AAT3680IKS-8.4-T1

Lithium-Ion Linear Battery Charge Controller General Description The AAT3680 BatteryManager™ is a member of AnalogicTech's Total Power Management IC™ family. This device is an advanced Lithium-Ion (LiIon) battery charge and management IC, specifically designed for low cost compact portable applications. In a single 8-pin package, the AAT3680 precisely regulates battery charge voltage and charge current. This device is capable of two trickle charge current levels controlled by one external pin. Battery charge temperature and charge state are carefully monitored for fault conditions. In the event of an over current, short circuit or over temperature failure, the device will automatically shut down, thus protecting the charging device and the battery under charge. A battery charge state monitor output pin is provided to indicate the battery charge status though a display LED. The battery charge status output is a serial interface which may also be read by a system microcontroller. The AAT3680 is available in an 8-pin MSOP or 12pin TSOPJW package, specified over -20 to 70°C range. AAT3680 Features • • • • • • • • • • • • • • BatteryManager™ 4.5V to 15V Input voltage range 1% Accurate Preset Voltages: 4.1V, 4.2V, 8.2V, 8.4V Low operation current, typically 0.5mA Programmable Charge Current Automatic recharge sequencing Battery temperature monitoring Deep discharge cell conditioning Fast trickle charge option with thermal over-ride Full battery charge auto turn off / sleep mode Over voltage, current and temperature protection Power on reset LED Charge Status Output or System Microcontroller serial interface Temperature range -20 to 70°C 8 pin MSOP, 12 pin TSOPJW package Preliminary Information Applications • • • • Cellular Phones Personal Digital Assistants (PDA's) Desktop Chargers USB Chargers Typical Application VP RSENSE 0.2Ω Q1 FZT788B BATT+ C2 10µF R1 2.5k DRV T2X VP CSI BAT BATT- AAT3680 VP TS RT1 TEMP VSS C1 4.7µF D1 RT2 STAT Battery Pack R2 1k 3680.2003.4.0.91 1 Lithium-Ion Linear Battery Charge Controller Pin Description Pin # SOP, TSSOP MSOP AAT3680 Symbol CSI BAT VP TS STAT VSS DRV T2X Function Current Sense Input. Battery voltage level sense input. Power supply input pin. Battery temperature sense input Battery charge status output. Connect an LED in series with 2.2kΩ from STAT to VP to monitor battery charge state. Common ground connection. Battery charge control output 2 x battery trickle charge control input. Connect this pin to VSS to double the battery trickle charge current. Leave this pin floating for normal trickle charge current (10% of full charge current). To enter microcontroller fast-read status, pull this pin high during power-up. 1 2 3 4 5 6 7 8 7 8 1 2 3 4 5 6 Pin Configuration MSOP-8 (Top View) VP 1 8 TSOPJW-12 (Top View) BAT CSI T2X DRV BAT CSI 1 2 2 8 7 6 5 6 5 TS STAT VSS 2 7 3 6 NC T2X DRV VSS 3 4 5 6 TS VP VP VP VP STAT 1 1 2 4 5 2 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller Absolute Maximum Ratings Symbol VP VCSI VT2X VBAT TJ TLEAD ESD AAT3680 (TA=25°C unless otherwise noted) Value -0.3 to 16 -0.3 to VP+0.3 -0.3 to 5.5 -0.3 to VP+0.3 -40 to 150 300 Note 1 Description VP relative to VSS CSI to GND T2X to GND BAT to GND Operating Junction Temperature Range Maximum Soldering Temperature (at Leads) ESD Rating Units V V V V °C °C kV Note: Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum rating should be applied at any one time. Note 1: IC devices are inherently ESD sensitive; handling precautions required. Thermal Information Symbol ΘJA ΘJA PD PD Description Maximum Thermal Resistance (TSOPJW-12) 2 Maximum Thermal Resistance (MSOP-8) 2 Maximum Power Dissipation (TSOPJW-12) 2 Maximum Power Dissipation (MSOP-8) 2 Value 120 150 1.0 833 Units °C/W °C/W W mW Note 2: Mounted on an FR4 printed circuit board. Recommended Operating Conditions Symbol VP IDRV T Description Operation Input Voltage DRV Pin Sink Current Ambient Temperature Range Conditions Min 4.5 -20 Typ Max 15 40 70 Units V mA °C 3680.2003.4.0.91 3 Lithium-Ion Linear Battery Charge Controller Electrical Characteristics values are at TA=25°C) Symbol IP ISLEEP ISTAT(HI) VSTAT(LOW) ISINK VOL@DRV AAT3680 (VIN = 4.5V to 15V, TA = -20 to 70°C unless otherwise noted. Typical Conditions VIN = 5.5V VIN = 5.5V, VCH = 4.1V, VCH = 4.2V VCH = 8.2V, VCH = 8.4V VIN = 5.5V VIN = 5.5V, ISINK = 5mA VIN = 5.5V ISINK = 5mA, VIN = 5.5V T = 25°C AAT3680-4.1 A see note 1 TA = 25°C AAT3680-4.2 see note 1 T = 25°C AAT3680-8.2 A see note 1 TA = 25°C AAT3680-8.4 see note 1 VIN = 5.5V, VCH = 4.1V, VCH = 4.2V VIN = 12V, VCH = 8.2V, VCH = 8.4V AAT3680-4.1 AAT3680-4.2 AAT3680-8.2 AAT3680-8.4 V = 4.1V, VCH = 4.2V T2X floating CH VCH = 8.2V, VCH = 8.4V T2X = VSS VIN = 15V VIN = 15V Description Operating Current Sleep Mode Current STAT high level output leakage current STAT low level sink current DRV pin sink current DRV pin output low Min Typ 0.5 2 3 Max Units 3 6 10 +1 0.6 1.0 4.125 4.141 4.225 4.242 8.249 8.282 8.450 8.484 110 110 3.06 3.16 6.22 6.32 mA µA µA V mA V -1 0.3 20 4.075 4.059 4.175 4.158 8.151 8.118 8.350 8.316 90 90 2.94 3.04 5.98 6.08 0.4 4.100 4.100 4.200 4.200 8.200 8.200 8.400 8.400 100 100 3.0 3.1 6.1 6.2 10 10 1.8 30 60 12 4.00 4.10 8.00 8.20 4.0 4.4 200 VCH Output Charge Voltage V VCS Charge Current Regulation mV VMIN Preconditioning Voltage Threshold V VTRICKLE T2X VTS1 VTS2 VTERM VRCH VUVLO VOVP VOCP Trickle-Charge Current Regulation Trickle Charge Current Gain Low Temperature Threshold High Temperature Threshold Charge termination threshold voltage mV 30.9 61.8 24 4.08 4.182 8.16 8.364 4.5 % VP % VP mV V V V % VCS VCH = 4.1V VCH = 4.2V Battery Recharge Voltage Threshold VCH = 8.2V VCH = 8.4V Undervoltage Lockout VIN rising, TA = 25°C Over-voltage Protection Threshold Over-current Protection Threshold 29.1 58.2 4 3.92 4.018 7.84 8.306 3.5 Note 1: The AAT3680 output charge voltage is specified over 0° to 50°C ambient temperature; operation over -20 to 70°C is guaranteed by design. 4 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller Functional Block Diagram Microcontroller Read Enable 2x Trickle Charge Control Current Loop Error Amp Loop Select MUX Driver AAT3680 T2X CSI DRV Microcontroller Status Generator VREF Voltage Loop Error Amp Charge Status Logic Control MUX STAT BAT Voltage Comparator LED Signal Generator TS Temperature Sense Comparator VSS VP Power-On Reset Under Voltage Lock Out Over Current / Short Circuit Protection Functional Description The AAT3680 is a Linear Charge Controller designed for one and two cell Lithium Ion or Lithium Polymer batteries. It is a full-featured battery management system IC with multiple levels of power savings, system communication and protection integrated inside. Refer to the block diagram and flow chart in this section. Cell Preconditioning Before starting charging, the AAT3680 checks several conditions in order to maintain a safe charging environment. The input supply must be above the minimum operating voltage, or undervoltage lockout threshold (VUVLO), for the charging sequence to begin. Also, the cell temperature, as reported by a thermistor connected to TS pin, must be within the proper window for safe charging. When these conditions have been met, and a battery is connected to the BAT pin, the AAT3680 checks the state of the battery. If the cell voltage is below VMIN, the AAT3680 begins preconditioning the cell. This is performed by charging the cell with 10% of the programmed constant-current amount. For example if the programmed charge current is 500mA, then the preconditioning mode (trickle charge) current will be 50mA. Cell preconditioning is a safety precaution for deeply discharged cells, and furthermore, limits the power dissipation in the pass transistor when the voltage across the device is largest. The AAT3680 features an optional T2X mode, which allows faster trickle-charging at approximately two times the default rate. This mode is selected by connecting the T2X pin to VSS. If an over-temperature fault is triggered, the fast trickle-charge will be latched off, and the AAT3680 will continue at the default 10% charge current. Constant Current Charging The cell preconditioning continues until the voltage on the BAT pin reaches VMIN. At this point, the AAT3680 begins constant-current charging (fast charging). Current level for this mode is programmed using a current sense resistor RSENSE between VP and CSI pins. The CSI pin monitors the voltage across RSENSE to provide feedback for the current control loop. The AAT3680 remains in constant current charge mode until the battery reaches the voltage regulation point, VCH. 3680.2003.4.0.91 5 Lithium-Ion Linear Battery Charge Controller Constant Voltage Charging When the battery's voltage reaches VCH during constant-current mode, the AAT3680 transitions to constant-voltage mode. The regulation voltage is factory programmed: 4.1V and 4.2V (or 8.2V and 8.4V for two-cell applications) are available to support different anode materials in Lithium Ion cells. In constant-voltage operation, the AAT3680 monitors the cell voltage and terminates the charging cycle when the voltage across RSENSE decreases to approximately 10mV. AAT3680 Charge Cycle Termination, Recharge Sequence After the charge cycle is complete, the AAT3680 latches off the pass device and automatically enters power-saving sleep mode. Either of two possible conditions will bring the IC out of sleep mode: the battery voltage at the BAT pin drops below VRCH (recharge threshold voltage) or the AAT3680 is reset by cycling the input supply through the power-on sequence. Falling below VRCH signals the IC that it is time to initiate a new charge cycle. Power On Reset Power On Reset UVLO VP > VUVLO No Shut Down Shut Down Mode Mode Yes Temperature Temperature Fault Fault No Temperature Test TS > VTS1 TS < VTS2 Yes Yes Low Current Conditioning Low Current Charge Conditioning (Trickle Charge) Charge Preconditioning Test VMIN > VBAT No Yes Current Current Charging Charging Mode Mode Current Phase Test VCH > VBAT No Voltage Phase Test VTERM < I BAT RSENSE Yes Voltage Voltage Charging Charging Mode Mode No < VRCH Charge Complete Charge Complete Latch Off Latch Off Figure 1: AAT3680 Operational Flow Chart 6 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller Sleep Mode When the input supply is disconnected, the charger automatically enters power-saving sleep mode. Only consuming an ultra-low 2µA in sleep mode, the AAT3680 minimizes battery drain when it is not charging.This feature is particularly useful in applications where the input supply level may fall below the battery charge or under-voltage lockout level. In such cases where the AAT3680 input voltage drops, the device will enter the sleep mode and automatically resume charging once the input supply has recovered from its fault condition. This makes the AAT3680 well suited for USB battery charger applications. it has not yet reached 4.2V to complete the charge cycle. If the battery is removed and then placed back on the charger, the charge cycle will not resume until the battery voltage drops below the VRCH threshold. In another case, a battery under charge is in the constant current mode and the cell voltage is 3.7V when the input supply is inadvertently removed and then restored. The battery is below the VRCH threshold and the charge cycle will immediately resume where it left off. AAT3680 LED Display Charge Status Output The AAT3680 provides a battery charge status output via the STAT pin. STAT is an open-drain serial data output capable of displaying five distinct status functions with one LED connected between the STAT pin and VP. There are four periods which determine a status word. Under default conditions each output period is one second long; thus one status word will take four seconds to display through an LED. The five modes include: 1. Sleep/Charge Complete: The IC goes into Sleep mode when no battery is present -OR- When the charge cycle is complete. 2. Fault: When an Over-Current (OC) condition is detected by the current sense and control circuit OR- When an Over-Voltage (OV) condition is detected at the BAT pin -OR- When a battery OverTemperature fault is detected on the TEMP pin. 3. Battery Conditioning: When the charge system is in the 1X or 2X trickle charge mode 4. Constant Current (CC) Mode: When the system is in the constant current charge mode. 5. Constant Voltage (CV) Mode: When the system is in the constant voltage charge mode. An additional feature of the LED status display is for a Battery Not Detected state. When the AAT3680 senses there is no battery connected to the BAT pin, the STAT output will turn the LED on and off at a rate dependant on the size of the output capacitor being used. The LED cycles on for two periods then remains off for two periods. See figure 2 below. Charge Inhibit The AAT3680 charging cycle is fully automatic; however, it is possible to stop the device from charging even when all conditions are met for proper charging. Switching the TS pin to either VP or VSS will force the AAT3680 to turn off the pass device and wait for a voltage between the low and high temperature voltage thresholds. Resuming Charge and the VRCH Threshold The AAT3680 will automatically resume charging under most conditions when a battery charge cycle is interrupted. Events such as an input supply interruption or under voltage, removal and replacement of the battery under charge or charging a partially drained battery are all possible. The AAT3680 will monitor the battery voltage and automatically resume charging in the appropriate mode based upon the measured battery cell voltage. The feature is useful for systems with an unstable input supply which could be the case when powering a charger from a USB bus supply. This feature is also beneficial for charging or "topping off" partially discharged batteries. The only restriction on resuming charge of a battery is the battery cell voltage must be below the battery recharge voltage threshold (VRCH) specification. There is VRCH threshold hysteresis built into the charge control system. This is done to prevent the charger from erroneously turning on and off one a battery charge cycle is complete. For example, the AAT3680-4.2 has a typical VRCH threshold of 4.1V. A battery under charge is above 4.1V, but is still in the constant voltage mode because 3680.2003.4.0.91 7 Lithium-Ion Linear Battery Charge Controller AAT3680 Charge Status Sleep / Charge Complete Temp., OC, OV Fault Battery Conditioning Constant Current Mode Constant Voltage Mode Output Status off / off / off / off on / on / off / off on / on / on / on on / on / on / off on / off / off / off LED Display on/off ON OFF ON OFF ON OFF ON OFF ON OFF on/off on/off on/off Figure 2: LED Display Output High Speed Data Reporting An optional system microcontroller interface can be enabled by pulling the T2X pin up to 4.5V to 5.5V during power-up sequence. The T2X pin should be pulled high with the use of a 100kΩ resistor. If the input supply to VP will not exceed 5.5V, then the T2X pin may be tied directly to VP through a 100kΩ resistor. Since this is a TTL level circuit, it may not be pulled higher than 5.5V without risk of damage to the device. When the high speed data report feature is enabled, the STAT output periods are sped up to 40µs, making the total status word 160µs in length. See Figure 3 below. An additional feature is the Output Status for Battery Not Detected state. When the AAT3680 senses there is no battery connected to the BAT pin, the STAT pin cycles for two periods, then remains off for two periods. When in High Speed Data Reporting, the AAT3680 will only trickle charge at the 2x trickle charge level. This is because the TX2 pin is pull high the enable the high speed data reporting. A status display LED may not be not be connected to the STAT pin when the high speed data reporting is being utilized. If both display modes are required, the display LED must be switched out the circuit before the T2X pin is pulled high. Failing to do so could cause problems with the high speed switching control circuits internal to the AAT3680. Charge Status Sleep / Charge Complete Temp., OC, OV Fault Battery Conditioning Constant Current Mode Constant Voltage Mode Output Status HI / HI / HI / HI LO / LO / HI / HI LO / LO / LO / LO LO / LO / LO / HI LO / HI / HI / HI STAT Level Figure 3: Microcontroller Interface Logic Output 8 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller RSENSE VP 0.2 Q1 FZT788B AAT3680 BATT+ VP C2 10µF R1 2.5k DRV CSI VP C1 4.7µF R2 100k VSS TX2 BAT TS STAT RT2 100k RT1 BATT- AAT3680 TEMP Battery Pack C3 0.1µF STAT High Speed Data Reporting Application Schematic Protection Circuitry The AAT3680 is truly a highly integrated battery management system IC including several protection features. In addition to battery temperature monitoring, the IC constantly monitors for over-current and over-voltage conditions; if an over-current situation occurs, the AAT3680 latches off the pass device to prevent damage to the battery or the system, and enters shutdown mode until the over-current event is terminated. An over voltage condition is defined as a condition where the voltage on the BAT pin exceeds the maximum battery charge voltage. If an over-voltage condition occurs, the IC turns off the pass device until voltage on the BAT pin drops below the maximum battery charge constant voltage threshold. The AAT3680 will resume normal operation after the over-current or over voltage condition is removed. During an over-current or over-voltage event, the STAT will report a FAULT signal. In the event of a battery over-temperature condition, the IC will turn off the pass device and report a FAULT signal on the STAT pin. After the system recovers from a temperature fault, the IC will resume operation in the 1X trickle charge mode to prevent damage to the system in the event a defective battery is placed under charge. Once the battery voltage rises above the trickle charge to constant current charge threshold, the IC will resume the constant current mode. Preconditioning (Trickle Charge) Phase Constant Current Phase Constant Voltage Phase Output Charge Voltage (VCH) Preconditioning Voltage Threshold (VMIN) Regulation Current (ICHARGE(REG)) Trickle Charge and Termination Threshold Figure 4: Typical Charge Profile 3680.2003.4.0.91 9 Lithium-Ion Linear Battery Charge Controller Applications Information Choosing an External Pass Device (PNP or PMOS) The AAT3680 is designed to work with either a PNP transistor or P-Channel Power MOSFET. Selecting one or the other requires looking at the design tradeoffs including performance versus cost issues. Refer to the following design guide for selecting the proper device: PNP Transistor: In this design example, we will use the following conditions: VP=5V (with 10% supply tolerance), ICHARGE(REG) = 600mA, 4.2V single cell Lithium Ion pack. VP is the input voltage to the AAT3680, and ICHARGE(REG) is the desired fast-charge current. 1. The first step is to determine the maximum power dissipation (PD) in the pass transistor. Worst case is when the input voltage is the highest and the battery voltage is at the lowest during fastcharge (this is referred to as VMIN, nominally 3.1V when the AAT3680-4.2 transitions from tricklecharge to constant-current mode). In this equation VCS is the voltage across RSENSE. PD = (VP(MAX) - VCS - VMIN) · ICHARGE(REG) PD = (5.5V - 0.1V - 3.1V) · 600mA PD = 1.38W 2. The next step is to determine which size package is needed to keep the junction temperature below its rated value, TJ(MAX). Using this value, and the maximum ambient temperature inside the system TA(MAX), calculate the thermal resistance RθJA required: RθJA = RθJA = (TJ(MAX) - TA(MAX)) PD (150 - 40) 1.38 3. Choose a collector-emitter (VCE) voltage rating greater than the input voltage. In this example, VP is 5.0V, so a 15V device is acceptable. 4. Choose a transistor with a collector current rating at least 50% greater than the programmed ICHARGE(REG) value. In this example we would select a device with at least 900mA rating. 5. Calculate the required current gain (β or hFE): βMIN = βMIN = IC(MAX) IB(MIN) 0.60 0.02 AAT3680 βMIN = 30 where IC(MAX) is the collector current (which is the same as ICHARGE(REG)), and IB(MIN) is the minimum amount of base current drive shown in Electrical Characteristics as ISINK. Important Note: The current gain (β or hFE) can vary a factor of 3 over temperature, and drops off significantly with increased collector current. It is critical to select a transistor with β, at full current and lowest temperature, greater than the βMIN calculated above. In summary, select a PNP transistor with ratings VCE ≥ 15V, RθJA ≤ 80°C/W, IC ≥ 900mA, βMIN ≥ 30 in a SOT223 (or better thermal) package. P-Channel Power MOSFET: In this design example, as shown in Figure 5, we will use the following conditions: VP = 5V (with 10% supply tolerance), ICHARGE(REG) = 750mA, 0.4V Schottky diode, 4.2V single cell Lithium Ion pack. VP is the input voltage to the AAT3680, and ICHARGE(REG) is the desired fast-charge current. 1. The first step is to determine the maximum power dissipation (PD) in the pass transistor. Worst case is when the input voltage is the highest and the battery voltage is at the lowest during fastcharge (this is referred to as VMIN, nominally 3.1V when the AAT3680-4.2 transitions from tricklecharge to constant-current mode). In this equation VCS is the voltage across RSENSE, and VD is the voltage across the reverse-current blocking diode. Refer to section below titled Schottky Diode for further details. Omit the value for VD in the equation below if the diode is not used. RθJA = 80°C/W It is recommended to choose a package with a lower RθJA than the number calculated above. A SOT223 package would be an acceptable choice, as it has an RθϑΑ of 62.5°C/W when mounted to a PCB with adequately sized copper pad soldered to the heat tab. 10 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller PD = (VP(MAX) - VCS - VD - VMIN) · ICHARGE(REG) PD = (5.5V - 0.1V - 0.4V - 3.1V) · 750mA PD = 1.4W 2. The next step is to determine which size package is needed to keep the junction temperature below its rated value, TJ(MAX). Using this value, and the maximum ambient temperature inside the system TA(MAX), calculate the thermal resistance RθJA required: RθJA = RθJA = (TJ(MAX) - TA(MAX)) PD (150 - 40) 1.4 5. Calculate the required threshold voltage to deliver ICHARGE(REG): VGS = (VCS + VOL@DRV) - VP(MIN) VGS = (0.1V + 0.1V) - 4.5V VGS = -4.3V where VGS is the available gate to source voltage provided by the AAT3680, VCS is the voltage across the sense resistor, VOL@DRV is the rated low voltage at the DRV pin, and VP(MIN) is the worst case input voltage (assuming 10% tolerance on the 5V supply). Choose a MOSFET device with sufficiently low VGS(TH) so the device will conduct the desired ICHARGE(REG). 6. Calculate the worst case maximum allowable RDS(ON) at worst case VGS voltage: RDS(ON) = RDS(ON) = (VP(MIN) - VCS(MAX) - VBAT(MAX)) ICHARGE(REG) (4.5V - 0.11V - 4.242V) 0.75A AAT3680 RθJA = 79°C/W It is recommended to choose a package with a lower RθJA than the number calculated above. A SOT223 package would be an acceptable choice, as it has an RθJA of 62.5°C/W when mounted to a PCB with adequately sized copper pad soldered to the heat tab. 3. Choose a drain-source (VDS) voltage rating greater than the input voltage. In this example, VP is 5.0V, so a 12V device is acceptable. 4. Choose a MOSFET with a drain current rating at least 50% greater than the programmed ICHARGE(REG) value. In this example we would select a device with at least 1.125A rating. Q1 RFD10P03L RDS(ON) = 197mΩ Select a P-Channel Power MOSFET with RDS(ON) lower than 197mΩ at VGS = -4.3V. In summary, select a P-Channel MOSFET with ratings VDS ≥ 12V, RθJA ≤ 79°C/W and RDS(ON) ≥ 197mΩ at VGS = -4.3V in a SOT223 (or better thermal) package. VP RSENSE 0.2Ω R4 100k BATT+ C2 10µF R1 1k DRV T2X VP CSI BAT BATT- AAT3680 VP TS RT1 TEMP VSS C1 4.7µF D1 RT2 STAT Battery Pack R2 1k Figure 5: Typical Applications Schematic Using P-Channel Power MOSFET 3680.2003.4.0.91 11 Lithium-Ion Linear Battery Charge Controller Choosing a Sense Resistor The charging rate recommended by Lithium Ion cell vendors is normally 1C, with a 2C absolute maximum rating. Charging at the highest recommended rate offers the advantage of shortened charging time without decreasing the battery's lifespan. This means that the suggested fast charge rate for a 500mAH battery pack is 500mA. The current sense resistor, RSENSE, programs the charge current according to the following equation: RSENSE = (VP -VCSI) ICHARGE(REG) be used because the AAT3680 checks to see that the voltage at TS is within a voltage window bounded by VTS1 and VTS2. Please see equations below for specifying resistors: RT1 and RT2 for use with NTC Thermistor RT1 = RT2 5 · RTH · RTC 3 · (RTC - RTH) 5 · RTH · RTC = (2 · RTC) - (7 · RTH) AAT3680 RT1 and RT2 for use with PTC Thermistor RT1 = RT2 5 · RTH · RTC 3 · (RTC - RTH) 5 · RTH · RTC = (2 · RTH) - (7 · RTC) Where ICHARGE(REG) is the desired typical charge current during constant-current charge mode. VP-VCSI is the voltage across RSENSE, shown in the Electrical Characteristic table as VCS. To program a nominal 500mA charge current during fast-charge, a 200mΩ value resistor should be selected. Calculate the worst case power dissipated in the sense resistor according to the following equation: P= P= (VCS)2 RSENSE (0.1)2 0.2 Where RTC is the thermistor's cold temperature resistance, and RTH is the thermistor's hot temperature resistance. See thermistor specifications for info. To ensure there is no dependence on the input supply changes, connect divider between VP and VSS. Disabling the temperature-monitoring function is achieved by applying a voltage between VTS1 and VTS2 on the TS pin. P = 50mW A 500mW LRC type sense resistor from IRC is adequate for this purpose. Higher value sense resistors can be used, decreasing the power dissipated in the sense resistor and pass transistor. The drawback of higher value sense resistors is that the charge cycle time is increased, so tradeoffs should be considered when optimizing the design. Capacitor Selection Input Capacitor In general, it is good design practice to place a decoupling capacitor between VP and VSS pins. An input capacitor in the range of 0.1µF to 4.7µF is recommended. If the source supply is unregulated, it may be necessary to increase the capacitance to keep the input voltage above the undervoltage lockout threshold. If the AAT3680 is to be used in a system with an external power supply source, such as a typical AC to DC wall adaptor, then a CIN capacitor in the range of 10µF should be used. A larger input capacitor in this application will minimize switching or power bounce effects when the power supply is "hot plugged" in. Thermistor The AAT3680 checks battery temperature before starting the charge cycle as well as during all stages of charging. This is accomplished by monitoring the voltage at the TS pin. Either a negativetemperature coefficient thermistor (NTC) or positive-temperature coefficient thermistor (PTC) can 12 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller Output Capacitor The AAT3680 does not need an output capacitor for stability of the device itself. However, a capacitor connected between BAT and VSS will control the output voltage when the AAT3680 is powered up when no battery is connected. The AAT3680 can become unstable if a high impedance load is placed across the BAT pin to VSS. Such a case is possible with aging Li-Ion battery cells. As cells age through repeated charge and discharge cycles, the internal impedance can rise over time. A 10µF or larger output capacitor will compensate for the adverse effects of a high impedance load and assure device stability over all operating conditions. voltage phases of the charging cycle, the battery under charge will discharge through the circuit pass transistor rendering it impossible to turn off. If the circuit is unable to turn off, the reverse leakage will eventually discharge the battery. A blocking diode will prevent this undesirable effect. MOSFET Circuit Application An reverse-blocking diode is generally required for the circuit shown in Figure 5. For this application, the blocking diode gives the system protection from a shorted input, when the AAT3680 is used with a P-Channel MOSFET. If there is no other protection in the system, a shorted input could discharge the battery through the body diode of the pass MOSFET. If a reverse-blocking diode is added to the system, a device should be chosen which can withstand the maximum constant- current charge current at the maximum system ambient temperature. Diode Selection Typically, a Schottky diode is used in reverse current blocking applications with the AAT3680. Other lower cost rectifier type diodes may also be used to save cost if sufficient input power supply head room is available. The blocking diode selection should based on merits of the device forward voltage (VF), current rating, input supply level versus the maximum battery charge voltage and cost. First, one must determine what the minimum diode forward voltage drop must be. Refer to the following equation where: VIN(MIN) = Minimum input supply level VBAT(MAX) = Maximum battery charge voltage required VF(TRAN) = Pass transistor forward voltage drop VF(DIODE) = Blocking diode forward voltage VIN(MIN) = VBAT(MAX) + VF(TRAN) + VF(DIODE) Based on the maximum constant current charge level set for the system, the next step is to determine the minimum current rating and power handling capacity for the blocking diode. The constant current charge level itself will dictate what the minimum AAT3680 Operation Under No-Load Under no-load conditions, that is when the AAT3680 is powered with no battery connected between the BAT pin and VSS, the output capacitor is charged up very quickly by the trickle charge control circuit to the BAT pin until the output reaches the recharge threshold (VRCH). At this point the AAT3680 will drop into the sleep mode. The output capacitor will discharge slowly by the capacitor's own internal leakage until the voltage seen at the BAT pin drops below the VRCH threshold. This 100mV cycle will continue at approximately 3Hz with a 0.1µF capacitor connected. A larger capacitor value will produce a slower voltage cycle. This operation mode can be observed by viewing the STAT LED blinking on and off at the rate established by the COUT value. For Desk Top Charger applications where it might not be desirable to have a "charger ready" blinking LED, a large COUT capacitor in the range of 100µF or more would prevent the operation of this mode. Reverse Current Blocking Diode Bi-Polar Circuit Application When using the AAT3680 with a PNP transistor, a reverse-blocking diode is not required because there is no current path from BAT to VP. However, it is advisable to still place a blocking diode between the bipolar transistor collector and the BAT pin connection to the circuit output. In the event where the input supply is interrupted or removed during the constant current or constant 3680.2003.4.0.91 13 Lithium-Ion Linear Battery Charge Controller current rating must be for a given blocking diode. The minimum power handling capacity must be calculated based on the constant current amplitude and the diode forward voltage (VF): Where: PD(MIN) = Minimum power rating for a diode selection VF = Diode forward voltage ICC = Constant current charge level for the system PD(MIN) = VF / ICC Schottky Diodes The reason for selecting a Schottky diode for this application is because Schottky diodes have a low forward voltage drop. The forward voltage (VF) for a Schottky diode is typically between 0.3V and 0.4V. A lower VF permits a lower voltage drop at the constant current charge level set by the system, less power will be dissipated in this element of the circuit. Schottky diode allow for lower power dissipation, smaller component package sizes and greater circuit layout densities. Rectifier Diodes Any general purpose rectifier diode can be used with the AAT3680 application circuit in place of a higher cost Schottky type diode. The design tradeoff is a rectifier diode has a high forward voltage drop. VF for a typical silicon rectifier diode is in the range of 0.7V. A higher VF will place a input supply voltage requirement for the battery charger system. This will also require a higher power rated diode since the voltage drop at the constant current charge amplitude will be greater. Refer to the previously stated equations to calculate the minimum VIN and diode PD for a given application. AAT3680 14 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller PCB Layout For the best results, it is recommended to physically place the battery pack as close as possible to the AAT3680's BAT pin. To minimize voltage drops in the PCB, keep the high current carrying traces adequately wide. For maximum power dissipation in the pass transistor, it is critical to provide enough copper to spread the heat. Refer to AAT3680 demo board PCB layout, see figures 6, 7 and 8 below. AAT3680 Figure 6: AAT3680 Demo Board Silk Screen / Assembly Drawing Figure 7: AAT3680 Demo Board Component Side Layout Figure 8: AAT3680 Demo Board Solder Side Layout 3680.2003.4.0.91 15 Lithium-Ion Linear Battery Charge Controller Evaluation Board Bill of Materials PNP Transistor Example Designator R3 R2 RT1 RT2 R1 C2 SW1 C1 C3 R4 U1 D1 D2 D3 Q1 AAT3680 Part Type 0.2Ω, 0.5 Watt 1kΩ, 5% 1MΩ, 5% 1MΩ, 5% 1.5kΩ, 5% 0.1µF Switch 4.7µF 10µF Not populated Li Ion Charge Controller IC Green LED 1.0A Schottky Diode 0.0 Ohm jumper PNP Transistor Footprint 1206 1206 0805 0805 0805 1206 1206 1206 MSOP-8 1206 SMA SOT223 Manufacturer IRC Various Various Various Various MuRata Mountain Switch MuRata MuRata AnalogicTech Various TSC Zetex Part Number LRC1206-01-R200F 10JS001 GRM42-6X5R75K10 GRM42-6X5R106K16 AAT3680IKS-4.2 LL5817 FZT788B P-Channel Power MOSFET Example Designator R3 R2 RT1 RT2 R1 C2 SW1 C1 C3 R4 U1 D1 D2 D3 Q1 Part Type 0.2Ω, 0.5W 1kΩ, 5% 1MΩ, 5% 1MΩ, 5% 1kΩ, 5% 0.1µF Switch 4.7µF 10µF 100kΩ, 5% Li Ion Charge Controller IC Green LED 0.0 Ohm jumper 1.0A Schottky Diode 30V P-Ch MOSFET, 0.2Ω Footprint 1206 1206 0805 0805 0805 1206 1206 1206 0805 MSOP-8 1206 SMA TO-252 Manufacturer IRC Various Various Various Various MuRata Mountain Switch MuRata MuRata Various AnalogicTech Various TSC Various Part Number LRC1206-01-R200F 10JS001 GRM42-6X5R75K10 GRM42-6X5R106K16 AAT3680IKS-4.2 LL5817 Various 16 3680.2003.4.0.91 Lithium-Ion Linear Battery Charge Controller Ordering Information Output Voltage MSOP-8 MSOP-8 MSOP-8 MSOP-8 TSOPJW-12 TSOPJW-12 TSOPJW-12 TSOPJW-12 Package 4.1V 4.2V 8.2V 8.4V 4.1V 4.2V 8.2V 8.4V Marking Part Number (Tape and Reel) AAT3680IKS-4.1-T1 AAT3680IKS-4.2-T1 AAT3680IKS-8.2-T1 AAT3680IKS-8.4-T1 AAT3680ITP-4.1-T1 AAT3680ITP-4.2-T1 AAT3680ITP-8.2-T1 AAT3680ITP-8.4-T1 AAT3680 Package Information MSOP8 4° ± 4° 1.95 BSC 3.00 ± 0.10 4.90 ± 0.10 0.60 ± 0.20 PIN 1 0.254 BSC 0.95 REF 3.00 ± 0.10 10° ± 5° 0.95 ± 0.15 0.85 ± 0.10 0.075 ± 0.075 0.65 BSC 0.30 ± 0.08 GAUGE PLANE 0.155 ± 0.075 3680.2003.4.0.91 17 Lithium-Ion Linear Battery Charge Controller TSOPJW-12 0.10 0.20 + 0.05 - AAT3680 2.40 ± 0.10 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 2.85 ± 0.20 7° NOM 3.00 ± 0.10 0.9625 ± 0.0375 0.04 REF + 0.10 1.00 - 0.065 0.055 ± 0.045 4° ± 4° 0.010 0.15 ± 0.05 0.45 ± 0.15 2.75 ± 0.25 Advanced Analogic Technologies, Inc. 830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 18 3680.2003.4.0.91