MAX1906XEGE-T [MAXIM]
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| 型号： | MAX1906XEGE-T |
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MAXIM INTEGRATED PRODUCTS |
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19-2455; Rev 0; 4/02
Li+ Battery-Pack Protector with
Integrated Fuse Driver
General Description
Features
The MAX1906 protects against overvoltage conditions
in lithium-ion/lithium polymer (Li+) battery packs by
blowing a three-terminal protection fuse. The IC should
be used in conjunction with resettable protection cir-
cuits to provide a high level of safety against over-
charging Li+ batteries. It can be used with 2-, 3-, or
4-series cell battery packs.
o Protects Against Overvoltage
o ±±1 Accꢀrate Protection ꢁTresTolꢂs
o Integrateꢂ 2.±s Faꢀlt-Delay ꢁimer
o Bꢀilt-in ±.5A SCR Fꢀse Driver
o ꢁest Moꢂe for Fꢀnctional Verification in
The MAX1906 monitors individual cell voltages. If any
cell voltage exceeds the overvoltage threshold for
greater than 2.1s, the MAX1906 activates an internal
SCR. The SCR sinks sufficient current to blow an exter-
nal protection fuse, permanently disabling the battery
pack. Alternatively, the IC can drive the gate of an
external MOSFET to blow the fuse.
Assembleꢂ Pack
o 8µA (max) Sꢀpply Cꢀrrent
o ±µA (max) Stanꢂby Cꢀrrent
o Protects Against Disconnecteꢂ B±P–B4P Pins
o Protects 2-, 3-, or 4-Series Li+ Battery Packs
The MAX1906 also offers protection against disconnect-
ed voltage sense pins. If a disconnected pin is detected,
the DISCON output is forced low. The MAX1906 includes
a test mode, which determines if the circuit is operating
correctly while in an assembled battery pack.
o Available in Small ±6-Pin QFN Package
(5mm x 5mm)
Ordering Information
The low-cost MAX1906 is available in a thermally
enhanced 16-pin QFN package.
PART
TEMP RANGE PIN-PACKAGE
CELLS
MAX1906SEGE -40°C to +85°C 16 QFN 5mm ✕ 5mm
MAX1906VEGE -40°C to +85°C 16 QFN 5mm ✕ 5mm
MAX1906XEGE -40°C to +85°C 16 QFN 5mm ✕ 5mm
2
3
4
Applications
2-, 3-, or 4-Series Li+ Battery Packs for
Portable Products
Minimal Operating Circuit
Pin Configuration
FUSE
PACK+
VCC
16 15 14 13
7
16
14
12
OUT
B4P
B3P
B2P
1
2
3
4
12
11 N.C.
I.C.
DRV
B2P
4
2
3
DISCON
OPTIONAL
PACK
CONTROLLER
MAX1906S/V/X
10
9
TEST
B1P
I.C.
MAX1906X
DRV
TEST
PKN
DISCON
10
8
B1P
BN
5
6
7
8
5
5mm x 5mm QFN
[]:MAX1906V, MAX1906X
():MAX1906X
PACK-
________________________________________________________________ Maxim Integrated Products
±
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.
Li+ Battery-Pack Protector with
Integrated Fuse Driver
ABSOLUTE MAXIMUM RATINGS
B4P to BN...............................................................-0.3V to +24V
B3P to BN...............................................................-0.3V to +18V
B2P to BN...............................................................-0.3V to +12V
B4P to B3P, B3P to B2P, B2P to B1P, B1P to BN ....-0.3V to +6V
TEST, DRV, DISCON to PKN....................................-0.3V to +6V
OUT to BN ..............................................................-0.3V to +24V
BN to PKN ...................................................................-2V to +2V
OUT Maximum Current .........................................................2.5A
Continuous Power Dissipation (T = +70°C, per JEDEC JESD51-7)
A
16-Pin QFN (derate 19mW/°C above +70°C ambient) ....1.5W
Operating Temperature Ranges..........................-40°C to +85°C
Storage Temperature.........................................-65°C to +150°C
Junction Temperature......................................................+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
(T = 0°C to +85°C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
20
UNITS
B4P Voltage Range
V
V
V
V
V
B3P Voltage Range
15
B2P Voltage Range
10
B1P Voltage Range
5
Overvoltage Detection Threshold
V
Cell voltage rising
4.4
2.0
4.45
4.5
OV_TH
Overvoltage Detection Threshold,
Test Mode
Cell voltage rising, test mode
2.225
2.4
V
Overvoltage Detection Hysteresis
SCR Release Threshold
Standby-Mode Threshold
Overvoltage Delay
V
Cell voltage falling
Cell voltage falling
Cell voltage falling
10
4.0
3.3
2.1
2.56
3
mV
V
OV_HYS
V
3.85
2.3
4.15
4.1
REL
V
t
1.85
2.45
s
OV
Sampling Interval
(Note 1)
(Note 2)
s
Supply Current
I
6
µA
µA
nA
SUP
Supply Current During Sampling
Standby Current
300
Individual cell voltages = 2.2V
(Note 3)
800
Intermediate Cell
Quiescent Current
0.5
1.5
1.6
nA
A
OUT Output Sink Current
OUT = 2V, current not internally limited
1.0
-1
2.0
2.0
OUT Voltage
(when SCR Is Triggered)
I
= 1.5A
V
OUT
OUT Leakage Current
OUT = 24V
+1
0.4
5.5
5.5
µA
V
DRV Output Voltage Low
V
I
I
I
= 200µA
= 5µA
DRVL
DRV
DRV
DRV
4.0
2.0
2
4.8
4.8
DRV Output Voltage High
V
V
DRVH
= -1mA
DRV Sink Current
I
V
V
= 2.5V
= 0V
mA
mA
ms
ms
V
DRV
DRV
DRVH
DRVL
DRV Source Current
I
2
Test-Mode Delay
t
(Note 4)
(Note 4)
1.2
160
0.4
+1
DLY
OUT
Test-Mode Output Duration
DISCON Output Voltage Low
DISCON Leakage Current
t
100
-1
130
I
= 1mA
= 3.3V
DISCON
V
µA
DISCON
2
_______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
ELECTRICAL CHARACTERISTICS (continued)
(T = 0°C to +85°C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
Test time per cell
MIN
TYP
MAX
UNITS
ms
V
Disconnected Pin Test Time
TEST Input High
0.2
2.2
17
Minimum TEST High Duration
TEST Input Low
50
5
µs
0.8
33
V
TEST Pulldown to PKN
kΩ
Thermal Impedance,
Junction to Case
°C/W
ELECTRICAL CHARACTERISTICS
(T = -40°C to +85°C, individual cell voltages = 4.2V, unless otherwise noted.)
A
PARAMETER
B4P Voltage Range
SYMBOL
CONDITIONS
MIN
TYP
MAX
20
UNITS
V
V
V
V
V
B3P Voltage Range
15
B2P Voltage Range
10
B1P Voltage Range
5
Overvoltage Detection Threshold
V
Cell voltage rising
4.35
1.95
4.55
OV_TH
Overvoltage Detection Threshold,
Test Mode
Cell voltage rising, test mode
2.45
V
SCR Release Threshold
Standby Mode Threshold
Overvoltage Delay
V
Cell voltage falling
Cell voltage falling
3.80
2.25
1.85
4.2
4.15
2.45
8
V
V
REL
t
s
OV
Supply Current
I
(Note 2)
µA
µA
A
SUP
Standby Current
Individual cell voltages = 2.2V
OUT = 2V, current not internally limited
1
OUT Output Sink Current
1.0
OUT Voltage
(when SCR Is Triggered)
I
= 1.5A
2.2
V
OUT
DRV Output Voltage Low
DRV Output Voltage High
DRV Output Voltage High
DRV Sink Current
V
I
I
I
= 200µA
= 5µA
0.4
5.5
5.5
V
V
DRVL
DRVH
DRVH
DRV
DRV
DRV
V
V
3.9
2.0
2
= -1mA
V
I
V
V
= 2.5V
= 0V
mA
mA
ms
ms
V
DRV
DRV
DRVH
DRVL
DRV Source Current
Test-Mode Delay
I
2
t
(Note 4)
(Note 4)
1.25
165
0.4
DLY
Test-Mode Output Duration
DISCON Output Voltage Low
TEST Input High
t
95
2.6
17
OUT
I
= 1mA
DISCON
V
TEST Input Low
0.8
33
V
TEST Pulldown to PKN
kΩ
Note 1: See the Normal Operating Mode section.
Note 2: The supply current is measured at the top cell and averaged over one sampling interval.
Note 3: Guaranteed by design.
Note 4: See Figure 7.
_______________________________________________________________________________________
3
Li+ Battery-Pack Protector with
Integrated Fuse Driver
Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)
A
OVERVOLTAGE THRESHOLD
STANDBY-MODE THRESHOLD
vs. TEMPERATURE
SUPPLY CURRENT
vs. TEMPERATURE
vs. TEMPERATURE
4.455
3.5
3.3
3.1
2.9
2.7
2.5
2.3
4.5
4.3
4.1
3.9
3.7
3.5
EQUAL VOLTAGE APPLIED
TO ALL CELL INPUTS (FALLING)
4.450
4.445
4.440
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
STANDBY CURRENT
vs. TEMPERATURE
THERMAL IMPEDANCE, CASE-TO-AMBIENT
vs. COPPER AREA
TIME-TO-MAX JUNCTION TEMPERATURE
vs. POWER DISSIPATION
80
60
40
20
0.70
0.68
0.66
10,000
1000
100
10
T
= +60°C
A
1oz COPPER
2
0.25in
2
0.50in
0.64
0.62
0.60
2
0.04in
1
-40
-15
10
35
60
85
0.01
0.1
1
2
10
1.0
1.5
2.0
2.5
3.0
TEMPERATURE (°C)
COPPER AREA (in )
POWER DISSIPATION (W)
INSTANTANEOUS ON-STATE VOLTAGE
vs. CURRENT
TEST-MODE TIMING
MAX1906 toc08
1.6
1.3
1.0
0.7
0.4
0.1
TEST PIN
VOLTAGE
5V/div
DRV PIN
VOLTAGE
5V/div
110°C
T = 25°C
J
DISCON PIN
VOLTAGE
5V/div
20ms/div
0.8
1.0
1.2
1.4
1.6
1.8
INSTANTANEOUS ON-STATE VOLTAGE (V)
4
_______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
Pin Description
PIN
NAME
DESCRIPTION
Internal Connection. Float pins 1 and 9.
MAX1906S MAX1906V MAX1906X
1, 9
1, 9
1, 9
I.C.
6, 11, 13, 15 6, 11, 13, 15 6, 11, 13, 15
N.C.
No Connection
MOSFET Driver Output. High when an overvoltage condition is detected.
Connect the DRV pin to the gate of an external MOSFET to blow the
protection fuse.
2
3
4
2
3
4
2
3
4
DRV
TEST
Test-Mode Input. Test mode is enabled with a pulse of minimum 50µs
duration on the TEST pin.
Disconnected Pin Output. This is an open-drain output and is high-Z during
normal operation. If B4P, B3P, B2P, or B1P is disconnected, this pin is
pulled low (see the Disconnected Pin Detection section).
DISCON
5
7
5
7
5
7
PKN
OUT
Pack Negative. A sense resistor may be connected between BN and PKN.
Anode Output of the SCR. Connect OUT to the fuse’s heater connection (see
the Protection Fuse Selection section).
Negative Terminal of Cell 1. Connect BN to the negative terminal of the first
series Li+ cell. BN is also chip ground, which is connected to the backside
paddle on the QFN package.
8
8
8
BN
Positive Terminal of Cell 1. Connect B1P to the positive terminal of the first
series Li+ cell.
10
12
—
—
10
12
14
—
10
12
14
16
B1P
B2P
B3P
B4P
Positive Terminal of Cell 2. Connect B2P to the positive terminal of the
second series Li+ cell.
Positive Terminal of Cell 3. Connect B3P to the positive terminal of the third
series Li+ cell.
Positive Terminal of Cell 4. Connect B4P to the positive terminal of the fourth
series Li+ cell.
enables the test mode. Figure 3 shows the cell connec-
tions for 2- and 3-series battery packs and Figure 4
shows the functional diagram for the MAX1906.
Detailed Description
The MAX1906 protects 2-, 3-, or 4-series Li+ battery
packs from overcharge by controlling a three-terminal
protection fuse. Figures 1 and 2 show two application
circuits using the MAX1906. The MAX1906 checks the
voltage of each cell at regular intervals. An overcharge
condition is detected if any cell voltage exceeds the
overvoltage threshold for more than 2.1s. The MAX1906
responds to an overcharge condition by turning on an
internal SCR (Figure 1) or an external MOSFET (Figure 2)
to blow a three-terminal protection fuse placed in series
with the charging path.
The MAX1906 can be used together with other
resettable protection circuits to provide a high level of
safety against overcharging Li+ batteries. Figure 5 shows
a typical application circuit using the MAX1906 together
with the MAX1924. The MAX1924 has a lower overvoltage
threshold than the MAX1906. If any cell voltage exceeds
4.35V (typ), the MAX1924 turns off the TKO and CGO
MOSFETs and opens the charging path. If the TKO or
CGO MOSFET fails and charging continues, the
MAX1906 blows the protection fuse and opens the charg-
ing path permanently once any cell voltage reaches
4.45V (typ). The MAX1924 also protects the battery pack
against undervoltage, charge current, discharge current,
and pack-short fault conditions. Refer to the MAX1894/
MAX1924 data sheets for complete details.
The MAX1906 checks for disconnected voltage sense
pins every time it exits the standby mode or test mode. If
a disconnected pin is detected, the DISCON pin is
latched low. The MAX1906 also includes a test mode,
which determines if the circuit is operating correctly while
in an assembled battery pack. A pulse on the TEST pin
_______________________________________________________________________________________
5
Li+ Battery-Pack Protector with
Integrated Fuse Driver
F1
PACK+
SFD-145B
R4
10Ω
7
16
VCC
R5
OUT
B4P
B3P
C4
R3
1kΩ
100kΩ
0.1µF
4
14
12
DISCON
C3
0.1µF
R2
1kΩ
MAX1906X
2
3
PACK
CONTROLLER
DRV
B2P
B1P
C2
0.1µF
R1
1kΩ
10
8
TEST
C1
0.1µF
5
PKN
BN
R
SENSE
PACK-
Figure 1. Typical Application Circuit for 4-Series Battery Packs—Using the Internal SCR to Blow the Protection Fuse
F1
PACK+
SFD-145B
R4
10Ω
7
16
VCC
OUT
B4P
B3P
R5
100kΩ
C4
R3
1kΩ
0.1µF
4
2
3
14
12
DISCON
C3
0.1µF
R2
1kΩ
MAX1906X
PACK
CONTROLLER
DRV
B2P
B1P
C2
0.1µF
R1
1kΩ
10
8
TEST
C1
0.1µF
5
PKN
BN
R
SENSE
PACK-
Figure 2. Typical Application Circuit for 4-Series Battery Packs—Using the External MOSFET to Blow the Protection Fuse
_______________________________________________________________________________________
6
Li+ Battery-Pack Protector with
Integrated Fuse Driver
16
14
12
16
OUT
IC
IC
OUT
IC
B3P
B2P
R3
10Ω
14
12
DISCON
DISCON
C3
R2
1kΩ
R2
0.1µF
10Ω
MAX1906S
MAX1906V
DRV
B2P
DRV
TEST
PKN
C2
C2
0.1µF
R1
1kΩ
R1
1kΩ
0.1µF
10
8
10
8
B1P
BN
TEST
PKN
B1P
BN
C1
0.1µF
C1
0.1µF
R
R
SENSE
SENSE
Figure 3. Cell Connections for 2- and 3-Series Battery Packs
B4P
OSCILLATOR
LINEAR
REGULATOR
STATE
MACHINE
FAULT
LOGIC
DRV
PKN
OUT
DRIVER
COMPARATOR
SCR
B4P
B3P
B2P
B1P
BN
SCR
DRIVER
MUX
BN
REF
TEST
LOGIC
TEST
PKN
Figure 4. MAX1906 Functional Diagram
_______________________________________________________________________________________
7
Li+ Battery-Pack Protector with
Integrated Fuse Driver
OVERDISCHARGE
THREE-TERMINAL
PROTECTION
R10
10Ω
PROTECTION FUSE
Si4435DY
PACK+
TRICKLE
CHARGE
16
SRC
C6
2.2µF
BSS84
SFD-145B
15
14
13
BN
DSO
CGO
TKO
OVERCHARGE
PROTECTION
R
TKO
510Ω
Si4435DY
CMPSH-3
R9
R4
MAX1924X
VCC
10Ω
51Ω
7
16
1
2
B4P
OUT
B4P
D1
C9
0.1µF
R5
100kΩ
C4
1.0µF
V
CC
R8
1kΩ
R3
1kΩ
C5
0.1µF
VDD
4
14
12
DISCON
B3P
B2P
3
5
B3P
B2P
DISCON
C8
C3
0.1µF
R7
1kΩ
R2
1kΩ
0.1µF
MAX1906X
TEST
12
11
2
3
SHDN
CTL
DRV
MICRO-
CONTROLLER
C7
0.1µF
C2
R1
1kΩ
R6
1kΩ
0.1µF
10
8
7
9
DISCON
TEST
B1P
BN
TEST
PKN
B1P
BN
C1
0.1µF
C6
0.1µF
GND
5
PKN
10
R
SENSE
0.02
PACK-
Figure 5. Typical Application Circuit—Using the MAX1906 with a MAX1924 Protection Circuit
this mode, the device draws 1µA (max) from the top
cell. Once any cell voltage goes above the standby-
mode threshold, the MAX1906 wakes up and goes into
the normal mode.
Modes of Operation
Normal Operating Mode
The MAX1906 operates in normal mode when at least 1
cell voltage is above the standby-mode threshold. In this
mode, the average supply current from the top cell is
8µA (max). The MAX1906 works by sampling cell volt-
ages for 0.8ms and then goes into an idle state for 2.56s
to complete a cycle. During the sampling period, the
MAX1906 typically consumes 300µA. In the idle state,
the MAX1906 typically consumes 3.2µA. Figure 6 shows
the device current consumption in different states.
Test Mode
The test mode is designed to verify the overvoltage
detection function in a fully assembled battery pack with-
out blowing the three-terminal protection fuse. Test mode
is invoked by a pulse with minimum duration of 50µs on
the TEST pin. The MAX1906 changes the overvoltage
threshold from 4.45V to 2.225V in the test mode and
samples each of the cell voltages. Individual cell volt-
ages are expected to be above 2.225V during the test
mode. If the MAX1906 detects overvoltage condition on
all cells during one sampling period, the DRV pin goes
Standby Mode
When all the cell voltages are below the standby-mode
threshold, the MAX1906 goes into the standby mode. In
8
_______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
STOP SAMPLING AND MONITOR ONLY
CELL UNDER MEASUREMENT
300µA
I
SUP
3.2µA
0.8ms
0.8ms
2.56s
2.1s
V
V
OV_TH
REL
V
B_P
4.8V
V
DRV
NOTE: ALL VALUES ARE TYPICAL.
Figure 6. Current Consumption of Chip in Different States
V
TEST
50µs
I
SUP
DRV
0.8ms
IF ALL CELLS ARE TESTED TO BE IN
OVERVOLTAGE CONDITION
V
130ms
V
DISCON
Figure 7. Timing Diagram for Test Mode
high and the DISCON pin is set to its high-impedance
state. After 130ms, the DRV pin is pulled low by the
MAX1906, exiting the test mode. The time period of
130ms has been chosen not to stress the three-terminal
protection fuse if an external MOSFET is used to blow the
fuse. The OUT pin is not affected by the test mode. See
the timing diagram for the test mode in Figure 7.
Entry into test mode is ignored if the MAX1906 has
detected an overvoltage condition and has activated
the 2.1s delay. Test mode remains disabled until the
MAX1906 exits the overvoltage condition. The
MAX1906 continues normal operation upon exit from
the test mode.
_______________________________________________________________________________________
9
Li+ Battery-Pack Protector with
Integrated Fuse Driver
SAMPLE MODE
EXIT FROM STANDBY MODE OR TEST MODE
SAMPLE B_P
SAMPLE MODE
NO
NO
ALL CELLS CHECKED?
YES
B_P > V
YES
?
OV_TH
CHECK DISCONNECTION
OF B_P PIN
STOP SAMPLING
AND START 2.1s
TIMER AND MONITOR
CELL CONTINUOUSLY
WAIT
2.56s
NO
IS B_P AT LEAST 1.2V ABOVE
NEGATIVE TERMINAL
NO
B_P > V
CONTINUOUSLY
OV_TH
AND TIMER = 2.1s?
YES
DISCON = L
YES
DRV = H
SCR LATCHED
NO
ALL PINS CHECKED?
NO
B_P < V AND THE
REL
YES
REST B_P < V
?
OV_TH
YES
DISCON = H
DRV = L
Figure 8. Overvoltage Protection
Figure 9. Disconnected Pin Description
threshold. The DRV pin then goes low, which turns off
an external MOSFET. The internal SCR does not
unlatch until power is removed.
Protection Features
Overvoltage Detection
If any cell voltage exceeds the overvoltage threshold,
the MAX1906 stops sampling and monitors the cell volt-
age continuously. If the overvoltage condition persists
for more than 2.1s, the device turns on an internal SCR
and also drives the DRV pin high. The internal SCR or
the external MOSFET sinks sufficient current to blow the
three-terminal protection fuse and permanently open
the battery pack’s charge path. See the overvoltage
protection flowchart in Figure 8. Also see the Fuse
Drive Options section for discussion on current capabil-
ity for both the internal SCR and external MOSFET.
Disconnected Pin Detection
The MAX1906 tests for disconnected voltage sense pins
each time it exits the standby or test mode. To check for
a disconnection, the MAX1906 applies a 10µA current
source to each B_P pin. A disconnected pin is detected
if the B_P pin under test falls to within 1.2V of the cell’s
negative terminal. The DISCON pin is then pulled low.
This condition persists while the MAX1906 is in normal
operating mode, and resets only when the MAX1906
enters the standby or test mode. See Figure 9 for the
disconnected pin detection flowchart.
The MAX1906 remains in overvoltage mode until the
cell voltage drops to 90% of the overvoltage threshold
(V
) and the rest of cells are below the overvoltage
REL
10 ______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
The fuse blows when sufficient power is dissipated in the
heater resistor to melt the fuse’s internal solder joints:
Design Procedure
Fuse Drive Options
The MAX1906 supports two methods for blowing the
external protection fuse: the internal SCR can be directly
connected to the fuse’s heater terminal or an external
MOSFET can be used to drive the heater. The design
procedure for both methods requires matching the drive
capabilities in the SCR or the MOSFET with the dissipa-
tion required to blow the fuse.
P
= V
× I
=
HEATER
HEATER
HEATER
2
V
− V
(
)
BATT_OV
SWITCH
R
HEATER
V
is the battery-pack voltage in the overvoltage
condition, which is typically 4.45V per cell. V
the voltage drop on the internal SCR or an external MOS-
FET. R is the resistance of the heater resistor.
BATT_OV
is
SWITCH
The SCR configuration is simple, low cost, and does not
require external components. The circuit in Figure 1 is
appropriate for fuses that require heater currents up to
2A. Since the voltage drop across the SCR can be up to
2V, care must be taken not to exceed the device’s power
HEATER
The time required to blow the protection fuse, or clear-
ing time, depends upon the power dissipation in the
heater resistor and the ambient temperature. Fuse man-
ufacturers typically provide a curve of clearing time vs.
voltage, and the clearing time vs. ambient temperature.
The greater the power dissipation in the heater resistor,
the quicker the fuse blows. Clearing time is also inverse-
ly proportional to ambient temperature. The heater resis-
tance for different operating current specifications can
range from a few ohms to a few hundred ohms. The
resistance should be selected based on the acceptable
clearing time and operating temperature range.
2
ratings. When greater than 1in of copper plane is avail-
able to conduct heat away from the MAX1906, it can dis-
sipate 1.6A at typically 1.7V indefinitely. When smaller
copper planes are used, the time to clear the fuse must
be less than the time for the MAX1906 to exceed its
absolute maximum thermal ratings.
The transient thermal characteristics for the MAX1906
are shown in the Typical Operating Characteristics.
Since the thermal resistance varies inversely with the
area of the copper plane attached to the device, the time
to reach thermal limit also varies with copper area.
For a battery pack requiring 4A of operating current, a
fuse with a 5A nominal current rating is appropriate. An
SFD-145B device made by Sony Chemical Corp. is
selected, which has a 22Ω fusible resistor. Based on
safety considerations, the clearing time should be no
more than 1s or 2s. This is commensurate with the
delay time required to detect the fault condition. The
power dissipated in the SCR when the fuse is blown is
approximately 1.3V ✕ 0.75A or 1W. To ensure that the
junction temperature in the MAX1906 never exceeds
150°C at 60°C ambient temperature, the required ther-
mal resistance must be:
External MOSFETs should be used with the MAX1906
when the heater current must be greater than 2.0A.
MOSFETs with the required thermal characteristics are
available from multiple manufacturers (see Table 1).
Figure 2 shows the typical application circuit using an
external MOSFET.
Protection Fuse Selection
Protection fuse characteristics can vary considerably
from manufacturer to manufacturer. Always review the
data sheet carefully when selecting the protection fuse.
Table 2 lists the contact information for manufacturers
of compatible fuses.
RθCA + RθJC < TMAX -TA / Pd
(
< (150°C-60°C) / (1W)
< 90°C/W
) (
)
There are two methods for opening the protection fuse.
The fuse can be blown through the heater or by too
much dissipation along the high-current path. The fuse
must be selected to accommodate the required operat-
ing current without placing stress on the fuse. Once the
nominal current-handling characteristics of the fuse are
set, determine the amount of drive current and the time
required to blow the fuse through the heater terminal.
These quantities are also listed in the fuse manufactur-
er’s data sheet.
where R
is the thermal impedance from junction to
θJC
case, and R
is the thermal impedance from case to
θCA
ambient. R
is fixed, and is about 5°C/W for the 16-lead
θJC
5mm ✕ 5mm QFN package. R
varies with copper
θCA
area, and is shown in the Typical Operating
Characteristics. Even though a combined thermal resis-
2
tance of 90°C/W is achievable with less than 0.04in of
copper area, it is advisable to include some margin to
2
reduce the rise in device temperature. Using 0.25in cop-
per area is conservative, and is available in most designs.
______________________________________________________________________________________ 11
Li+ Battery-Pack Protector with
Integrated Fuse Driver
The MAX1906 has internal ESD diodes on each B_P pin
RC Filters On Cell Inputs
The MAX1906 has an unused pin placed between
each of the cell connections. These extra pins minimize
the risk of a solder short between pins during the assem-
bly process. Resistors in series with each B_P pin
are recommended to limit the current in case there is a
short between adjacent B_P pins (see the Typical
Application Circuits).
for ESD protection up to 2kV. When higher ESD ratings
are needed, capacitors (typically 0.1µF) can be added
across adjacent B_P pins (see the Typical Application
Circuits). The RC filters improve the device immunity to
ESD.
Layout Guidelines
Good layout is important to minimize the effects of
noise on the system and ensure accurate voltage mea-
surements. Use appropriate trace widths for the high-
current paths and keep traces short to minimize para-
sitic inductance and capacitance. Provide adequate
space and board area for the sense resistor to dissi-
pate heat. Place RC filters close to B1P–B4P pins. If
some amount of heat sinking is needed to use the inter-
nal SCR, connect the exposed backside paddle to as
large a copper area as practical.
The MAX1906 is powered from the top cell during the
sampling period. The 300µA typical sampling current,
multiplied by a 10Ω series resistor can move the over-
voltage trip point on the top cell by 3mV. The intermedi-
ate cell quiescent current is typically 500pA. A 1kΩ
resistor in series with any cell except the top one alters
the overvoltage trip point by typically 0.5mV. It is rec-
ommended to use a resistor of 10Ω in series with the
top cell and 1kΩ resistors in series with the rest of the
cells to achieve the desired overvoltage threshold toler-
ance while limiting the potential short-circuit current.
Chip Information
TRANSISTOR COUNT: 4027
PROCESS: BiCMOS
Table 1. MOSFET Suppliers
SUPPLIER
USA PHONE
408-721-2181
310-322-3331
408-988-8000
FACTORY FAX
408-721-1635
310-322-3332
408-567-8979
WEBSITE
www.fairchildsemi.com
www.irf.com
Fairchild
International Rectifier
Vishay Siliconix
www.vishay.com
Table 2. Recommended Fuse Manufacturers
MANUFACTURER
Sony Chemicals Corp.
Uchihashi Estec Co., Ltd
PHONE
+81-3-3279-0448
+81-6-6962-6661
FAX
+81-3-5255-8448
+81-6-6962-6669
WEBSITE
www.sccj.co.jp/html_e/
www.uchihashi.co.jp/
12 ______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
______________________________________________________________________________________ 13
Li+ Battery-Pack Protector with
Integrated Fuse Driver
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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