Datasheet MAX1645AEEI Datasheet (Maxim)

General Description

The MAX1645 are high-efficiency battery chargers 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 transition 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 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-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

♦ 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

CVS

PDS

CSSP

CSSN

BST

DHI

INT

DLOV

DLO

PGND

CSIP

CSIN

PDL

SDA

SCL

THM

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, V

BATT

= +16.8V, V

DCIN

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

= +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)

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

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

+ 0.3V)

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

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

Continuous Power Dissipation (T

= +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 < V

DCIN

< 28V

CVS

referred to V

BATT

, V

CVS

rising

PDS

= V

CSSP

- 2V, V

DCIN

= 16V

PDS = CSSP

PDS

= 0

0 < V

DCIN

< 6V, VDD= 5V, V

SCL

= 5V,

SDA

= 5V

CVS

referred to V

BATT

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

-150 -100 -50

PDL-OFF

PDL Load Switch Turn-Off Threshold

10 50

PDS Turn-Off Current

µA

100 150 300

PDS Turn-On Current

81012

PDS Output Low Voltage, PDS Below CSSP

100 200 300

PDS-HYS

PDS Charging Source Switch Threshold Hysteresis

50 100 150

PDS-OFF

PDS Charging Source Switch Turn-Off Threshold

2.4 2.8

BATT Undervoltage Threshold (Note 2)

4.066 4.096 4.126

REF

REF Output Voltage

1.7 6

DCIN

DCIN Supply Current

828

DCIN

µA

80 150

VDDQuiescent Current

2.1 2.5

2.55 2.8

VDDUndervoltage Threshold

2.8 5.65

VDDInput Voltage Range (Note 1)

0.7 2

DCIN Supply Current Charging Inhibited

7.5 7.85

DCIN Undervoltage Threshold

7 7.4

5.15 5.4 5.65

LDO

LDO Output Voltage

UNITSMIN TYP MAXSYMBOLPARAMETER

DCIN rising

DCIN falling

VDDrising

VDDfalling

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, V

BATT

= +16.8V, V

DCIN

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

= +25°C.)

CCV/CCI/CCS Clamp Voltage (Note 4)

CCV

= V

CCI

= V

CCS

= 0.25V to 2V

150 300 600

61.6 128 194.4

BATT

= 1V,

CSI

= 50mΩ

BATT

= 1V,

CSI

= 50mΩ

MAX1645A

CSSN Input Bias Current -100 35 100 mAV

CSSP

= C

CSSN

= V

DCIN

= 0 to 28V

CLS

= 2.048V

CLS

= 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

61.6 128 194.4

4.714 5.12 5.526 A

PDL Turn-Off Current

PDL Load Switch Threshold Hysteresis

PDL-HYS

100 200 300

612

PDL Turn-On Resistance

50 100 150

kΩ

2.282 2.56 2.838

BATT Undervoltage Charge Current

20 128 200

BATT/CSIP/CSIN Input Voltage Range

020

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

CLS

= V

REF

/2 to V

REF

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

BATT

= 16.8V

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

CSIP

- V

CSIN

= 150.4mV

CONDITIONS

ChargingVoltage() = 0x20D0

MAX1645

ChargingVoltage() = 0x3130

ChargingVoltage() = 0x41A0

CVS

= 28V

ChargingVoltage() = 0x1060

= 50mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V

CSS

= 40mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V, charge inhibited

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V, V

DCIN

= 0

CSSP

= V

CSSN

= V

DCIN

= 0 to 28V

CVS

referred to V

BATT

CSSP

= V

CSSN

= 28V, V

DCIN

= 0

CSSN

- V

PDL

= 1V

From BATT to CCV

From CSSP/CSSN to CCS, V

CLS

= 2.048V,

CSSP

- V

CSSN

= 102.4mV

PDL to GND

MAX1645/MAX1645A

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

4 _______________________________________________________________________________________

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

CSI

= 50mΩ

DLOV

= V

LDO

, DLO low

DCIN

= 28V, V

BATT

= VLX= 20V

DCIN

= 0, V

BATT

= VLX= 20V

THM

= 4% of VDDto 96% of VDD,

= 2.8V to 5.65V

DHI high

CONDITIONS

SDA Output Low Sink Current

µA

-1 1

SDA/SCL Input Bias Current

220

SDA/SCL Input Hysteresis

1.4

SDA/SCL Input High Voltage

0.6

SDA/SCL Input Low Voltage

Thermistor Comparator Threshold Hysteresis

6 7.5 9

Thermistor Underrange Threshold

% of V

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

51015

Maximum On-Time

µs

1 1.25 1.5

OFF

Minimum Off-Time

Ω

614

DLO Output Resistance

Ω

6 14

DHI Output Resistance

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

LX Input Quiescent Current

µA

615

BST Supply Current

UNITSMIN TYP MAXSYMBOLPARAMETER

INT

= 1mA

INT

= 5.65V

25 200

µA

INT Output High Leakage INT Output Low Voltage

HD:DAT

SDA Hold Time from SCL

250

SU:DAT

SDA Setup Time from SCL

µs

HIGH

SCL High Period

µs

4.7

LOW

SCL Low Period

µs

4.7

SU:STA

Start Condition Setup Time from SCL

µs

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

= +25°C.)

% of V

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, V

BATT

= +16.8V, V

DCIN

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

= +25°C.)

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

140 175 210

WDT

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

µs

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

DCIN Undervoltage Threshold

7.85 V

DCIN Supply Current Charging Inhibited

VDDInput Voltage Range (Note 1)

2.8 5.65

VDDUndervoltage Threshold

2.8 V

2.1

VDDQuiescent Current I

150

µA

DCIN Typical Operating Range V

DCIN

828

DCIN Supply Current I

DCIN

REF Output Voltage V

REF

4.035 4.157

BATT Undervoltage Threshold (Note 2)

2.4 2.8

PDS Charging Source Switch Turn-Off Threshold

PDS-OFF

50 150

PDS Charging Source Switch Threshold Hysteresis

PDS-HYS

100 300

PDS Output Low Voltage, PDS Below CSSP

812

PDS Turn-On Current

100 300

µA

PDS Turn-Off Current

PDL Load Switch Turn-Off Threshold

PDL-OFF

-150 -50

PDL Load Switch Threshold Hysteresis

PDL-HYS

100 300

PDL Turn-Off Current

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

CVS

referred to V

BATT

, V

CVS

falling

CVS

referred to V

BATT

0 < V

DCIN

< 6V, VDD= 5V, V

SCL

= 5V,

SDA

= 5V

PDS

= 0

PDS = CSSP

PDS

= V

CSSP

- 2V, V

DCIN

= 16V

CVS

referred to V

BATT

, V

CVS

rising

CVS

referred to V

BATT

CSSN

- V

PDL

= 1V

8V < V

DCIN

< 28V

DCIN rising

DCIN falling

VDDrising

VDDfalling

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, V

BATT

= +16.8V, V

DCIN

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

Maximum Duty Cycle

Minimum Off-Time t

OFF

1 1.5

µs

Maximum On-Time t

515

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

BATT Charge Current (Note 3) I0

2.608 3.408

15.2 240.8

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

µA

BATT Undervoltage Charge Current

20 200

BATT/CSIP/CSIN Input Voltage Range

020

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

CONDITIONS

BATT

= 1V, R

CSI

= 50mΩ

ChargingVoltage() = 0x1060

ChargingVoltage() = 0x20D0

ChargingVoltage() = 0x3130

ChargingVoltage() = 0x41A0

CSI

= 50mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V, charge inhibited

CSS

= 40mΩ

Total of I

BATT

, I

CSIP,

and I

CSIN

;

BATT

= 0 to 20V, V

DCIN

= 0

CSSP

= V

CSSN

= V

DCIN

= 28V

CSSP

= V

CSSN

= 28V, V

DCIN

= 0

PDL to GND

From BATT to CCV

CVS

= 28V

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,

CSSP

- V

CSSN

= 102.4mV

CCV

= V

CCI

= V

CCS

= 0.25V to 2V

ChargingCurrent() = 0x0BC0

ChargingCurrent() = 0x0080

CLS

= 4.096V

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/MAX1645A

Advanced Chemistry-Independent, Level 2

Battery Chargers 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

Start Condition Hold Time from SCL

Start Condition Setup Time from SCL

SU:STA

4.7

µs

HD:STA

µs

SDA Setup Time from SCL t

SU:DAT

250

PARAMETER SYMBOL MIN MAX UNITS

DLO Output Resistance

Ω

DHI Output Resistance

Ω

Inductor Peak Current Limit

5.0 7.0

DLOV Supply Current

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

BST Supply Current

µA

Thermistor Hot Threshold

22 25

% of V

Thermistor Underrange Threshold

SDA/SCL Input Low Voltage

0.6

SDA/SCL Input High Voltage

1.4

SDA/SCL Input Bias Current

-1 1

µA

SDA Output Low Sink Current

INT Output High Leakage

µA

INT Output Low Voltage

200

SCL High Period t

HIGH

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

CSI

= 50mΩ

DLOV

= V

LDO

, DLO low

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

DCIN

= 28V, V

BATT

= VLX= 20V

SDA

= 0.4V

DCIN

= 0, V

BATT

= VLX= 20V

INT

= 5.65V

INT

= 1mA

DHI high

% of V

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)

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)

LDO

(V)

MAX1645/MAX1645A

Advanced Chemistry-Independent, Level 2 Battery Chargers 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

16V

14V

12V

1.5V

CCV

CCI

BATT

0.5V

2ms/div

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

1ms/div

CCI

CCV

CCI

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

DCIN

(V)

LDO

(V)

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)

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

WDT

140 210

SDA Output Data Valid from SCL

µs

PARAMETER SYMBOL MIN MAX UNITSCONDITIONS

MAX1645/MAX1645A

Advanced Chemistry-Independent, Level 2

Battery Chargers with Input Current Limiting

_______________________________________________________________________________________ 9

100

0 1000500 1500 2000 2500 3000

EFFICIENCY vs. BATTERY CURRENT

(VOLTAGE-CONTROL LOOP)

MAX1645 toc07

BATTERY CURRENT (mA)

EFFICIENCY (%)

A: V

DCIN

= 20V, ChargingVoltage() = 16.8V

B: V

DCIN

= 16V, ChargingVoltage() = 8.4V

100

0 1000500 1500 2000 2500 3000

EFFICIENCY vs. BATTERY CURRENT

(CURRENT-CONTROL LOOP)

MAX1645 toc08

ChargingCurrent() (CODE)

EFFICIENCY (%)

A: V

DCIN

= 20V, V

BATT

= 16.8V

B: V

DCIN

= 16V, V

BATT

= 8.4V

A B

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

-0.1

-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 (%)

BATT

= 0

MEASURED AT AVAILABLE CODES

-5

-2

-3

-4

-1

0 1000500 1500 2000 2500 3000

CURRENT-SETTING ERROR

vs. ChargingCurrent() CODE

MAX1645 toc11

ChargingCurrent() (CODE)

BATT CURRENT ERROR (%)

BATT

= 12.6V

MEASURED AT AVAILABLE CODES

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)

BATT

CLS

= 2V

CSS

= 40mΩ

BATT

= 16.8V SOURCE CURRENT LIMIT = 2.5A ChargingCurrent() = 3008mA ChargingVoltage() = 18,432mV

1.0

0.5

2.0

1.5

3.0

2.5

3.5

042 6 8 101214161820

SOURCE/BATT CURRENT vs. V

BATT

WITH SOURCE CURRENT LIMIT

MAX1645 toc13

BATT

(V)

SOURCE/BATT CURRENT (A)

BATT

LOAD

= 2A

CLS

= 2V

CSS

= 40mΩ

ChargingVoltage() = 18,432mV ChargingCurrent() = 3008mA SOURCE CURRENT LIMIT = 2.5A

Typical Operating Characteristics (continued)

(Circuit of Figure 1, V

DCIN

= 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) V

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

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

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 voltage 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 currentregulation 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/MAX1645A voltage DACs have 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/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 current; 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 50mΩ sense resistor (R2 in Figure 1) is required to achieve the correct CODE/current 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. V

CLS

is set by a resistor-divider

between REF and GND.

The input source current is the sum of the device current, 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:

SOURCE

= I

LOAD

+ [(I

CHARGE

· V

BATT)

/ (VIN· η)]

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

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:

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:

MAX

= (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 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/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

DLOV

BST

PGND

DLO

CSIP

CSIN

PDL

BATT

THM

SCL

SDA

INT

BATTERY

HOST

1N4148

1µF

R13

C23

0.1µF

1µF

100k

0.1µF

0.01µF

10k

C11

0.01µF

C10

0.01µF

P1 FDS6675 D1

1N5821

22µF

0.04Ω

C20, 1µF

C19, 1µF

R14

4.7Ω

R15

4.7Ω

C6 1µF

1N4148

R12

33Ω

C16

0.1µF

C14

0.1µF

FDS6680

FDS6612A

22µH

1N5821

10k

C12 1µF

10k

R10 10k

C13

1.5nF

10k

0.05Ω

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

REF

PDL

CSS

CSSP

CSSN

CLS

CSIP

CSIN

SCL

SDA

THM

CSI

BATT

GMI

GMV

SMB

DACI

DACV

TEMP

DC-DC

DHI

BST

DHI

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, V

DD,

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 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 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 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 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 battery 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, the part will be in its Power-On Reset state. No charging will occur when VDDis 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 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/MAX1645A are SMBus slave devices and do not initiate communication on the bus. They receive commands and respond to queries for status information. Figure 3 shows examples of the SMBus Write-Word and ReadWord 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 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/ MAX1645A’s internal state. The latched bits, THERMISTOR_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

ACK

0MSB LSB

1b8 bits

ACK

COMMAND

BYTE

0MSB LSB

1b7 bits

SLAVE

ADDRESS

0MSB LSB

1b8 bits

ACK

LOW

DATA

BYTE

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

LOW DATA BYTE

ACK

8 bits 1b

MSB LSB 0

SLAVE

ADDRESS

7 bits 1b

MSB LSB 1

ACK

COMMAND

BYTE

ACK

8 bits 1b

MSB LSB 0

SACK

SLAVE

ADDRESS

7 bits 1b

MSB LSB 0

ever 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/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

HIGH

LOW

HD:STA

SU:STA

SU:DAT

HD:DAT

SCL

SDA

SU:DAT

HD:DAT

Figure 4. SMBus Serial Interface Timing—Address

Figure 5. SMBus Serial Interface Timing—Acknowledgment

MOST SIGNIFICANT BIT

OF DATA CLOCKED

INTO MASTER

SCL

SDA

R/W BIT

CLOCKED

INTO SLAVE

ACKNOWLEDGE

INTO MASTER

BIT CLOCKED

SLAVE PULLING SDA LOW

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., V

from 0 to +3.3V)

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/MAX1645A

Advanced Chemistry-Independent, Level 2

Battery Chargers 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/MAX1645A

Advanced Chemistry-Independent, Level 2 Battery Chargers 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/MAX1645A

Advanced Chemistry-Independent, Level 2

Battery Chargers 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.

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/MAX1645A

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

22 ______________________________________________________________________________________

Table 6. AlarmWarning()

Command: 0x16

OTHER_ALARM

0 = Charge normally 1 = Terminate charging

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/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 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/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 currentregulation-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/ 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 voltage 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 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/ 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 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/MAX1645A 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/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 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/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 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/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 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.

16.800V

18.432V

REF

= 4.096V

VDCIN > 20V

1.024V

0x0400

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

CCVCCICCS

GMS

GMI

GMV

DACV

DACI

CLS

DLO

DHI

CSI

1µs

BST

CCMP

ZCMP

IMIN

CHG

CSS

CSSP ADAPTER IN

CSSN

BST

DHI

LDO

BST

DLO

CSIP

CSIN

OUT

BATT

BATTERY

MAX1645/MAX1645A

70k

20k

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 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

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/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 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 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 450Ω will cause both the THERMISTOR_HOT and the THERMISTOR_UR bits to be set). The thermistor may be replaced by fixedvalue 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

RESISTANCE (kΩ)

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

Not Allowed

WAKE-UP CHARGE

Not allowed by MAX1645

Allowed for Timeout Period by MAX1645A

Not Allowed

Allowed for Timeout Period

Float Charge*

DESCRIPTION

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 manipulate 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 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/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 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).

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

SYSTEM POWER

CONTROL

AC-DC

CONVERTER

(UNREGULATED)

SYSTEM POWER

SUPPLY

DC (UNREGULATED) / V

BATTERY

SAFETY SIGNAL

BATTERY

DC (UNREGULATED)

+12V, -12V

SYSTEM HOST

(SMBus HOST)

SMART

BATTERY

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 (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

Figure 11. Typical System Using Multiple Smart Batteries

AC-DC

CONVERTER

(UNREGULATED)

DC (UNREGULATED) / V

BATTERY

NOTE: SB 1 POWERING SYSTEM SB 2 CHARGING

+12V, -12V

SYSTEM HOST (SMBus HOST)

SMART BATTERY

SELECTOR

SMBus

SAFETY SIGNAL

CHARGE

BATT

SAFETY

SIGNAL

BATT

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 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.

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() 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 chemistry 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 V

CVS

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).

SAT

= 3A + 1/2 ∆I

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

with the following equation:

∆I

= 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

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%

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%

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/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 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 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 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, V

, 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/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

LOAD

ADAPTER IN

MAX1645A

CVS DCIN

REF

CLS

AGND

DAC

CCV

CCI

CCS

DDS

CSSP

CSSN

LDO

DHI

DLOV

BST

PGND

DLO

CSIP

CSIN

PDL

BATT

THM

SCL

SDA

INT

BATTERY

HOST

Typical Operating Circuit

Datasheet MAX1645AEEI Datasheet (Maxim)

Specifications and Main Features

Frequently Asked Questions

User Manual