Maxim MAX1906XEGE Li battery-pack protector with integrated fuse driver Datasheet

19-2455; Rev 0; 4/02
Li+ Battery-Pack Protector with
Integrated Fuse Driver
Features
♦ Protects Against Overvoltage
The MAX1906 also offers protection against disconnected 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.
♦ Available in Small 16-Pin QFN Package
(5mm x 5mm)
The low-cost MAX1906 is available in a thermally
enhanced 16-pin QFN package.
Applications
2-, 3-, or 4-Series Li+ Battery Packs for
Portable Products
♦ ±1% Accurate Protection Thresholds
♦ Integrated 2.1s Fault-Delay Timer
♦ Built-in 1.5A SCR Fuse Driver
♦ Test Mode for Functional Verification in
Assembled Pack
♦ 8µA (max) Supply Current
♦ 1µA (max) Standby Current
♦ Protects Against Disconnected B1P–B4P Pins
♦ Protects 2-, 3-, or 4-Series Li+ Battery Packs
Ordering Information
PART
TEMP RANGE
MAX1906SEGE -40°C to +85°C
MAX1906VEGE -40°C to +85°C
MAX1906XEGE -40°C to +85°C
B3P
DRV
MAX1906X
B2P
3
TEST
5
PKN
B1P
BN
15
14
13
I.C.
1
12
B2P
DRV
2
11
N.C.
TEST
3
10
B1P
DISCON
4
9
I.C.
14
12
MAX1906S/V/X
10
8
5
6
7
8
BN
2
DISCON
16
16
OUT
OPTIONAL
PACK
CONTROLLER
B4P
N.C.
4
OUT
PKN
7
N.C.
VCC
I.C. [B3P]
FUSE
PACK+
N.C.
Pin Configuration
I.C. (B4P)
Minimal Operating Circuit
PIN-PACKAGE
CELLS
16 QFN 5mm ✕ 5mm
2
16 QFN 5mm ✕ 5mm
3
16 QFN 5mm ✕ 5mm
4
5mm x 5mm QFN
PACK-
[]:MAX1906V, MAX1906X
():MAX1906X
________________________________________________________________ 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.
1
MAX1906
General Description
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 circuits to provide a high level of safety against overcharging Li+ batteries. It can be used with 2-, 3-, or
4-series cell battery packs.
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 external protection fuse, permanently disabling the battery
pack. Alternatively, the IC can drive the gate of an
external MOSFET to blow the fuse.
MAX1906
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 (TA = +70°C, per JEDEC JESD51-7)
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
(TA = 0°C to +85°C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at TA = +25°C.)
MAX
UNITS
B4P Voltage Range
PARAMETER
20
V
B3P Voltage Range
15
V
B2P Voltage Range
10
V
B1P Voltage Range
5
V
Overvoltage Detection Threshold
SYMBOL
VOV_TH
Overvoltage Detection Threshold,
Test Mode
Overvoltage Detection Hysteresis
SCR Release Threshold
Cell voltage rising
4.4
4.45
4.5
V
Cell voltage rising, test mode
2.0
2.225
2.4
V
Cell voltage falling
Cell voltage falling
3.85
4.0
4.15
V
Cell voltage falling
2.3
3.3
4.1
V
1.85
2.1
2.45
s
6
µA
tOV
ISUP
10
(Note 1)
2.56
(Note 2)
3
Supply Current During Sampling
Individual cell voltages = 2.2V
Intermediate Cell
Quiescent Current
(Note 3)
OUT Output Sink Current
OUT = 2V, current not internally limited
OUT Voltage
(when SCR Is Triggered)
IOUT = 1.5A
OUT Leakage Current
DRV Output Voltage High
mV
s
300
Standby Current
DRV Output Voltage Low
TYP
VREL
Sampling Interval
Supply Current
MIN
VOV_HYS
Standby-Mode Threshold
Overvoltage Delay
CONDITIONS
OUT = 24V
VDRVL
VDRVH
µA
800
0.5
1.0
nA
nA
1.5
2.0
A
1.6
2.0
V
+1
µA
0.4
V
-1
IDRV = 200µA
IDRV = 5µA
4.0
4.8
5.5
IDRV = -1mA
2.0
4.8
5.5
V
DRV Sink Current
IDRV
VDRVH = 2.5V
2
mA
DRV Source Current
IDRV
VDRVL = 0V
2
mA
Test-Mode Delay
tDLY
(Note 4)
Test-Mode Output Duration
tOUT
(Note 4)
DISCON Output Voltage Low
IDISCON = 1mA
DISCON Leakage Current
VDISCON = 3.3V
2
100
130
-1
_______________________________________________________________________________________
1.2
ms
160
ms
0.4
V
+1
µA
Li+ Battery-Pack Protector with
Integrated Fuse Driver
MAX1906
ELECTRICAL CHARACTERISTICS (continued)
(TA = 0°C to +85°C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
Disconnected Pin Test Time
CONDITIONS
MIN
Test time per cell
TEST Input High
TYP
MAX
0.2
ms
50
µs
2.2
Minimum TEST High Duration
V
TEST Input Low
TEST Pulldown to PKN
17
Thermal Impedance,
Junction to Case
UNITS
0.8
V
33
kΩ
5
°C/W
ELECTRICAL CHARACTERISTICS
(TA = -40°C to +85°C, individual cell voltages = 4.2V, unless otherwise noted.)
MAX
UNITS
B4P Voltage Range
PARAMETER
20
V
B3P Voltage Range
15
V
B2P Voltage Range
10
V
B1P Voltage Range
5
V
Overvoltage Detection Threshold
SYMBOL
VOV_TH
Overvoltage Detection Threshold,
Test Mode
SCR Release Threshold
VREL
Standby Mode Threshold
Overvoltage Delay
tOV
Supply Current
ISUP
CONDITIONS
MIN
TYP
Cell voltage rising
4.35
4.55
V
Cell voltage rising, test mode
1.95
2.45
V
Cell voltage falling
3.80
4.2
V
Cell voltage falling
2.25
4.15
V
1.85
2.45
s
(Note 2)
8
µA
Standby Current
Individual cell voltages = 2.2V
1
µA
OUT Output Sink Current
OUT = 2V, current not internally limited
OUT Voltage
(when SCR Is Triggered)
IOUT = 1.5A
1.0
A
2.2
V
DRV Output Voltage Low
VDRVL
IDRV = 200µA
0.4
V
DRV Output Voltage High
VDRVH
IDRV = 5µA
3.9
5.5
V
DRV Output Voltage High
VDRVH
IDRV = -1mA
2.0
5.5
V
DRV Sink Current
IDRV
VDRVH = 2.5V
2
DRV Source Current
IDRV
VDRVL = 0V
2
Test-Mode Delay
tDLY
(Note 4)
Test-Mode Output Duration
tOUT
DISCON Output Voltage Low
(Note 4)
95
IDISCON = 1mA
TEST Input High
mA
1.25
ms
165
ms
0.4
V
2.6
TEST Input Low
TEST Pulldown to PKN
Note 1:
Note 2:
Note 3:
Note 4:
mA
17
V
0.8
V
33
kΩ
See the Normal Operating Mode section.
The supply current is measured at the top cell and averaged over one sampling interval.
Guaranteed by design.
See Figure 7.
_______________________________________________________________________________________
3
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
STANDBY-MODE THRESHOLD
vs. TEMPERATURE
3.3
4.445
4.5
4.3
SUPPLY CURRENT (µA)
4.450
EQUAL VOLTAGE APPLIED
TO ALL CELL INPUTS (FALLING)
3.1
2.9
2.7
2.3
10
35
60
85
3.9
3.5
-40
-15
10
35
60
85
-40
-15
10
60
85
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
MAX1906 toc04
0.70
0.68
1oz COPPER
10,000
TA = +60°C
1000
0.64
TIME (s)
RθCA (°C/W)
0.66
0.25in2
60
0.50in2
100
40
10
0.62
0.04in2
0.60
20
-40
-15
10
35
60
85
1
0.01
0.1
INSTANTANEOUS ON-STATE VOLTAGE
vs. CURRENT
10
1.0
1.5
2.0
TEST-MODE TIMING
MAX1906 toc07
1.3
TEST PIN
VOLTAGE
5V/div
1.0
DRV PIN
VOLTAGE
5V/div
110°C
0.7
TJ = 25°C
0.4
DISCON PIN
VOLTAGE
5V/div
0.1
0.8
1.0
1.2
1.4
1.6
1.8
2.5
POWER DISSIPATION (W)
MAX1906 toc08
1.6
INSTANTANEOUS ON-STATE CURRENT (A)
1
COPPER AREA (in2)
TEMPERATURE (°C)
20ms/div
INSTANTANEOUS ON-STATE VOLTAGE (V)
4
35
TEMPERATURE (°C)
MAX1906 toc06
-15
MAX1906 toc05
-40
4.1
3.7
2.5
4.440
MAX1906 toc03
MAX1906 toc01
3.5
CELL VOLTAGE (V)
CELL VOLTAGE (V)
4.455
SUPPLY CURRENT
vs. TEMPERATURE
MAX1906 toc02
OVERVOLTAGE THRESHOLD
vs. TEMPERATURE
STANDBY CURRENT (µA)
MAX1906
Li+ Battery-Pack Protector with
Integrated Fuse Driver
_______________________________________________________________________________________
3.0
Li+ Battery-Pack Protector with
Integrated Fuse Driver
PIN
MAX1906S
MAX1906V
MAX1906X
1, 9
1, 9
1, 9
6, 11, 13, 15 6, 11, 13, 15 6, 11, 13, 15
NAME
DESCRIPTION
I.C.
Internal Connection. Float pins 1 and 9.
N.C.
No Connection
2
2
2
DRV
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.
3
3
3
TEST
Test-Mode Input. Test mode is enabled with a pulse of minimum 50µs
duration on the TEST pin.
4
4
4
DISCON
5
5
5
PKN
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).
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).
7
7
7
OUT
8
8
8
BN
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.
10
10
10
B1P
Positive Terminal of Cell 1. Connect B1P to the positive terminal of the first
series Li+ cell.
12
12
12
B2P
Positive Terminal of Cell 2. Connect B2P to the positive terminal of the
second series Li+ cell.
—
14
14
B3P
Positive Terminal of Cell 3. Connect B3P to the positive terminal of the third
series Li+ cell.
—
—
16
B4P
Positive Terminal of Cell 4. Connect B4P to the positive terminal of the fourth
series Li+ cell.
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 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
enables the test mode. Figure 3 shows the cell connections for 2- and 3-series battery packs and Figure 4
shows the functional diagram for the MAX1906.
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 charging 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.
_______________________________________________________________________________________
5
MAX1906
Pin Description
MAX1906
Li+ Battery-Pack Protector with
Integrated Fuse Driver
F1
PACK+
SFD-145B
VCC
7
B4P
OUT
R4
10Ω
16
R5
100kΩ
4
MAX1906X
2
PACK
CONTROLLER
B3P
DISCON
C4
0.1µF R3
1kΩ
14
C3
0.1µF R2
1kΩ
12
B2P
DRV
3
B1P
TEST
C2
0.1µF R1
1kΩ
10
C1
0.1µF
5
BN
PKN
8
RSENSE
PACK-
Figure 1. Typical Application Circuit for 4-Series Battery Packs—Using the Internal SCR to Blow the Protection Fuse
F1
PACK+
SFD-145B
VCC
7
OUT
B4P
R5
100kΩ
4
PACK
CONTROLLER
DISCON
B3P
MAX1906X
2
DRV
14
12
C4
0.1µF R3
1kΩ
C3
0.1µF R2
1kΩ
B2P
3
TEST
R4
10Ω
16
B1P
10
C2
0.1µF R1
1kΩ
C1
0.1µF
5
PKN
BN
8
RSENSE
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
IC
DISCON
DRV
MAX1906S
TEST
B2P
B1P
16
14
B3P
DISCON
R2
10Ω
12
10
IC
OUT
DRV
MAX1906V
B2P
C2
R1
0.1µF
1kΩ
B1P
TEST
16
BN
R3
10Ω
14
12
10
C3
R2
0.1µF 1kΩ
C2
R1
0.1µF
1kΩ
C1
0.1µF
C1
0.1µF
PKN
MAX1906
IC
OUT
8
BN
PKN
8
RSENSE
RSENSE
Figure 3. Cell Connections for 2- and 3-Series Battery Packs
B4P
OSCILLATOR
LINEAR
REGULATOR
STATE
MACHINE
DRV
DRIVER
FAULT
LOGIC
PKN
COMPARATOR
OUT
SCR
B4P
B3P
SCR
DRIVER
MUX
BN
B2P
B1P
REF
BN
TEST
LOGIC
TEST
PKN
Figure 4. MAX1906 Functional Diagram
_______________________________________________________________________________________
7
MAX1906
Li+ Battery-Pack Protector with
Integrated Fuse Driver
OVERDISCHARGE
PROTECTION
THREE-TERMINAL
PROTECTION FUSE
R10
10Ω
Si4435DY
PACK+
TRICKLE
CHARGE
16
SRC
C6
2.2µF
BSS84
SFD-145B
15
OVERCHARGE
PROTECTION
RTKO
510Ω
14
BN
DSO
CGO
Si4435DY
13
VCC
7
OUT
B4P
16
DISCON
B3P
14
DISCON
2
C8
0.1µF
MAX1906X
DRV
B2P
12
C7
0.1µF
TEST
3
TEST
B1P
10
R3
1kΩ
R8
1kΩ
R7
1kΩ
R2
1kΩ
R1
1kΩ
R6
1kΩ
PKN
BN
MAX1924X
1
C4
1.0µF
C5
0.1µF
2
B4P
VCC
VDD
3
B3P
C3
0.1µF
5
SHDN
B2P
8
TEST
12
MICROCONTROLLER
C2
0.1µF
7
CTL
11
DISCON
B1P
C1
0.1µF
C6
0.1µF
5
CMPSH-3
D1
C9
0.1µF
R5
100kΩ
4
R4
51Ω
R9
10Ω
TKO
GND
9
BN
PKN
RSENSE
0.02
10
PACK-
Figure 5. Typical Application Circuit—Using the MAX1906 with a MAX1924 Protection Circuit
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 voltages 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.
Standby Mode
When all the cell voltages are below the standby-mode
threshold, the MAX1906 goes into the standby mode. In
8
this mode, the device draws 1µA (max) from the top
cell. Once any cell voltage goes above the standbymode threshold, the MAX1906 wakes up and goes into
the normal mode.
Test Mode
The test mode is designed to verify the overvoltage
detection function in a fully assembled battery pack without 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 voltages 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
_______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
MAX1906
STOP SAMPLING AND MONITOR ONLY
CELL UNDER MEASUREMENT
300µA
ISUP
3.2µA
0.8ms
2.56s
0.8ms
2.1s
VOV_TH
VREL
VB_P
4.8V
VDRV
NOTE: ALL VALUES ARE TYPICAL.
Figure 6. Current Consumption of Chip in Different States
VTEST
50µs
ISUP
0.8ms
IF ALL CELLS ARE TESTED TO BE IN
OVERVOLTAGE CONDITION
VDRV
130ms
VDISCON
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
MAX1906
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 > VOV_TH ?
CHECK DISCONNECTION
OF B_P PIN
YES
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 > VOV_TH CONTINUOUSLY
AND TIMER = 2.1s?
YES
DISCON = L
YES
DRV = H
SCR LATCHED
NO
B_P < VREL AND THE
REST B_P < VOV_TH ?
YES
NO
ALL PINS CHECKED?
YES
DISCON = H
DRV = L
Figure 8. Overvoltage Protection
Protection Features
Overvoltage Detection
If any cell voltage exceeds the overvoltage threshold,
the MAX1906 stops sampling and monitors the cell voltage 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 capability for both the internal SCR and external MOSFET.
The MAX1906 remains in overvoltage mode until the
cell voltage drops to 90% of the overvoltage threshold
(VREL) and the rest of cells are below the overvoltage
10
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.
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.
______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
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 dissipation required to blow the fuse.
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
ratings. When greater than 1in2 of copper plane is available to conduct heat away from the MAX1906, it can dissipate 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.
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.
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 operating 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 manufacturer’s data sheet.
The fuse blows when sufficient power is dissipated in the
heater resistor to melt the fuse’s internal solder joints:
PHEATER = VHEATER × IHEATER =
(VBATT _ OV − VSWITCH )2
RHEATER
VBATT_OV is the battery-pack voltage in the overvoltage
condition, which is typically 4.45V per cell. VSWITCH is
the voltage drop on the internal SCR or an external MOSFET. RHEATER is the resistance of the heater resistor.
The time required to blow the protection fuse, or clearing time, depends upon the power dissipation in the
heater resistor and the ambient temperature. Fuse manufacturers 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 inversely proportional to ambient temperature. The heater resistance 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.
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 thermal resistance must be:
RθCA + RθJC < (TMAX - TA ) / (Pd)
< (150°C - 60°C) / (1W)
< 90°C / W
where RθJC is the thermal impedance from junction to
case, and RθCA is the thermal impedance from case to
ambient. RθJC is fixed, and is about 5°C/W for the 16-lead
5mm ✕ 5mm QFN package. RθCA varies with copper
area, and is shown in the Typical Operating
Characteristics. Even though a combined thermal resistance of 90°C/W is achievable with less than 0.04in2 of
copper area, it is advisable to include some margin to
reduce the rise in device temperature. Using 0.25in2 copper area is conservative, and is available in most designs.
______________________________________________________________________________________
11
MAX1906
Design Procedure
MAX1906
Li+ Battery-Pack Protector with
Integrated Fuse Driver
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 assembly 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).
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 overvoltage trip point on the top cell by 3mV. The intermediate 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 recommended 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 tolerance while limiting the potential short-circuit current.
The MAX1906 has internal ESD diodes on each B_P pin
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 measurements. Use appropriate trace widths for the highcurrent paths and keep traces short to minimize parasitic inductance and capacitance. Provide adequate
space and board area for the sense resistor to dissipate heat. Place RC filters close to B1P–B4P pins. If
some amount of heat sinking is needed to use the internal SCR, connect the exposed backside paddle to as
large a copper area as practical.
Chip Information
TRANSISTOR COUNT: 4027
PROCESS: BiCMOS
Table 1. MOSFET Suppliers
SUPPLIER
Fairchild
International Rectifier
Vishay Siliconix
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
www.vishay.com
Table 2. Recommended Fuse Manufacturers
MANUFACTURER
Sony Chemicals Corp.
Uchihashi Estec Co., Ltd
12
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/
______________________________________________________________________________________
Li+ Battery-Pack Protector with
Integrated Fuse Driver
______________________________________________________________________________________
13
MAX1906
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.)
MAX1906
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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