Datasheet MAX1645EEI Datasheet (Maxim)

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
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General Description

The MAX1645 is a high-efficiency battery charger
capable of charging batteries of any chemistry type. It
uses the Intel System Management Bus (SMBus) to
control voltage and current charge outputs.

When charging lithium-ion (Li+) batteries, the MAX1645
automatically transitions from regulating current to reg­ulating voltage. The MAX1645 can also limit line input
current so as not to exceed a predetermined current
drawn from the DC source. A 175sec charge safety
timer prevents “runaway charging” should the
MAX1645 stop receiving charging voltage/current com­mands.

The MAX1645 employs a next-generation synchronous
buck control circuitry that lowers the minimum input-to­output 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
♦ 175sec 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

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

________________________________________________________________

Maxim Integrated Products

1

19-1566; Rev 0a; 10/99

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

TOP VIEW

1

DCIN

2

LDO

3

CLS

4

REF

5

CCS

6

CCI

7

CCV

8

GND

9

BATT

10

DAC

11

V

DD

12

THM

13

SCL

14

SDA

MAX1645

QSOP

28
27
26
25
24
23
22
21
20
19
18
17
16
15

CVS
PDS
CSSP
CSSN
BST
DHI
LX
DLOV
DLO
PGND
CSIP
CSIN
PDL
INT

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +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 (V

CSSP

+ 0.3V)

BST to LX..................................................................-0.3V to +6V

DHI to LX...................................................-0.3V to (V

BST

+ 0.3V)

CSIP, CSIN, BATT to GND .....................................-0.3V to +22V

LDO to GND.....................-0.3V to (lower of 6V or V

DCIN

+ 0.3V)

DLO to GND ...........................................-0.3V to (V

DLOV

+ 0.3V)

REF, DAC, CCV, CCI, CCS, CLS to GND.....-0.3V to (V

LDO

+ 0.3V)

V

DD

, SCL, SDA, INT, DLOV to GND.........................-0.3V to +6V

THM to GND...............................................-0.3V to (V

DD

+ 0.3V)

PGND to GND .......................................................-0.3V to +0.3V

LDO Continuous Current.....................................................50mA

Continuous Power Dissipation (T

A

= +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, 10sec).............................+300°C

8V < V

DCIN

< 28V

V

CVS

referred to V

BATT

, V

CVS

rising

V

PDS

= V

CSSP

- 2V, V

DCIN

= 16V

PDS = CSSP

I

PDS

= 0

0 < V

DCIN

< 6V, VDD= 5V, V

SCL

= 5V,

V

SDA

= 5V

V

CVS

referred to V

BATT

V

CVS

referred to V

BATT

, V

CVS

falling

When the SMB res­ponds to commands

8V < V

DCIN

< 28V

8V < V

DCIN

< 28V

When AC_PRESENT
switches

When I

CHARGE

drops to 128mA

8V < V

DCIN

< 28V, 0 < I

LDO

< 15mA

0 < I

REF

< 200µA

CONDITIONS

mV

-150 -100 -50

V

PDL-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

V

PDS-HYS

PDS Charging Source Switch
Threshold Hysteresis

mV

50 100 150

V

PDS-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

V

REF

REF Output Voltage

mA

1.7 6

I

DCIN

DCIN Supply Current

V

828

V

DCIN

µA

80 150

I

DD

VDDQuiescent Current

2.1 2.5

V

2.55 2.8

VDDUndervoltage Threshold

V

2.8 5.65

VDDInput 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

V

LDO

LDO Output Voltage

UNITSMIN TYP MAXSYMBOLPARAMETER

DCIN rising
DCIN falling

VDDrising
VDDfalling

DCIN Typical Operating Range

GENERAL SPECIFICATIONS

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +25°C.)

V

CCV

= V

CCI

= V

CCS

= 0.25V to 2V

PDL to GND

From CSSP/CSSN to CCS, V

CLS

= 2.048V,

V

CSSP

- V

CSSN

= 102.4mV

From BATT to CCV

V

CSSN

- V

PDL

= 1V

V

CSSP

= V

CSSN

= 28V, V

DCIN

= 0

V

CVS

referred to V

BATT

V

CSSP

= V

CSSN

= V

DCIN

= 0 to 28V

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V, V

DCIN

= 0

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V, charge inhibited

R

CSS

= 40mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V

R

CS

= 50mΩ

Charging Voltage() = 0x1060

V

CVS

= 28V
ChargingVoltage() = 0x41A0
ChargingVoltage() = 0x3130

V

BATT

= 1V, R

CSI

= 50mΩ

ChargingVoltage() = 0x20D0

CONDITIONS

From CSIP/SCIN to CCI, ChargingCurrent() =
0x0BC0, V

CSIP

- V

CSIN

= 150.4mV

From BATT to CCV, ChargingVoltage() =
0x41A0, V

BATT

= 16.8V

V

CLS

= V

REF

/2 to V

REF

mV

150 300 600

CCV/CCI/CCS Clamp Voltage
(Note 4)

µA/mV

V/V

200 500

Battery Voltage-Error Amp DC
Gain

µA

-1 1

CSSP/CSSN Quiescent Current

µA-100 540 1000CSSP Input Bias Current

µA

-5 5

Total BATT Standby Current

µA

-100 100

Total BATT Quiescent Current

µA

-700 700

Total BATT Input Bias Current

V

020

BATT/CSIP/CSIN Input Voltage
Range

mA

20 128 200

BATT Undervoltage Charge
Current

2.282 2.56 2.838

kΩ

50 100 150

PDL Turn-On Resistance

mA

612

mV

100 200 300

V

PDL-HYS

PDL Load Switch Threshold
Hysteresis

PDL Turn-Off Current

A

4.714 5.12 5.526

mA

61.6 128 194.4

A

2.798 3.008 3.218

I0BATT Charge Current (Note 3)

4.150 4.192 4.234

µA

620

CVS Input Bias Current

16.666 16.8 16.934

V0BATT Full-Charge Voltage V

12.492 12.592 12.692

8.333 8.4 8.467

UNITSMIN TYP MAXSYMBOLPARAMETER

0.5 1 2

Input Current-Error Amp
Transconductance

µA/mV

0.5 1 2

Battery Current-Error Amp
Transconductance

µA/mV

0.111 0.222 0.444

Battery Voltage-Error Amp
Transconductance

µA

-1 0.05 1

CLS Input Bias Current

DCIN Source Current Limit
(Note 3)

ChargingCurrent() =
0x0BC0

ChargingCurrent() =
0x0080

V

CLS

= 4.096V

V

CLS

= 2.048V

V

CSSP

= C

CSSN

= V

DCIN

= 0 to 28V mA-100 35 100CSSN Input Bias Current

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

4 _______________________________________________________________________________________

V

SDA

= 0.4V

All 4 comparators, VDD= 2.8V to 5.65V

VDD= 2.8V to 5.65V, V

THM

falling

VDD= 2.8V to 5.65V, V

THM

falling

DLO high or low, V

DLOV

= 4.5V

DHI high or low, V

BST

- VLX= 4.5V

VDD= 2.8V to 5.65V, V

THM

falling

VDD= 2.8V to 5.65V, V

THM

falling

R

CSI

= 50mΩ

V

DLOV

= V

LDO

, DLO low

V

DCIN

= 28V, V

BATT

= VLX= 20V

V

DCIN

= 0, V

BATT

= VLX= 20V

V

THM

= 4% of VDDto 96% of VDD,

V

DD

= 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 V

DD

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

t

ON

Maximum On-Time

µs

1 1.25 1.5

t

OFF

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

I

INT

= 1mA

V

INT

= 5.65V

mV

25 200

µA

1

INT Output High Leakage
INT Output Low Voltage

ns

0

t

HD:DAT

SDA Hold Time from SCL

ns

250

t

SU:DAT

SDA Setup Time from SCL

µs

4

t

HIGH

SCL High Period

µs

4.7

t

LOW

SCL Low Period

µs

4.7

t

SU:STA

Start Condition Setup Time
from SCL

µs

4

t

HD:STA

Start Condition Hold Time
from SCL

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +25°C.)

% of V

DD

% of V

DD

% of V

DD

% of V

DD

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

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at

T

A

= +25°C.)

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

sec

140 175 210

t

WDT

Maximum Charge Period
Without a ChargingVoltage() or
Charging Current() Loaded

µs

1

t

DV

SDA Output Data Valid from SCL

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)

PARAMETER SYMBOL MIN MAX UNITS

LDO Output Voltage V

LDO

5.15 5.65

V

7

DCIN Undervoltage Threshold

7.85
V

DCIN Supply Current Charging
Inhibited

2

mA

VDDInput Voltage Range
(Note 1)

2.8 5.65

V

VDDUndervoltage Threshold

2.8
V

2.1

VDDQuiescent Current I

DD

150

µA

DCIN Typical Operating Range V

DCIN

828

V

DCIN Supply Current I

DCIN

6

mA

REF Output Voltage V

REF

4.035 4.157

V

BATT Undervoltage Threshold
(Note 2)

2.4 2.8

V

PDS Charging Source Switch
Turn-Off Threshold

V

PDS-OFF

50 150

mV

PDS Charging Source Switch
Threshold Hysteresis

V

PDS-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

V

PDL-OFF

-150 -50

mV

PDL Load Switch Threshold
Hysteresis

V

PDL-HYS

100 300

mV

PDL Turn-Off Current

6

mA

CONDITIONS

0 < I

REF

< 200µA

8V < V

DCIN

< 28V, 0 < I

LDO

< 15mA

When I

CHARGE

drops to 128mA

When AC_PRESENT
switches

8V < V

DCIN

< 28V

8V < V

DCIN

< 28V

When the SMB res­ponds to commands

V

CVS

referred to V

BATT

, V

CVS

falling

V

CVS

referred to V

BATT

0 < V

DCIN

< 6V, VDD= 5V, V

SCL

= 5V,

V

SDA

= 5V

I

PDS

= 0

PDS = CSSP
V

PDS

= V

CSSP

- 2V, V

DCIN

= 16V

V

CVS

referred to V

BATT

, V

CVS

rising

V

CVS

referred to V

BATT

V

CSSN

- V

PDL

= 1V

8V < V

DCIN

< 28V

DCIN rising
DCIN falling

VDDrising
VDDfalling

GENERAL SPECIFICATIONS

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

6 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)

Maximum Duty Cycle

99

%

Minimum Off-Time t

OFF

1 1.5

µs

Maximum On-Time t

ON

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

V

BATT

= 1V, R

CSI

= 50mΩ

ChargingVoltage() = 0x1060

ChargingVoltage() = 0x20D0

ChargingVoltage() = 0x3130

ChargingVoltage() = 0x41A0

R

CSI

= 50mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V, charge inhibited

R

CSS

= 40mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

V

BATT

= 0 to 20V, V

DCIN

= 0

V

CSSP

= V

CSSN

= V

DCIN

= 28V

V

CSSP

= V

CSSN

= 28V, V

DCIN

= 0

PDL to GND

From BATT to CCV

V

CVS

= 28V

V

CLS

= V

REF

/2 to V

REF

From BATT to CCV, ChargingVoltage() =
0x41A0, V

BATT

= 16.8V

From CSIP/CSIN to CCI, ChargingCurrent() =
0x0BC0, V

CSIP-VCSIN

= 150.4mV

From CSSP/CSSN to CCS, V

CLS

= 2.048V,

V

CSSP

- V

CSSN

= 102.4mV

V

CCV

= V

CCI

= V

CCS

= 0.25V to 2V

ChargingCurrent() =
0x0BC0

ChargingCurrent() =
0x0080

V

CLS

= 4.096V

V

CLS

= 2.048V

CSSN Input Bias Current

-100 100

µAV

CSSP

= V

CSSN

= V

DCIN

= 28V

DC-TO-DC CONVERTER SPECIFICATIONS

ERROR AMPLIFIER SPECIFICATIONS

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

_______________________________________________________________________________________ 7

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +18V, TA= -40°C to +85°C, unless otherwise noted. Guaranteed by design.)

SDA Hold Time from SCL t

HD:DAT

0

ns

Start Condition Hold Time
from SCL

Start Condition Setup Time
from SCL

t

SU:STA

4.7

µs

t

HD:STA

4

µs

SDA Setup Time from SCL t

SU: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

1

µA

BST Supply Current

15

µA

Thermistor Hot Threshold

22 25

% of V

DD

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

6

mA

INT Output High Leakage

1

µA

INT Output Low Voltage

200

mV

SCL High Period t

HIGH

4

µs

SCL Low Period t

LOW

4.7

µs

CONDITIONS

VDD= 2.8V to 5.65V, V

THM

falling

DLO high or low, V

DLOV

= 4.5V

VDD= 2.8V to 5.65V, V

THM

falling

DHI high or low, V

BST

- VLX= 4.5V

R

CSI

= 50mΩ

V

DLOV

= V

LDO

, DLO low

V

THM

= 4% of VDDto 96% of VDD,

VDD= 2.8V to 5.65V
VDD= 2.8V to 5.65V, V

THM

falling

VDD= 2.8V to 5.65V, V

THM

falling

V

DCIN

= 28V, V

BATT

= VLX= 20V

V

SDA

= 0.4V

V

DCIN

= 0, V

BATT

= VLX= 20V

V

INT

= 5.65V

I

INT

= 1mA

DHI high

% of V

DD

% of V

DD

% of V

DD

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)

V

REF

(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)

V

LDO

(V)

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

8 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 1, V

DCIN

= 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

V

CCV

/V

CCI

I

BATT

V

BATT

1V

0.5V

2ms/div

CCV

CCV

CCV

BATTERY REMOVED BATTERY INSERTED

LOAD-TRANSIENT RESPONSE

(STEP IN LOAD CURRENT)

MAX1645 toc02

ChargingCurrent() = 3008mA
V

BATT

= 16V
LOAD STEP: 0A TO 2A
I

SOURCE

LIMIT = 2.5A

CCS

CCS

CCS

4A
2A
0

2A

1V

0

1ms/div

CCI

CCI

CCI

V

CCV

/V

CCI

I

BATT

V

BATT

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

V

DCIN

(V)

V

LDO

(V)

I

LOAD

= 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)

V

REF

(V)

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= +3.3V, V

BATT

= +16.8V, V

DCIN

= +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 I

CHARGE

= 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

t

WDT

140 210

sec

SDA Output Data Valid
from SCL

t

DV

1

µs

PARAMETER SYMBOL MIN MAX UNITSCONDITIONS

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

_______________________________________________________________________________________

9

Typical Operating Characteristics (continued)

(Circuit of Figure 1, V

DCIN

= 20V, TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. BATTERY CURRENT

(VOLTAGE-CONTROL LOOP)

100

95
90
85
80
75
70

EFFICIENCY (%)

65
60

A: V

= 20V, ChargingVoltage() = 16.8V

DCIN

55

= 16V, ChargingVoltage() = 8.4V

B: V

DCIN

50

0 1000500 1500 2000 2500 3000

BATTERY CURRENT (mA)

A
B

MAX1645 toc07

EFFICIENCY vs. BATTERY CURRENT

(CURRENT-CONTROL LOOP)

100

95
90
85
80
75
70

EFFICIENCY (%)

65
60

A: V

= 20V, V

DCIN

55

B: V

DCIN

50

0 1000500 1500 2000 2500 3000

= 16.8V

BATT

= 16V, V

= 8.4V

BATT

ChargingCurrent() (CODE)

A
B

0.001

MAX1645 toc08

0.01

0.1

1.0

DROP IN BATT OUTPUT VOLTAGE (%)

10

OUTPUT VI CHARACTERISTICS

ChargingVoltage() = 16,800mV
ChargingCurrent() = 3008mA

0 1500 2000500 1000 2500 3000 3500

LOAD CURRENT (mA)

MAX1645 toc09

BATT VOLTAGE ERROR

vs. ChargingVoltage() CODE

0.3

0.2

0.1

0

-0.1

BATT VOLTAGE ERROR (%)

-0.2
I

= 0

BATT

MEASURED AT AVAILABLE CODES

-0.3

0000 80004000 12000 16000 20000

ChargingVoltage() (CODE)

SOURCE/BATT CURRENT vs. LOAD CURRENT

WITH SOURCE CURRENT LIMIT

3.5

3.0

2.5

2.0

1.5
V

= 2V

CLS

= 40mΩ

R

CSS

1.0
V

SOURCE/BATT CURRENT (A)

= 16.8V

BATT

SOURCE CURRENT LIMIT = 2.5A

0.5

ChargingCurrent() = 3008mA
ChargingVoltage() = 18,432mV

0

0 1.00.5 1.5 2.0 2.5

I

IN

LOAD CURRENT (A)

I

BATT

MAX1645 toc10

MAX1645 toc12

CURRENT-SETTING ERROR

vs. ChargingCurrent() CODE

5
4
3
2
1
0

-1

-2

BATT CURRENT ERROR (%)

-3
V

= 12.6V

BATT

-4
MEASURED AT AVAILABLE CODES

-5

0 1000500 1500 2000 2500 3000

ChargingCurrent() (CODE)

SOURCE/BATT CURRENT vs. V

WITH SOURCE CURRENT LIMIT

3.5

3.0

2.5

2.0

1.5
I

= 2A

LOAD

= 2V

V

CLS

1.0

= 40mΩ

R

SOURCE/BATT CURRENT (A)

CSS

ChargingVoltage() = 18,432mV

0.5

ChargingCurrent() = 3008mA
SOURCE CURRENT LIMIT = 2.5A

0

042 6 8101214161820

I

IN

V

(V)

BATT

MAX1645 toc11

BATT

MAX1645 toc13

I

BATT

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

10 ______________________________________________________________________________________

Pin Description

Battery Voltage OutputBATT9
DAC Voltage Output DAC10
Logic Circuitry Supply Voltage Input (2.8V to 5.65V) V

DD

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 10kΩ resistor 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

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 11

Detailed Description

The MAX1645 consists 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 voltage and the cur­rent set by the SMBus interface. The MAX1645 features
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 current limit.

Setting Output Voltage

The MAX1645’s voltage DAC has a 16mV LSB and an

18.432V full scale. The SMBus specification allows for a
16-bit ChargingVoltage() command that translates to a
1mV LSB and a 65.535V full-scale voltage; therefore,
the ChargingVoltage() value corresponds to the output
voltage in millivolts. The MAX1645 ignores the first four
LSBs and uses 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’s current DAC has 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 current; the
ChargingCurrent() value corresponds to the charging
voltage in milliamps. The MAX1645 drops the first six
LSBs and uses 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 50mΩ
sense resistor (R2 in Figure 1) is required to achieve
the correct CODE/current scaling.

Input Current Limiting

The MAX1645 limits the current drawn by the charger
when the load current becomes high. The device limits
the charging current so the AC adapter voltage is not

loaded down. An internal amplifier compares the volt­age between CSSP and CSSN to the voltage at CLS/20.
V

CLS

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 cur­rent is generated by the DC-DC converter; therefore, the
actual source current required is determined as follows:

I

SOURCE

= I

LOAD

+ [(I

CHARGE

· V

BATT)

/ (VIN· η)]

where η is the efficiency of the DC-DC converter (typi­cally 85% to 95%).

V

CLS

determines the threshold voltage of the CSS com­parator. 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:

I

MAX

= V

CLS

/ (20 · R1)

(Limit V

CSSP

- V

CSSN

to between 102.4mV and

204.8mV.)
The configuration in Figure 1 provides an input current

limit of:

I

MAX

= (2.048V / 20) / 0.04Ω = 2.56A

LDO Regulator

The LDO provides a +5.4V supply derived from DCIN
and 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 actually powered by
DLOV and BST, which must be connected to LDO
through a lowpass filter and a diode as shown in Figure

1. See also the

MOSFET Drivers

section. The LDO also
supplies the 4.096V reference and most of the control
circuitry. Bypass LDO with a 1µF capacitor.

VDDSupply

This input provides power to the SMBus interface and
the thermistor comparators. Typically connect VDDto
LDO or, to keep the SMBus interface of the MAX1645
active while the supply to DCIN is removed, connect an
external supply to VDD.

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

12 ______________________________________________________________________________________

ADAPTER IN

Figure 1. Typical Application Circuit

R5

10k

C11

0.01µF

R13

1k

C23

0.1µF

R3

100k

R4

100k

C10

0.01µF

CVS
DCIN

REF

CLS

GND

DAC
CCV

CCI

CCS

MAX1645

CSSP

CSSN

LDO

DLOV

PGND

CSIP

CSIN
PDL

BATT

THM

SCL
SDA

PDS

BST

DLO

V

P1
FDS6675 D1

R14

4.7Ω

C20, 1µF

C19, 1µF

4.7Ω

C6
1µF

DHI

N1

FDS6680

LX

N2

FDS6612A

DD

INT

C12
1µF

C18

0.1µF

R7
10k

C13

1.5nF

C24

0.1µF

R10
10k

1N5821

R15

C14

0.1µF

D2

R11

R16

1Ω

1N5821

R1

0.04Ω

R12

33Ω

D3

1N4148

C16

0.1µF

L1

22µH

1Ω

R2

0.05Ω

R6

10k

R8

10k

R9
10k

D4

1N4148

C5

1µF

C7

1µF

C8

0.1µF

C9

0.01µF

22µF

C1

FDS6675

C2

22µF

LOAD

P2

BATTERY

HOST

C4
22µF

C3
22µF

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 13

Figure 2. Functional Diagram

CSSP

CSSN

CLS

CSIP

CSIN

CSS

GMS

CSI

GMI

BATT

GMV

MAX1645

LVC

DHI

DC-DC

DLO

BST

DHI

LX

DLOV

DLO

PGND

CCS
CCI
CCV

CVS
BATT

V

DD

SCL
SDA

INT

THM

SMB

TEMP

DACI

DACV

PDL

VL

REF

PDS

PDS

PDL

DCIN

LDO

REF

GND

DAC

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

14 ______________________________________________________________________________________

Operating Conditions

The MAX1645 changes its operation depending on the
voltages at DCIN, BATT, V

DD,

and THM. Several impor-

tant operating states follow:

• AC Present. When DCIN is > 7.5V, the battery is
considered to be in an AC Present state. In this con­dition, both the LDO and REF will function properly
and battery charging is allowed. When AC is pre­sent, the AC_PRESENT bit (bit 15) in the
ChargerStatus() register is set to “1.”

• Power Fail. When DCIN is < BATT + 0.3V, the
MAX1645 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
uses the THM pin to detect when a battery is con­nected to the charger. When the battery is present,
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 MAX1645 registers are reset. With no battery pre­sent, the charger will still try to regulate the BATT pin
voltage at 18.432V 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 unaf­fected and, when the BATT voltage exceeds 2.7V,
normal charging resumes. ChargingVoltage() is unaf­fected and can be set as low as 1.024V.

• VDDUndervoltage. When VDD< 2.5V, the VDDsup­ply is in an undervoltage state, and the SMBus inter­face will not respond to commands. Coming out of
the undervoltage condition, MAX1645 will be in its
Power-On Reset state. No charging will occur when
VDDis under voltage.

SMBus Interface

The MAX1645 receives 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 uses the SMBus Read-Word and Write­Word protocols to communicate with the battery being
charged, as well as with any host system that monitors
the battery-to-charger communications as a Level 2
SMBus charger. The MAX1645 is an SMBus slave

device and does not initiate communication on the bus.
It receives commands and responds 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 the MAX1645 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 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 is
version 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 THER­MISTOR_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’s inter­nal state. The latched bits, THERMISTOR_HOT and
ALARM_INHIBITED, are cleared whenever BATTERY_
PRESENT = 0 or ChargerMode() is written with
POR_RESET = 1. The ALARM_INHIBITED status bit can
also be cleared by writing a new charging current OR
charging voltage.

MAX1645

______________________________________________________________________________________ 15

Advanced Chemistry-Independent, Level 2

Battery Charger 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

S

SLAVE

ADDRESS

W

7 bits 1b

MSB LSB 0

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

16 ______________________________________________________________________________________

MOST SIGNIFICANT

Figure 4. SMBus Serial Interface Timing—Address

Figure 5. SMBus Serial Interface Timing—Acknowledgment

START

CONDITION

ADDRESS BIT (A6)

CLOCKED INTO SLAVE

A5 CLOCKED

INTO SLAVE

A4 CLOCKED

INTO SLAVE

SCL

A3 CLOCKED

INTO SLAVE

SDA

t

SU:STA

SCL

SDA

t

HD:STA

t

SU:DAT

INTO SLAVE

R/W BIT

CLOCKED

t

HD:DAT

t

LOW

t

DV

ACKNOWLEDGE

BIT CLOCKED
INTO MASTER

SLAVE PULLING
SDA LOW

t

SU:DAT

MOST SIGNIFICANT BIT

OF DATA CLOCKED

INTO MASTER

t

DV

t

HD:DAT

t

HIGH

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger 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

BIT

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

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

18 ______________________________________________________________________________________

Table 2. ChargerMode()

Command: 0x12
*State at chip initial power-on (i.e., V

DD

from 0 to +3.3V)

13 Not implemented
14 Not implemented
15 Not implemented

NAME DESCRIPTION

0 INHIBIT_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.

1 ENABLE_POLLING Not implemented

BIT

2 POR_RESET

0 = No change.
1 = Change the ChargingVoltage() to 0xFFFF and the ChargingCurrent()

to 0x00C0; clear the THERMISTOR_HOT and ALARM_INHIBITED flip­flops.

3 RESET_TO_ZERO Not implemented

7 Not implemented

6 POWER_FAIL_MASK

0* = Interrupt on either edge of the POWER_FAIL status bit.
1 = Do not interrupt because of a POWER_FAIL bit change.

5 BATTERY_PRESENT_ MASK

0* = Interrupt on either edge of the BATTERY_PRESENT status bit.
1 = Do not interrupt because of a BATTERY_PRESENT bit change.

4 AC_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.

9 Not implemented

8 Not implemented

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 19

NAME FUNCTION

0 CHARGE_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.

1 MASTER_MODE Always returns “0”

BIT

2 VOLTAGE_NOT_REG

0 = Battery voltage is limited at the set point.
1 = Battery voltage is less than the set point.

3 CURRENT_NOT_REG

0 = Battery current is limited at the set point.
1 = Battery current is less than the set point.

7 VOLTAGE_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.

6 CURRENT_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.

5 LEVEL_3 Always returns a “0”

4 LEVEL_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.

9 THERMISTOR_COLD

0 = THM is < 75.5% of the reference voltage.
1 = THM is > 75.5% of the reference voltage.

8 THERMISTOR_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

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

20 ______________________________________________________________________________________

Table 4. ChargerCurrent()

Command: 0x14

NAME FUNCTION

0 Not used. Normally a 1mA weight.
1 Not used. Normally a 2mA weight.

BIT

2 Not used. Normally a 4mA weight.
3 Not used. Normally an 8mA weight.

7 Charge Current, DACI 1

0 = Adds 0mA of charger-current compliance.
1 = Adds 128mA of charger-current compliance.

6 Charge Current, DACI 0

0 = Adds 0mA of charger-current compliance.
1 = Adds 64mA of charger-current compliance, 128mA min.

5 Not used. Normally a 32mA weight.

4 Not 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.

9 Charge Current, DACI 3

0 = Adds 0mA of charger-current compliance.
1 = Adds 512mA of charger-current compliance.

8 Charge Current, DACI 2

0 = Adds 0mA of charger-current compliance.
1 = Adds 256mA of charger-current compliance.

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 21

Table 5. ChargingVoltage()

Command: 0x15

BIT NAME FUNCTION

0 Not used. Normally a 1mV weight.
1 Not used. Normally a 2mV weight.

PIN

2 Not used. Normally a 4mV weight.
3 Not used. Normally an 8mV weight.

7 Charge Voltage, DACV 3

0 = Adds 0mV of charger-voltage compliance.
1 = Adds 128mV of charger-voltage compliance, 1.024V min.

6 Charge Voltage, DACV 2

0 = Adds 0mV of charger-voltage compliance.
1 = Adds 64mV of charger-voltage compliance, 1.024V min.

5 Charge Voltage, DACV 1

0 = Adds 0mV of charger-voltage compliance.
1 = Adds 32mV of charger-voltage compliance, 1.024V min.

4 Charge 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.

9 Charge Voltage, DACV 5

0 = Adds 0mV of charger-voltage compliance.
1 = Adds 512mV of charger-voltage compliance, 1.024V min.

8 Charge 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

Advanced Chemistry-Independent, Level 2
Battery Charger 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

0 Error Code Not used
1 Error Code Not used

BIT

2 Error Code Not used
3 Error Code Not used

7 INITIALIZING Not used

6 DISCHARGING Not used

5 FULLY_CHARGED Not used

4 FULLY_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

9 REMAINING_CAPACITY_ ALARM Not used

8 REMAINING_TIME_ ALARM Not used

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 23

ChargingCurrent() (POR: 0x0080)

The ChargingCurrent() command uses the Write-Word
protocol (Figure 3a). The command code for Charging­Current() is 0x14 (0b00010100). The 16-bit binary num­ber formed by D15–D0 represents the current-limit set
point (I0) in milliamps. However, since the MAX1645 has
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 50mΩ sense resistor (R2 in Figure 1) is
required to achieve the correct CODE/current scaling.

The power-on reset value for the ChargingCurrent() reg­ister is 0x0080; thus, the first time a MAX1645 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 volt­age set point (V0) in millivolts; however, since the
MAX1645 has 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 bat­tery 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 over­range, 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() reg­ister is 0x4880; thus, the first time a MAX1645 is 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 compliance 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 if
D15, D14, D13, D12, or D11 of the Write-Word protocol
data equals 1. Table 6 summarizes the Alarm-

Warning() command’s function. The ALARM_INHIBITED
status bit remains set until the battery 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 switching regula­tor remains off.

Interrupts and Alert Response Address

The MAX1645 requests an interrupt by pulling the INT
pin low. An interrupt is normally requested 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_PRESENT_MASK (bit 5), or AC_PRESENT_MASK
(bit 4).

All interrupts are cleared by sending any command to
the MAX1645, 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
responds to the AlertResponse() address with 0x13,
which is its address and a trailing “1.”

Figure 6. Average Voltage Between CSIP and CSIN vs. Charging
Current() Code

150.4

102.4

51.2

IN CURRENT REGULATION (mV)

AVERAGE (CSIP-CSIN) VOLTAGE

6.4

0x0400

0x0080

128

1024

0x0800

2048 65535

0XFFFF

0x0BC0

3008

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

24 ______________________________________________________________________________________

Charger Timeout

The MAX1645 includes a timer that terminates 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 terminated.

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 employs a buck regulator with a boot­strapped NMOS high-side switch and a low-side NMOS
synchronous rectifier.

DC-DC Controller

The control scheme is a constant off-time, variable fre­quency, cycle-by-cycle current mode. The off-time is
constant for a given BATT voltage; it varies with V

BATT

to keep the ripple current constant. During low-dropout
operation, a maximum on-time of 10ms allows the con­troller to achieve >99% duty cycle with continuous con­duction. Figure 8 shows the controller functional
diagram.

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 VLXto V

BST

. When the low-side

18.432V

Figure 7. ChargingVoltage() Code to Voltage Mapping

16.800V

= 4.096V

V

REF

VDCIN > 20V

12.592V

8.400V

VOLTAGE SET POINT (V0)

4.192V

1.024V

0

0x0400

0

0x20Dx 0x41A00x313x 0x48000x106x

ChargingVoltage() D15–D0 DATA

0xFFFF

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 25

Figure 8. DC-to-DC Converter Functional Diagram

10ms

RESET

4.0V

0.25V

IMAX

CCMP

IMIN

S

BST

RQ

MAX1645

RQ

CHG

Q

S

1µs

CSSP ADAPTER IN

CSS

CSSN
BST

DHI

DHI

LX

DLO

DLO

R1

LDO

C

BST

L1

0.1V

ZCMP

CCVCCICCS

CONTROL

LVC

CSIP

CSI

GMS

GMI

GMV

DACV

DACI

ON

CLS

R

FC

70k

R

FI

20k

CSIN
BATT

C

OUT

R2

BATTERY

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

26 ______________________________________________________________________________________

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 intro­duces 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 V

DD

is

powered from an external voltage source.

Thermistor Bits

Figure 9 shows the expected electrical behavior of a
103ETB-type thermistor (nominally 10kΩ at +25°C ±5%
or better) to be used with the MAX1645:

• 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 bat­tery. 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 charger is stopped
unless the HOT_STOP bit is cleared in the
ChargerMode() command.

• 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 450Ω will 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
case, it is the responsibility of the battery pack to
manipulate the resistance to obtain correct charger
behavior.

Load and Source Switch Drivers

The MAX1645 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 P­channel 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 P­channel 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 has a 99.99% duty-cycle capability with
a 10ms maximum on-time and 1µs off-time. This allows
the charger to achieve dropout performance 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)

.

Figure 9. Typical Thermistor Characteristics

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)

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 27

Applications Information

Smart Battery Charging

System/Background Information

A smart battery charging system, at a minimum, con­sists of a smart battery and smart battery charger com­patible 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
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 (resis­tance, 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 sys­tem. This configuration may be used to “condition” bat­tery 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
(Table 7). Level 3 smart battery chargers are supersets
of Level 2 chargers and, as such, support all Level 2
charger commands.

V

Figure 10. Typical Single Smart Battery System

CC

+12V, -12V

SYSTEM
POWER
SUPPLY

DC (UNREGULATED) / V

BATTERY

SYSTEM
POWER

CONTROL

V

BATTERY

DC (UNREGULATED)

CONVERTER

(UNREGULATED)

AC

AC-DC

SYSTEM HOST
(SMBus HOST)

CRITICAL EVENTS

BATTERY DATA/STATUS REQUESTS

SMART

BATTERY

SAFETY
SIGNAL

CHARGING VOLTAGE/CURRENT

REQUESTS

CRITICAL EVENTS

MAX1645

SMART BATTERY

CHARGER

SMBus

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

28 ______________________________________________________________________________________

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() mes­sages it receives from the battery. In Level 2 charging,
the smart battery is completely responsible for initiating
the communication and providing the charging algo­rithm to the charger.

The smart battery is in the best position to tell the smart
battery charger how it needs to be charged. The charg­ing 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-

Figure 11. Typical System Using Multiple Smart Batteries

V

Level 3

Level 3Level 2

Level 3Slave/Master

Slave only

MODIFIED FROM

BATTERY

CHARGE ALGORITHM SOURCE

BATTERY

SMBus MODE

Table 7. Smart Battery Charger Type
by SMBus Mode and Charge Algorithm
Source

Note:

Level 1 smart battery chargers were defined in the ver­sion 0.95a specification. While they can correctly interpret
smart battery end-of-charge messages, minimizing over­charge, 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.

CC

+12V, -12V

SYSTEM

POWER
SUPPLY

DC (UNREGULATED) / V

BATTERY

NOTE: SB 1 POWERING SYSTEM
SB 2 CHARGING

SMART BATTERY 1

SMART BATTERY 2

AC

AC-DC

CONVERTER

(UNREGULATED)

SYSTEM HOST
(SMBus HOST)

BATTERY DATA/STATUS REQUESTS

BATT

V

SMART BATTERY

SELECTOR

CRITICAL EVENTS

BATT

SAFETY

SIGNAL

SMBus

V

SMBus

SAFETY

SIGNAL

SMBus

SMBus

SAFETY SIGNAL

V

CHARGE

MAX1645

SMART

BATTERY

CHARGER

MAX1645

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

______________________________________________________________________________________ 29

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 9 lists the recommended components and refers
to the circuit of Figure 1; Table 8 lists the suppliers’
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 3A
or higher. This diode may not be necessary if P1 is
used. The P-channel MOSFET P1 turns on when V

CVS

>

V

BATT

. This eliminates the voltage drop and power con­sumption of the Schottky diode. To minimize power loss,
select a MOSFET with an R

DS(ON)

of 50mΩ or 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
R

DS(ON)

of 50mΩ or 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 I

GATE

= Q

GATE

· f (where f
is the DC-DC converter maximum switching frequency
of 400kHz).

The low-side switch N2 should also have a current rat­ing of at least 3A, have an R

DS(ON)

of 100mΩ or 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 MOS­FET with an R

DS(ON)

of 50mΩ or 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 1/2 of the current ripple (∆IL).

I

SAT

= 3A + 1/2 ∆I

L

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 ∆I

L

with the following equation:

∆IL= 16Vµs / L

Higher inductor values decrease the ripple current.
Smaller inductor values require higher saturation cur­rent 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 10kΩ
resistor 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, respectively. To achieve acceptable accuracy, R6
should be 10kΩ and 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 tran­sients that exceed 0.5V due to large current changes
and parasitic component inductance. To achieve prop­er battery and input current compliance, the current­sense input signals should be filtered to remove large
common-mode transients. The input current limit sens­ing circuitry is the most sensitive case due to large cur­rent steps in the input filter capacitors (C1 and C2) in

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 8. Components Suppliers

MAX1645

Advanced Chemistry-Independent, Level 2
Battery Charger with Input Current Limiting

30 ______________________________________________________________________________________

Table 9. 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 >100kΩ input 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

Advanced Chemistry-Independent, Level 2

Battery Charger with Input Current Limiting

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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.

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 evaluation
kit manual for examples. A ground plane is essential for
optimum performance. In most applications, the circuit
will be located on a multilayer board, and full use of the
four or more copper layers 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 con­nections.

• 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 top­layer copper so they do not go through vias.

The resulting top-layer subground plane is con­nected 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 high­current paths should also be minimized, but
focusing primarily on short ground and current­sense 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 ana­log 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

Advanced Chemistry-Independent, Level 2
Battery Charger 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

© 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Typical Operating Circuit

ADAPTER IN

CVS
DCIN

REF

CLS

MAX1645

DDS

CSSP

CSSN

LDO

LOAD

AGND

DAC
CCV

CCI

CCS

BST

DLOV

DHI

DLO

PGND

CSIP

CSIN

PDL

BATT

THM

V

SCL

SDA

INT

LX

BATTERY

DD

HOST