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19-2455; Rev 0; 4/02
Li+ Battery-Pack Protector with Integrated Fuse Driver
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. 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. The low-cost MAX1906 is available in a thermally enhanced 16-pin QFN package. o Protects Against Overvoltage o 1% Accurate Protection Thresholds o Integrated 2.1s Fault-Delay Timer o Built-in 1.5A SCR Fuse Driver o Test Mode for Functional Verification in Assembled Pack o 8A (max) Supply Current o 1A (max) Standby Current o Protects Against Disconnected B1P-B4P Pins o Protects 2-, 3-, or 4-Series Li+ Battery Packs o Available in Small 16-Pin QFN Package (5mm x 5mm)
Features
MAX1906
Ordering Information
PART TEMP RANGE MAX1906SEGE -40C to +85C MAX1906VEGE -40C to +85C MAX1906XEGE -40C to +85C PIN-PACKAGE CELLS 16 QFN 5mm 5mm 2 16 QFN 5mm 5mm 3 16 QFN 5mm 5mm 4
Applications
2-, 3-, or 4-Series Li+ Battery Packs for Portable Products
Minimal Operating Circuit
I.C. (B4P)
FUSE PACK+ VCC 7 OUT B4P 16
Pin Configuration
I.C. [B3P] 14 N.C. N.C. 13 12 11 B2P N.C. B1P I.C. 10 9 8 BN
16 I.C.
4 DISCON B3P 14
15
1 2 3 4 5 PKN 6 N.C. 7 OUT
DRV
12
OPTIONAL PACK CONTROLLER
2
DRV
MAX1906X
B2P
TEST DISCON
MAX1906S/V/X
3 TEST 5 B1P
10
PKN
BN
8
5mm x 5mm QFN
PACK-
[]:MAX1906V, MAX1906X ():MAX1906X
________________________________________________________________ Maxim Integrated Products
1
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Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
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 = +70C, per JEDEC JESD51-7) 16-Pin QFN (derate 19mW/C above +70C ambient) ....1.5W Operating Temperature Ranges..........................-40C to +85C Storage Temperature.........................................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +85C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER B4P Voltage Range B3P Voltage Range B2P Voltage Range B1P Voltage Range Overvoltage Detection Threshold Overvoltage Detection Threshold, Test Mode Overvoltage Detection Hysteresis SCR Release Threshold Standby-Mode Threshold Overvoltage Delay Sampling Interval Supply Current Supply Current During Sampling Standby Current Intermediate Cell Quiescent Current OUT Output Sink Current OUT Voltage (when SCR Is Triggered) OUT Leakage Current DRV Output Voltage Low DRV Output Voltage High DRV Sink Current DRV Source Current Test-Mode Delay Test-Mode Output Duration DISCON Output Voltage Low DISCON Leakage Current VDRVL VDRVH IDRV IDRV tDLY tOUT Individual cell voltages = 2.2V (Note 3) OUT = 2V, current not internally limited IOUT = 1.5A OUT = 24V IDRV = 200A IDRV = 5A IDRV = -1mA VDRVH = 2.5V VDRVL = 0V (Note 4) (Note 4) IDISCON = 1mA VDISCON = 3.3V -1 100 130 4.0 2.0 2 2 1.2 160 0.4 +1 4.8 4.8 -1 1.0 0.5 1.5 1.6 2.0 2.0 +1 0.4 5.5 5.5 ISUP tOV (Note 1) (Note 2) VOV_HYS VREL VOV_TH Cell voltage rising Cell voltage rising, test mode Cell voltage falling Cell voltage falling Cell voltage falling 3.85 2.3 1.85 4.4 2.0 4.45 2.225 10 4.0 3.3 2.1 2.56 3 300 800 6 4.15 4.1 2.45 SYMBOL CONDITIONS MIN TYP MAX 20 15 10 5 4.5 2.4 UNITS V V V V V V mV V V s s A A nA nA A V A V V mA mA ms ms V A
2
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Li+ Battery-Pack Protector with Integrated Fuse Driver
ELECTRICAL CHARACTERISTICS (continued)
(TA = 0C to +85C, individual cell voltages = 4.2V unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Disconnected Pin Test Time TEST Input High Minimum TEST High Duration TEST Input Low TEST Pulldown to PKN Thermal Impedance, Junction to Case 17 5 SYMBOL CONDITIONS Test time per cell 2.2 50 0.8 33 MIN TYP 0.2 MAX UNITS ms V s V k C/W
MAX1906
ELECTRICAL CHARACTERISTICS
(TA = -40C to +85C, individual cell voltages = 4.2V, unless otherwise noted.)
PARAMETER B4P Voltage Range B3P Voltage Range B2P Voltage Range B1P Voltage Range Overvoltage Detection Threshold Overvoltage Detection Threshold, Test Mode SCR Release Threshold Standby Mode Threshold Overvoltage Delay Supply Current Standby Current OUT Output Sink Current OUT Voltage (when SCR Is Triggered) DRV Output Voltage Low DRV Output Voltage High DRV Output Voltage High DRV Sink Current DRV Source Current Test-Mode Delay Test-Mode Output Duration DISCON Output Voltage Low TEST Input High TEST Input Low TEST Pulldown to PKN 17 VDRVL VDRVH VDRVH IDRV IDRV tDLY tOUT tOV ISUP (Note 2) Individual cell voltages = 2.2V OUT = 2V, current not internally limited IOUT = 1.5A IDRV = 200A IDRV = 5A IDRV = -1mA VDRVH = 2.5V VDRVL = 0V (Note 4) (Note 4) IDISCON = 1mA 2.6 0.8 33 95 3.9 2.0 2 2 1.25 165 0.4 1.0 2.2 0.4 5.5 5.5 VREL VOV_TH Cell voltage rising Cell voltage rising, test mode Cell voltage falling Cell voltage falling 4.35 1.95 3.80 2.25 1.85 SYMBOL CONDITIONS MIN TYP MAX 20 15 10 5 4.55 2.45 4.2 4.15 2.45 8 1 UNITS V V V V V V V V s A A A V V V V mA mA ms ms V V V k
Note 1: Note 2: Note 3: Note 4:
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
Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
OVERVOLTAGE THRESHOLD vs. TEMPERATURE
MAX1906 toc01
STANDBY-MODE THRESHOLD vs. TEMPERATURE
MAX1906 toc02
SUPPLY CURRENT vs. TEMPERATURE
MAX1906 toc03
4.455
3.5 3.3 CELL VOLTAGE (V) 3.1 2.9 2.7 2.5 EQUAL VOLTAGE APPLIED TO ALL CELL INPUTS (FALLING)
4.5
4.3 SUPPLY CURRENT (A)
CELL VOLTAGE (V)
4.450
4.1
3.9
4.445
3.7
4.440 -40 -15 10 35 60 85 TEMPERATURE (C)
2.3 -40 -15 10 35 60 85 TEMPERATURE (C)
3.5 -40 -15 10 35 60 85 TEMPERATURE (C)
STANDBY CURRENT vs. TEMPERATURE
MAX1906 toc04
THERMAL IMPEDANCE, CASE-TO-AMBIENT vs. COPPER AREA
MAX1906 toc05
TIME-TO-MAX JUNCTION TEMPERATURE vs. POWER DISSIPATION
TA = +60C 1000 TIME (s)
MAX1906 toc06
0.70
80 1oz COPPER
10,000
STANDBY CURRENT (A)
0.68
0.66
RCA (C/W)
60 100
0.25in2
0.50in2
0.64
40 0.62 10 0.04in2 20 -40 -15 10 35 60 85 0.01 0.1 1 10 TEMPERATURE (C) COPPER AREA (in2) 1 1.0 1.5 2.0 2.5 3.0 POWER DISSIPATION (W)
0.60
INSTANTANEOUS ON-STATE VOLTAGE vs. CURRENT
INSTANTANEOUS ON-STATE CURRENT (A)
MAX1906 toc07
TEST-MODE TIMING
MAX1906 toc08
1.6
1.3
TEST PIN VOLTAGE 5V/div
1.0 110C 0.7 TJ = 25C 0.4
DRV PIN VOLTAGE 5V/div
DISCON PIN VOLTAGE 5V/div 0.8 1.0 1.2 1.4 1.6 1.8 20ms/div
0.1 INSTANTANEOUS ON-STATE VOLTAGE (V)
4
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Li+ Battery-Pack Protector with Integrated Fuse Driver
Pin Description
PIN MAX1906S 1, 9 MAX1906V 1, 9 MAX1906X 1, 9 NAME I.C. N.C. DRV DESCRIPTION Internal Connection. Float pins 1 and 9. 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. Test-Mode Input. Test mode is enabled with a pulse of minimum 50s 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). 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. Positive Terminal of Cell 1. Connect B1P to the positive terminal of the first series Li+ cell. 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.
MAX1906
6, 11, 13, 15 6, 11, 13, 15 6, 11, 13, 15 2 2 2
3
3
3
TEST
4 5 7
4 5 7
4 5 7
DISCON PKN OUT
8
8
8
BN
10 12 -- --
10 12 14 --
10 12 14 16
B1P B2P B3P B4P
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.
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Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
F1 PACK+ SFD-145B R4 10
VCC
7
OUT
B4P
16
R5 100k 4 DISCON B3P 14
C4 0.1F R3 1k C3 0.1F R2 1k C2 0.1F R1 1k C1 0.1F
PACK CONTROLLER
2 DRV
MAX1906X
B2P
12
3 TEST B1P
10
5
PKN
BN
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 R4 10
VCC R5 100k
7
OUT
B4P
16
4
DISCON
B3P
14
C4 0.1F R3 1k C3 0.1F R2 1k C2 0.1F R1 1k C1 0.1F
PACK CONTROLLER
2 DRV
MAX1906X
B2P
12
3 TEST B1P
10
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 MAX1906
OUT IC 16 OUT IC 16 R3 10 C3 R2 0.1F 1k C2 R1 0.1F 1k C1 0.1F PKN RSENSE BN 8 RSENSE
DISCON
IC
14 R2 10
DISCON
B3P
14
DRV
MAX1906S
B2P
12
DRV C2 R1 0.1F 1k TEST C1 0.1F
MAX1906V
B2P
12
TEST
B1P
10
B1P
10
PKN
BN
8
Figure 3. Cell Connections for 2- and 3-Series Battery Packs
B4P LINEAR REGULATOR OSCILLATOR STATE MACHINE DRV DRIVER FAULT LOGIC
PKN COMPARATOR OUT SCR SCR DRIVER BN REF B4P B3P MUX B2P B1P BN
TEST LOGIC PKN
TEST
Figure 4. MAX1906 Functional Diagram _______________________________________________________________________________________ 7
Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
THREE-TERMINAL PROTECTION FUSE PACK+ TRICKLE CHARGE SFD-145B BSS84 15 RTKO 510 OVERCHARGE PROTECTION Si4435DY 13 TKO BN 16 SRC C6 2.2F OVERDISCHARGE PROTECTION Si4435DY R10 10
DSO
14
CGO
VCC
7 R5 100k 4
OUT
B4P
16 C9 0.1F
R9 10
R4 51
CMPSH-3 1 D1 C4 1.0F 2 B4P VCC
MAX1924X
DISCON
B3P
14 C8 0.1F
R8 1k
R3 1k
C5 0.1F
VDD 3 B3P TEST MICROCONTROLLER 7 CTL B1P GND 9 BN PKN 10 11 DISCON
DISCON
2
MAX1906X
DRV B2P
12 C7 0.1F
R7 1k
R2 1k
C3 0.1F 5 C2 0.1F B2P SHDN
12
TEST
3 TEST B1P
10 C6 0.1F
R6 1k
R1 1k
C1 0.1F
5
PKN
BN
8 RSENSE 0.02
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 8A (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 300A. In the idle state, the MAX1906 typically consumes 3.2A. Figure 6 shows the device current consumption in different states.
this mode, the device draws 1A (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 50s 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
Standby Mode
When all the cell voltages are below the standby-mode threshold, the MAX1906 goes into the standby mode. In
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Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
STOP SAMPLING AND MONITOR ONLY CELL UNDER MEASUREMENT 300A ISUP
3.2A
0.8ms
2.56s
2.1s
0.8ms
VB_P
VOV_TH VREL
4.8V VDRV
NOTE: ALL VALUES ARE TYPICAL.
Figure 6. Current Consumption of Chip in Different States
VTEST
50s
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
Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
SAMPLE MODE
EXIT FROM STANDBY MODE OR TEST MODE
SAMPLE B_P
SAMPLE MODE
NO
ALL CELLS CHECKED?
NO
B_P > VOV_TH ?
YES
YES STOP SAMPLING AND START 2.1s TIMER AND MONITOR CELL CONTINUOUSLY
CHECK DISCONNECTION OF B_P PIN
WAIT 2.56s
NO
IS B_P AT LEAST 1.2V ABOVE NEGATIVE TERMINAL
B_P > VOV_TH CONTINUOUSLY AND TIMER = 2.1s?
NO
YES
YES DRV = H SCR LATCHED
DISCON = L
NO
ALL PINS CHECKED?
NO
B_P < VREL AND THE REST B_P < VOV_TH ?
YES
YES
DISCON = H
DRV = L
Figure 8. Overvoltage Protection
Figure 9. Disconnected Pin Description
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
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 10A 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
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 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. The fuse blows when sufficient power is dissipated in the heater resistor to melt the fuse's internal solder joints: PHEATER = VHEATER x IHEATER =
MAX1906
(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 22 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 150C at 60C ambient temperature, the required thermal resistance must be: RCA + RJC < (TMAX - TA ) / (Pd) < (150C - 60C) / (1W) < 90C / W where RJC is the thermal impedance from junction to case, and RCA is the thermal impedance from case to ambient. RJC is fixed, and is about 5C/W for the 16-lead 5mm 5mm QFN package. RCA varies with copper area, and is shown in the Typical Operating Characteristics. Even though a combined thermal resistance of 90C/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.
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.
______________________________________________________________________________________
11
Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
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 300A typical sampling current, multiplied by a 10 series resistor can move the overvoltage trip point on the top cell by 3mV. The intermediate cell quiescent current is typically 500pA. A 1k 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 10 in series with the top cell and 1k 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 0.1F) 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 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/
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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.)
MAX1906
______________________________________________________________________________________
13
Li+ Battery-Pack Protector with Integrated Fuse Driver MAX1906
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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