19-0653; Rev 0; 11/06
KIT
ATION
EVALU
BLE
AVAILA
Complete Backup Management
IC for NiMH Batteries
General Description
Features
o
o
o
o
o
o
o
o
o
o
Charges 1- or 2-Cell NiMH Backup Batteries
Programmable Charge Current
DC Trickle Charge Mode for Maximum Cell Life
Deep-Recovery Charge Restores Cells < 1V
Programmable Charge Timer
Programmable Charge-Voltage Limit and Battery
UVLO
Reverse Current Blocking on BATT, LDO, and
Boost—No Diodes Needed
No Battery Drain When Off (< 50nA)
Thermistor Sensing Disables Standard Charge
Battery Restart Charge Threshold Prevents
Overcharge
MAX8672
The MAX8672 complete power manager for backup
batteries in smart devices offers feature-programmable
battery charging and main-system backup. The device
includes a charger for 1- or 2-cell NiMH backup batter-
ies. A low-quiescent current synchronous-rectified
boost converter and LDO supply up to 20mA during
system backup. The BST output is internally set to regu-
late at 3.05V. The MAX8672 LDO is powered from the
boost converter output and is adjustable from 1.5V to
3.05V.
The MAX8672 features programmable charge current,
undervoltage lockout (UVLO), and maximum cell volt-
age. Charging is controlled by both a timer and ther-
mistor monitor. Battery UVLO prevents excessive
battery discharge and keeps inactive-battery drain cur-
rent below 50nA. In addition, both LDO and boost con-
verter outputs block reverse current so that diodes are
not needed when connecting these outputs directly to
system supplies. The MAX8672 requires that a valid
system supply be present before system backup oper-
ation can occur.
The MAX8672 is available in a 14-pin, 3mm x 3mm TDFN
package and is rated for -40°C to +85°C operation.
Ordering Information
PART
MAX8672ETD+T
PIN-PACKAGE
14 TDFN-14 (3mm x 3mm)
PKG CODE
T14334+2
The MAX8672 operates in the -40°C to +85°C extended
operating temperature range.
+Denotes
lead-free package.
Applications
PDA, Palmtop, and Wireless Handhelds
Smart Cell Phones
Typical Operating Circuit
CT
THRM
MAX8672
Pin Configuration
THRM
CHGV
2.7V TO 5.5V INPUT
IN
CHGV
DR
GND
LDO
TOP VIEW
CHGI
TRKI
BST
10
FBL
14
13
12
11
LX
9
8
FBL
BATT
MAX8672
BACKUP BATTERY
CONNECTION
UV
LDO
1.75V
1
CT
2
CHGI
3
TRKI
4
BATT
5
IN
6
DR
7
UV
GND
LX
BST
3.05V
TDFN
(3mm x 3mm)
________________________________________________________________
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.
Complete Backup Management
IC for NiMH Batteries
MAX8672
ABSOLUTE MAXIMUM RATINGS
IN, BATT, BST, LDO, UV to GND ..........................-0.3V to +6.0V
FBL to GND ...............................................-0.3V to (V
BST
+ 0.3V)
CT, CHGI, TRKI, CHGV, THRM,
DR to GND ...............................................-0.3V to (V
IN
+ 0.3V)
ILX ..................................................................................0.9A
RMS
Continuous Power Dissipation (T
A
= +70°C)
14-Pin, 3mm x 3mm TDFN
(derate 18.2 mW/°C above +70°C) .........................1454.5mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°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
IN
= 3.6V, T
A
= -40°C to +85°C, C
CT
= 0.1µF, unless otherwise noted.) (Note 1)
PARAMETER
IN Voltage Range
IN Undervoltage Lockout Threshold
IN Supply Current
Internal Load Current on BST
(Note 2)
BATT Quiescent Supply
Current—Backup Mode
BATT Quiescent Supply Current—Charging
BATT Leakage Current to IN
Total BATT Battery Leakage Current During
UVLO (BATT, LX, and DR Leakage)
CHARGER AND BATTERY
1mA
≤
I
BATT(CHG)
≤
20mA,
V
IN
- V
BATT
> 400mV
CHGI Current-Limit Accuracy
I
BATT(CHG)
= 1mA, V
IN
-
V
BATT
> 400mV
0.1mA
≤
I
BATT(CHG)
≤
1mA,
V
IN
- V
BATT
> 400mV
CHGI Bias Voltage
CHGI Resistor Range
I
BATT(TRK)
= 1mA
TRKI Current-Limit Accuracy
DC Trickle-Current Programming Range
Charge-Current Programming Range
TRKI Bias Voltage
TRKI Resistor Range
Charger Dropout Voltage
V
IN
- V
BATT
where I
BATT(CHG)
falls by 10% of initial
value; V
IN
= 3.6V, I
BATT(CHG)
= 20mA
100
250
I
BATT(TRK)
= 0.1mA
I
BATT(TRK)
I
BATT(CHG)
T
A
= -40 C to +85 C
T
A
= 0
o
C to +85
o
C
T
A
= -40 C to +85 C
o
o
o
o
CONDITIONS
V
IN
rising, hysteresis = 100mV (typ)
V
BATT
> V
BATT(CHG)
V
IN
= 3.3V
V
BST
= 3.3V, no
BST or LDO load,
boost and LDO on
V
IN
= 0V
T
A
= -40°C to +50°C
T
A
= -40°C to +85°C
MIN
2.7
2.20
TYP
2.45
40
117
91
91
3
3
0.01
0.07
5
50
MAX
5.5
2.60
100
170
125
150
UNITS
V
V
µA
µA
V
BATT
= 1.55V, V
BST
= 3.3V,
V
IN
= 0V, V
BATT(CHG)
= 1.5V
V
BATT
= 1.55V, V
BST
= 3.3V, V
IN
= 3.6V
V
BATT
= 3.0V,
V
IN
= 0V
V
BATT
= 0 to 3.0V
T
A
= +25 C
T
A
= +85 C
T
A
= -40°C to +50°C
T
A
= +85 C
o
o
o
µA
µA
0.1
50
µA
nA
T
A
= -40
o
C to +85
o
C
T
A
= 0
o
C to +85
o
C
T
A
= -40
o
C to +85
o
C
T
A
= -40
o
C to +85
o
C
-10
-10
-15
-20
600
5
-10
-10
-15
0.1
0.1
600
+10
+10
+15
+20
mV
kΩ
%
mA
mA
mV
1000
kΩ
mV
%
1000
+10
+10
+15
1
20
2
_______________________________________________________________________________________
Complete Backup Management
IC for NiMH Batteries
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, T
A
= -40°C to +85°C, C
CT
= 0.1µF, unless otherwise noted.) (Note 1)
PARAMETER
CHGV Output Current
CHGV Resistor Range
V
BATT(CHG)
Voltage-Limit Adjust Range
V
BATT(CHG)
Voltage-Limit Accuracy
V
BATT(TRK)
to V
BATT(CHG)
Ratio
V
BATT(RSTRT)
to V
BATT(CHG)
Ratio
V
BATT(DR)
to V
BATT(CHG)
Ratio
Measured at BATT
T
A
= +25 C
R
CHGV
= 28.7kΩ
T
A
= 0 C to +50 C
T
A
= -30
o
C to +85
o
C
Sets 1.41V when V
CHGV
= 1.5V, measured at BATT
Sets 1.225V when V
CHGV
= 1.5V, measured at BATT
Sets 1.00V when V
CHGV
= 1.5V, measured at BATT; this
is the V
BATT
above which deep recovery (DR) turns off;
the falling threshold is typically 50mV below this
I
DR
= 0 to 10mA
Does not include
capacitor error
T
A
= +25 C
T
A
= -40
o
C to +85
o
C
2
44
-2
42.00
325.5
45
-1
2
T
A
rising
T
A
falling
T
A
falling
T
A
rising
V
UV
= 1V
49.9
0.8
R
UV
= 49.9kΩ
T
A
= 0
o
C to +50
o
C
T
A
= -30 C to +85 C
o
o
o
o
o
o
o
MAX8672
CONDITIONS
V
CHGV
= 1V
MIN
28.7
1.50
-1
-1.25
-2.25
0.926
0.799
0.653
0.775
TYP
13
MAX
57.4
3.00
+1
+1.25
+2.25
UNITS
µA
kΩ
V
%
—
—
—
—
%
%
min
o
o
o
0.940
0.816
0.667
0.816
10
0.954
0.832
0.680
0.861
20
20
25
2000
46
0
45.42
358.6
V
DR
Output Voltage to V
BATT(CHG)
Ratio Measured at BATT; no load on DR
DR Load Regulation
Charge-Timer Accuracy
Timer Adjust Range
Thermistor Hot-Trip Point
Thermistor Cold-Trip Point
Thermistor Temperature Hysteresis
Hot-Trip Thermistor Resistance
Cold-Trip Thermistor Resistance
UV Output Current
UV Resistor Range
UV Battery-Cutoff Programmable Range
UV Battery-Cutoff Accuracy
LDO
LDO Output-Voltage Range
FBL Regulation Voltage
LDO Output Current
LDO Load Regulation
LDO Dropout Voltage
LDO Dropout Resistance
FBL Input Bias Current
Using external resistors, no load
V
BST
= 3.3V, V
LDO
= 3.05V
(Note 3)
V
BST
= 3.3V, V
LDO
= 3.05V, I
LDO
= 1mA to 20mA
V
LDO
= 2.5V, I
LDO
= 10mA
V
LDO
= 2.5V
V
FBL
= 1.25V
T
A
= +25 C
T
A
= +85 C
o
o
CHGI timer period, C
CT
= 0.047µF = 8h (480min)
R
THERM
= 100kΩ at T
A
= +25 C, T
A
rising
R
THERM
= 100kΩ at T
A
= +25
o
C, T
A
falling
C
C
C
43.71
48.15
342.0
302.0
4
kΩ
µA
215
3.5
+2
+3.25
3.05
kΩ
V
%
-2
-3.25
1.5
1.225
1.25
0.08
50
5
3
15
V
V
mA
%/mA
mV
Ω
1.275
20
0.2
100
50
nA
_______________________________________________________________________________________
3
Complete Backup Management
IC for NiMH Batteries
MAX8672
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, T
A
= -40°C to +85°C, C
CT
= 0.1µF, unless otherwise noted.) (Note 1)
PARAMETER
BOOST CONVERTER
BST Output Voltage
Boost Output Current
LX Current Limit
n-Channel On-Resistance
p-Channel On-Resistance
n-Channel Maximum On-Time
p-Channel Off-Current Threshold
I
LX
= 200mA
I
LX
= -200mA
3.5
5
1-cell input (Note 3)
400
500
0.4
0.7
5
20
2.989
3.05
3.111
20
600
1
2
6.5
35
V
mA
mA
Ω
Ω
µs
mA
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Parameters are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2:
BATT current is higher due to boost ratio and efficiency.
Note 3:
Total load from both BST and LDO cannot exceed 20mA.
Typical Operating Characteristics
(V
IN
= 3.6V, Circuit of Figure 6, T
A
= +25°C, unless otherwise noted.)
1-CELL CHARGE CURRENT (I
CHG
)
vs. BATTERY VOLTAGE (V
BATT
)
MAX8672 toc01
2-CELL CHARGE CURRENT (I
CHG
)
vs. BATTERY VOLTAGE (V
BATT
)
MAX8672 toc02
1-CELL CHARGE CURRENT (I
CHG
)
vs. INPUT VOLTAGE (V
IN
)
I
CHG
= 20mA
MAX8672 toc03
25
I
CHG
= 20mA
20
CHARGE CURRENT (mA)
V
BST
= 3.3V,
V
BATT(CHG)
= 1.5V,
R
DR
= 274Ω,
V
BATT
RISING
25
I
CHG
= 20mA
20
CHARGE CURRENT (mA)
V
BST
= 3.3V,
V
BATT(CHG)
= 3V,
R
DR
= 549Ω,
V
BATT
RISING
25
20
CHARGE CURRENT (mA)
15
10
5
0
V
BATT
= 1.2V,
R
CHGV
= 28.7kΩ,
V
BST
= 3.3V
15
15
10
I
CHG
= 3mA
5
I
CHG
= 200μA
0
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
BATTERY VOLTAGE (V)
10
I
CHG
= 3mA
I
CHG
= 3mA
5
I
CHG
= 200μA
0
0.5
1.0
1.5
0
0
-5
2.0
2.5
3.0
3.5
0
I
CHG
= 200μA
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
BATTERY VOLTAGE (V)
2-CELL CHARGE CURRENT (I
CHG
)
vs. INPUT VOLTAGE (V
IN
)
MAX8672 toc04
CHARGE CURRENT (I
CHG
)
vs. TEMPERATURE
MAX8672 toc05
BATTERY-CHARGE PROFILE
(2 NiMH CELLS)
MAX8672 toc06
25
20
CHARGE CURRENT (mA)
15
10
5
0
-5
0
V
BATT
= 2.4V,
R
CHGV
= 57.6kΩ,
V
BST
= 3.3V
I
CHG
= 20mA
2.15
3.5
3.0
2.5
V
BATT
(V)
2.0
1.5
1.0
CHARGE
TERMINATION
AT V
BATT(CHG)
TRICKLE
CHARGE
STARTS AT
V
BATT(TRK)
CHARGE CURRENT (mA)
2.10
2.05
I
CHG
= 3mA
2.00
V
BATT
= 2.4V,
V
BST
= 3.3V,
R
CHGI
= 49.9kΩ
-40
-15
35
10
TEMPERATURE (°C)
60
85
0.5
0
0
I
CHG
= 200μA
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
1.95
V
IN
= 4V, V
BST
= 3.3V, R1 = 402kΩ,
R2 = 24.9kΩ, R3 = 165kΩ, R4 = R5 = 124kΩ,
R6 = 56kΩ, R7 = OPEN, R8 = SHORT,
R9 = 110kΩ, C1 = 0.047μF
60
120 180 240 300 360 420
TIME (min)
480
4
_______________________________________________________________________________________
Complete Backup Management
IC for NiMH Batteries
Typical Operating Characteristics (continued)
(V
IN
= 3.6V, Circuit of Figure 6, T
A
= +25°C, unless otherwise noted.)
BST EFFICIENCY
vs. BST LOAD CURRENT
MAX8672 toc07
MAX8672
BATT INPUT CURRENT (WHILE BOOSTING)
vs. BATT VOLTAGE
MAX8672 toc08
BST OUTPUT VOLTAGE
vs. BST LOAD CURRENT
V
IN
= NOT CONNECTED
BST OUTPUT VOLTAGE (V)
3.1
MAX8672 toc09
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
V
IN
= NOT CONNECTED
1
10
V
BATT
= 2.4V
V
BATT
= 1.2V
500
450
400
BATT CURRENT (μA)
350
300
250
200
150
100
50
0
I
LDO
,I
BST
= 0A,
V
IN
= NOT CONNECTED,
BACKUP MODE
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.0
V
BATT
= 1.2V
2.9
V
BATT
= 2.4V
2.8
3.2
0
30
60
90
120
150
180
BST LOAD CURRENT (mA)
100
BST LOAD CURRENT (mA)
BATT VOLTAGE (V)
DR CURRENT (I
DR
)
vs. BATTERY VOLTAGE (V
BATT
)
MAX8672 toc10
BATT INPUT LEAKAGE CURRENT DURING UVLO
vs. TEMPERATURE
BATT INPUT LEAKAGE CURRENT (nA)
17.5
15.0
CT FREQUENCY (Hz)
12.5
10.0
7.5
5.0
2.5
0.0
V
IN
= V
BST
= V
LDO
= 0V
V
BATT
= 0.9V
R
CHGV
= 28.7kΩ
-40
-15
10
35
60
85
TEMPERATURE (°C)
15.5
15.0
-40
17.0
16.5
16.0
MAX8672 toc11
CT FREQUENCY vs. TEMPERATURE
MAX8672 toc12
25
20.0
18.0
17.5
20
DR CURRENT (mA)
15
V
BATT(CHG)
= 3.0V
10
5
V
BATT(CHG)
=
1.5V
0
0.5
1.0
15
2.0
R
DR
= 100Ω
2.5
3.0
0
C
CT
= 0.047μF, X7R, 10%
-15
10
35
60
85
TEMPERATURE (°C)
BATTERY VOLTAGE (V)
MAX BATT CHARGE VOLTAGE
vs. TEMPERATURE (1-CELL NiMH)
MAX8672 toc13
LIGHT-LOAD SWITCHING WAVEFORMS
MAX8672 toc14
1.55
MAX BATT CHARGE VOLTAGE (V)
1.53
V
BST
50mV/div
V
LX
1V/div
3.05V
1.51
1.49
0V
1.47
R
CHGV
= 28.7kΩ
1.45
-40
-15
10
35
60
85
TEMPERATURE (°C)
I
LX
200mA/div
10μs/div
I
BST
= 2mA
0A
_______________________________________________________________________________________
5
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