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ISL6297
Datasheet September 27, 2005 FN9215.0
Li-ion/Li Polymer Battery Charger
The ISL6297 is a Dual-Mode Lithium Ion battery charger optimized for cellular phone travel charger applications. It uses Intersil's patent-pending dual-mode charge technology to minimize the heat normally generated in a linear charger. By minimizing the heat generation, the ISL6297 can be placed inside the connector of the travel charger to completely remove the influence of the adapter cable on the charging performance. The ISL6297 is an enhancement of the original ISL6292B. New features include improved accuracy, pre-charge circuit verification, and enhanced LED indicator function. Working with a current-limited AC/DC converter, the dualmode charger charges a Li-ion battery with the same current profile as a traditional linear charger. The constant charge current is determined by the current limit of the AC/DC converter. The constant output voltage is fixed at 4.2V. When the battery voltage is below 2.8V, the charger preconditions the battery with a low trickle-charge current. The charge status is indicated by a bi-color LED. A safety timer prevents charging a dead battery for an excessively long period. The ISL6297 also features THERMAGUARDTM, a thermal foldback function that automatically reduces the charge current when the internal die temperature exceeds a 100C limit to prevent further temperature rise. This function removes the concern of thermal failure in the targeted space-limited applications. An ambient temperature monitoring circuit allows users to set two separate temperature limit levels, for charge and non-charge conditions. The thermally-enhanced QFN package further improves the thermal performance of the ISL6297 in spacelimited applications.
Features
* Complete Charger for Single-Cell Li-ion Batteries * Integrated Pass Element and Current Sensor * No External Blocking Diode Required * Very Low Thermal Dual-Mode Operation * 0.7% Voltage Accuracy with Remote Sense * Pre-charge circuit verification with LED status indication * Drives a bi-color LED * Programmable Safety Timer * Programmable Current Limit up to 1.5A * Programmable End-of-Charge Current * THERMAGUARDTM Charge Current Thermal Foldback * NTC Thermistor Interface for Battery Temperature Monitor * Two-Level Ambient Temperature Setting * Guaranteed to Operate at 2.65V After Start-Up * Ambient Temperature Range: -20C to 70C * Thermally-Enhanced QFN Packages * QFN Package: - Compliant to JEDEC PUB95 MO-220 QFN - Quad Flat No Leads - Package Outline - Near Chip Scale Package footprint, which improves PCB efficiency and has a thinner profile * Pb-Free Plus Anneal Available (RoHS Compliant)
Applications
* * * * * PDAs, Cell Phones and Smart Phones Portable Instruments, MP3 Players Medical Handhelds Self-Charging Battery Packs Stand-Alone Chargers
Pinout
ISL6297 16 LD QFN TOP VIEW
BAT BAT VIN VIN
Ordering Information
PART NUMBER
12 VSEN 11 TEMP 10 IMIN 9 IREF
16 VIN GRN RED TIME 1 2 3 4 5 GND
15
14
13
PART TEMP. MARKING RANGE (C) ISL6297CR 6297CRZ -20 to 70 -20 to 70
PACKAGE
PKG. DWG. #
ISL6297CR ISL6297CR-T ISL6297CRZ (See Note)
16 Ld 4x4 QFN L16.4x4 16 Ld 4x4 QFN L16.4x4 (Pb-free)
ISL6297CR 16 Ld 4x4 QFN Tape and Reel
6 DT
7 EN
8 V2P9
ISL6297CRZ-T 6297CRZ (See Note)
16 Ld 4x4 QFN Tape and Reel (Pb-free)
NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Thermaguard is a trademark of Intersi Americas Inc. Copyright Intersil Americas Inc. 2005. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
ISL6297
Absolute Maximum Ratings
Supply Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 7V All Other Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to 5.5V
Thermal Information
Thermal Resistance (Notes 1, 2) JA (C/W) JC (C/W) 4x4 QFN Package . . . . . . . . . . . . . . . . 41 4 Junction Temperature Range . . . . . . . . . . . . . . . . .-55C to +150C Operating Temperature Range . . . . . . . . . . . . . . . . .-40C to +85C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65C to +150C Maximum Lead Temperature (Soldering 10s) . . . . . . . . . . . . +300C
Recommended Operating Conditions
Ambient Temperature Range . . . . . . . . . . . . . . . . . . . .-20C to 70C Supply Voltage, VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3V to 6.5V Maximum Pin Voltage (Except VIN). . . . . . . . . . . . . . . . . . . . . 5.25V
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES: 1. JA is measured in free air with the component mounted on a high effective thermal conductivity test board with "direct attach" features. See Tech Brief TB379. 2. JC, "case temperature" location is at the center of the exposed metal pad on the package underside. See Tech Brief TB379.
Electrical Specifications
PARAMETER
Typical values are tested at VIN = 5V and 25C ambient temperature. Maximum and minimum values are guaranteed over recommended operating conditions, unless otherwise noted. SYMBOL TEST CONDITIONS MIN TYP MAX UNITS
POWER-ON RESET, OVER VOLTAGE PROTECTION, PRE-REGULATOR Rising VIN Threshold Falling VIN Threshold 2.9V Reference Output Voltage 2.9V Reference Output Current VIN-BAT Comparator Offset STANDBY CURRENT VBAT Pin Sink Current VIN Pin Supply Current VIN Pin Supply Current Charger Reverse Current VOLTAGE REGULATION Output Voltage Dropout Voltage CHARGE CURRENT Charge/Protection Current Trickle Charge Current End-of-Charge Current CHARGE VOLTAGE THRESHOLDS Short-circuit Threshold Trickle Charge Threshold - Rising Trickle Charge Threshold - Falling Recharge Threshold - Falling Difference from Final Battery Voltage Open Circuit Test Threshold- Rising VOCR VSC VMIN VMIN VRECHRG 0.9 2.7 2.6 3.90 1.0 2.9 2.7 4.00 -210 4.4 1.1 3.2 3.0 4.08 V V V V mV V ICHARGE ITRICKLE RIREF = 80k, VBAT = 3.7V, VIN = 5V RIREF = 80k, VBAT = 2.0V, VIN = 5V RIMIN = 133k 900 85 56 1000 110 63 1100 135 70 mA mA mA VCH VBAT = 3.7V, ICHARGE = 0.65A 4.17 4.20 250 4.23 300 V mV ISTANDBY IVIN1 IVIN2 VIN floating or EN pin is floating BAT Pin floating, EN = LOW BAT Pin floating, EN = HIGH VIN = 4.3V, VSEN = BAT= 4.5V, EN = HIGH 1.0 0.5 3.0 1.5 1.0 6.0 A mA mA A V2P9 ILOAD = 2mA 2.9 2.3 30 3.4 2.4 2.9 4.0 2.65 30 V V V mA mV
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ISL6297
Electrical Specifications
PARAMETER BATTERY TEMPERATURE MONITORING Low Temperature Threshold Low Temperature Hysteresis High Temperature Threshold High Temperature Hysteresis DT Pin MOSFET On Resistance Charge Current Foldback Threshold (Note 4) Current Foldback Gain (Note 5) OSCILLATOR Oscillation Period LOGIC INPUT AND OUTPUT EN Input Low EN Pin External Pull Down to Disable LED Sink Current (RED, GRN) LED Leakage Current NOTES: 3. The actual current may be lower due to the thermal foldback. 4. Guaranteed by design and characterization to be typically 100oC 15%. 5. Guaranteed by design and characterization. Pin Voltage = 1.0V 5 10 0.8 50 1 V k mA A TOSC CTIME = 15nF 2.7 3.0 3.3 ms RDT TFOLD GFOLD VTMAX V2P9 = 2.88V VTMIN V2P9 = 2.88V 1.94 135 .704 160 2.0 167 .718 185 25 100 100 2.06 199 .732 200 V mV V mV C mA/C Typical values are tested at VIN = 5V and 25C ambient temperature. Maximum and minimum values are guaranteed over recommended operating conditions, unless otherwise noted. (Continued) SYMBOL TEST CONDITIONS MIN TYP MAX UNITS
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ISL6297 Pin Description
PIN # 1, 15, 16 2 3 4 5 6 7 8 PIN NAME VIN GRN RED TIME GND DT EN V2P9 DESCRIPTION VIN is the input power source. VIN can withstand up to 28V input. Open-drain LED drive pin. This pin sinks a constant-current 10mA to drive a green LED in a bi-color LED pack. Open-drain LED drive pin. This pin sinks a constant-current 10mA to drive a red LED in a bi-color LED pack. Timer Programming Input. The TIME pin determines the oscillation period by connecting a timing capacitor between this pin and GND. The oscillator provides a time reference for the charger. GND is the connection to system ground. Delta Temperature Setting Input. This pin sets the temperature difference before and after the charging starts. This pin can also be used as an indication whether or not the charger is charging. Enable Input. Connect EN LOW to enable the charger. Pull it HIGH or leave it floating to disable the charger. This pin is pulled up to 2.9V when left floating. Untrimmed 2.9V voltage output. This pin outputs a 2.9V voltage source when the input voltage is above POR threshold, independent on the EN pin input. The V2P9 output is used to power the LEDs, the NTC circuit, or for other functions. The maximum output current is 30mA. This output can also be used as an indication for adapter presence. This is the programming input for the constant charging current in a linear charger. In the typical application of a dual-mode charger, the IREF pin programs the trickle charge current as well as the protection current level. IMIN is the programmable input for the end-of-charge current. Temperature setting input. An external NTC thermistor is connected to this pin for ambient temperature sensing. Battery remote voltage sensing feedback pin. This pin allows remote sense of the battery pack voltage. Connect this pin as close as possible to the battery positive terminal with a separate trace to minimize the impact of parasitic resistance. This pin also serves the function of compensating for voltage drop caused by the connector contact resistance. BAT is the charger output. Exposed Pad. This pad is internally connected to GND. Connect as much copper as possible to this pad on the component or other layers through thermal vias to maximize the thermal performance.
9 10 11 12
IREF IMIN TEMP VSEN
13, 14 -
BAT EPAD
Typical Application
Input C1 VIN BAT To Battery C3 V2P9 C2 D2 D1 R1 RT RS R2 DT TEMP ISL6297 CTIME TIME RED GRN GND IREF RIMIN IMIN RIREF BATVSEN R3 EN C4 ID BAT+
NOTE: Temperature limit components selected for a temperature Range of -5C to 45C (not charging) See Example, page 14
C1: 1F X5R ceramic capacitor C3: 10F X5R ceramic capacitor C2, C4: 0.1F X5R ceramic capacitor CTIME : 22nF X5R or better timing capacitor D1, D2: dual-color (red and green) LED in one package RIREF : 80k, 1% RIMIN : 133k, 1%
R1: R2: RT: RS: R3:
15k, 1% TBD, value dependent on the T (1.37k for 10C delta) MuRata NCP18XH103J -- 10k at 25C, 5% (0603 size) 41.2 10k, 5% (R3 and C4 are for improving ESD protection)
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ISL6297 Block Diagram
VIN C1
Q MAIN
BAT
Temperature Monitoring IT
References QSEN VRECHRG VCONVER 100000:1 Current Mirror ISEN VPOR VMIN VCH
V2P9
VIN
Input_OK
+ VPOR
+ 50mV
VSEN
IREF RIREF IMIN RIMIN
IR Current References IMIN
+ CA CHRG V+ A-
+ -
VCH +
Trickle/Fast ISEN + MIN_I
Minbat
VMIN + VRECHRG
Recharge
V2P9 TEMP Under Temp NTC Interface
LOGIC
+ Batcon
VCONVER
DT
Over Temp
RED
TIME GND
OSC
COUNTER
GRN
Input_OK EN
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ISL6297 State Diagram
Plug-in Indicator POR RED GREEN YELLOW OFF CHARGER: OFF 500ms Idle LED: CHARGER: OFF OFF ENABLE Delay 500ms LED: CHARGER: OFF OFF LED: 500ms 500ms
DISABLE
DISABLE or POR
Open Battery Fault LED: CHARGER: Battery (+) Terminal Disconnected OFF OFF
Connection Verify (70ms) Temp Fault Cleared (Return to previous state) LED: OUTPUT: CHARGER: OFF Up to VIN TRICKLE
DISABLE or POR
Battery (+) Terminal Connected Temperature Fault LED: YELLOW CHARGER: OFF Short Circuit Test LED: CHARGER: TIMEOUT: RED TRICKLE RESTART VSEN <1V after 384 cycles Non-Temperature Fault LED: YELLOW (Blink) CHARGER: OFF
Any Temp Fault
VSEN > 1V before 384 cycles Trickle Charge LED: CHARGER: RED TRICKLE VSEN > 2.8V before 1/8 TIMEOUT VSEN < 2.8V after 1/8 TIMEOUT
Recharge LED: CHARGER: GREEN ON TIMEOUT and VSEN > 3.7V ICHG > IMIN
Fast Charge LED: CHARGER: RED ON TIMEOUT and VSEN < 3.7V ICHG > IMIN
Charge Termination LED: CHARGER: GREEN OFF
VSEN > 4.05V and ICHG < IMIN Timer Restart LED: GREEN CHARGER: ON TIMEOUT: RESTART
VSEN > 4.05V and ICHG < IMIN before TIMEOUT End of Charge LED: CHARGER: GREEN ON TIMEOUT
DISABLE or POR
VSEN < 4.00V
Charge Complete LED: CHARGER: GREEN OFF
Note: In the "Connection Verify" state, the output current is limited to ITRICKLE. In this state, with a battery connected, the output voltage rises no higher than the battery voltage. Also in this state, with no battery connected, the output voltage rises to VIN. In all other states, the output voltage is limited to 4.2V (typ).
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ISL6297 Theory of Operation
The ISL6297 is based on the Intersil Patent-pending dualmode charging technology. This allows the ISL6297 to function as a traditional linear charger when powered with a voltage-source adapter. However, when powered with a current-limited adapter, the charger minimizes the thermal dissipation commonly seen in traditional linear chargers. This dual-mode technology generates very low heat, which enables the charger to be used in space-limited applications. The ISL6297 charges a Lithium Ion battery using the constant current (CC) and constant voltage (CV) profile specified by battery cell manufacturers. As a linear charger, the constant charge current IREF is programmable up to 1.5A with an external resistor. The constant charge voltage VCH is regulated by the ISL6297 at 4.2V with a 0.7% accuracy over the entire recommended operating range. The ISL6297 always preconditions the battery with 10% of the programmed current at the beginning of a charge cycle, until the battery voltage is verified to be above the minimum fast charge voltage, VMIN. This low-current preconditioning charge mode is named trickle mode. A thermal-foldback feature removes the thermal concern typically seen in linear chargers. The charger reduces the charge current automatically as the IC internal temperature rises above 100oC to prevent further temperature rise. The thermal-foldback feature guarantees safe operation when the printed circuit board (PCB) is space limited for thermal dissipation.
Trickle Mode Constant Current Mode Constant Voltage Mode Inhibit
Figure 1 shows the typical charge curves in a traditional linear charger powered with a constant-voltage adapter. The power dissipation PCH is given by the following equations:
P CH = ( V IN -V BAT ) x I CHARGE (EQ. 1)
where ICHARGE is the charge current. The maximum power dissipation occurs at the beginning of the CC mode. The maximum power the IC is capable of dissipating is dependent on the thermal impedance of the printed-circuit board (PCB). Figure 1 shows, with dotted lines, two cases in which the charge currents are limited by the maximum power dissipation capability due to the thermal foldback. To take advantage of the low-heat feature of the ISL6297, a current-limited AC/DC converter is required as the power supply to the charger. The current-limited supply has the I-V characteristics shown in Figure 2. The supply is a DC source before the load current reaches the limited current ILIM. Once the current limit is reached, the supply current cannot increase further; instead, the supply voltage falls. The current-limited supply is a voltage source with an equivalent output impedance or a current source, depending on its operating region, as shown in Figure 2.
VNL VFL rO VNL I LIM C rO = (VNL - VFL)/ILIM B
A
VIN VCH VMIN
Input Voltage Battery Voltage
ILIM
FIGURE 2. THE I-V CHARACTERISTICS OF THE CURRENTLIMITED AC/DC CONVERTER
IREF Charge Current IREF/10 P1 P2 P3 Power Dissipation
In this mode of operation, the constant current is determined by the current limit ILIM of the supply during the constantcurrent charge mode. To ensure dual-mode operation, the current protection level set by the ISL6297 IREF pin should be higher than ILIM. In the constant-voltage charge mode, the battery voltage is regulated at 4.2V. When the battery voltage is below the specified VMIN voltage, the charger preconditions the battery using trickle charge mode. Figure 3 shows the typical waveforms in a charge cycle of the dual mode operation. When the battery voltage is below VMIN, the trickle charge mode is in effect. Since the charge current is much less than the ILIM, the AC/DC converter operates in the voltage source region. Once the battery voltage exceeds VMIN, the charger fully turns on the internal P-channel power MOSFET. The AC/DC converter operates
TIMEOUT
FIGURE 1. TYPICAL CHARGE CURVES USING A CONSTANT-VOLTAGE ADAPTER
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ISL6297
Trickle Mode VIN VCH VMIN IREF ILIM Charge Current IREF/10 Constant Current Mode Input Voltage Battery Voltage Constant Voltage Mode Inhibit
Appropriate design of the adapter can further reduce the peak power dissipation of the ISL6297. One simple approach is to design the AC/DC converter output voltage just high enough (normally lower than 5V) to fully charge the battery. More information can be found in the ISL6292 datasheet available at http://www.intersil.com.
Functional Overview
After applying power to the ISL6297, but before charging starts, the ISL6297 gives a "Plug-in indication" by sequencially turning on a red, a green and a yellow indicator. The indicator then turns off. This verifies that the AC/DC adapter and the ISL6297 have properly powered up. The ISL6297 then waits in an idle mode until the enable pin indicates that the battery pack has been plugged in. A 500ms delay give time for the pins to be connected prior to the start of a connection verification operation. In the connection verification, the ISL6297 determines if the battery positive pin is connected. If not, the charge operation does not start and the LED remains off. If the battery is firmly connected, the ISL6297 checks to see if the battery is good and that the battery connection is not short-circuited. If no faults are detected the ISL6297 starts a trickle charge and turns on the red LED charge indicator. Once the battery voltage reaches VMIN, the charger outputs a constant current until the battery voltage reaches VCH. The ISL6297 then holds the voltage constant. As the battery charges, the current supplied to the battery decreases. When the charge current drops to IMIN, the ISL6297 issues an EOC indication, which consists of the LED changing colors from red to green. An end of charge indication will also occur at the end of a user programmable TIMEOUT period even if the cell is not completely charged. If the battery voltage drops to a recharge threshold after the end of charge, the ISL6297 recharges the battery until the voltage again reaches 4.2V and the current drops below IMIN. At this point, the charger again turns off. The recharge cycle continues indefinitely until the charger is turned off by disconnecting the battery, which sets the EN pin high. An external NTC thermistor allows the ISL6297 to monitor the ambient temperature. If the ambient temperature is out range, the charger will not operate. Because the printedcircuit board (PCB) temperature rises during charge, the ISL6297 provides a higher temperature limit during the charge operation. The ISL6297 also features a thermal-foldback function that reduces the charge current if the IC internal temperature reaches 100C to prevent further temperature rise.
P1 P2 TIMEOUT
Power Dissipation
FIGURE 3. TYPICAL CHARGE CURVES USING A CURRENTLIMITED ADAPTER
in the current-limited region and its voltage is pulled down to a level slightly higher than the battery voltage. As shown in Figure 3, the charge current is ILIM and is lower than IREF. As the battery voltage reaches the 4.2V VCH level, the charge current starts to decrease. The AC/DC supply moves out of the current-limit region and becomes a voltage source again. When the charge current reaches a programmable end-of-charge (EOC) level set by the IMIN pin, the charger sends out an EOC indication. When using a current-limited adapter, the thermal situation in the ISL6297 is totally different from the voltage limited case. Figure 3 shows the typical charge curves when a current-limited adapter is employed. The operation requires that the IREF level be programmed higher than the limited current ILIM of the adapter. The key difference in the charger operation under such conditions occurs during the CC mode. The power dissipation in the CC mode becomes:
P CH = R DS ( ON ) x I CHARGE
2
(EQ. 2)
where rDS(ON) is the resistance when the main MOSFET is fully turned on. This power is typically much less than the peak power in the traditional linear mode. When using a current-limited adapter, the worst power dissipation typically occurs at the beginning of the CV mode, as shown in Figure 3. The equation EQ.1 also applies to the dual mode operation during the CV mode. When using a very small PCB whose thermal impedance is relatively large, it is possible that the internal temperature can still reach the thermal foldback threshold. In that case, the IC is thermally protected by lowering the charge current, as shown with the dotted lines in the charge current and power curves.
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ISL6297 Applications Information
Power-On Reset (POR)
The ISL6297 has a 3.4V rising POR threshold. Before the input voltage reaches the POR threshold, the V2P9 pin outputs 0V and the charger is disabled. Once the POR threshold is reached, all counters are reset to zero, the charge state machine is reset, the V2P9 pin outputs 2.9V, the open-drain MOSFET on the DT pin is turned on, and the ambient temperature monitoring circuit starts to function.
Connection Verification
The EN pin going low starts a 500ms delay. After the delay, the ISL6297 turns on the charger for 70ms with a trickle charge current and an output voltage of VIN. If no battery is connected, the VSEN voltage will go up to approximately VIN. If no battery is detected after the 70ms period, the ISL6297 terminates the charge operation, turns off the output voltage, and sets the LEDs off. The device remains in this state until the EN pin is toggled or the device goes through a power cycle. (See Figure 5.) If the battery is connected within the 70ms open battery detect period, the voltage on VSEN pin needs to drop below the (falling) threshold of about 4.3V before the end of the 70ms period. If not, then the battery has not been properly connected and an open battery connection fault condition exists, requiring a power cycle or a toggle of EN. After the 500ms delay, if a battery is connected, the VSEN voltage will remain below the 4.4V threshold and the ISL6297 assumes that the battery is connected. The device turns on the Red LED to indicate a charge operation and starts a short circuit detection. (See Figure 4.) If the battery positive terminal comes loose and reconnects after this time, the charge operation sequence continues, but the LED indicates an end of charge condition, regardless of the state of charge.
EN Pin
If all other charge conditions are met, pulling the EN pin low starts the ISL6297 charge operation. In a typical application, EN connects to the ID pin of a battery pack. Inside the battery pack the ID pin connects to ground through a resistance of less than 27k. When the battery is not attached to the charger, the ISL6297 internally pulls the EN pin high to disable the charger. An RC filter on the ISL6297 EN input improves the charger ESD protection. Table 1 summarizes the status of each pin when the EN pin disables the IC.
TABLE 1. SUMMARY OF PIN BEHAVIOR WHEN THE IC IS DISABLED BY THE EN PIN PIN V2P9 RED GRN DT IREF IMIN TEMP Outputs 2.9V. High impedance. High impedance. Low impedance. Outputs 0.8V. Outputs 0.8V. The temperature monitoring circuit remains functioning. BEHAVIOR
Short Circuit Detection
To detect a short circuit condition the ISL6297 forces the trickle charge current to the battery. If, after 384 cycles, the battery voltage is below 1V, the ISL6297 considers the battery or connection to be short-circuited. In this condition, the charger turns off and a flashing yellow indicator displays the occurance of this "non-temperture" fault. To clear a short circuit fault condition requires that the enable pin be toggled, by removing the battery pack, or by cycling the power on the charger.
Plug-in Indication
After power is applied to the ISL6297 and VIN exceeds the POR threshold, the LEDs provide a Plug-in Indication sequence. First the RED LED turns on for 500ms, then the GREEN LED turns on for 500ms, then both turn on for 500ms (giving a YELLOW indication), and finally all the LEDs turn off. The ISL6297 turns on an LED by pulling the output line LOW with a constant current of 10mA (typical). A typical bi-color LED needs no series resistor for the LED connection, however, current can be minimized by adding a serial resistor in each LED path.
Trickle Charge
If there is no short circuit the voltage is higher than 1V and the charge operation continues with a trickle charge. In the trickle charge, the ISL6297 applies 10% of the programmed current to the battery. If the voltage on the cell is greater than 2.8V after 15 clock cycles, then the ISL6297 applies the full constant current charge to the cell. However, if the voltage on the cell does not rise above 2.8V in one eighth (1/8) of the TIMEOUT period, then a non-temperature fault occurs and the charger is turned off. A flashing yellow indicator announces this condition.
Idle Condition and Battery Connection
Once VIN is greater than (VBAT + 50mV) and the temperature is within the allowed range the ISL6297 is ready to start the charge operation. Charging is initiated by plugging in the battery, which pulls the EN pin low.
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ISL6297
VIN
Short Circuit Test Connection Verification
V2P9 500ms 500ms 500ms 500ms
70ms 500ms
DT
RED GRN LEDs EN Battery (+) connection verified 4.4V VSEN 384 cycles max. Check if BAT > 1V If not: FAULT off Red Green Yellow off Red Charge Starts
ICHG
Trickle current
FIGURE 4. EVENT SEQUENCE AT POWER UP
programmed at least 30% higher than the ILIM. IREF can be calculated by using the following equation:
500ms
EN
Battery connected here, but voltage remains above the battery detect (falling) threshold - Open battery detected
5 0.8V I REF = ---------------- x 10 ( A ) R IREF
(EQ. 3)
The trickle charge current is 10% of IREF, that is,
4 0.8V I Trickle = ---------------- x 10 ( A ) R IREF
VIN
VSEN ICHG
4.4V
4.3V 70ms Trickle current
(EQ. 4)
Charge terminates. EN or POR required before charge sequence starts again
FIGURE 5. OPEN BATTERY DETECTED
The ISL6297 has a comparator with a 50mV offset voltage to ensure the input voltage is higher than the battery voltage before charging starts (see the Block Diagram). This condition, coupled with an RDS(on) of about 400m (max) requires ILIM be higher than 125mA. The upper limit for ILIM is 1.5A.
Charge Current and RIREF Selection
When the ISL6297 is used as a traditional linear charger, the RIREF sets the constant charge current. When working with a dual-mode, current-limited supply, the CC current is determined by the supply limited current ILIM. IREF needs to be programmed higher than ILIM and is used as an overcurrent protection. Taking into account the tolerance of both the ILIM and IREF, it is recommended the IREF be
EOC Current and RIMIN Selection
The EOC current level is programmed by the IMIN pin and can be calculated by the following equation:
4 0.8V I MIN = ---------------- x 10 ( A ) R IMIN
(EQ. 5)
The EOC current has a programming range up to 400mA. To qualify as an EOC condition, the battery voltage must be above the recharge threshold given in the Electrical
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ISL6297
POR Threshold VIN
V2P9
EN 500ms DT Impedance
Charge Cycle Charge Cycle
RED 15 cycles to 1/8 TIMEOUT GRN
VSEN
2.8V min.
Recharge
15 cycles
ICHG
IMIN
TIMEOUT
IMIN
FIGURE 6. OPERATION WAVEFORMS
Specification table and the charge current needs to drop below the IMIN level for 3 to 4 cycles of the internal oscillator.
Internal Oscillator
The internal oscillator establishes a timing reference. The oscillation period is programmable with an external timing capacitor, CTIME, as shown in Typical Applications. The oscillator charges the timing capacitor to 1.5V and then discharges it to 0.5V in one period, both with 10A current. The period TOSC is:
T OSC = 0.2 x 10 x C TIME
6
not reached full charge. At this point, if the voltage is above 4.05V, the recharge mechanism will continue to charge the cell until the current drops below IMIN. If the TIMEOUT counter expires before the battery reaches 4.05V, then the end of charge indication goes active, but the charger turns off. The charger cannot leave this condition without toggling the enable pin or cycling the power. The trickle mode charge has a time limit of 1/8 TIMEOUT. If the battery voltage does not reach VMIN within that time period, a TIMEOUT fault is issued and the charger turns off with a flashing Yellow LED indicator. The charger stays in trickle mode for at least 15 cycles of the internal oscillator and, at most, 1/8 of TIMEOUT. Once the ISL6297 detects that the battery reaches the EOC condition, it resets the TIMEOUT counter. At the end of this TIMEOUT period, the charger turns off and does not start again until the battery reaches a recharge condition.
( sec onds )
(EQ. 6)
A 15nF capacitor results in a 3ms oscillation period. The accuracy of the period is mainly dependent on the accuracy of the capacitance and the internal current source.
Total Charge Time and CTIME Selection
The time allowed for the battery to charge before an end of charge indication is limited to the duration of the TIMEOUT counter. The TIMEOUT period can be calculated by:
C TIME TIMEOUT = 14 x ----------------1nF ( minutes ) (EQ. 7)
Recharge Threshold
Once the charger reaches an end of charge condition and the charger turns off, if the battery voltage drops below the recharge threshold given in the Electrical Specification table, the charger starts a re-charge cycle. This is identical to an inital charge cycle, except the indicator remains green.
where CTIME is the timing capacitor shown in the Typical Application circuit. A 1nF capacitor leads to 14 minutes of TIMEOUT. For example, a 15nF capacitor sets the TIMEOUT to be 3.5 hours. The EOC indication goes active when the TIMEOUT counter expires, even if the battery has 11
LED Indications
The LED indicators show a number of conditions. On initial power on reset, the LEDs sequence through red, green and
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ISL6297
yellow. Once the charge begins, the ISL6297 pulls the RED pin low to drive a red indicator. Once the charge properly finishes (either when the EOC condition is qualified or when the TIMEOUT completes) the ISL6297 releases the RED output and pulls the GRN pin low to drive a green indicator while the red indicator turns off. The green LED remains on unless the input power is recycled, or a fault occurs. During a recharge operation, the indicator remains green. When a temperature fault happens, both the RED and the GRN pins turn on to indicate a yellow color. This fault is cleared automatically when the temperature again returns to the normal region. If the FAULT is non-temperature related, the yellow indicator flashes. This type of fault is latched and can only be reset by toggling the EN pin or cycling the input power. Table 2 summarizes the LED indications. Because the LED outputs provide a constant 10mA current sink, no external resistors are necessary.
TABLE 2. LED INDICATION SUMMARY STATUS Plug In Indication RED GRN L H L H Charging Full Charge (EOC) or recharging Short circuit Error or trickle charge TIMEOUT error Over/Under Ambient Temperature Idle state L H L H L H H L L H H L L H L H INDICATION Red (500ms) Green (500ms) Yellow (500ms) Off (500ms) Red Green Yellow (Flashing 1Hz rate) Yellow Off or Battery (+) terminal not connected
BAT
VSEN R2 VA +
VREF
R3
Enable
Q1
FIGURE 7. THE INTERNAL VOLTAGE FEEDBACK CIRCUIT
THERMAGUARDTM Charge Current Thermal Foldback
Over-heating is always a concern in a linear charger or in the linear region for a dual mode charger. The charge current thermal foldback function in the ISL6297 frees users from the over-heating concern. Figure 8 shows the current signals at the summing node of the current error amplifier CA in the Block Diagram. IR is the reference. IT is the current from the Temperature Monitoring block. The IT has no impact on the charge current until the internal temperature reaches approximately 100C; then IT rises at a rate of 1A/C. When IT rises, the current control loop forces the sensed current ISEN to reduce at the same rate. As a mirrored current, the charge current is 100,000 times that of the sensed current and reduces at a rate of 100mA/C. For a charger with the constant charge current set at 1A, the charge current is reduced to zero when the internal temperature rises to 110C. The actual charge current settles between 100C to 110C.
IR
VSEN Pin
When the charger is providing a large current to the cell, there can be significant voltage drop in the PCB trace between the charger output and the battery positive terminal. To minimize this effect, the VSEN pin input provides a low current monitoring path. This provides a more accurate reading of the battery voltage. Figure 7 shows the internal voltage feedback circuit.
100OC
IT
ISEN
Temperature
FIGURE 8. CURRENT SIGNALS AT THE AMPLIFIER CA INPUT
Usually the charge current should not drop below IMIN because of the thermal foldback. If, in some extreme case this does happen, the charger does not indicate end-ofcharge unless the battery voltage is already above the recharge threshold.
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ISL6297
Ambient Temperature Sensing
The TEMP pin sets the allowable ambient temperature range for charging the battery. Typically, an NTC (negative temperature coefficient) resistor is mounted on the printed circuit board (PCB) to monitor the ambient temperature. Due to the self-heating of the PCB during charging, the ISL6297 provides the DT pin to set a higher temperature threshold during the charge operation. Figure 9 shows the internal circuit for the ambient temperature sensing function. Two comparators form a window comparator whose high-threshold is VTMIN and lowthreshold is VTMAX. These two thresholds are given in the Electrical Specifications. The two MOSFETs (Q1 and Q2) create a hysteresis for each comparator, respectively. The DT pin is shorted to GND via the internal Q3 MOSFET when the charger is not charging, resulting in the equivalent circuit shown in Figure 10 (A). The on-resistance of Q3 is typically 50 and is negligible compared to the external resistors. When the charger starts to charge, Q3 is turned off to set a higher temperature range determined by the external resistor RD. The equivalent circuit is shown in Figure 10 (B). The DT pin provides a higher shut down ambient temperature during the charger operation.
2.9V R1 100K R2 75K RU TEMP
VTMIN (2.0V) VTMIN- (1.83V) TEMP Pin Voltage
V2P9 RU TEMP RT
DT
V2P9 RU TEMP RT
RQ3 GND
RD GND
(A)
(B)
FIGURE 10. EQUIVALENT CIRCUITS FOR THE NTC DIVIDER (A) BEFORE CHARGING STARTS (B) DURING CHARGING
When the TEMP pin voltage is "out of the window," as determined by the VTMIN and VTMAX, the ISL6297 stops charging and indicates a fault condition. When the temperature returns to the set range, the charger continues the charge cycle.
2.9V
V2P9
Under Temp CP1
+
VTMIN To TEMP Pin Q1
Over Temp
CP2
+
VTMAX Q2
R3 25K R4 4K DT
RT
VTMAX+ (0.788V) VTMAX (0.714V) 0V Under Temp Over Temp
CHG
Q3 GND
RD
FIGURE 11. CRITICAL VOLTAGE LEVELS FOR TEMP PIN
FIGURE 9. THE INTERNAL AND EXTERNAL CIRCUIT FOR THE NTC INTERFACE
As the temperature falls, the TEMP pin voltage rises. When it exceeds the 2.0V VTMIN threshold, an under temperature condition exists. This condition does not clear until the TEMP pin voltage falls back below the threshold minus the hysteresis voltage (VTMIN-). Similarly, an over-temperature condition exists when the TEMP pin voltage falls below the 0.714V VTMAX threshold and does return to normal temperature operation until the voltage rises above the threshold plus the hysteresis voltage (VTMAX+). The actual accuracy of the 2.9V supply voltage is not important because all the thresholds and the TEMP pin voltage are ratios determined by the resistor dividers, as shown in Figure 9.
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The ratio, K, of the TEMP pin voltage to the bias voltage is:
RT K = --------------------RT + RU (EQ. 8)
With the series resistor RS, EQ. 12 can be re-written as:
RS + R TCOLD ------------------------------------- = 6.84 R S + R THOT (EQ. 15)
and
K R T = ------------ x R 1-K U (EQ. 9)
Once the thermistor and the temperature limits are selected, RS and RU can be calculated using:
R TCOLD - 6.84R THOT R S = ------------------------------------------------------------5.84 (EQ. 16)
At VTMIN,
2.0K = ---------- = 0.6844 2.88 (EQ. 10)
and
R U = 0.44 x ( R S + R TCOLD ) (EQ. 17)
Similarly, at VTMAX.
0.718 * K = -------------- = 0.2493 2.88 (EQ. 11)
To summarize, the NTC thermistor circuit design requires three steps: 1. Find an NTC thermistor that satisfies EQ. 14. The temperature limits are determined by the application requirement. 2. Calculate the series resistance according to EQ. 16. 3. Calculate the pull-up resistance according to EQ. 17. Example: The charger is designed to charge the battery with the temperature range from -5C to 45C. The 10k NTC thermistor NCP15XH103F03RC from Murata (http://www.murata.com) satisfies EQ. 14. The resistance values for this thermistor are given in Table 3. The typical resistance at -5C and 45C are: RTCOLD = 33.8922k and RTHOT = 4.9169k. Using EQ. 16 and EQ. 17 result in:
Using these equations to calculate the ratio of the thermistor hot to cold resistance results in:
2.27R U R TCOLD ----------------------- = ----------------------- = 6.84 * R THOT 0.332R U (EQ. 12)
and
R U = 0.44R TCOLD (EQ. 13)
where RTCOLD and RTHOT are the NTC thermistor resistance values at the cold and hot temperature limits respectively. It is usually difficult to find an NTC thermistor that has the exact ratio given in EQ. 12. A thermistor with a ratio larger than 6.84, that is:
R TCOLD ----------------------- 6.84 R THOT (EQ. 14)
RS = 41.6 and RU = 14.931k. Selecting RS = 41.2 and RU = 15k gives a low temperature threshold of -5.1C and a high temperature threshold of 44.9C.
TABLE 3. RESISTANCE TABLE OF NCP15XH103F03RC
can be used in series with a regular resistor to form an effective thermistor that has the right ratio, as shown in Figure 12.
V2P8 RU TEMP
TEMP (C) -10 -5 0
Effective NTC Thermistor
RS
R-LOW (k) 41.4765 33.1462 26.6780 20.7560 19.9227 5.7443 4.8333 4.0833 3.4634
R-CENTER (k) 42.5062 33.8922 27.2186 21.1230 20.2666 5.8336 4.9169 4.1609 3.5350
R-HIGH (k) 43.5570 34.6515 27.7675 21.4944 20.6143 5.9238 5.0015 4.2395 3.6076
ISL6297
6 7 40 45 50 55
RT
GND
FIGURE 12. EFFECTIVE NTC THERMISTOR CIRCUIT
14
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Hysteresis Temperature Calculation
Re-arranging EQ. 8, and including the effect of RS, gives:
K R T = ------------ x R U - R S 1-K (EQ. 18) 45C+T
44.7C 32.0C Less than 2C 0.6C -5.1C
Using the K/(1-K) ratio at the hysteresis threshold, equation 18 provides the NTC thermistor resistance at the threshold. Continuing the example above, the thermistor values are found to be 26.2k and 7.3k respectively at the low and high hysteresis temperatures. The corresponding temperatures are found from Table 3. Cold recovery is about 1.0C and the hot recovery is about 33.9C. In other words, the hysteresis temperatures for the low and high limits are approximately 6.1C and 11.0C, respectively.
Temperature Tolerance Calculation
The temperature accuracy is affected by the accuracy of the thresholds, RS, RU, and the NTC thermistor. Using the maximum ratio K, maximum possible RU, and minimum RS results in the maximum value of RT from EQ. 18, that is:
K MAX R TMAX = ------------------------ x R UMAX - R SMIN 1 - K MAX (EQ. 19)
FIGURE 13. BOARD TEMPERATURE MONITORING. WHEN NOT CHARGING, THE TEMPERATURE WINDOW IS BETWEEN -5C AND 45C. ONCE THE CHARGER STARTS, THE TEMPERATURE WINDOW IS ~-3C TO 45C+ T
2.9V Bias Voltage
A pre-regulator provides a regulated 2.9V on the V2P9 pin, unless VIN drops below 2.9V plus 250mV (typical). Then the output voltage tracks the input voltage with a 250mV dropout voltage. The 2.9V output turns off when VIN drops below the VIN (falling) threshold. A minimum 0.1F X5R ceramic capacitor is required for decoupling the pre-regulator. The V2P9 output is used for biasing external circuits. The maximum loading current on this pin is 30mA. Mainly, the load current comes from the indication LEDs.
From the Electrical Specification table, the maximum K at cold is found to be 0.71. Assuming the resistors have 1% accuracy, the maximum RU is 15.15k and the minimum RS is 40.8. The resultant maximum RT is then found to be 36.3k and the corresponding temperature is about negative 6.4C. Hence the temperature tolerance is 1.3C. Similarly, at high temperature, the minimum K is .24, the minimum RU value is 14.85k and the maximum RS is 41.6. Hence, the highest temperature is 46.0C and the tolerance is 1.1C.
Board Layout Recommendations
The ISL6297 is targeted for space-limited applications. In order to maximize the current capability, it is very important that the exposed pad under the package is properly soldered to the board and is connected to other layers through thermal vias. More thermal vias and more copper attached to the exposed pad usually result in better thermal performance. On the other hand, the number of vias is limited by the size of the pad. The exposed pads for the 4x4 QFN package are able to have 5 vias. As much copper as possible should be connected to the exposed pad to minimize the thermal impedance. Refer to the ISL6297 evaluation board for layout examples.
Charging Temperature Range
The selection of RD follows the following equation:
R D = R T ( @45 C ) - R T ( @45 C + T )
o o
(EQ. 20)
where RT(@45C) is the thermistor resistance at 45C and the RT (@45C + T) is the resistance at some desired temperature difference above 45C. Figure 13 shows the temperature windows before, during, and after charging. From the example, before and after charging, the temperature window is -5C to 45C with 6C and 4C hysteresis. During charging, the high temperature limit changes to 45C + T. If this limit is exceeded, the charger is stopped and the temperature has to come back to below 41C for the charging to be allowed again. The low temperature limit is also increased. However, the RD typically has a much lower resistance than the NTC at low temperature, therefore, the influence on the temperature threshold is not as much as at high temperature. Typically, the low temperature threshold is raised by less than 2C, as shown in Figure 13. 15
Related Literature
* Technical Brief TB363 "Guidelines for Handling and Processing Moisture Sensitive Surface Mount Devices (SMDs)" * Technical Brief TB379 "Thermal Characterization of Packaged Semiconductor Devices" * Technical Brief TB389 "PCB Land Pattern Design and Surface Mount Guidelines for QFN Packages"
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ISL6297 Quad Flat No-Lead Plastic Package (QFN) Micro Lead Frame Plastic Package (MLFP)
L16.4x4
16 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE (COMPLIANT TO JEDEC MO-220-VGGC ISSUE C) MILLIMETERS SYMBOL A A1 A2 A3 b D D1 D2 E E1 E2 e k L L1 N Nd Ne P 0.25 0.50 1.95 1.95 0.23 MIN 0.80 NOMINAL 0.90 0.20 REF 0.28 4.00 BSC 3.75 BSC 2.10 4.00 BSC 3.75 BSC 2.10 0.65 BSC 0.60 16 4 4 0.60 12 0.75 0.15 2.25 2.25 0.35 MAX 1.00 0.05 1.00 NOTES 9 9 5, 8 9 7, 8 9 7, 8 8 10 2 3 3 9 9 Rev. 5 5/04 NOTES: 1. Dimensioning and tolerancing conform to ASME Y14.5-1994. 2. N is the number of terminals. 3. Nd and Ne refer to the number of terminals on each D and E. 4. All dimensions are in millimeters. Angles are in degrees. 5. Dimension b applies to the metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip. 6. The configuration of the pin #1 identifier is optional, but must be located within the zone indicated. The pin #1 identifier may be either a mold or mark feature. 7. Dimensions D2 and E2 are for the exposed pads which provide improved electrical and thermal performance. 8. Nominal dimensions are provided to assist with PCB Land Pattern Design efforts, see Intersil Technical Brief TB389. 9. Features and dimensions A2, A3, D1, E1, P & are present when Anvil singulation method is used and not present for saw singulation. 10. Depending on the method of lead termination at the edge of the package, a maximum 0.15mm pull back (L1) maybe present. L minus L1 to be equal to or greater than 0.3mm.
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com 16
FN9215.0 September 27, 2005

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