high-efficiency synchronous-rectified step-down DC-DC
0.7% is maintained while using 1% resistors. The per-
converter controls charging voltage and current. The
cell battery termination voltage is a function of the bat-
device also includes input-source current limiting and
tery chemistry. Consult the battery manufacturer to
analog inputs for setting the charge current and charge
determine this voltage. Connect VCTL to LDO to select
voltage. Control charge current and voltage using the
the internal default setting V
cells, or program the battery voltage with the following
equation:
= 4.2V × number of
BATT
ICTL and VCTL inputs, respectively. Both ICTL and
VCTL are ratiometric with respect to REFIN, allowing
compatibility with DACs or microcontrollers (µCs).
Ratiometric ICTL and VCTL improve the accuracy of the
⎛
⎞
⎞
⎛
V
VCTL
V
= CELLS × 4V + 0.4 ×
⎜
⎜
charge current and voltage set point by matching V
RE-
BATT
⎟ ⎟
V
⎝
⎠
⎠
⎝
REFIN
to the reference of the host. For standard applica-
FIN
tions, internal set points for ICTL and VCTL provide 3A
charge current (with 0.015Ω sense resistor), and 4.2V
(per cell) charge voltage. Connect ICTL and VCTL to
LDO to select the internal set points. The MAX1908
safely conditions overdischarged cells with 300mA (with
0.015Ω sense resistor) until the battery-pack voltage
exceeds 3.1V × number of series-connected cells. The
SHDN input allows shutdown from a microcontroller or
thermistor.
CELLS is the programming input for selecting cell count.
Connect CELLS as shown in Table 2 to charge 2, 3, or 4
Li+ cells. When charging other cell chemistries, use
CELLS to select an output voltage range for the charger.
The internal error amplifier (GMV) maintains voltage
regulation (Figure 3). The voltage error amplifier is
compensated at CCV. The component values shown in
Figures 1 and 2 provide suitable performance for most
applications. Individual compensation of the voltage reg-
ulation and current regulation loops allows for optimal
compensation (see the Compensation section).
The DC-DC converter uses external n-channel
MOSFETs as the buck switch and synchronous rectifier
to convert the input voltage to the required charging
current and voltage. The Typical Application Circuit
shown in Figure 1 uses a µC to control charging cur-
rent, while Figure 2 shows a typical application with
charging voltage and current fixed to specific values
for the application. The voltage at ICTL and the value of
RS2 set the charging current. The DC-DC converter
generates the control signals for the external MOSFETs
to regulate the voltage and the current set by the VCTL,
ICTL, and CELLS inputs.
Table 1. Versions Comparison
MAX8765/
MAX8765A
DESCRIPTION
MAX1908
MAX8724
Conditioning
Charge Feature
Yes
Yes
No
No
ICTL Shutdown
Mode
Yes
No
The MAX1908/MAX8724/MAX8765/MAX8765A feature
a voltage regulation loop (CCV) and two current regula-
tion loops (CCI and CCS). The CCV voltage regulation
loop monitors BATT to ensure that its voltage does not
exceed the voltage set by VCTL. The CCI battery cur-
rent regulation loop monitors current delivered to BATT
to ensure that it does not exceed the current limit set by
ICTL. A third loop (CCS) takes control and reduces the
battery-charging current when the sum of the system
load and the battery-charging input current exceeds
the input current limit set by CLS.
ACOK Enable
Condition
REFIN must REFIN must Independent
be ready be ready of REFIN
Table 2. Cell-Count Programming
CELLS
CELL COUNT
GND
2
3
4
Open
V
REFIN
Setting the Battery-Regulation Voltage
The MAX1908/MAX8724/MAX8765/MAX8765A use a
high-accuracy voltage regulator for charging voltage.
The VCTL input adjusts the charger output voltage.
VCTL contoltage can vary from 0 to V
, provid-
REFIN
ing a 10% adjustment range on the V
regulation
BATT
14
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Typical Application Circuits
RS1
0.01Ω
TO EXTERNAL
LOAD
AC ADAPTER INPUT
8.5V TO 28V
D1
C1
2 × 10µF
0.1µF
0.1µF
D2
CSSP
DCIN
CSSN
CELLS
R6
59kΩ
1%
OPEN (3 CELLS SELECT)
R7
19.6kΩ
1%
C5
1µF
LDO
C13
R13
1µF
33Ω
LDO
VCTL
D3
BST
DAC OUTPUT
ICTL
DLOV
12.6V OUTPUT VOLTAGE
C15
0.1µF
C16
1µF
V
REFIN
CC
R8
1MΩ
ACIN
N1a
DHI
LX
ACOK
SHDN
ICHG
OUTPUT
N1b
DLO
ADC INPUT
MAX1908
MAX8724
MAX8765
MAX8765A
L1
PGND
10µH
ADC INPUT
IINP
CCV
CSIP
C14
0.1µF
C20
R10
R9
R5
1kΩ
0.1µF
10kΩ
20kΩ
RS2
0.015Ω
HOST
C11
0.1µF
CSIN
BATT
GND
CCI
+
BATT
CCS
C9
0.01µF
C10
0.01µF
C4
22µF
REF
CLS
AVDD/REF
R19, R20, R21
10kΩ
7.5A INPUT
CURRENT LIMIT
C12
1µF
SMART
BATTERY
SCL
SDA
SCL
SDA
ADC INPUT
GND
TEMP
BATT-
PGND
GND
Figure 1. µC-Controlled Typical Application Circuit
Maxim Integrated
15
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Typical Application Circuits (continued)
AC ADAPTER
INPUT
8.5V TO 28V
RS1
0.01Ω
TO EXTERNAL
LOAD
P1
R11
15kΩ
C1
2 × 10µF
0.01µF 0.01µF
R12
12kΩ
REFIN (4 CELLS SELECT)
CSSP
ACOK
CSSN
D2
R6
59kΩ
1%
CELLS
R7
19.6kΩ
1%
DCIN
LDO
C5
1µF
LDO
R14
10.5kΩ
1%
VCTL
LDO
C13
R13
1µF
33Ω
D3
REFIN
BST
R15
8.25kΩ
1%
DLOV
C15
C16
0.1µF
1µF
ICTL
N1a
16.8V OUTPUT VOLTAGE
2.5A CHARGE LIMIT
R16
8.25kΩ
1%
DHI
LX
ACIN
R19
C12
10kΩ
1%
1.5nF
N1b
FROM HOST µP
(SHUTDOWN)
N
DLO
MAX1908
MAX8724
MAX8765
MAX8765A
L1
10µH
SHDN
PGND
R20
10kΩ
1%
ICHG
IINP
CSIP
CCV
R5
1kΩ
RS2
0.015Ω
C11
0.1µF
CSIN
BATT
GND
CCI
+
BATT
CCS
C9
0.01µF
C10
0.01µF
C4
22µF
BATTERY
THM
BATT-
REF
CLS
C12
1µF
R17
19.1kΩ
1%
PGND GND
R18
22kΩ
1%
4A INPUT CURRENT LIMIT
Figure 2. Typical Application Circuit with Fixed Charging Parameters
16
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Functional Diagram
DCIN
SHDN
GND
23.5%
REFIN
LDO
RDY
5.4V
LINEAR
REGULATOR
4.096V
REFERENCE
REF
MAX1908
MAX8724
MAX8765
MAX8765A
LOGIC
BLOCK
MAX1908/MAX8724 ONLY
1/55
GND
REFIN
ICTL
SRDY
ACIN
ACOK
DCIN
x
N
REF/2
CCS
CLS
75mV
REF
IINP
GM
GMS
CSSP
CSSN
LEVEL
SHIFTER
ICHG
GM
CSI
CSIP
CSIN
LEVEL
SHIFTER
BST
DHI
LX
GMI
75mV
REFIN
x
LEVEL
SHIFTER
ICTL
CCI
DRIVER
MAX1908 ONLY
3.1V/CELL
BATT
BAT_UV
LVC
DC-DC
LVC
CONVERTER
R1
REFIN
GMV
CELL
SELECT
LOGIC
CELLS
DLOV
DLO
DRIVER
CCV
PGND
400mV
REFIN
x
VCTL
4V
Figure 3. Functional Diagram
Maxim Integrated
17
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
threshold is exceeded, ensuring the battery charger
does not load down the AC adapter voltage. An internal
amplifier compares the voltage between CSSP and
Setting the Charging-Current Limit
The ICTL input sets the maximum charging current. The
current is set by current-sense resistor RS2, connected
between CSIP and CSIN. The full-scale differential
voltage between CSIP and CSIN is 75mV; thus, for a
0.015Ω sense resistor, the maximum charging current
is 5A. Battery-charging current is programmed with
ICTL using the equation:
CSSN to the voltage at CLS. V
can be set by a
CLS
resistive divider between REF and GND. Connect CLS
to REF for the full-scale input current limit. The CLS volt-
age range for the MAX1908/MAX8724 is from 1.6V to
REF, while the MAX8765/MAX8765A CLS voltage is
from 1.1V to REF.
V
0.075
RS2
ICTL
The input current is the sum of the device current, the
charger input current, and the load current. The device
current is minimal (3.8mA) in comparison to the charge
and load currents. Determine the actual input current
required as follows:
I
=
×
CHG
V
REFIN
The input voltage range for ICTL is V
/32 to V
.
REFIN
REFIN
The MAX1908/MAX8724 shut down if ICTL is forced
below V /100 (min), while the MAX8765/MAX8765A
REFIN
⎛
⎞
I
× V
BATT
does not.
CHG
I
= I
+
INPUT
LOAD
⎜
⎟
V
× η
⎝
⎠
Connect ICTL to LDO to select the internal default full-
scale, charge-current sense voltage of 45mV. The
charge current when ICTL = LDO is:
IN
where η is the efficiency of the DC-DC converter.
determines the reference voltage of the GMS
V
CLS
0.045V
RS2
error amplifier. Sense resistor RS1 and V
determine
CLS
I
=
CHG
the maximum allowable input current. Calculate the
input current limit as follows:
where RS2 is 0.015Ω, providing a charge-current set
V
0.075
RS1
CLS
I
=
×
point of 3A.
INPUT
V
REF
The current at the ICHG output is a scaled-down replica
of the battery output current being sensed across CSIP
and CSIN (see the Current Measurement section).
Once the input current limit is reached, the charging
current is reduced until the input current is at the
desired threshold.
When choosing the current-sense resistor, note that the
voltage drop across this resistor causes further power
loss, reducing efficiency. However, adjusting ICTL to
reduce the voltage across the current-sense resistor
can degrade accuracy due to the smaller signal to the
input of the current-sense amplifier. The charging-
current-error amplifier (GMI) is compensated at CCI
(see the Compensation section).
When choosing the current-sense resistor, note that the
voltage drop across this resistor causes further power
loss, reducing efficiency. Choose the smallest value for
RS1 that achieves the accuracy requirement for the
input current-limit set point.
Conditioning Charge
The MAX1908 includes a battery-voltage comparator
that allows a conditioning charge of overdischarged Li+
battery packs. If the battery-pack voltage is less than
3.1V × number of cells programmed by CELLS, the
MAX1908 charges the battery with 300mA current when
using sense resistor RS2 = 0.015Ω. After the
battery voltage exceeds the conditioning charge thresh-
old, the MAX1908 resumes full-charge mode, charging
to the programmed voltage and current limits. The
MAX8724/MAX8765/MAX8765A do not offer this feature.
Setting the Input Current Limit
The total input current (from an AC adapter or other DC
source) is a function of the system supply current and
the battery-charging current. The input current regulator
limits the input current by reducing the charging
current when the input current exceeds the input
current-limit set point. System current normally fluc-
tuates as portions of the system are powered up or
down. Without input current regulation, the source must
be able to supply the maximum system current and the
maximum charger input current simultaneously. By using
the input current limiter, the current capability of the AC
adapter can be lowered, reducing system cost.
AC Adapter Detection
Connect the AC adapter voltage through a resistive
divider to ACIN to detect when AC power is available,
as shown in Figure 1. ACIN voltage rising trip point is
V
/2 with 20mV hysteresis. ACOK is an open-drain
REF
The MAX1/MAX8724/MAX8765/MAX8765A limit the
battery charge current when the input current-limit
output and is high impedance when ACIN is less than
18
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
DC-DC Converter
The MAX1908/MAX8724/MAX8765/MAX8765A employ
a buck regulator with a bootstrapped nMOS high-side
switch and a low-side nMOS synchronous rectifier.
V
/2. Since ACOK can withstand 30V (max), ACOK
REF
can drive a p-channel MOSFET directly at the charger
input, providing a lower dropout voltage than a
Schottky diode (Figure 2). In the MAX1908/MAX8724
the ACOK comparator is enabled after REFIN is ready.
In the MAX8765/MAX8765A, the ACOK comparator is
independent of REFIN.
CCV, CCI, CCS, and LVC Control Blocks
The MAX1908/MAX8724/MAX8765/MAX8765A control
input current (CCS control loop), charge current (CCI
control loop), or charge voltage (CCV control loop),
depending on the operating condition.
Current Measurement
Use ICHG to monitor the battery-charging current being
sensed across CSIP and CSIN. The ICHG voltage is
proportional to the output current by the equation:
The three control loops, CCV, CCI, and CCS are brought
together internally at the LVC amplifier (lowest voltage
clamp). The output of the LVC amplifier is the feedback
control signal for the DC-DC controller. The output of the
V
ICHG
= ICHG x RS2 x G
x R9
ICHG
where I
is the battery-charging current, G
is
ICHG
CHG
G
amplifier that is the lowest sets the output of the LVC
M
the transconductance of ICHG (3µA/mV typ), and R9 is
the resistor connected between ICHG and ground.
Leave ICHG unconnected if not used.
amplifier and also clamps the other two control loops to
within 0.3V above the control point. Clamping the other
two control loops close to the lowest control loop ensures
fast transition with minimal overshoot when switching
between different control loops.
Use IINP to monitor the system input current being
sensed across CSSP and CSSN. The voltage of IINP is
proportional to the input current by the equation:
DC-DC Controller
The MAX1908/MAX8724/MAX8765/MAX8765A feature a
variable off-time, cycle-by-cycle current-mode control
scheme. Depending upon the conditions, the MAX1908/
MAX8724/MAX8765/MAX8765A work in continuous or
discontinuous-conduction mode.
V
= I
x RS1 x G
x R10
IINP
INPUT
IINP
where I
is the DC current being supplied by the AC
INPUT
adapter power, G
(3µA/mV typ), and R10 is the resistor connected between
IINP and ground. ICHG and IINP have a 0 to 3.5V output
voltage range. Leave IINP unconnected if not used.
is the transconductance of IINP
IINP
Continuous-Conduction Mode
With sufficient charger loading, the MAX1908/MAX8724/
MAX8765/MAX8765A operate in continuous-conduction
mode (inductor current never reaches zero) switching at
400kHz if the BATT voltage is within the following range:
LDO Regulator
LDO provides a 5.4V supply derived from DCIN and
can deliver up to 10mA of load current. The MOSFET
drivers are powered by DLOV and BST, which must be
connected to LDO as shown in Figure 1. LDO supplies
the 4.096V reference (REF) and most of the control cir-
cuitry. Bypass LDO with a 1µF capacitor to GND.
3.1V x (number of cells) < V
< (0.88 x V
)
BATT
DCIN
The operation of the DC-DC controller is controlled by
the following four comparators as shown in Figure 4:
Shutdown
The MAX1908/MAX8724/MAX8765/MAX8765A feature
a low-power shutdown mode. Driving SHDN low shuts
down the MAX1908/MAX8724/MAX8765/MAX8765A. In
shutdown, the DC-DC converter is disabled and CCI,
CCS, and CCV are pulled to ground. The IINP and
ACOK outputs continue to function.
• IMIN—Compares the control point (LVC) against
0.15V (typ). If IMIN output is low, then a new cycle
cannot begin.
• CCMP—Compares the control point (LVC) against the
charging current (CSI). The high-side MOSFET on-
time is terminated if the CCMP output is high.
SHDN can be driven by a thermistor to allow automatic
shutdown of the MAX1908/MAX8724/MAX8765/
MAX8765A when the battery pack is hot. The shutdown
• IMAX—Compares the charging current (CSI) to 6A
(RS2 = 0.015Ω). The high-side MOSFET on-time is
terminated if the IMAX output is high and a new cycle
cannot begin until IMAX goes low.
falling threshold is 23.5% (typ) of V
with 1%
REFIN
V
hysteresis to provide smooth shutdown when
REFIN
driven by a thermistor.
• ZCMP—Compares the charging current (CSI) to
333mA (RS2 = 0.015Ω). If ZCMP output is high, then
both MOSFETs are turned off.
Maxim Integrated
19
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
DC-DC Functional Diagram
5ms
S
R
CSSP
AC ADAPTER
RESET
1.8V
MAX1908
MAX8724
MAX8765
MAX8765A
BST
CSS
X20
RS1
LDO
D3
IMAX
CCMP
IMIN
CSSN
BST
Q
N1a
DHI
LX
R
S
Q
C
BST
DHI
CHG
Q
L1
0.15V
0.1V
N1b
DLO
DLO
t
OFF
GENERATOR
CSIP
ZCMP
CSI
X20
RS2
CSIN
BATT
GMS
GMI
LVC
C
OUT
BATTERY
GMV
SETV
CONTROL SETI
CELL
SELECT
LOGIC
CLS
CELLS
CCS CCI
CCV
Figure 4. DC-DC Functional Diagram
20
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
In normal operation, the controller starts a new cycle by
turning on the high-side n-channel MOSFET and
turning off the low-side n-channel MOSFET. When the
charge current is greater than the control point (LVC),
CCMP goes high and the off-time is started. The
off-time turns off the high-side n-channel MOSFET and
turns on the low-side n-channel MOSFET. The opera-
tional frequency is governed by the off-time and is
Discontinuous Conduction
The MAX1908/MAX8724/MAX8765/MAX8765A enter dis-
continuous-conduction mode when the output of the LVC
control point falls below 0.15V. For RS2 = 0.015Ω, this
corresponds to 0.5A:
0.15V
20 × RS2
IMIN =
= 0.5A
dependent upon V
and V
. The off-time is set
BATT
DCIN
by the following equations:
for RS2 = 0.015Ω.
In discontinuous mode, a new cycle is not started until
the LVC voltage rises above 0.15V. Discontinuous-
mode operation can occur during conditioning charge
of overdischarged battery packs, when the charge cur-
rent has been reduced sufficiently by the CCS control
loop, or when the battery pack is near full charge (con-
stant-voltage-charging mode).
V
− V
DCIN
BATT
t
= 2.5µs ×
OFF
t
V
DCIN
L × I
RIPPLE
− V
BATT
=
ON
V
CSSN
MOSFET Drivers
The low-side driver output DLO switches between
PGND and DLOV. DLOV is usually connected through
a filter to LDO. The high-side driver output DHI is boot-
where:
V
× t
OFF
L
BATT
I
=
RIPPLE
strapped off LX and switches between V and V
.
BST
LX
When the low-side driver turns on, BST rises to one
diode voltage below DLOV.
1
+ t
f =
Filter DLOV with a lowpass filter whose cutoff frequency
is approximately 5kHz (Figure 1):
t
ON
OFF
These equations result in fixed-frequency operation
over the most common operating conditions.
1
1
f
=
=
= 4.8kHz
C
2πRC 2π × 33Ω × 1µF
At the end of the fixed off-time, another cycle begins if
the control point (LVC) is greater than 0.15V, IMIN =
high, and the peak charge current is less than 6A (RS2
= 0.015Ω), IMAX = high. If the charge current exceeds
IMAX, the on-time is terminated by the IMAX compara-
tor. IMAX governs the maximum cycle-by-cycle current
limit and is internally set to 6A (RS2 = 0.015Ω). IMAX
protects against sudden overcurrent faults.
Dropout Operation
The MAX1908/MAX8724/MAX8765/MAX8765A have 99%
duty-cycle capability with a 5ms (max) on-time and 0.3µs
(min) off-time. This allows the charger to achieve dropout
performance limited only by resistive losses in the DC-DC
converter components (D1, N1, RS1, and RS2, Figure 1).
Replacing diode D1 with a p-channel MOSFET driven by
ACOK improves dropout performance (Figure 2). The
dropout voltage is set by the difference between DCIN
and CSIN. When the dropout voltage falls below 100mV,
the charger is disabled; 200mV hysteresis ensures that
the charger does not turn back on until the dropout volt-
age rises to 300mV.
If, during the off-time, the inductor current goes to zero,
ZCMP = high, both the high- and low-side MOSFETs
are turned off until another cycle is ready to begin.
There is a minimum 0.3µs off-time when the (V
-
DCIN
≥ 0.88 ×
V
V
) differential becomes too small. If V
BATT
DCIN
BATT
, then the threshold for minimum off-time is
is fixed at 0.3µs. A maximum on-
reached and the t
OFF
Compensation
Each of the three regulation loops—input current limit,
charging current limit, and charging voltage limit—are
compensated separately using CCS, CCI, and CCV,
respectively.
time of 5ms allows the controller to achieve > 99% duty
cycle in continuous-conduction mode. The switching
frequency in this mode varies according to the equation:
1
f =
L × I
RIPPLE
+ 0.3µs
V
− V
(
)
CSSN
BATT
Maxim Integrated
21
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
where R varies with load according to R = V /I
BATT CHG.
L
L
Output zero due to output capacitor ESR:
BATT
1
f
=
GM
OUT
Z _ESR
2πR
× C
OUT
ESR
The loop transfer function is given by:
LTF = GM × R × GMV × R ×
OGMV
R
R
L
ESR
CCV
OUT
L
GMV
C
OUT
1+ sC
× R
1+ sC × R
(
)(
)
OUT
ESR
CV
CV
1+ sC × R
1+ sC
× R
L
(
)(
)
CV
OGMV
OUT
R
CV
R
OGMV
REF
Assuming the compensation pole is a very low
frequency, and the output zero is a much higher fre-
quency, the crossover frequency is given by:
C
CV
GMV × R
× GM
OUT
CV
f
=
CO_CV
Figure 5. CCV Loop Diagram
2πC
OUT
CCV Loop Definitions
Compensation of the CCV loop depends on the para-
meters and components shown in Figure 5. C and
To calculate R and C values of the circuit of Figure 2:
Cells = 4
CV
CV
CV
C
OUT
= 22µF
R
are the CCV loop compensation capacitor and
CV
V
I
= 16.8V
= 2.5A
BATT
CHG
series resistor. R
(ESR) of the charger output capacitor (C
equivalent charger output load, where R = V
CHG
is the equivalent series resistance
ESR
). R is the
L
OUT
/
BATT
GMV = 0.125µA/mV
L
I
. The equivalent output impedance of the GMV
GM
= 3.33A/V
OUT
amplifier, R
≥ 10MΩ. The voltage amplifier
OGMV
R
OGMV
= 10MΩ
transconductance, GMV = 0.125µA/mV. The DC-DC
converter transconductance, GM = 3.33A/V:
f = 400kHz
OUT
Choose crossover frequency to be 1/5th the
MAX1908’s 400kHz switching frequency:
1
GM
=
OUT
A
× RS2
CSI
GMV × R
× GM
OUT
CV
f
=
= 80kHz
CO_CV
2πC
OUT
where A
= 20, and RS2 is the charging current-
CSI
sense resistor in the Typical Application Circuits.
Solving yields R = 26kΩ.
CV
The compensation pole is given by:
Conservatively set R = 1kΩ, which sets the crossover
CV
frequency at:
1
f
=
P _CV
f
= 3kHz
2πR
× C
CV
CO_CV
OGMV
Choose the output-capacitor ESR so the output-capacitor
zero is 10 times the crossover frequency:
The compensation zero is given by:
1
1
f
=
R
=
= 0.24Ω
Z _CV
ESR
2πR
× C
CV
2π × 10× f
× C
OUT
CV
CO_CV
The output pole is given by:
1
f
=
= 2.412MHz
Z_ESR
2πR
× C
1
ESR
OUT
f
=
P _OUT
2πR × C
L
OUT
22
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
The 22µF ceramic capacitor has a typical ESR of
CCI Loop Definitions
0.003Ω, which sets the output zero at 2.412MHz.
Compensation of the CCI loop depends on the parame-
ters and components shown in Figure 7. C is the CCI
CI
The output pole is set at:
loop compensation capacitor. A
is the internal gain
CSI
of the current-sense amplifier. RS2 is the charge cur-
1
f
=
= 1.08kHz
P _OUT
rent-sense resistor, RS2 = 15mΩ. R
is the equiva-
OGMI
2πR × C
L
OUT
lent output impedance of the GMI amplifier ≥ 10MΩ.
GMI is the charge-current amplifier transconductance
where:
= 1µA/mV. GM
is the DC-DC converter transcon-
OUT
ductance = 3.3A/V. The CCI loop is a single-pole sys-
∆V
∆I
BATT
CHG
tem with a dominant pole compensation set by f
:
R
=
= Battery ESR
) so it is equivalent to
P_CI
L
1
f
=
P _CI
Set the compensation zero (f
Z_CV
2πR
× C
CI
OGMI
the output pole (f
= 1.08kHz), effectively produc-
P_OUT
ing a pole-zero cancellation and maintaining a single-
pole system response:
The loop transfer function is given by:
R
1
OGMI
LTF = GM
× A × RS2× GMI
CSI
f
=
OUT
Z _CV
1+ sR
× C
2πR
× C
OGMI
CI
CV
CV
Since:
1
C
=
= 147nF
1
CV
2πR × 1.08kHz
GM
=
CV
OUT
A
× RS2
CSI
Choose C
= 100nF, which sets the compensation
CV
The loop transfer function simplifies to:
zero (f
) at 1.6kHz. This sets the compensation pole:
Z_CV
1
R
OGMI
f
=
= 0.16Hz
LTF = GMI ×
P _CV
2πR
× C
CV
1+ sR
× C
OGMV
OGMI
CI
CCV LOOP PHASE
vs. FREQUENCY
CCV LOOP GAIN
vs. FREQUENCY
80
60
-45
-60
40
-75
20
-90
0
-105
-120
-135
-20
-40
-60
1
10
100
1k
10k
100k
1M
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 6. CCV Loop Gain/Phase vs. Frequency
Maxim Integrated
23
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
To calculate the CCI loop compensation pole, C :
CI
GMI = 1µA/mV
CSIP
CSIN
GM
= 3.33A/V
OUT
GM
OUT
R
= 10MΩ
OGMI
RS2
CSI
f = 400kHz
Choose crossover frequency f
to be 1/5th the
CI
CO_
MAX1908/MAX8724/MAX8765/MAX8765A switching
frequency:
CCI
C
GMI
GMI
f
=
= 80kHz
CO_CI
2πC
CI
R
OGMI
CI
Solving for C , C = 2nF.
ICTL
CI CI
To be conservative, set C = 10nF, which sets the
CI
crossover frequency at:
Figure 7. CCI Loop Diagram
GMI
2π10nF
f
=
= 16kHz
CO_CI
The crossover frequency is given by:
GMI
The compensation pole, f
is set at:
P_CI
f
=
CO_CI
2πC
CI
GMI
f
=
= 0.0016Hz
P_CI
2πR
× C
CI
The CCI loop dominant compensation pole:
1
OGMI
CCS Loop Definitions
Compensation of the CCS loop depends on the parame-
ters and components shown in Figure 9. C is the CCS
f
=
P _CI
2πR
× C
CI
OGMI
CS
loop compensation capacitor. A
is the internal gain of
CSS
where the GMI amplifier output impedance, R
10MΩ.
=
OGMI
the current-sense amplifier. RS1 is the input current-
sense resistor, RS1 = 10mΩ. R
is the equivalent
OGMS
output impedance of the GMS amplifier ≥ 10MΩ. GMS is
CCI LOOP GAIN
vs. FREQUENCY
CCI LOOP PHASE
vs. FREQUENCY
100
0
80
60
-15
-30
40
-45
20
-60
0
-75
-20
-40
-60
-90
-105
0.1
1
10 100 1k
FREQUENCY (Hz)
10k 100k 1M
0.1
1
10 100 1k
FREQUENCY (Hz)
10k 100k 1M
24
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
the charge-current amplifier transconductance = 1µA/mV.
GM is the DC-DC converter transconductance =
IN
3.3A/V. The CCS loop is a single-pole system with a dom-
CSSP
CSSN
inant pole compensation set by f
:
P_CS
GM
IN
RS1
CSS
1
f
=
P _CS
2πR
× C
CS
OGMS
The loop transfer function is given by:
CCS
C
R
OGMS
LTF = GM × A
× RS1× GMS×
CSS
GMS
IN
1+ sR
× C
OGMS
CS
R
OGMS
Since:
CS
CLS
1
GM
=
IN
A
× RS1
CSS
Then, the loop transfer function simplifies to:
Figure 9. CCS Loop Diagram
R
OGMS
The CCS loop dominant compensation pole:
1
LTF = GMS×
1+ sR
× C
OGMS
CS
f
=
P _CS
2πR
× C
CS
OGMS
The crossover frequency is given by:
GMS
where the GMS amplifier output impedance, R
10MΩ.
To calculate the CCI loop compensation pole, C
=
OGMS
f
=
CO_CS
2πC
CS
:
CS
GMS = 1µA/mV
GM = 3.33A/V
IN
R
OGMS
= 10MΩ
f = 400kHz
CCS LOOP GAIN
vs. FREQUENCY
CCS LOOP PHASE
vs. FREQUENCY
100
0
-15
-30
-45
-60
-75
-90
80
60
40
20
0
-20
-40
-60
-105
0.1
0.1
1
10 100 1k
FREQUENCY (Hz)
10k 100k 1M
1
10 100 1k
FREQUENCY (Hz)
10k 100k 1M
Figure 10. CCS Loop Gain/Phase vs. Frequency
Maxim Integrated
25
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Choose crossover frequency f
MAX1908/MAX8724/MAX8765/MAX8765A switching
frequency:
to be 1/5th the
where:
or:
CO_CS
t
= 2.5µs × (V
– V
)/V
OFF
DCIN
BATT DCIN
V
BATT
< 0.88 × V
DCIN
GMS
f
=
= 80kHz
CO_CS
2πC
t
= 0.3µs
OFF
CS
V
> 0.88 × V
BATT
DCIN
Solving for C , C = 2nF.
CS CS
Figure 11 illustrates the variation of ripple current vs.
battery voltage when charging at 3A with a fixed 19V
input voltage.
To be conservative, set C
crossover frequency at:
= 10nF, which sets the
CS
Higher inductor values decrease the ripple current.
Smaller inductor values require higher saturation cur-
rent capabilities and degrade efficiency. Designs for
GMS
2π10nF
f
=
= 16kHz
CO_CS
ripple current, I
= 0.3 × I
usually result in a
RIPPLE
CHG
The compensation pole, f
is set at:
P_CS
good balance between inductor size and efficiency.
Input Capacitor
Input capacitor C1 must be able to handle the input
ripple current. At high charging currents, the DC-DC
converter operates in continuous conduction. In this
case, the ripple current of the input capacitor can be
approximated by the following equation:
1
f
=
= 0.0016Hz
P_CS
2πR
× C
CS
OGMS
Component Selection
Table 3 lists the recommended components and refers
to the circuit of Figure 2. The following sections
describe how to select these components.
2
I
= I
D − D
C1 CHG
Inductor Selection
Inductor L1 provides power to the battery while it is
being charged. It must have a saturation current of at
where:
= input capacitor ripple current.
I
least the charge current (I
), plus 1/2 the current rip-
C1
CHG
ple I
:
RIPPLE
D = DC-DC converter duty ratio.
= battery-charging current.
I
= I
+ (1/2) I
CHG RIPPLE
SAT
I
CHG
Ripple current varies according to the equation:
Input capacitor C1 must be sized to handle the maxi-
mum ripple current that occurs during continuous con-
duction. The maximum input ripple current occurs at
50% duty cycle; thus, the worst-case input ripple cur-
I
= (V
) × t
/L
OFF
RIPPLE
BATT
RIPPLE CURRENT vs.
BATTERY VOLTAGE
rent is 0.5 × I
. If the input-to-output voltage ratio is
CHG
such that the DC-DC converter does not operate at a
50% duty cycle, then the worst-case capacitor current
occurs where the duty cycle is nearest 50%.
1.5
1.0
0.5
0
3 CELLS
The input capacitor ESR times the input ripple current
sets the ripple voltage at the input, and should not
exceed 0.5V ripple. Choose the ESR of C1 according to:
4 CELLS
0.5V
ESR
<
C1
I
C1
V
= 19V
VCTL = ICTL = LDO
DCIN
The input capacitor size should allow minimal output
voltage sag at the highest switching frequency:
8
9
10 11 12 13 14 15 16 17 18
(V)
V
BATT
I
dV
dt
C1
2
= C1
Figure 11. Ripple Current vs. Battery Voltage
26
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
where dV is the maximum voltage sag of 0.5V while
delivering energy to the inductor during the high-side
MOSFET on-time, and dt is the period at highest oper-
ating frequency (400kHz):
the MOSFET. Choose N1b with either an internal
Schottky diode or body diode capable of carrying the
maximum charging current during the dead time. The
Schottky diode D3 provides the supply current to the
high-side MOSFET driver.
I
2.5µs
C1
C1>
×
Layout and Bypassing
2
0.5V
Bypass DCIN with a 1µF capacitor to power ground
(Figure 1). D2 protects the MAX1908/MAX8724/
MAX8765/MAX8765A when the DC power source input
is reversed. A signal diode for D2 is adequate because
DCIN only powers the internal circuitry. Bypass LDO,
REF, CCV, CCI, CCS, ICHG, and IINP to analog
ground. Bypass DLOV to power ground.
Both tantalum and ceramic capacitors are suitable in
most applications. For equivalent size and voltage
rating, tantalum capacitors have higher capacitance,
but also higher ESR than ceramic capacitors. This
makes it more critical to consider ripple current and
power-dissipation ratings when using tantalum capaci-
tors. A single ceramic capacitor often can replace two
tantalum capacitors in parallel.
Good PC board layout is required to achieve specified
noise, efficiency, and stable performance. The PC
board layout artist must be given explicit instructions—
preferably, a pencil sketch showing the placement of
the power-switching components and high-current rout-
ing. Refer to the PC board layout in the MAX1908 eval-
uation kit for examples. Separate analog and power
grounds are essential for optimum performance.
Output Capacitor
The output capacitor absorbs the inductor ripple cur-
rent. The output capacitor impedance must be signifi-
cantly less than that of the battery to ensure that it
absorbs the ripple current. Both the capacitance and
ESR rating of the capacitor are important for its effec-
tiveness as a filter and to ensure stability of the DC-DC
converter (see the Compensation section). Either tanta-
lum or ceramic capacitors can be used for the output
filter capacitor.
Use the following step-by-step guide:
1) Place the high-power connections first, with their
grounds adjacent:
MOSFETs and Diodes
Schottky diode D1 provides power to the load when the
AC adapter is inserted. This diode must be able to
deliver the maximum current as set by RS1. For
reduced power dissipation and improved dropout per-
formance, replace D1 with a p-channel MOSFET (P1)
as shown in Figure 2. Take caution not to exceed the
a) Minimize the current-sense resistor trace lengths,
and ensure accurate current sensing with Kelvin
connections.
b) Minimize ground trace lengths in the high-current
paths.
c) Minimize other trace lengths in the high-current
paths.
maximum V
limit the V
of P1. Choose resistors R11 and R12 to
GS
.
d) Use > 5mm wide traces.
GS
The n-channel MOSFETs (N1a, N1b) are the switching
devices for the buck controller. High-side switch N1a
should have a current rating of at least the maximum
charge current plus one-half the ripple current and
e) Connect C1 to high-side MOSFET (10mm max
length).
f) LX node (MOSFETs, inductor (15mm max
length)).
have an on-resistance (R
) that meets the power
DS(ON)
Ideally, surface-mount power components are flush
against one another with their ground terminals
almost touching. These high-current grounds are
then connected to each other with a wide, filled zone
of top-layer copper, so they do not go through vias.
dissipation requirements of the MOSFET. The driver for
N1a is powered by BST. The gate-drive requirement for
N1a should be less than 10mA. Select a MOSFET with a
low total gate charge (Q
) and determine the
GATE
required drive current by I
= Q
× f (where f is
GATE
GATE
the DC-DC converter’s maximum switching frequency).
The resulting top-layer power ground plane is
connected to the normal ground plane at the
MAX1908/MAX8724/MAX8765/MAX8765As’ back-
side exposed pad. Other high-current paths should
also be minimized, but focusing primarily on short
ground and current-sense connections eliminates
most PC board layout problems.
The low-side switch (N1b) has the same current rating
and power dissipation requirements as N1a, and
should have a total gate charge less than 10nC. N2 is
used to provide the starting charge to the BST capacitor
(C15). During the dead time (50ns, typ) between N1a
and N1b, current is carried by the body diode of
Maxim Integrated
27
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
2) Place the IC and signal components. Keep the
main switching node (LX node) away from sensitive
analog components (current-sense traces and REF
capacitor). Important: The IC must be no further
than 10mm from the current-sense resistors.
bypass capacitors close to the IC. The bulk capac-
itors can be placed further away.
3) Use a single-point star ground placed directly
below the part at the backside exposed pad of the
MAX1908/MAX8724/MAX8765/MAX8765A.
Connect the power ground and normal ground to
this node.
Keep the gate-drive traces (DHI, DLO, and BST)
shorter than 20mm, and route them away from the
current-sense lines and REF. Place ceramic
Table 3. Component List for Circuit of Figure 2
DESIGNATION QTY
DESCRIPTION
Schottky diode
DESIGNATION QTY
DESCRIPTION
10µF, 50V 2220-size ceramic
capacitors
D3
1
Central Semiconductor CMPSH1-4
C1
C4
2
1
TDK C5750X7R1H106M
10µH, 4.4A inductor
Sumida CDRH104R-100NC
TOKO 919AS-100M
L1
1
22µF, 25V 2220-size ceramic
capacitor
TDK C5750X7R1E226M
Dual, n-channel, 8-pin SO MOSFET
Fairchild FDS6990A or FDS6990S
N1
P1
1
1
1µF, 25V X7R ceramic capacitor
(1206)
Murata GRM31MR71E105K
Taiyo Yuden TMK316BJ105KL
TDK C3216X7R1E105K
Single, p-channel, 8-pin SO MOSFET
Fairchild FDS6675
C5
1
2
4
R5
R6
1
1
1
1
1
1
1
2
1
1
2
1kΩ 5% resistor (0603)
59kΩ 1% resistor (0603)
19.6kΩ 1% resistor (0603)
12kΩ 5% resistor (0603)
15kΩ 5% resistor (0603)
33Ω 5% resistor (0603)
10.5kΩ 1% resistor (0603)
8.25kΩ 1% resistors (0603)
19.1kΩ 1% resistor (0603)
22kΩ 1% resistor (0603)
10kΩ 1% resistors (0603)
0.01µF, 16V ceramic capacitors (0402)
Murata GRP155R71E103K
Taiyo Yuden EMK105BJ103KV
TDK C1005X7R1E103K
R7
C9, C10
R11
R12
R13
0.1µF, 25V X7R ceramic capacitors
(0603)
Murata GRM188R71E104K
TDK C1608X7R1E104K
R14
C11, C14,
C15, C20
R15, R16
R17
1µF, 6.3V X5R ceramic capacitors
(0603)
Murata GRM188R60J105K
Taiyo Yuden JMK107BJ105KA
TDK C1608X5R1A105K
R18
R19, R20
C12, C13, C16
3
0.01Ω 1%, 0.5W 2010 sense resistor
Vishay Dale WSL2010 0.010 1.0%
IRC LRC-LR2010-01-R010-F
RS1
1
10A Schottky diode (D-PAK)
Diodes, Inc. MBRD1035CTL
ON Semiconductor MBRD1035CTL
D1 (optional)
D2
1
1
0.015Ω 1%, 0.5W 2010 sense
resistor
Vishay Dale WSL2010 0.015 1.0%
IRC LRC-LR2010-01-R015-F
RS2
U1
1
1
Schottky diode
Central Semiconductor
CMPSH1–4
MAX1908ETI+, MAX8724ETI+, or
MAX8765ETI+, MAX8765AETI+
28
Maxim Integrated
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Package Information
Chip Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
TRANSISTOR COUNT: 3772
PROCESS: BiCMOS
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
28 TQFN-EP
T2855-6
21-0140
Maxim Integrated
29
MAX1908/MAX8724/MAX8765/MAX8765A
Low-Cost Multichemistry Battery Chargers
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
5
2/03
Initial release
Added the MAX8765A to the data sheet.
—
11/09
1–30
Maxim cannot me responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves he 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.
30
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
©
The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.
2009 Maxim Integrated
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