19-1182; Rev 3; 10/01
UAL
IT MAN
TION K
A
SHEET
EVALU
S DATA
W
FOLLO
Switch-Mode Lithium-Ion
Battery-Charger
____________________________Features
♦
Charges 1 to 4 Li+ Battery Cells
♦
±0.75% Voltage-Regulation Accuracy
Using 1% Resistors
♦
Provides up to 4A without Excessive Heating
♦
90% Efficient
♦
Uses Low-Cost Set Resistors and
N-Channel Switch
♦
Up to 24V Input
♦
Up to 18V Maximum Battery Voltage
♦
300kHz Pulse-Width Modulated (PWM) Operation
Low-Noise, Small Components
♦
Stand-Alone Operation—No Microcontroller
Needed
General Description
The MAX745 provides all functions necessary for
charging lithium-ion (Li+) battery packs. It provides a
regulated charging current of up to 4A without getting
hot, and a regulated voltage with only ±0.75% total
error at the battery terminals. It uses low-cost, 1% resis-
tors to set the output voltage, and a low-cost N-channel
MOSFET as the power switch.
The MAX745 regulates the voltage set point and charg-
ing current using two loops that work together to transi-
tion smoothly between voltage and current regulation.
The per-cell battery voltage regulation limit is set
between 4V and 4.4V using standard 1% resistors, and
then the number of cells is set from 1 to 4 by pin-strap-
ping. Total output voltage error is less than ±0.75%.
For a similar device with an SMBus™ microcontroller
interface and the ability to charge NiCd and NiMH cells,
refer to the MAX1647 and MAX1648. For a low-cost Li+
charger using a linear-regulator control scheme, refer
to the MAX846A.
MAX745
Ordering Information
PART
MAX745C/D
MAX745EAP
TEMP RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
Dice*
20 SSOP
________________________Applications
Li+ Battery Packs
Desktop Cradle Chargers
Cellular Phones
Notebook Computers
Hand-Held Instruments
*Dice
are tested at T
A
= +25°C.
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
V
IN
(UP TO 24V)
DCIN
VL
BST
DHI
LX
N
CELL
COUNT
SELECT
ON
OFF
CELL0
CELL1
THM/SHDN
REF
SETI
VADJ
MAX745
DLO
N
I
CHARGE
CS
R
SENSE
SET PER
CELL VOLTAGE
WITH 1% RESISTORS
STATUS
BATT
CCV
CCI
GND
IBAT
PGND
VOUT
1–4 Li+ CELLS
(UP TO 18V)
SMBus is a trademark of Intel Corp.
________________________________________________________________
Maxim Integrated Products
1
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.
Switch-Mode Lithium-Ion
Battery Charger
MAX745
ABSOLUTE MAXIMUM RATINGS
DCIN to GND ............................................................-0.3V to 26V
BST, DHI to GND ......................................................-0.3V to 30V
BST to LX ....................................................................-0.3V to 6V
DHI to LX............................................(LX - 0.3V) to (BST + 0.3V)
LX to GND ................................................-0.3V to (DCIN + 0.3V)
VL to GND...................................................................-0.3V to 6V
CELL0, CELL1, IBAT, STATUS, CCI, CCV, REF, SETI,
VADJ, DLO, THM/SHDN to GND.................-0.3V to (VL + 0.3V)
BATT, CS to GND .....................................................-0.3V to 20V
PGND to GND..........................................................-0.3V to 0.3V
VL Current ...........................................................................50mA
Continuous Power Dissipation (T
A
= +70°C)
SSOP (derate 8.00mW/°C above +70°C) ....................640mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature.........................................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DCIN
= 18V, V
BATT
= 8.4V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
SUPPLY AND REFERENCE
DCIN Input Voltage Range
DCIN Quiescent Supply Current
VL Output Voltage
REF Output Voltage
REF Output Load Regulation
SWITCHING REGULATOR
Oscillator Frequency
DHI Maximum Duty Cycle
DHI On-Resistance
DLO On-Resistance
BATT Input Current
Output high or low
Output high or low
VL < 3.2V, V
BATT
= 12V
VL > 5.15V, V
BATT
= 12V
VL < 3.2V, V
CS
= 12V
VL > 5.15V, V
CS
= 12V
4V < V
BATT
< 16V
(Note 1)
SETI = V
REF
(full scale)
SETI = 400mV
Not including VADJ resistor tolerance
With 1% tolerance VADJ resistors
170
14
-0.65
-0.75
0
±1.5
185
18
205
22
+0.65
+0.75
6.0V < V
DCIN
< 24V, logic inputs = VL
6.0V < V
DCIN
< 24V, no load
T
A
= +25°C
6.0V < V
DCIN
< 24V
0 < I
REF
< 1mA
270
89
5.15
4.17
4.16
CONDITIONS
MIN
6
4
5.40
4.2
4.2
10
300
93
4
6
7
14
5
500
5
400
19
TYP
MAX
24
6
5.65
4.23
4.24
20
330
UNITS
V
mA
V
V
mV/mA
kHz
%
Ω
Ω
µA
CS Input Current
BATT, CS Input Voltage Range
CS to BATT Offset Voltage
CS to BATT
Current-Sense Voltage
Absolute Voltage Accuracy
µA
V
mV
mV
%
2
_______________________________________________________________________________________
Switch-Mode Lithium-Ion
Battery Charger
MAX745
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= 18V, V
BATT
= 8.4V,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C, unless otherwise noted.)
PARAMETER
ERROR AMPLIFIERS
GMV Amplifier Transconductance
GMI Amplifier Transconductance
GMV Amplifier Output Current
GMI Amplifier Output Current
CCI Clamp Voltage with Respect to CCV
CCV Clamp Voltage with Respect to CCI
CONTROL INPUTS/OUTPUTS
CELL0, CELL1 Input Bias Current
SETI Input Voltage Range
VADJ Adjustment Range
SETI, VADJ Input Bias Current
VADJ Input Voltage Range
THM/SHDN Rising Threshold
THM/SHDN Falling Threshold
STATUS Output Low Voltage
STATUS Output Leakage Current
IBAT Output Current vs.
Current-Sense Voltage
IBAT Compliance Voltage Range
Charger in current-regulation mode,
STATUS sinking 1mA
Charger in voltage-regulation mode,
V
STATUS
= 5V
V
IBAT
= 2V
0
0.9
2
(Note 1)
1.1V < V
CCV
< 3.5V
1.1V < V
CCI
< 3.5V
25
25
-1
0
10
-10
0
2.20
2.01
2.3
2.1
+10
V
REF
2.34
2.19
0.2
1
CONDITIONS
MIN
TYP
800
200
±130
±320
80
80
200
200
+1
V
REF
MAX
UNITS
µA/V
µA/V
µA
µA
mV
mV
µA
V
%
nA
V
V
V
V
µA
µA/mV
V
ELECTRICAL CHARACTERISTICS
(V
DCIN
= 18V, V
BATT
= 8.4V,
T
A
= -40°C to +85°C,
unless otherwise noted. Limits over temperature are guaranteed by design.)
PARAMETER
SUPPLY AND REFERENCE
VL Output Voltage
REF Output Voltage
SWITCHING REGULATOR
(Note 1)
Oscillator Frequency
DHI On-Resistance
DLO On-Resistance
CS to BATT Full-Scale
Current-Sense Voltage
Absolute Voltage Accuracy
Not including VADJ resistors
Note 1:
When V
SETI
= 0V, the battery charger turns off.
Output high or low
Output high or low
165
-1.0
260
340
7
14
205
+1.0
kHz
Ω
Ω
mV
%
CONDITIONS
6.0V < V
DCIN
< 24V, no load
6.0V < V
DCIN
< 24V
MIN
5.10
4.14
TYP
MAX
5.70
4.26
UNITS
V
V
_______________________________________________________________________________________
3
Switch-Mode Lithium-Ion
Battery Charger
MAX745
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, V
DCIN
= 18V, V
BATT
= 4.2V, CELL0 = CELL1 = GND, C
VL
= 4.7µF C
REF
= 0.1µF. Circuit of Figure 1, unless otherwise
noted.)
BATTERY VOLTAGE
vs. CHARGING CURRENT
MAX745/TOC-01
CURRENT-SENSE VOLTAGE
vs. SETI VOLTAGE
180
CURRENT-SENSE VOLTAGE (mV)
160
140
120
100
80
60
40
20
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
SETI VOLTAGE (V)
R1 = 0.2Ω
MAX745/TOC-02
4.5
4.0
3.5
BATTERY VOLTAGE (V)
3.0
2.5
2.0
1.5
1.0
0.5
0
0
R1 = 0.2Ω
R16 = SHORT
R12 = OPEN CIRCUIT
200
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
CHARGING CURRENT (A)
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX745/TOC-06
VOLTAGE LIMIT
vs. VADJ VOLTAGE
4.40
PER-CELL VOLTAGE LIMIT (V)
4.35
4.30
4.25
4.20
4.15
4.10
4.05
4.00
3.95
MAX745/TOC-03
4.205
4.204
REFERENCE VOLTAGE (V)
4.203
4.202
4.201
4.200
4.199
4.198
4.197
4.196
4.195
0
25
50
TEMPERATURE (°C)
75
4.45
100
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
VADJ VOLTAGE (V)
VL LOAD REGULATION
MAX745/TOC-04
REFERENCE LOAD REGULATION
4.24
REFERENCE VOLTAGE (V)
4.23
4.22
4.21
4.20
4.19
4.18
4.17
4.16
4.15
MAX745/TOC-05
5.50
5.45
VL OUTPUT VOLTAGE (V)
5.40
5.35
5.30
5.25
5.20
5.15
5.10
5.05
0
0
5
10
15
20
4.25
25
0
500
1000
1500
2000
2500
3000
VL OUTPUT CURRENT (mA)
REFERENCE CURRENT (µA)
4
_______________________________________________________________________________________
Switch-Mode Lithium-Ion
Battery Charger
______________________________________________________________Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11, 12
NAME
IBAT
DCIN
VL
CCV
CCI
THM/
SHDN
REF
VADJ
SETI
GND
CELL1,
CELL0
STATUS
BATT
CS
PGND
DLO
DHI
LX
BST
FUNCTION
Current-Sense Amplifier’s Analog Current-Source Output. See the
Monitoring Charge Current
section for a
detailed description.
Charger Input Voltage. Bypass DCIN with a 0.1µF capacitor.
Chip Power Supply. Output of the 5.4V linear regulator from DCIN. Bypass VL with a 4.7µF capacitor.
Voltage-Regulation-Loop Compensation Point
Current-Regulation-Loop Compensation Point
Thermistor Sense-Voltage Input. THM/SHDN also performs the shutdown function. If pulled low,
the charger turns off.
4.2V Reference Voltage Output. Bypass REF with a 0.1µF or greater capacitor.
Voltage-Adjustment Pin. VADJ is tied to a 1% tolerance external resistor-divider to adjust the voltage set
point by 10%, eliminating the need for precision 0.1% resistors. The input voltage range is 0V to V
REF
.
SETI is externally tied to the resistor-divider between REF and GND to set the charging current.
Analog Ground
Logic Inputs to Select Cell Count. See Table 1 for cell-count programming.
An open-drain MOSFET sinks current when in current-regulation mode, and is high impedance when in volt-
age-regulation mode. Connect STATUS to VL through a 1kΩ to 100kΩ pullup resistor. STATUS can also drive
an LED for visual indication of regulation mode (see MAX745 EV kit). Leave STATUS floating if not used.
Battery-Voltage-Sense Input and Current-Sense Negative Input
Current-Sense Positive Input
Power Ground
Low-Side Power MOSFET Driver Output
High-Side Power MOSFET Driver Output
Power Connection for the High-Side Power MOSFET Source
Power Input for the High-Side Power MOSFET Driver
MAX745
13
14
15
16
17
18
19
20
_______________Detailed Description
The MAX745 is a switch-mode, Li+ battery charger that
can achieve 90% efficiency. The charge voltage and
current are set independently by external resistor-
dividers at SETI and VADJ, and at pin connections at
CELL0 and CELL1. VADJ is connected to a resistor-
divider to set the charging voltage. The output voltage-
adjustment range is ±5%, eliminating the need for 0.1%
resistors while still achieving 0.75% set accuracy using
1% resistors.
The MAX745 consists of a current-mode, pulse-width-
modulated (PWM) controller and two transconductance
error amplifiers: one for regulating current (GMI) and
the other for regulating voltage (GMV) (Figure 2). The
error amplifiers are controlled through the SETI and
VADJ pins. Whether the MAX745 is controlling voltage
or current at any time depends on the battery state. If
the battery is discharged, the MAX745 output reaches
the current-regulation limit before the voltage limit,
causing the system to regulate current. As the battery
charges, the voltage rises to the point where the volt-
age limit is reached and the charger switches to regu-
lating voltage. The STATUS pin indicates whether the
charger is regulating current or voltage.
Voltage Control
To set the voltage limit on the battery, connect a resis-
tor- divider to VADJ from REF. A 0V to V
REF
change at
VADJ sets a ±5% change in the battery limit voltage
around 4.2V. Since the 0 to 4.2V range on VADJ results
in only a 10% change on the voltage limit, the resistor-
divider’s accuracy does not need to be as high as the
output voltage accuracy. Using 1% resistors for the
voltage dividers typically results in no more than 0.1%
degradation in output voltage accuracy. VADJ is inter-
nally buffered so that high-value resistors can be used
to set the output voltage. When the voltage at VADJ is
5
_______________________________________________________________________________________
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