General Description
The MAX1645 are high-efficiency battery chargers capa-
ble of charging batteries of any chemistry type. It uses the
Intel System Management Bus (SMBus) to control volt-
age and current charge outputs.
When charging lithium-ion (Li+) batteries, the MAX1645
automatically transition from regulating current to regu-
lating voltage. The MAX1645 can also limit line input
current so as not to exceed a predetermined current
drawn from the DC source. A 175s charge safety timer
prevents “runaway charging” should the MAX1645 stop
receiving charging voltage/ current commands.
The MAX1645 employs a next-generation synchronous
buck control circuity that lowers the minimum input-to-
output voltage drop by allowing the duty cycle to
exceed 99%. The MAX1645 can easily charge one to
four series Li+ cells.
Applications
Notebook Computers
Point-of-Sale Terminals
Personal Digital Assistants
Features
♦Input Current Limiting
♦175s Charge Safety Timeout
♦128mA Wake-Up Charge
♦Charges Any Chemistry Battery: Li+, NiCd,
NiMH, Lead Acid, etc.
♦Intel SMBus 2-Wire Serial Interface
♦Compliant with Level 2 Smart Battery Charger
Spec Rev. 1.0
♦+8V to +28V Input Voltage Range
♦Up to 18.4V Battery Voltage
♦11-Bit Battery Voltage Setting
♦±0.8% Output Voltage Accuracy with Internal
Reference
♦3A max Battery Charge Current
♦6-Bit Charge Current Setting
♦99.99% max Duty Cycle for Low-Dropout Operation
♦Load/Source Switchover Drivers
♦>97% Efficiency
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
________________________________________________________________ Maxim Integrated Products 1
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
CVS
PDS
CSSP
CSSN
BST
DHI
INT
LX
DLOV
DLO
PGND
CSIP
CSIN
PDL
SDA
SCL
THM
VDD
DAC
BATT
GND
CCV
CCI
CCS
REF
CLS
LDO
DCIN
QSOP
TOP VIEW
MAX1645
MAX1645A
19-1566; Rev 2; 1/01
PART
MAX1645EEI -40°C to +85°C
TEMP. RANGE PIN-PACKAGE
28 QSOP
Typical Operating Circuit appears at end of data sheet.
SMBus is a trademark of Intel Corp.
Pin Configuration Ordering Information
MAX1645AEEI -40°C to +85°C 28 QSOP
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.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°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.
DCIN, CVS, CSSP, CSSN, LX to GND....................-0.3V to +30V
CSSP to CSSN, CSIP to CSIN ...............................-0.3V to +0.3V
PDS, PDL to GND ...................................-0.3V to (VCSSP + 0.3V)
BST to LX..................................................................-0.3V to +6V
DHI to LX...................................................-0.3V to (VBST + 0.3V)
CSIP, CSIN, BATT to GND .....................................-0.3V to +22V
LDO to GND .....................-0.3V to (lower of 6V or VDCIN + 0.3V)
DLO to GND ...........................................-0.3V to (VDLOV + 0.3V)
REF, DAC, CCV, CCI, CCS, CLS to GND.....-0.3V to (VLDO + 0.3V)
VDD, SCL, SDA, INT, DLOV to GND.........................-0.3V to +6V
THM to GND...............................................-0.3V to (VDD + 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
LDO Continuous Current.....................................................50mA
Continuous Power Dissipation (TA= +70°C)
28-Pin QSOP (derate 10.8mW/°C above +70°C).........860mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature.........................................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
8V < VDCIN < 28V
VCVS referred to VBATT, VCVS rising
VPDS = VCSSP - 2V, VDCIN = 16V
PDS = CSSP
IPDS = 0
0 < VDCIN < 6V, VDD = 5V, VSCL = 5V,
VSDA = 5V
VCVS referred to VBATT
VCVS referred to VBATT, VCVS falling
When the SMB res-
ponds to commands
8V < VDCIN < 28V
8V < VDCIN < 28V
When AC_PRESENT
switches
When ICHARGE drops to 128mA
8V < VDCIN < 28V, 0 < ILDO < 15mA
0 < IREF < 200µA
CONDITIONS
mV
-150 -100 -50
VPDL-OFF
PDL Load Switch Turn-Off
Threshold
mA
10 50
PDS Turn-Off Current
µA
100 150 300
PDS Turn-On Current
V
81012
PDS Output Low Voltage, PDS
Below CSSP
mV
100 200 300
VPDS-HYS
PDS Charging Source Switch
Threshold Hysteresis
mV
50 100 150
VPDS-OFF
PDS Charging Source Switch
Turn-Off Threshold
V
2.4 2.8
BATT Undervoltage Threshold
(Note 2)
V
4.066 4.096 4.126
VREF
REF Output Voltage
mA
1.7 6
IDCIN
DCIN Supply Current
V
828
VDCIN
µA
80 150
IDD
VDD Quiescent Current
2.1 2.5 V
2.55 2.8
VDD Undervoltage Threshold
V
2.8 5.65
VDD Input Voltage Range
(Note 1)
mA
0.7 2
DCIN Supply Current Charging
Inhibited
V
7.5 7.85
DCIN Undervoltage Threshold 7 7.4
V
5.15 5.4 5.65
VLDO
LDO Output Voltage
UNITSMIN TYP MAXSYMBOLPARAMETER
DCIN rising
DCIN falling
VDD rising
VDD falling
DCIN Typical Operating Range
GENERAL SPECIFICATIONS
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°C.)
CCV/CCI/CCS Clamp Voltage
(Note 4) VCCV = VCCI = VCCS = 0.25V to 2V 150 300 600 mV
61.6 128 194.4
VBATT = 1V,
RCSI = 50mΩ
VBATT = 1V,
RCSI = 50mΩ
MAX1645A
CSSN Input Bias Current -100 35 100 mAVCSSP = CCSSN = VDCIN = 0 to 28V
VCLS = 2.048V
VCLS = 4.096V
ChargingCurrent() =
0x0080
ChargingCurrent() =
0x0BC0
DCIN Source Current Limit
(Note 3)
CLS Input Bias Current -1 0.05 1 µA
Battery Voltage-Error Amp
Transconductance 0.111 0.222 0.444 µA/mV
Battery Current-Error Amp
Transconductance 0.5 1 2 µA/mV
Input Current-Error Amp
Transconductance 0.5 1 2
PARAMETER SYMBOL MIN TYP MAX UNITS
8.333 8.4 8.467
12.492 12.592 12.692 VBATT Full-Charge Voltage V0
16.666 16.8 16.934
CVS Input Bias Current 620
µA
4.150 4.192 4.234
BATT Charge Current (Note 3) I0
2.798 3.008 3.218 A
61.6 128 194.4 mA
4.714 5.12 5.526 A
PDL Turn-Off Current
PDL Load Switch Threshold
Hysteresis VPDL-HYS 100 200 300 mV
612 mA
PDL Turn-On Resistance 50 100 150 kΩ
2.282 2.56 2.838
BATT Undervoltage Charge
Current
20 128 200
mA
BATT/CSIP/CSIN Input Voltage
Range 020
V
Total BATT Input Bias Current -700 700 µA
Total BATT Quiescent Current -100 100 µA
Total BATT Standby Current -5 5 µA
CSSP Input Bias Current -100 540 1000 µA
CSSP/CSSN Quiescent Current -1 1 µA
Battery Voltage-Error Amp DC
Gain 200 500 V/V
µA/mV
VCLS = VREF/2 to VREF
From BATT to CCV, ChargingVoltage() =
0x41A0, VBATT = 16.8V
From CSIP/SCIN to CCI, ChargingCurrent() =
0x0BC0, VCSIP - VCSIN = 150.4mV
CONDITIONS
ChargingVoltage() = 0x20D0
MAX1645
ChargingVoltage() = 0x3130
ChargingVoltage() = 0x41A0
VCVS = 28V
ChargingVoltage() = 0x1060
RCS = 50mΩ
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V
RCSS = 40mΩ
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V, charge inhibited
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V, VDCIN = 0
VCSSP = VCSSN = VDCIN = 0 to 28V
VCVS referred to VBATT
VCSSP = VCSSN = 28V, VDCIN = 0
VCSSN - VPDL = 1V
From BATT to CCV
From CSSP/CSSN to CCS, VCLS = 2.048V,
VCSSP - VCSSN = 102.4mV
PDL to GND
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
4 _______________________________________________________________________________________
VSDA = 0.4V
All 4 comparators, VDD = 2.8V to 5.65V
VDD = 2.8V to 5.65V, VTHM falling
VDD = 2.8V to 5.65V, VTHM falling
DLO high or low, VDLOV = 4.5V
DHI high or low, VBST - VLX = 4.5V
VDD = 2.8V to 5.65V, VTHM falling
VDD = 2.8V to 5.65V, VTHM falling
RCSI = 50mΩ
VDLOV = VLDO, DLO low
VDCIN = 28V, VBATT = VLX = 20V
VDCIN = 0, VBATT = VLX = 20V
VTHM = 4% of VDD to 96% of VDD,
VDD = 2.8V to 5.65V
DHI high
CONDITIONS
mA
6
SDA Output Low Sink Current
µA
-1 1
SDA/SCL Input Bias Current
mV
220
SDA/SCL Input Hysteresis
V
1.4
SDA/SCL Input High Voltage
V
0.6
SDA/SCL Input Low Voltage
1
Thermistor Comparator
Threshold Hysteresis
6 7.5 9
Thermistor Underrange
Threshold
% of VDD
22 23.5 25
Thermistor Hot Threshold
74 75.5 77
Thermistor Cold Threshold
89.5 91 92.5
Thermistor Overrange Threshold
µA-1 1THM Input Bias Current
ms
51015
tON
Maximum On-Time
µs
1 1.25 1.5
tOFF
Minimum Off-Time
Ω
614
DLO Output Resistance
Ω
6 14
DHI Output Resistance
A
5.0 6.0 7.0
Inductor Peak Current Limit
µA
5 10
DLOV Supply Current
%
99 99.99
Maximum Duty Cycle
µA
200 500
LX Input Bias Current
µA
1
LX Input Quiescent Current
µA
615
BST Supply Current
UNITSMIN TYP MAXSYMBOLPARAMETER
IINT = 1mA
VINT = 5.65V
mV
25 200
µA
1
INT Output High Leakage
INT Output Low Voltage
ns
0
tHD:DAT
SDA Hold Time from SCL
ns
250
tSU:DAT
SDA Setup Time from SCL
µs
4
tHIGH
SCL High Period
µs
4.7
tLOW
SCL Low Period
µs
4.7
tSU:STA
Start Condition Setup Time
from SCL
µs
4
tHD:STA
Start Condition Hold Time
from SCL
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°C.)
% of VDD
% of VDD
% of VDD
% of VDD
DC-TO-DC CONVERTER SPECIFICATIONS
THERMISTOR COMPARATOR SPECIFICATIONS
SMB INTERFACE LEVEL SPECIFICATIONS (VDD = 2.8V to 5.65V)
SMB INTERFACE TIMING SPECIFICATIONS (VDD = 2.8V to 5.65V, Figures 4 and 5)
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°C.)
CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER
s
140 175 210
tWDT
Maximum Charge Period
Without a ChargingVoltage() or
Charging Current() Loaded
µs
1
tDV
SDA Output Data Valid from SCL
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
PARAMETER SYMBOL MIN MAX UNITS
LDO Output Voltage VLDO 5.15 5.65 V
7
DCIN Undervoltage Threshold 7.85 V
DCIN Supply Current Charging
Inhibited 2mA
VDD Input Voltage Range
(Note 1) 2.8 5.65 V
VDD Undervoltage Threshold 2.8 V
2.1
VDD Quiescent Current IDD 150 µA
DCIN Typical Operating Range VDCIN 828
V
DCIN Supply Current IDCIN 6mA
REF Output Voltage VREF 4.035 4.157 V
BATT Undervoltage Threshold
(Note 2) 2.4 2.8 V
PDS Charging Source Switch
Turn-Off Threshold VPDS-OFF 50 150 mV
PDS Charging Source Switch
Threshold Hysteresis VPDS-HYS 100 300 mV
PDS Output Low Voltage, PDS
Below CSSP 812
V
PDS Turn-On Current 100 300 µA
PDS Turn-Off Current 10 mA
PDL Load Switch Turn-Off
Threshold VPDL-OFF -150 -50 mV
PDL Load Switch Threshold
Hysteresis VPDL-HYS 100 300 mV
PDL Turn-Off Current 6mA
CONDITIONS
0 < IREF < 200µA
8V < VDCIN < 28V, 0 < ILDO < 15mA
When ICHARGE drops to 128mA
When AC_PRESENT
switches
8V < VDCIN < 28V
8V < VDCIN < 28V
When the SMB res-
ponds to commands
VCVS referred to VBATT, VCVS falling
VCVS referred to VBATT
0 < VDCIN < 6V, VDD = 5V, VSCL = 5V,
VSDA = 5V
IPDS = 0
PDS = CSSP
VPDS = VCSSP - 2V, VDCIN = 16V
VCVS referred to VBATT, VCVS rising
VCVS referred to VBATT
VCSSN - VPDL = 1V
8V < VDCIN < 28V
DCIN rising
DCIN falling
VDD rising
VDD falling
GENERAL SPECIFICATIONS
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
Maximum Duty Cycle 99 %
Minimum Off-Time tOFF 1 1.5 µs
Maximum On-Time tON 515
ms
PARAMETER SYMBOL MIN MAX UNITS
4.124 4.260
8.266 8.534
12.391 12.793
BATT Full-Charge Voltage V0
16.532 17.068
V
BATT Charge Current (Note 3) I0
2.608 3.408 A
15.2 240.8 mA
DCIN Source Current Limit
(Note 3)
4.358 5.882 A
2.054 3.006
CVS Input Bias Current
PDL Turn-On Resistance 50 150 kΩ
20 µA
BATT Undervoltage Charge
Current 20 200 mA
BATT/CSIP/CSIN Input Voltage
Range 020
V
Total BATT Input Bias Current -700 700 µA
Total BATT Quiescent Current -100 100 µA
Total BATT Standby Current -5 5 µA
CSSP/Input Bias Current -100 1000 µA
CSSP/CSSN Quiescent Current -1 1 µA
Battery Voltage-Error Amp DC
Gain 200 V/V
CLS Input Bias Current -1 1 µA
Battery Voltage-Error Amp
Transconductance 0.111 0.444 µA/mV
Battery Current-Error Amp
Transconductance 0.5 2 µA/mV
Input Current-Error Amp
Transconductance 0.5 2 µA/mV
CCV/CCI/CCS Clamp Voltage
(Note 4) 150 600 mV
CONDITIONS
VBATT = 1V, RCSI = 50mΩ
ChargingVoltage() = 0x1060
ChargingVoltage() = 0x20D0
ChargingVoltage() = 0x3130
ChargingVoltage() = 0x41A0
RCSI = 50mΩ
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V, charge inhibited
RCSS = 40mΩ
Total of IBATT, ICSIP, and ICSIN;
VBATT = 0 to 20V, VDCIN = 0
VCSSP = VCSSN = VDCIN = 28V
VCSSP = VCSSN = 28V, VDCIN = 0
PDL to GND
From BATT to CCV
VCVS = 28V
VCLS = VREF/2 to VREF
From BATT to CCV, ChargingVoltage() =
0x41A0, VBATT = 16.8V
From CSIP/CSIN to CCI, ChargingCurrent() =
0x0BC0, VCSIP -VCSIN = 150.4mV
From CSSP/CSSN to CCS, VCLS = 2.048V,
VCSSP - VCSSN = 102.4mV
VCCV = VCCI = VCCS = 0.25V to 2V
ChargingCurrent() =
0x0BC0
ChargingCurrent() =
0x0080
VCLS = 4.096V
VCLS = 2.048V
CSSN Input Bias Current -100 100 µAVCSSP = VCSSN = VDCIN = 28V
DC-TO-DC CONVERTER SPECIFICATIONS
ERROR AMPLIFIER SPECIFICATIONS
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
_______________________________________________________________________________________ 7
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
SDA Hold Time from SCL tHD:DAT 0ns
Start Condition Hold Time
from SCL
Start Condition Setup Time
from SCL tSU:STA 4.7 µs
tHD:STA 4µs
SDA Setup Time from SCL tSU:DAT 250 ns
PARAMETER SYMBOL MIN MAX UNITS
DLO Output Resistance 14 Ω
DHI Output Resistance 14 Ω
Inductor Peak Current Limit 5.0 7.0 A
DLOV Supply Current 10 µA
THM Input Bias Current -1 1 µA
Thermistor Overrange Threshold 89.5 92.5
Thermistor Cold Threshold 74 77
LX Input Quiescent Current
LX Input Bias Current 500 µA
1µA
BST Supply Current 15 µA
Thermistor Hot Threshold 22 25
% of VDD
Thermistor Underrange
Threshold 69
SDA/SCL Input Low Voltage 0.6 V
SDA/SCL Input High Voltage 1.4 V
SDA/SCL Input Bias Current -1 1 µA
SDA Output Low Sink Current 6mA
INT Output High Leakage 1µA
INT Output Low Voltage 200 mV
SCL High Period tHIGH 4µs
SCL Low Period tLOW 4.7 µs
CONDITIONS
VDD = 2.8V to 5.65V, VTHM falling
DLO high or low, VDLOV = 4.5V
VDD = 2.8V to 5.65V, VTHM falling
DHI high or low, VBST - VLX = 4.5V
RCSI = 50mΩ
VDLOV = VLDO, DLO low
VTHM = 4% of VDD to 96% of VDD,
VDD = 2.8V to 5.65V
VDD = 2.8V to 5.65V, VTHM falling
VDD = 2.8V to 5.65V, VTHM falling
VDCIN = 28V, VBATT = VLX = 20V
VSDA = 0.4V
VDCIN = 0, VBATT = VLX = 20V
VINT = 5.65V
IINT = 1mA
DHI high
% of VDD
% of VDD
% of VDD
SMB INTERFACE LEVEL SPECIFICATIONS (VDD = 2.8V to 5.65V)
THERMISTOR COMPARATOR SPECIFICATIONS
SMB INTERFACE TIMING SPECIFICATIONS (VDD = 2.8V to 5.65V, Figures 4 and 5)
4.090
4.092
4.096
4.094
4.098
4.100
0 10050 150 200 250 300
REFERENCE VOLTAGE LOAD REGULATION
MAX1645 toc05
LOAD CURRENT (µA)
VREF (V)
5.20
5.30
5.25
5.35
5.50
5.55
5.45
5.40
5.60
0 468102 1214161820
LDO LOAD REGULATION
MAX1645 toc04
LOAD CURRENT (mA)
VLDO (V)
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
8 _______________________________________________________________________________________
Typical Operating Characteristics
(Circuit of Figure 1, VDCIN = 20V, TA = +25°C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
(BATTERY REMOVAL AND REINSERTION)
MAX1645 toc01
ChargingVoltage() = 15000mV
ChargingCurrent() = 1000mA
CCI CCI
CCI
16V
14V
12V
1A
0
1.5V
VCCV/VCCI IBATT VBATT
1V
0.5V
2ms/div
CCV
CCV
CCV
BATTERY REMOVED BATTERY INSERTED
LOAD-TRANSIENT RESPONSE
(STEP IN LOAD CURRENT)
MAX1645 toc02
ChargingCurrent() = 3008mA
VBATT = 16V
LOAD STEP: 0A TO 2A
ISOURCE LIMIT = 2.5A
CCS CCS
CCS
4A
2A
0
2A
1V
0
1ms/div
CCI CCI
CCI
VCCV/VCCI IBATT VBATT
5.20
5.25
5.30
5.35
5.40
5.45
5.50
5.55
5.60
5 1015202530
LDO LINE REGULATION
MAX1645 toc03
VDCIN (V)
VLDO (V)
ILOAD = 0
4.080
4.090
4.085
4.100
4.095
4.105
4.110
-40 20 40-20 0 60 80 100
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX1645 toc06
TEMPERATURE (°C)
VREF (V)
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VDD = +3.3V, VBATT = +16.8V, VDCIN = +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)
Note 1: Guaranteed by meeting the SMB timing specs.
Note 2: The charger reverts to a trickle-charge mode of ICHARGE = 128mA below this threshold.
Note 3: Does not include current-sense resistor tolerance.
Note 4: Voltage difference between CCV, and CCI or CCS when one of these three pins is held low and the others try to pull high.
Maximum Charge Period
Without a ChargingVoltage() or
Charging Current() loaded
tWDT 140 210 s
SDA Output Data Valid
from SCL tDV 1µs
PARAMETER SYMBOL MIN MAX UNITSCONDITIONS
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
_______________________________________________________________________________________ 9
50
65
60
55
70
75
80
85
90
95
100
0 1000500 1500 2000 2500 3000
EFFICIENCY vs. BATTERY CURRENT
(VOLTAGE-CONTROL LOOP)
MAX1645 toc07
BATTERY CURRENT (mA)
EFFICIENCY (%)
A: VDCIN = 20V, ChargingVoltage() = 16.8V
B: VDCIN = 16V, ChargingVoltage() = 8.4V
B
A
50
65
60
55
70
75
80
85
90
95
100
0 1000500 1500 2000 2500 3000
EFFICIENCY vs. BATTERY CURRENT
(CURRENT-CONTROL LOOP)
MAX1645 toc08
ChargingCurrent() (CODE)
EFFICIENCY (%)
A: VDCIN = 20V, VBATT = 16.8V
B: VDCIN = 16V, VBATT = 8.4V
A
B
10
1.0
0.1
0.01
0.001
OUTPUT VI CHARACTERISTICS
MAX1645 toc09
LOAD CURRENT (mA)
DROP IN BATT OUTPUT VOLTAGE (%)
0 1500 2000500 1000 2500 3000 3500
ChargingVoltage() = 16,800mV
ChargingCurrent() = 3008mA
-0.3
0
-0.1
-0.2
0.1
0.2
0.3
0000 80004000 12000 16000 20000
BATT VOLTAGE ERROR
vs. ChargingVoltage() CODE
MAX1645 toc10
ChargingVoltage() (CODE)
BATT VOLTAGE ERROR (%)
IBATT = 0
MEASURED AT AVAILABLE CODES
-5
-2
-3
-4
-1
0
1
2
3
4
5
0 1000500 1500 2000 2500 3000
CURRENT-SETTING ERROR
vs. ChargingCurrent() CODE
MAX1645 toc11
ChargingCurrent() (CODE)
BATT CURRENT ERROR (%)
VBATT = 12.6V
MEASURED AT AVAILABLE CODES
0
1.0
0.5
2.0
1.5
3.0
2.5
3.5
0 1.00.5 1.5 2.0 2.5
SOURCE/BATT CURRENT vs. LOAD CURRENT
WITH SOURCE CURRENT LIMIT
MAX1645 toc12
LOAD CURRENT (A)
SOURCE/BATT CURRENT (A)
IIN
IBATT
VCLS = 2V
RCSS = 40mΩ
VBATT = 16.8V
SOURCE CURRENT LIMIT = 2.5A
ChargingCurrent() = 3008mA
ChargingVoltage() = 18,432mV
0
1.0
0.5
2.0
1.5
3.0
2.5
3.5
042 6 8 101214161820
SOURCE/BATT CURRENT vs. VBATT
WITH SOURCE CURRENT LIMIT
MAX1645 toc13
VBATT (V)
SOURCE/BATT CURRENT (A)
IIN
IBATT
ILOAD = 2A
VCLS = 2V
RCSS = 40mΩ
ChargingVoltage() = 18,432mV
ChargingCurrent() = 3008mA
SOURCE CURRENT LIMIT = 2.5A
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VDCIN = 20V, TA = +25°C, unless otherwise noted.)
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
10 ______________________________________________________________________________________
Pin Description
Battery Voltage OutputBATT9
DAC Voltage Output DAC10
Logic Circuitry Supply Voltage Input (2.8V to 5.65V) VDD
11
Thermistor Voltage Input THM12
SMB Clock Input SCL13
Charging Source Compensation Capacitor Connection. Connect a 0.01µF capacitor from CCS to GND.CCS5
Battery Current-Loop Compensation Capacitor Connection. Connect a 0.01µF capacitor from CCI to GND. CCI6
Battery Voltage-Loop Compensation Capacitor Connection. Connect a 10kΩresistor in series with a 0.01µF
capacitor to GND.
CCV7
Ground GND8
4.096V Reference Voltage OutputREF4
Source Current Limit InputCLS3
PIN
5.4V Linear-Regulator Voltage Output. Bypass with a 1µF capacitor to GND.LDO2
DC Supply Voltage InputDCIN1
FUNCTIONNAME
Inductor Voltage Sense InputLX22
High-Side NMOS Driver OutputDHI23
High-Side Driver Bootstrap Voltage Input. Bypass with 0.1µF capacitor to LX.BST24
Charging Source Current-Sense Negative InputCSSN25
Charging Source Current-Sense Positive InputCSSP26
Battery Current-Sense Positive InputCSIP18
Power GroundPGND19
Low-Side NMOS Driver OutputDLO20
Low-Side NMOS Driver Supply Voltage. Bypass with 0.1µF capacitor to GND.DLOV21
Battery Current-Sense Negative InputCSIN17
PMOS Load Switch Driver OutputPDL16
Interrupt Output. Open-drain output. Needs external pull-up.
INT
15
SMB Data Input/Output. Open-drain output. Needs external pull-up.SDA14
Charging Source PMOS Switch Driver OutputPDS27
Charging Source Voltage InputCVS28
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 11
Detailed Description
The MAX1645/MAX1645A consist of current-sense
amplifiers, an SMBus interface, transconductance
amplifiers, reference circuitry, and a DC–DC converter
(Figure 2). The DC–DC converter generates the control
signals for the external MOSFETs to maintain the volt-
age and the current set by the SMBus interface. The
MAX1645/MAX1645A feature a voltage-regulation loop
and two current-regulation loops. The loops operate
independently of each other. The voltage-regulation
loop monitors BATT to ensure that its voltage never
exceeds the voltage set point (V0). The battery current-
regulation loop monitors current delivered to BATT to
ensure that it never exceeds the current-limit set point
(I0). The battery current-regulation loop is in control as
long as BATT voltage is below V0. When BATT voltage
reaches V0, the current loop no longer regulates. A
third loop reduces the battery-charging current when
the sum of the system (the main load) and the battery
charger input current exceeds the charging source cur-
rent limit.
Setting Output Voltage
The MAX1645/MAX1645A voltage DACs have a 16mV
LSB and an 18.432V full scale. The SMBus specifica-
tion allows for a 16-bit ChargingVoltage() command
that translates to a 1mV LSB and a 65.535V full-scale
voltage; therefore, the ChargingVoltage() value corre-
sponds to the output voltage in millivolts. The
MAX1645/MAX1645A ignore the first four LSBs and use
the next 11 LSBs to control the voltage DAC. All codes
greater than or equal to 0b0100 1000 0000 0000
(18432mV) result in a voltage overrange, limiting the
charger voltage to 18.432V. All codes below 0b0000
0100 0000 0000 (1024mV) terminate charging.
Setting Output Current
The MAX1645/MAX1645A current DACs have a 64mA
LSB and a 3.008A full scale. The SMBus specification
allows for a 16-bit ChargingCurrent() command that
translates to a 1mA LSB and a 65.535A full-scale cur-
rent; the ChargingCurrent() value corresponds to the
charging voltage in milliamps. The MAX1645/
MAX1645A drop the first six LSBs and use the next
six LSBs to control the current DAC. All codes above
0b00 1011 1100 0000 (3008mA) result in a current
overrange, limiting the charger current to 3.008A. All
codes below 0b0000 0000 1000 0000 (128mA) turn the
charging current off. A 50mΩsense resistor (R2 in
Figure 1) is required to achieve the correct CODE/cur-
rent scaling.
Input Current Limiting
The MAX1645/MAX1645A limit the current drawn by the
charger when the load current becomes high. The
devices limit the charging current so the AC adapter
voltage is not loaded down. An internal amplifier, CSS,
compares the voltage between CSSP and CSSN to the
voltage at CLS/20. VCLS is set by a resistor-divider
between REF and GND.
The input source current is the sum of the device cur-
rent, the charge input current, and the load current. The
device current is minimal (6mA max) in comparison to
the charge and load currents. The charger input cur-
rent is generated by the DC-DC converter; therefore, the
actual source current required is determined as follows:
ISOURCE = ILOAD + [(ICHARGE ·VBATT) / (VIN ·η)]
where ηis the efficiency of the DC-DC converter (typi-
cally 85% to 95%).
VCLS determines the threshold voltage of the CSS com-
parator. R3 and R4 (Figure 1) set the voltage at CLS.
Sense resistor R1 sets the maximum allowable source
current. Calculate the maximum current as follows:
IMAX = VCLS / (20 ·R1)
(Limit VCSSP - VCSSN to between 102.4mV and
204.8mV.)
The configuration in Figure 1 provides an input current
limit of:
IMAX = (2.048V / 20) / 0.04Ω= 2.56A
LDO Regulator
An integrated LDO regulator provides a +5.4V supply
derived from DCIN, which can deliver up to 15mA of
current. The LDO sets the gate-drive level of the NMOS
switches in the DC-DC converter. The drivers are actu-
ally powered by DLOV and BST, which must be con-
nected to LDO through a lowpass filter and a diode as
shown in Figure 1. See also the MOSFET Drivers sec-
tion. The LDO also supplies the 4.096V reference and
most of the control circuitry. Bypass LDO with a 1µF
capacitor.
VDD Supply
This input provides power to the SMBus interface and
the thermistor comparators. Typically connect VDD to
LDO or, to keep the SMBus interface of the
MAX1645/MAX1645A active while the supply to DCIN is
removed, connect an external supply to VDD.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
12 ______________________________________________________________________________________
LOAD
ADAPTER IN
MAX1645A
CVS
DCIN
REF
CLS
GND
DAC
CCV
CCI
CCS
PDS
CSSP
CSSN
LDO
DHI
LX
DLOV
BST
PGND
DLO
CSIP
CSIN
PDL
BATT
THM
VDD
SCL
SDA
INT
BATTERY
HOST
D4
1N4148
C5
1µF
R13
1k
C23
0.1µF
C7
1µF
R3
100k
R4
100k
C8
0.1µF
C9
0.01µF
R5
10k
C11
0.01µF
C10
0.01µF
P1
FDS6675 D1
1N5821
C2
22µF
C1
22µF
R1
0.04Ω
C20, 1µF
C19, 1µF
R14
4.7Ω
R15
4.7Ω
C6
1µFD3
1N4148
R12
33Ω
C16
0.1µF
C14
0.1µF
N1
FDS6680
N2
FDS6612A
L1
22µH
D2
1N5821
R9
10k
C12
1µFR8
10k
R6
10k
R10
10k
C13
1.5nF
R7
10k
R2
0.05Ω
P2
FDS6675 C4
22µF
C3
22µF
C18
0.1µF
R16
1Ω
R11
1Ω
C24
0.1µF
Figure 1. Typical Application Circuit
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 13
LVC
GMS
PDS
VL
REF
PDL
CSS
CSSP
CSSN
CLS
CSIP
CSIN
VDD
SCL
SDA
THM
CSI
BATT
GMI
GMV
SMB DACI
DACV
TEMP
DC-DC
DHI
BST
DHI
LX
DLOV
DLO
PGND
CCS
CCI
CCV
CVS
BATT
PDS
PDL
DCIN
LDO
REF
GND
DAC
DLO
MAX1645/MAX1645A
INT
Figure 2. Functional Diagram
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
14 ______________________________________________________________________________________
Operating Conditions
The MAX1645/MAX1645A change their operation
depending on the voltages at DCIN, BATT, VDD, and
THM. Several important operating states follow:
•AC Present. When DCIN is > 7.5V, the battery is
considered to be in an AC Present state. In this con-
dition, both the LDO and REF will function properly
and battery charging is allowed. When AC is pre-
sent, the AC_PRESENT bit (bit 15) in the
ChargerStatus() register is set to “1.”
•Power Fail. When DCIN is < BATT + 0.3V, the part is
in the Power Fail state, since the charger doesn’t
have enough input voltage to charge the battery. In
Power Fail, the PDS input PMOS switch is turned off
and the POWER_FAIL bit (bit 13) in the
ChargerStatus() register is set to “1.”
•Battery Present. When THM is < 91% of VDD, the
battery is considered to be present. The MAX1645/
MAX1645A use the THM pin to detect when a battery
is connected to the charger. When the battery is pre-
sent, the BATTERY_PRESENT bit (bit 14) in the
ChargerStatus() register is set to “1” and charging
can proceed. When the battery is not present, all of
the registers are reset. With no battery present, the
charger will perform a "Float" charge to minimize
contact arcing on battery connection. "Float" charge
will still try to regulate the BATT pin voltage at 18.32V
with 128mA of current compliance.
•Battery Undervoltage. When BATT < 2.5V, the bat-
tery is in an undervoltage state. This causes the
charger to reduce its current compliance to 128mA.
The content of the ChargingCurrent() register is unaf-
fected and, when the BATT voltage exceeds 2.7V,
normal charging resumes. ChargingVoltage() is unaf-
fected and can be set as low as 1.024V.
•VDD Undervoltage. When VDD < 2.5V, the VDD sup-
ply is in an undervoltage state, and the SMBus inter-
face will not respond to commands. Coming out of
the undervoltage condition, the part will be in its
Power-On Reset state. No charging will occur when
VDD is under voltage.
SMBus Interface
The MAX1645/MAX1645A receive control inputs from
the SMBus interface. The serial interface complies with
the SMBus specification (refer to the System
Management Bus Specification from Intel Corporation).
Charger functionality complies with the Intel/Duracell
Smart Charger Specification for a Level 2 charger.
The MAX1645/MAX1645A use the SMBus Read-Word
and Write-Word protocols to communicate with the bat-
tery being charged, as well as with any host system
that monitors the battery-to-charger communications as
a Level 2 SMBus charger. The MAX1645/MAX1645A
are SMBus slave devices and do not initiate communi-
cation on the bus. They receive commands and
respond to queries for status information. Figure 3
shows examples of the SMBus Write-Word and Read-
Word protocols, and Figures 4 and 5 show the SMBus
serial-interface timing.
Each communication with these parts begins with the
MASTER issuing a START condition that is defined as a
falling edge on SDA with SCL high and ends with a
STOP condition defined as a rising edge on SDA with
SCL high. Between the START and STOP conditions,
the device address, the command byte, and the data
bytes are sent. The MAX1645/MAX1645As’ device
address is 0x12 and supports the charger commands
as described in Tables 1–6.
Battery Charger Commands
ChargerSpecInfo()
The ChargerSpecInfo() command uses the Read-Word
protocol (Figure 3b). The command code for
ChargerSpecInfo() is 0x11 (0b00010001). Table 1 lists
the functions of the data bits (D0–D15). Bit 0 refers to
the D0 bit in the Read-Word protocol. The
MAX1645/MAX1645A comply with level 2 Smart Battery
Charger Specification Revision 1.0; therefore, the
ChargerSpecInfo() command returns 0x01.
ChargerMode()
The ChargerMode() command uses the Write-Word
protocol (Figure 3a). The command code for
ChargerMode() is 0x12 (0b00010010). Table 2 lists the
functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the Write-Word protocol.
To charge a battery that has a thermistor impedance in
the HOT range (i.e., THERMISTOR_HOT = 1 and THER-
MISTOR_UR = 0), the host must use the Charger
Mode() command to clear HOT_STOP after the battery
is inserted. The HOT_STOP bit returns to its default
power-up condition (“1”) whenever the battery is
removed.
ChargerStatus()
The ChargerStatus() command uses the Read-Word
protocol (Figure 3b). The command code for Charger
Status() is 0x13 (0b00010011). Table 3 describes the
functions of the data bits (D0–D15). Bit 0 refers to the
D0 bit in the Read-Word protocol.
The ChargerStatus() command returns information
about thermistor impedance and the MAX1645/
MAX1645A’s internal state. The latched bits, THERMIS-
TOR_HOT and ALARM_INHIBITED, are cleared when-
MAX1645/MAX1645A
______________________________________________________________________________________ 15
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
Figure 3. SMBus a) Write-Word and b) Read-Word Protocols
Preset to
0b0001001
D7 D0 D15 D8
ChargerMode() = 0x12
ChargingCurrent() = 0x14
ChargerVoltage() = 0x15
AlarmWarning() = 0x16
Preset to
0b0001001
Preset to
0b0001001
D7 D0 D15 D8
ChargerSpecInfo() =
0x11
ChargerStatus() =
0x13
0
1b
ACK
0MSB LSB
1b8 bits
ACK
COMMAND
BYTE
0MSB LSB
1b7 bits
W
SLAVE
ADDRESS
S
0MSB LSB
1b8 bits
ACK
LOW
DATA
BYTE
P
0MSB LSB
1b8 bits
ACK
HIGH
DATA
BYTE
a) Write-Word Format
b) Read-Word Format
Legend:
S = Start Condition or Repeated Start Condition P = Stop Condition
ACK = Acknowledge (logic low) NACK = NOT Acknowledge (logic high)
W = Write Bit (logic low) R = Read Bit (logic high)
MASTER TO SLAVE
SLAVE TO MASTER
HIGH
DATA
BYTE
NACK
8 bits 1b
MSB LSB 1
P
LOW
DATA
BYTE
ACK
8 bits 1b
MSB LSB 0
SLAVE
ADDRESS R
7 bits 1b
MSB LSB 1
ACK
1b
0
COMMAND
BYTE ACK
8 bits 1b
MSB LSB 0
SACK
1b
0
SSLAVE
ADDRESS W
7 bits 1b
MSB LSB 0
ever BATTERY_PRESENT = 0 or ChargerMode() is writ-
ten with POR_RESET = 1. The ALARM_INHIBITED sta-
tus bit can also be cleared by writing a new charging
current OR charging voltage.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
16 ______________________________________________________________________________________
START
CONDITION
MOST SIGNIFICANT
ADDRESS BIT (A6)
CLOCKED INTO SLAVE
A5 CLOCKED
INTO SLAVE
A4 CLOCKED
INTO SLAVE
A3 CLOCKED
INTO SLAVE
tHIGH
tLOW
tHD:STA
tSU:STA tSU:DAT tHD:DAT
SCL
SDA
tSU:DAT tHD:DAT
tDV
SLAVE PULLING
SDA LOW
tDV
MOST SIGNIFICANT BIT
OF DATA CLOCKED
INTO MASTER
ACKNOWLEDGE
BIT CLOCKED
INTO MASTER
R/W BIT
CLOCKED
INTO SLAVE
SCL
SDA
Figure 4. SMBus Serial Interface Timing—Address
Figure 5. SMBus Serial Interface Timing—Acknowledgment
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 17
Returns a “0”Reserved8
Returns a “0”Reserved9
Returns a “0”Reserved10
Returns a “0”Reserved11
Returns a “0”Reserved12
Returns a “0,” indicating no smart battery selector functionalitySELECTOR_SUPPORT4
Returns a “0”Reserved5
Returns a “0”Reserved6
Returns a “0”Reserved7
Returns a “0” for Version 1.0CHARGER_SPEC3
Returns a “0” for Version 1.0CHARGER_SPEC2
Returns a “0” for Version 1.0CHARGER_SPEC1
Returns a “1” for Version 1.0CHARGER_SPEC0
DESCRIPTIONNAME
Returns a “0”Reserved15
Returns a “0”Reserved14
Returns a “0”Reserved13
Table 1. ChargerSpecInfo()
Command: 0x11
BIT
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
18 ______________________________________________________________________________________
Table 2. ChargerMode()
Command: 0x12
*State at chip initial power-on (i.e., VDD from 0 to +3.3V)
13 Not implemented
14 Not implemented
15 Not implemented
NAME DESCRIPTION
0INHIBIT_CHARGE
0* = Allow normal operation; clear the CHG_INHIBITED flip-flop.
1 = Turn off the charger; set the CHG_INHIBITED flip-flop.
The CHG_INHIBITED flip-flop is not affected by any other commands.
1ENABLE_POLLING Not implemented
BIT
2POR_RESET
0 = No change.
1 = Change the ChargingVoltage() to 0xFFFF and the ChargingCurrent()
to 0x00C0; clear the THERMISTOR_HOT and ALARM_INHIBITED flip-
flops.
3RESET_TO_ZERO Not implemented
7Not implemented
6POWER_FAIL_MASK 0* = Interrupt on either edge of the POWER_FAIL status bit.
1 = Do not interrupt because of a POWER_FAIL bit change.
5BATTERY_PRESENT_ MASK 0* = Interrupt on either edge of the BATTERY_PRESENT status bit.
1 = Do not interrupt because of a BATTERY_PRESENT bit change.
4AC_PRESENT_MASK 0* = Interrupt on either edge of the AC_PRESENT status bit.
1 = Do not interrupt because of an AC_PRESENT bit change.
12 Not implemented
11 Not implemented
10 HOT_STOP
0 = The THERMISTOR_HOT status bit does not turn off the charger.
1* = The THERMISTOR_HOT status bit does turn off the charger.
THERMISTOR_HOT is reset by either POR_RESET or
BATTERY_PRESENT = 0 status bit.
9Not implemented
8Not implemented
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 19
NAME FUNCTION
0CHARGE_INHIBITED
0* = Ready to charge Smart Battery.
1 = Charger is inhibited, I(chg) = 0mA.
This status bit returns the value of the CHG_INHIBITED flip-flop.
1MASTER_MODE Always returns “0”
BIT
2VOLTAGE_NOT_REG 0 = Battery voltage is limited at the set point.
1 = Battery voltage is less than the set point.
3CURRENT_NOT_REG 0 = Battery current is limited at the set point.
1 = Battery current is less than the set point.
7VOLTAGE_OR
0 = The ChargingVoltage() value is valid for the MAX1645.
1* = The ChargingVoltage() value exceeds the MAX1645 output range, i.e.,
programmed ChargingVoltage() exceeds 1843mV.
6CURRENT_OR
0* = The ChargingCurrent() value is valid for the MAX1645.
1 = The ChargingCurrent() value exceeds the MAX1645 output range, i.e.,
programmed ChargingCurrent() exceeds 3008mA.
5LEVEL_3 Always returns a “0”
4LEVEL_2 Always returns a “1”
12 ALARM_INHIBITED
Returns the state of the ALARM_INHIBITED flip-flop. This flip-flop is set by either a
watchdog timeout or by writing an AlarmWarning() command with bits 11, 12, 13, 14,
or 15 set. This flip-flop is cleared by BATTERY_PRESENT = 0, writing a “1” into the
POR_RESET bit in the ChargerMode() command, or by receiving successive
ChargingVoltage() and ChargingCurrent() commands. POR: 0.
11 THERMISTOR_UR 0 = THM is > 7.5% of the reference voltage.
1 = THM is < 7.5% of the reference voltage.
10 THERMISTOR_HOT
0 = THM has not dropped to < 23.5% of the reference voltage.
1 = THM has dropped to < 23.5% of the reference voltage.
THERMISTOR_HOT flip-flop cleared by BATTERY_PRESENT = 0 or writing a “1” into
the POR_RESET bit in the ChargerMode() command.
9THERMISTOR_COLD 0 = THM is < 75.5% of the reference voltage.
1 = THM is > 75.5% of the reference voltage.
8THERMISTOR_OR 0 = THM is < 91% of the reference voltage.
1 = THM is > 91% of the reference voltage.
Table 3. ChargerStatus()
15 AC_PRESENT 0 = DCIN is below the 7.5V undervoltage threshold.
1 = DCIN is above the 7.5V undervoltage threshold.
14 BATTERY_PRESENT 0 = No battery is present (based on THM input).
1 = Battery is present (based on THM input).
13 POWER_FAIL 0 = The charging source voltage CVS is above the BATT voltage.
1 = The charging source voltage CVS is below the BATT voltage.
Command: 0x13
*State at chip initial power-on.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
20 ______________________________________________________________________________________
Table 4. ChargerCurrent()
Command: 0x14
NAME FUNCTION
0Not used. Normally a 1mA weight.
1Not used. Normally a 2mA weight.
BIT
2Not used. Normally a 4mA weight.
3Not used. Normally an 8mA weight.
7Charge Current, DACI 1 0 = Adds 0mA of charger-current compliance.
1 = Adds 128mA of charger-current compliance.
6Charge Current, DACI 0 0 = Adds 0mA of charger-current compliance.
1 = Adds 64mA of charger-current compliance, 128mA min.
5Not used. Normally a 32mA weight.
4Not used. Normally a 16mA weight.
12–15 0 = Adds 0mA of charger current compliance.
1 = Sets charger compliance into overrange, 3008mA.
11 Charge Current, DACI 5 0 = Adds 0mA of charger-current compliance.
1 = Adds 2048mA of charger-current compliance, 3008mA max.
10 Charge Current, DACI 4 0 = Adds 0mA of charger-current compliance.
1 = Adds 1024mA of charger-current compliance.
9Charge Current, DACI 3 0 = Adds 0mA of charger-current compliance.
1 = Adds 512mA of charger-current compliance.
8Charge Current, DACI 2 0 = Adds 0mA of charger-current compliance.
1 = Adds 256mA of charger-current compliance.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 21
Table 5. ChargingVoltage()
Command: 0x15
BIT NAME FUNCTION
0Not used. Normally a 1mV weight.
1Not used. Normally a 2mV weight.
PIN
2Not used. Normally a 4mV weight.
3Not used. Normally an 8mV weight.
7Charge Voltage, DACV 3 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 128mV of charger-voltage compliance, 1.024V min.
6Charge Voltage, DACV 2 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 64mV of charger-voltage compliance, 1.024V min.
5Charge Voltage, DACV 1 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 32mV of charger-voltage compliance, 1.024V min.
4Charge Voltage, DACV 0 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 16mV of charger-voltage compliance, 1.024V min.
12 Charge Voltage, DACV 8 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 4096mV of charger-voltage compliance.
11 Charge Voltage, DACV 7 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 2048mV of charger-voltage compliance.
10 Charge Voltage, DACV 6 0 = Adds 0mA of charger-voltage compliance.
1 = Adds 1024mV of charger-voltage compliance.
9Charge Voltage, DACV 5 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 512mV of charger-voltage compliance, 1.024V min.
8Charge Voltage, DACV 4 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 256mV of charger-voltage compliance, 1.024V min.
13 Charge Voltage, DACV 9 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 8192mV of charger-voltage compliance.
14 Charge Voltage, DACV 10 0 = Adds 0mV of charger-voltage compliance.
1 = Adds 16384mV of charger-voltage compliance, 18432mV max.
15 Charge Voltage, Overrange 0 = Adds 0mV of charger-voltage compliance.
1 = Sets charger compliance into overrange, 18432mV.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
22 ______________________________________________________________________________________
Table 6. AlarmWarning()
Command: 0x16
13 OTHER_ALARM 0 = Charge normally
1 = Terminate charging
14 TERMINATE_CHARGE_ ALARM 0 = Charge normally
1 = Terminate charging
15 OVER_CHARGE_ALARM 0 = Charge normally
1 = Terminate charging
BIT NAME DESCRIPTION
0Error Code Not used
1Error Code Not used
BIT
2Error Code Not used
3Error Code Not used
7INITIALIZING Not used
6DISCHARGING Not used
5FULLY_CHARGED Not used
4FULLY_DISCHARGED Not used
12 OVER_TEMP_ALARM 0 = Charge normally
1 = Terminate charging
11 TERMINATE_ DISCHARGE_ALARM 0 = Charge normally
1 = Terminate charging
10 Reserved Not used
9REMAINING_CAPACITY_ ALARM Not used
8REMAINING_TIME_ ALARM Not used
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 23
ChargingCurrent() (POR: 0x0080)
The ChargingCurrent() command uses the Write-Word
protocol (Figure 3a). The command code for Charging-
Current() is 0x14 (0b00010100). The 16-bit binary num-
ber formed by D15–D0 represents the current-limit set
point (I0) in milliamps. However, since the
MAX1645/MAX1645A have 64mA resolution in setting
I0, the D0–D5 bits are ignored as shown in Table 4.
Figure 6 shows the mapping between I0 (the current-
regulation-loop set point) and the ChargingCurrent()
code. All codes above 0b00 1011 1100 0000 (3008mA)
result in a current overrange, limiting the charger current
to 3.008A. All codes below 0b0000 0000 1000 0000
(128mA) turn the charging current off. A 50mΩsense
resistor (R2 in Figure 1) is required to achieve the cor-
rect CODE/current scaling.
The power-on reset value for the ChargingCurrent() reg-
ister is 0x0080; thus, the first time a MAX1645/
MAX1645A is powered on, the BATT current regulates
to 128mA. Any time the battery is removed, the
ChargingCurrent() register returns to its power-on reset
state.
ChargingVoltage() (POR: 0x4800)
The ChargingVoltage() command uses the Write-Word
protocol (Figure 3a). The command code for
ChargingVoltage() is 0x15 (0b00010101). The 16-bit
binary number formed by D15–D0 represents the volt-
age set point (V0) in millivolts; however, since the
MAX1645/MAX1645A have 16mV resolution in setting
V0, the D0, D1, D2, and D3 bits are ignored as shown in
Table 5.
The ChargingVoltage command is used to set the bat-
tery charging voltage compliance from 1.024V to
18.432V. All codes greater than or equal to 0b0100
1000 0000 0000 (18432mV) result in a voltage over-
range, limiting the charger voltage to 18.432V. All codes
below 0b0000 0100 0000 0000 (1024mV) terminate
charge. Figure 7 shows the mapping between V0
(the voltage-regulation-loop set point) and the
ChargingVoltage() code.
The power-on reset value for the ChargingVoltage() reg-
ister is 0x4880; thus, the first time a MAX1645/
MAX1645A are powered on, the BATT voltage regulates
to 18.432V. Any time the battery is removed, the
ChargingVoltage() register returns to its power-on reset
state. The voltage at DAC corresponds to the set com-
pliance voltage divided by 4.5.
AlarmWarning() (POR: Not Alarm)
The AlarmWarning() command uses the Write-Word
protocol (Figure 3a). The command code for
AlarmWarning() is 0x16 (0b00010110). AlarmWarning()
sets the ALARM_INHIBITED status bit in the
MAX1645/MAX1645A if D15, D14, D13, D12, or D11 of
the Write-Word protocol data equals 1. Table 6 summa-
rizes the Alarm-Warning() command’s function. The
ALARM_INHIBITED status bit remains set until the bat-
tery is removed, a ChargerMode() command is written
with the POR_RESET bit set, or new ChargingCurrent()
AND ChargingVoltage() values are written. As long as
ALARM_INHIBITED = 1, the MAX1645/MAX1645A
switching regulators remain off.
Interrupts and Alert Response Address
The MAX1645/MAX1645A request an interrupt by
pulling the INT pin low. An interrupt is normally request-
ed when there is a change in the state of the
ChargerStatus() bits POWER_FAIL (bit 13),
BATTERY_PRESENT (bit 14), or AC_PRESENT (bit 15).
Therefore, the INT pin will pull low whenever the AC
adapter is connected or disconnected, the battery is
inserted or removed, or the charger goes in or out of
dropout. The interrupts from each of the ChargerStatus()
bits can be masked by an associated ChargerMode()
bit POWER_FAIL_MASK (bit 6), BATTERY_PRE-
SENT_MASK (bit 5), or AC_PRESENT_MASK (bit 4).
All interrupts are cleared by sending any command to
the MAX1645/MAX1645A, or by sending a command to
the AlertResponse() address, 0x19, using a modified
Receive Byte protocol. In this protocol, all devices that
set an interrupt will try to respond by transmitting their
address, and the device with the highest priority, or
most leading 0’s, will be recognized and cleared. The
process will be repeated until all devices requesting
interrupts are addressed and cleared. The MAX1645/
6.4
0x0080
128 2048 65535
0x0800 0XFFFF
3008
0x0BC0
1024
0x0400
51.2
150.4
AVERAGE (CSIP-CSIN) VOLTAGE
IN CURRENT REGULATION (mV)
102.4
Figure 6. Average Voltage Between CSIP and CSIN vs. Charging
Current() Code
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
24 ______________________________________________________________________________________
MAX1645A respond to the AlertResponse() address
with 0x13, which is their address and a trailing “1.”
Charger Timeout
The MAX1645/MAX1645A include a timer that termi-
nates charge if the charger has not received a
ChargingVoltage() or ChargingCurrent() command in
175sec. During charging, the timer is reset each time a
ChargingVoltage() or ChargingCurrent() command is
received; this ensures that the charging cycle is not ter-
minated.
If timeout occurs, charging will terminate and both
ChargingVoltage() and ChargingCurrent() commands
are required to restart charging. A power-on reset will
also restart charging at 128mA.
DC-to-DC Converter
The MAX1645/MAX1645A employ a buck regulator with
a boot-strapped NMOS high-side switch and a low-side
NMOS synchronous rectifier.
DC-DC Controller
The control scheme is a constant off-time, variable fre-
quency, cycle-by-cycle current mode. The off-time is
constant for a given BATT voltage; it varies with VBATT
to keep the ripple current constant. During low-dropout
operation, a maximum on-time of 10ms allows the con-
troller to achieve >99% duty cycle with continuous con-
duction. Figure 8 shows the controller functional
diagram.
16.800V
18.432V
VREF = 4.096V
VDCIN > 20V
0
1.024V
00x0400 0x20Dx 0x41A00x313x 0x48000x106x
4.192V
12.592V
ChargingVoltage() D15–D0 DATA
VOLTAGE SET POINT (V0)
8.400V
0xFFFF
Figure 7. ChargingVoltage() Code to Voltage Mapping
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 25
Figure 8. DC-to-DC Converter Functional Diagram
IMAX
RESET
4.0V
0.25V
0.1V
10ms
LVC
CONTROL
ON
CCVCCICCS
GMS
GMI
GMV
DACV
DACI
CLS
DLO
DHI
CSI
1µs
BST
S
RQ
CCMP
ZCMP
IMIN
CHG
RQ
S
CSS
CSSP ADAPTER IN
CSSN
BST
DHI
LX
R1 LDO
CBST
L1
R2
DLO
CSIP
CSIN
COUT
BATT
BATTERY
MAX1645/MAX1645A
RFC
70k
RFI
20k
Q
MOSFET Drivers
The low-side driver output DLO swings from 0V to DLOV.
DLOV is usually connected through a filter to LDO. The
high-side driver output DHI is bootstrapped off LX and
swings from VLX to VBST. When the low-side driver turns
on, BST rises to one diode voltage below DLOV.
Filter DLOV with an RC circuit whose cutoff frequency
is about 50kHz. The configuration in Figure 1 intro-
duces a cutoff frequency of around 48kHz.
f = 1 / 2πRC = 1 / (2 ·π· 33Ω·0.1µF) = 48kHz
Thermistor Comparators
Four thermistor comparators evaluate the voltage at the
THM input to determine the battery temperature. This
input is meant to be used with the internal thermistor
connected to ground inside the battery pack. Connect
the output of the battery thermistor to THM. Connect a
resistor from THM to VDD. The resistor-divider sets the
voltage at THM. When the charger is not powered up,
the battery temperature can still be determined if VDD is
powered from an external voltage source.
Thermistor Bits
Figure 9 shows the expected electrical behavior of a
103ETB-type thermistor (nominally 10kΩat +25°C ±5%
or better) to be used with the MAX1645/MAX1645A:
• THERMISTOR_OR bit is set when the thermistor
value is >100kΩ. This indicates that the thermistor is
open or a battery is not present. The charger is set to
POR, and the BATTERY_PRESENT bit is cleared.
• THERMISTOR_COLD bit is set when the thermistor
value is >30kΩ. The thermistor indicates a cold bat-
tery. This bit does not affect the charge.
• THERMISTOR_HOT bit is set when the thermistor
value is <3kΩ. This is a latched bit and is cleared by
removing the battery or sending a POR with the
ChargerMode() command. The MAX1645 charger is
stopped unless the HOT_STOP bit is cleared in the
ChargerMode() command. The MAX1645A charger
is stopped unless the HOT_STOP bit is cleared in the
ChargerMode() command or the RES_UR bit is set.
See Table 7.
• THERMISTOR_UR bit is set when the thermistor
value is <500Ω(i.e., THM is grounded).
Multiple bits may be set depending on the value of the
thermistor (e.g., a thermistor that is 450Ωwill cause both
the THERMISTOR_HOT and the THERMISTOR_UR bits
to be set). The thermistor may be replaced by fixed-
value resistors in battery packs that do not require the
thermistor as a secondary fail-safe indicator. In this
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
26 ______________________________________________________________________________________
1000
100
10
RESISTANCE (kΩ)
1
0.1
-40
-50 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110
TEMPERATURE (°C)
Figure 9. Typical Thermistor Characteristics
Table 7. Thermistor Bit Settings
*See Battery Present item under Operating Conditions for more information.
CONTROLLED
CHARGE
Not allowed by MAX1645
Allowed by MAX1645A
Not Allowed
Allowed
Allowed
Not Allowed
WAKE-UP CHARGE
Not allowed by MAX1645
Allowed for Timeout
Period by MAX1645A
Not Allowed
Allowed for Timeout
Period
Allowed for Timeout
Period
Float Charge*
DESCRIPTION
Under Range
Under Range
Hot
Normal
Cold
Over Range
REG_UR and RES_HOT
RES_UR and RES_HOT
THERMISTOR
STATUS BIT
RES_HOT
(None)
RES_OR and RES_COLD
RES_COLD
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 27
case, it is the responsibility of the battery pack to manip-
ulate the resistance to obtain correct charger behavior.
Load and Source Switch Drivers
The MAX1645/MAX1645A can drive two P-channel
MOSFETs to eliminate voltage drops across the
Schottky diodes, which are normally used to switch the
load current from the battery to the main DC source:
• The source switch P1 is controlled by PDS. This P-
channel MOSFET is turned on when CVS rises to
300mV above BATT and turns off when CVS falls to
100mV above BATT. The same signal that controls
the PDS also sets the POWER_FAIL bit in the
Charger Status() register. See Operating Conditions.
• The load switch P2 is controlled by PDL. This P-
channel MOSFET is turned off when the CVS rises to
100mV below BATT and turns on when CVS falls to
300mV below BATT.
Dropout Operation
The MAX1645/MAX1645A have a 99.99% duty-cycle
capability with a 10ms maximum on-time and 1µs off-
time. This allows the charger to achieve dropout perfor-
mance limited only by resistive losses in the DC-DC
converter components (P1, R1, N1, R2; see Figure 1).
The actual dropout voltage is limited to 300mV between
CVS and BATT by the power-fail comparator (see
Operating Conditions).
Applications Information
Smart Battery Charging
System/Background Information
A smart battery charging system, at a minimum, con-
sists of a smart battery and smart battery charger com-
patible with the Smart Battery System Specifications
using the SMBus.
A system may use one or more smart batteries. Figure 10
shows a single-battery system. This configuration is
typically found in notebook computers, video cameras,
cellular phones, or other portable electronic equipment.
Another configuration uses two or more smart batteries
(Figure 11). The smart battery selector is used either to
SYSTEM
POWER
CONTROL
AC-DC
CONVERTER
(UNREGULATED)
AC
SYSTEM
POWER
SUPPLY
DC (UNREGULATED) / VBATTERY
SAFETY
SIGNAL
VBATTERY DC (UNREGULATED)
VCC
+12V, -12V
SYSTEM HOST
(SMBus HOST)
SMART
BATTERY
CRITICAL EVENTS
CRITICAL EVENTS
CHARGING VOLTAGE/CURRENT
REQUESTS
BATTERY DATA/STATUS REQUESTS
SMART BATTERY
CHARGER
SMBus
MAX1645A
Figure 10. Typical Single Smart Battery System
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
28 ______________________________________________________________________________________
connect batteries to the smart battery charger or the
system, or to disconnect them, as appropriate. For
each battery, three connections must be made: power
(the battery’s positive and negative terminals), the
SMBus (clock and data), and the safety signal (resis-
tance, typically temperature dependent). Additionally,
the system host must be able to query any battery so it
can display the state of all batteries present in the system.
Figure 11 shows a two-battery system where battery 2
is being charged while battery 1 is powering the sys-
tem. This configuration may be used to “condition” bat-
tery 1, allowing it to be fully discharged prior to
recharge.
Smart Battery Charger Types
Two types of smart battery chargers are defined: Level 2
and Level 3. All smart battery chargers communicate
with the smart battery using the SMBus; the two types
differ in their SMBus communication mode and whether
they modify the charging algorithm of the smart battery
Figure 11. Typical System Using Multiple Smart Batteries
AC-DC
CONVERTER
(UNREGULATED)
AC
DC (UNREGULATED) / VBATTERY
NOTE: SB 1 POWERING SYSTEM
SB 2 CHARGING
VCC
+12V, -12V
SYSTEM HOST
(SMBus HOST) SMART BATTERY
SELECTOR
SMBus
SMBus
SMBus
SAFETY SIGNAL
VCHARGE
VBATT
SAFETY
SIGNAL
VBATT
SAFETY
SIGNAL
SMART BATTERY 1 SMART BATTERY 2
CRITICAL EVENTS
BATTERY DATA/STATUS REQUESTS
SMART
BATTERY
CHARGER
SMBus
MAX1645A
SYSTEM
POWER
SUPPLY
Level 3
Level 3Level 2
Level 3Slave/Master
Slave only
MODIFIED FROM
BATTERY
CHARGE ALGORITHM SOURCE
BATTERY
SMBus MODE
Table 8. Smart Battery Charger Type
by SMBus Mode and Charge Algorithm
Source
Note: Level 1 smart battery chargers were defined in the ver-
sion 0.95a specification. While they can correctly interpret
smart battery end-of-charge messages, minimizing over-
charge, they do not provide truly chemistry-independent
charging. They are no longer defined by the Smart Battery
Charger Specification and are explicitly not compliant with this
and subsequent Smart Battery Charger Specifications.
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 29
(Table 8). Level 3 smart battery chargers are supersets
of Level 2 chargers and, as such, support all Level 2
charger commands.
Level 2 Smart Battery Charger
The Level 2 or smart battery-controlled smart battery
charger interprets the smart battery’s critical warning
messages and operates as an SMBus slave device to
respond to the smart battery’s ChargingVoltage() and
ChargingCurrent() messages. The charger is obliged to
adjust its output characteristics in direct response to
the ChargingVoltage() and ChargingCurrent() mes-
sages it receives from the battery. In Level 2 charging,
the smart battery is completely responsible for initiating
the communication and providing the charging algo-
rithm to the charger.
The smart battery is in the best position to tell the smart
battery charger how it needs to be charged. The charg-
ing algorithm in the battery may request a static charge
condition or may choose to periodically adjust the
smart battery charger’s output to meet its present
needs. A Level 2 smart battery charger is truly chem-
istry independent and, since it is defined as an SMBus
slave device only, the smart battery charger is relatively
inexpensive and easy to implement.
Selecting External Components
Table 10 lists the recommended components and
refers to the circuit of Figure 1; Table 9 lists the suppli-
ers’ contacts. The following sections describe how to
select these components.
MOSFETs and Schottky Diodes
Schottky diode D1 provides power to the load when the
AC adapter is inserted. Choose a 3A Schottky diode or
higher. This diode may not be necessary if P1 is used.
The P-channel MOSFET P1 turns on when VCVS >
VBATT. This eliminates the voltage drop and power con-
sumption of the Schottky diode. To minimize power loss,
select a MOSFET with an RDS(ON) of 50mΩor less. This
MOSFET must be able to deliver the maximum current
as set by R1. D1 and P1 provide protection from
reversed voltage at the adapter input.
The N-channel MOSFETs N1 and N2 are the switching
devices for the buck controller. High-side switch N1
should have a current rating of at least 6A and have an
RDS(ON) of 50mΩor less. The driver for N1 is powered
by BST; its current should be less than 10mA. Select a
MOSFET with a low total gate charge and determine
the required drive current by IGATE = QGATE ·f (where f
is the DC-DC converter maximum switching frequency
of 400kHz).
The low-side switch N2 should also have a current rat-
ing of at least 3A, have an RDS(ON) of 100mΩor less,
and a total gate charge less than 10nC. N2 is used to
provide the starting charge to the BST capacitor C14.
During normal operation, the current is carried by
Schottky diode D2. Choose a 3A or higher Schottky
diode.
D3 is a signal-level diode, such as the 1N4148. This
diode provides the supply current to the high-side
MOSFET driver.
The P-channel MOSFET P2 delivers the current to the
load when the AC adapter is removed. Select a MOS-
FET with an RDS(ON) of 50mΩor less to minimize power
loss and voltage drop.
Inductor Selection
Inductor L1 provides power to the battery while it is
being charged. It must have a saturation current of at
least 3A plus 1/2of the current ripple (∆IL).
ISAT = 3A + 1/2∆IL
The controller determines the constant off-time period,
which is dependent on BATT voltage. This makes the
ripple current independent of input and battery voltage
and should be kept to less than 1A. Calculate the ∆IL
with the following equation:
∆IL= 21Vµs / L
Higher inductor values decrease the ripple current.
Smaller inductor values require higher saturation cur-
Capacitor
CMSH series
Central
Semiconductor
NSQ03A04
1N5817–1N5822
595D seriesSprague
Motorola
Nihon
Diode
TPS series,
TAJ series
LR2010-01 series
WSL seriesDale
IRC
AVX
Sense Resistor
Si4435/6
FDS series
IRF7309Internal Rectifier
Fairchild
Vishay-Siliconix
MOSFET
PART
UP2 series
D03316P series
CDRH127 series
MANUFACTURER
Sumida
Coilcraft
Coiltronics
COMPONENT
Inductor
Table 9. Component Suppliers
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
30 ______________________________________________________________________________________
Table 10. Component Selection
0.1µF, >30V ceramic capacitor C23
40V, 2A schottky diodes
Central Semiconductor CMSH2-40
D1, D2
Small-signal diodes
Central Semiconductor CMPSH-3
D3, D4
22µH, 3.6A buck inductor
Sumida CDRH127-220
L1
30V, 11.5A, high-side N-channel MOSFET (SO-8)
Fairchild FDS6680
N1 High-Side MOSFET
0.1µF ceramic capacitorsC8, C14, C16
0.01µF ceramic capacitorsC9, C10, C11 Compensation Capacitors
1500pF ceramic capacitorC13
0.1µF, >20V ceramic capacitors C18, C24
1µF ceramic capacitorsC6, C7, C12
1µF, >30V ceramic capacitorsC5, C19, C20
22µF, 25V low-ESR tantalum capacitors
AVX TPSD226M025R0200
C3, C4 Output Capacitors
22µF, 35V low-ESR tantalum capacitors
AVX TPSE226M035R0300
C1, C2 Input Capacitors
DESCRIPTIONDESIGNATION
40mΩ±1%, 0.5W battery current-sense resistor
Dale WSL-2010/40mΩ/1%
R1
30V, 11A P-Channel MOSFET load and source switches
Fairchild FDS6675
P1, P2
30V, 8.4A, low-side N-channel MOSFET
Fairchild FDS6612A or
30V, signal level N-channel MOSFET
2N7002
N2 Low-Side MOSFET
50mΩ±1%, 0.5W source current-sense resistor
Dale WSL-2010/50mΩ/1%
R2
R3 + R4 >100kΩinput current-limit setting resistorsR3, R4
33Ω±5% resistorR12
1kΩ±5% resistorR13
4.7Ω±5% resistorsR14, R15
1Ω±5% resistorsR11, R16
10kΩ±5% resistors R5, R7, R8, R9, R10
10kΩ±1% temperature sensor network resistorR6
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
______________________________________________________________________________________ 31
rent capabilities and degrade efficiency. Typically, a
22µH inductor is ideal for all operating conditions.
Other Components
CCV, CCI, and CCS are the compensation points for the
three regulation loops. Bypass CCV with a 10kΩresistor
in series with a 0.01µF capacitor to GND. Bypass CCI
and CCS with 0.01µF capacitors to GND. R7 and R13
serve as protection resistors to THM and CVS, respec-
tively. To achieve acceptable accuracy, R6 should be
10kΩand 1% to match the internal battery thermistor.
Current-Sense Input Filtering
In normal circuit operation with typical components, the
current-sense signals can have high-frequency tran-
sients that exceed 0.5V due to large current changes
and parasitic component inductance. To achieve prop-
er battery and input current compliance, the current-
sense input signals should be filtered to remove large
common-mode transients. The input current limit sens-
ing circuitry is the most sensitive case due to large cur-
rent steps in the input filter capacitors (C1 and C2) in
Figure 1. Use 1µF ceramic capacitors from CSSP and
CSSN to GND. Smaller 0.1µF ceramic capacitors can
be used on the CSIP and CSIN inputs to GND since the
current into the battery is continuous. Place these
capacitors next to the single-point ground directly
under the MAX1645/MAX1645A.
Layout and Bypassing
Bypass DCIN with a 1µF to GND (Figure 1). D4 protects
the device when the DC power source input is
reversed. A signal diode for D4 is adequate as DCIN
only powers the LDO and the internal reference.
Bypass LDO, BST, DLOV, and other pins as shown in
Figure 1.
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
power-switching components and high-current routing.
Refer to the PC board layout in the MAX1645/
MAX1645A evaluation kit manual for examples. A
ground plane is essential for optimum performance. In
most applications, the circuit will be located on a multi-
layer board, and full use of the four or more copper lay-
ers is recommended. Use the top layer for high-current
connections, the bottom layer for quiet connections
(REF, CCV, CCI, CCS, DAC, DCIN, VDD, and GND),
and the inner layers for an uninterrupted ground plane.
Use the following step-by-step guide:
1) Place the high-power connections first, with their
grounds adjacent:
• Minimize current-sense resistor trace lengths and
ensure accurate current sensing with Kelvin con-
nections.
• Minimize ground trace lengths in the high-current
paths.
• Minimize other trace lengths in the high-current
paths:
• Use > 5mm-wide traces
• Connect C1 and C2 to high-side MOSFET
(10mm max length)
• Connect rectifier diode cathode to low-side.
MOSFET (5mm max length)
• LX node (MOSFETs, rectifier cathode, inductor:
15mm max length). 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.
The resulting top-layer subground plane is con-
nected to the normal inner-layer ground plane
at the output ground terminals, which ensures
that the IC’s analog ground is sensing at the
supply’s output terminals without interference
from IR drops and ground noise. Other high-
current paths should also be minimized, but
focusing primarily on short ground and current-
sense connections eliminates about 90% of all
PC board layout problems.
2) Place the IC and signal components. Keep the main
switching nodes (LX nodes) away from sensitive ana-
log components (current-sense traces and REF
capacitor). Important: The IC must be no further
than 10mm from the current-sense resistors.
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 bypass
capacitors close to the IC. The bulk capacitors can
be placed further away. Place the current-sense
input filter capacitors under the part, connected
directly to the GND pin.
3) Use a single-point star ground placed directly below
the part. Connect the input ground trace, power
ground (subground plane), and normal ground to
this node.
Chip Information
TRANSISTOR COUNT: 6996
MAX1645/MAX1645A
Advanced Chemistry-Independent, Level 2
Battery Chargers with Input Current Limiting
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.
32 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
LOAD
ADAPTER IN
MAX1645A
CVS
DCIN
REF
CLS
AGND
DAC
CCV
CCI
CCS
DDS
CSSP
CSSN
LDO
DHI
LX
DLOV
BST
PGND
DLO
CSIP
CSIN
PDL
BATT
THM
VDD
SCL
SDA
INT
BATTERY
HOST
Typical Operating Circuit
