ACE4702 2 Cell Li-ion Battery Charger IC Description The ACE4702 is a PWM switch-mode lithium ion battery charger controller for 2 cell li-ion battery in a small package using few external components. The ACE4702 is specially designed for charging lithium ion battery with constant current and constant voltage mode. In constant voltage mode, the regulation voltage is fixed at 8.4V with ±1% accuracy. The constant charging current is programmable with a single sense resistor. Deeply discharged batteries are automatically trickle charged at 15% of the programmed constant charging current until the cell voltage exceeds 2.8V/cell. The charge cycle is terminated once the charging current drops to a level set by an on-chip resistor and an external resistor, and a new charge cycle automatically restarts if the battery voltage falls below 4V/cell. ACE4702 will automatically enter sleep mode when input voltage is lower than battery voltage. Other features include undervoltage lockout, battery temperature monitoring and status indication, etc. ACE4702 is available in a space-saving 16-pin TSSOP package. Features • • • • • • • • • • • • • • • • • Wide Input Voltage: 7.5V to 28V Complete Charger Controller for 2 cell Lithium-ion Battery Charge Current Up to 5A High PWM Switching Frequency: 300KHz Constant Charging Voltage Accuracy: ±1% Charging Current is programmed with a sense resistor Automatic Conditioning of Deeply Discharged Batteries End-of-Charge Current can be set by an external resistor Battery Temperature Monitoring Automatic Recharge Charger Status Indication Soft Start Battery Overvoltage Protection Operating Ambient Temperature -40℃ to ＋85℃ Available in 16 pin TSSOP Package Pb-free, RoHS Compliant, and Halogen Free Application • • • • • Portable DVD, Walkie-Talkie Notebook Computers Battery-Backup Systems Portable Industrial and Medical Equipment Standalone Battery Chargers VER 1.1 1 ACE4702 2 Cell Li-ion Battery Charger IC Absolute Maximum Ratings Parameter Max Unit Voltage from VCC, VG, DRV, CHRG, DONE to GND -0.3 ~ 30 V Voltage from CSP, BAT to GND -0.3 ~ 28 V Voltage from COM3 to GND V Storage Temperature 6.5 -0.3 ~ VCOM3+0.3 -65 ~ 150 ℃ Operating Ambient Temperature -40 ~ 85 ℃ Lead Temperature (Soldering, 10 seconds) 300 ℃ Voltage from Other Pins to GND V 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 above 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. Packaging Type TSSOP-16 TSSOP-16 Description 1 VG 2 PGND Function Internal Voltage Regulator. VG internally supplies power to gate driver, connect a 100nF capacitor between VG pin and VCC pin. Power Ground. 3 GND Analog Ground. 4 5 Open-Drain Output. When the battery is being charged, this pin is pulled low CHRG by an internal switch. Otherwise this pin is in high impedance state. Open-Drain Output. When the charging is terminated, this pin is pulled low DONE by an internal switch. Otherwise this pin is in high impedance state. VER 1.1 2 ACE4702 2 Cell Li-ion Battery Charger IC 6 TEMP 7 EOC 8 COM 1 9 COM 2 10 test 11 COM 3 12 NC 13 CSP 14 BAT Battery Temperature Monitoring Input. Connect an NTC resistor from this pin to GND. End-of-Charge Current Setting Pin. Connect this pin to GND directly or via a resistor. Loop Compensation Input 1. Connect a 470pF capacitor from this pin to GND. Loop Compensation Input 2. Connect a 220nF capacitor in series with an 120Ω resistor from this pin to GND. Test pin. Connected this pin to GND Loop Compensation Input 3. Connect an 100nF capacitor from this pin to GND. No Connection Positive Input for Charging Current Sensing. This pin and the BAT pin measure the voltage drop across the sense resistor RCS to provide the current signals required. Battery Voltage Sensing Input and the Negative Input for Charging Current Sensing. A precision divider sets the regulation voltage on this pin in constant voltage mode. 15 VCC 16 DRV External DC Power Supply Input. VCC is also the power supply for internal circuit. Bypass this pin with a capacitor. Drive the gate of external P-channel MOSFET. VER 1.1 3 ACE4702 2 Cell Li-ion Battery Charger IC Typical Application Circuit ACE4702 Figure 1 Typical Application Circuit Ordering information ACE4702 XX + H Halogen - free Pb - free LM : TSSOP-16 VER 1.1 4 ACE4702 2 Cell Li-ion Battery Charger IC Electrical Characteristics VCC=15V,TA=-40~85℃, unless otherwise noted. Parameter Symbol Input Voltage Range VCC 7.5 Undervoltage lockout Threshold UVLO 4.2 Operating Current IVCC No switching Regulation Voltage IREG Current Sense VCS Conditions Min Typ Max Units 28 V 6 7.3 V 1 1.55 2.1 mA Constant voltage mode 8.316 8.4 8.484 V VBAT>5.6V*VCSP- VBAT 190 200 210 VBAT>5.6V*VCSP- VBAT 18 30 42 15 25 uA 5.6 5.8 V mV Current into BAT Pin IBAT Termination or Sleep Mode Precharge Threshold VPRE VFB rising Precharge Threshold Hysteresis HPRE VFB falling 0.2 V Recharge Threshold VRE VFB falling 8 V Overvoltage Trip Level Vov VBAT rising 1.06 1.08 1.1 Overvoltage Clear Level Vclr VBAT falling 0.98 1 1.02 41 53 65 uA 1.61 5.4 VREG Temp Pin Pull up Current Iup High Threshold Vthh TEMP Voltage Rising 1.57 1.65 V Low Threshold Vthl TEMP Voltage Falling 0.145 0.175 0.205 V CHRG Pin CHRG Pin Sink Current CHRG Leakage Current ICHRG VCHRG=1V, charge mode ILK1 VCHRG=25V, termination mode 7 12 18 mA 1 uA 18 mA 1 uA 360 kHZ DONE Pin DONE Sink Current IDONE VDONE=1V, termination mode DONE Leakage Current ILK2 VDON=25V, charge mode 7 12 Oscillator Switching Frequency fosc Maximum Duty Cycle Dmax 240 300 94 % Sleep Mode Sleep Mode Threshold (measure VCC-VBAT) VSLP VCC falling Sleep mode Release Threshold (measure VCC-VBAT) VSLPR VCC rising VBAT=8V VBAT=12V VBAT=18V VBAT=8V VBAT=12V VBAT=18V 0.06 0.1 0.18 0.26 0.32 0.38 0.1 0.14 0.23 0.32 0.42 0.47 0.14 0.18 0.28 0.39 0.52 0.58 V V VER 1.1 5 ACE4702 2 Cell Li-ion Battery Charger IC DRV Pin VDRV High (VCC－VDRV) VH IDRV＝-10mA 60 mV VDRV Low (VCC－VDRV) VL 5.8 V Rise Time tr Fall Time tf IDRV＝0mA Cload＝2nF, 10% to 90% Cload＝2nF, 90% to 10% 30 40 65 ns 30 40 65 ns Note 1: VOC is the regulation voltage at BAT pin in constant voltage mode Detailed Description The ACE4702 is a constant current, constant voltage Li-Ion battery charger controller that adopts PWM step-down (buck) switching architecture. The charge current is set by an external sense resistor (RCS) across the CSP and BAT pins. The final battery regulation voltage in constant voltage mode is internally set to 8.4V for ACE4702 with 1% accuracy. A charge cycle begins when the voltage at the VCC pin rises above the UVLO level and is greater than the battery voltage by VSLPR. At the beginning of the charge cycle, if the battery voltage is less than 5.6V, the charger goes into trickle charge mode. The trickle charge current is internally set to 15%(Typical) of the full-scale current. When the battery voltage exceeds 5.6V, the charge goes into full-scale constant current charge mode. In constant current mode, the charge current is set by the external sense resistor RCS and an internal 200mV reference, so the charge current equals to 200mV/Rcs. When the battery voltage approaches the regulation voltage, the charger goes into constant voltage mode, and the charge current will start to decrease When the charge current drops to a level that is set by the resistor at EOC pin, the charger cycle is terminated, the DRV pin is pulled up to VCC, and an internal comparator turns off the internal pull-down N-channel MOSFET at the CHRG pin to indicate that the charge cycle is terminated. During the charge cycle termination status, another internal pull-down N-channel MOSFET at the DONE pin is turned on to indicated the termination status. To restart the charge cycle, just remove and reapply the input voltage. Also, a new charge cycle will begin if the battery voltage drops below the recharge threshold voltage of 4V/cell. When the input voltage is not present, the charger goes into sleep mode. A 10kΩ NTC (negative temperature coefficient) thermistor can be connected from the TEMP pin to ground for battery temperature qualification. The charge cycle is suspended If the battery temperature is outside of the acceptable range. An overvoltage comparator guards against voltage transient overshoots (>8% of regulation voltage). In this case, P-channel MOSFET is turned off until the overvoltage condition is cleared. This feature is useful for battery load dump or sudden removal of battery. VER 1.1 6 ACE4702 2 Cell Li-ion Battery Charger IC The charging profile is shown in Figure 2. Figure 2 The Charging Profile Application Information Undervoltage Lockout (UVLO) An undervoltage lockout circuit monitors the input voltage and keeps the charger off if VCC falls below 6V(Typical). Trickle Charge Mode At the beginning of a charge cycle, if the battery voltage is below 5.6%V, the charger goes into trickle charge mode with the charge current reduced to 15% of the full-scale current. Charge Current Setting The full-scale charge current, namely the charge current in constant current mode, is decided by the following formula: Where: ICH is the constant charge current RCS is the resistor between the CSP pin and BAT pin End-of-Over Charge Current Setting End-of-over charge current can be set by connecting a resistor from EOC pin to GND, and is decided by the following equation: VER 1.1 7 ACE4702 2 Cell Li-ion Battery Charger IC Where: IEOC is the end-of-over charge current in Ampere Rext is the external resistance from EOC pin to GND in Ω. Rext can not be great than 100KΩ, otherwise the charging may not be terminated correctly. RCS is the current sense resistance between CSP pin and BAT pin in Ω It is our interest to calculate the ratio between IEOC and ICH: When Rext=0Ω, the minimum IEOC/ICH=9.17% When Rext=100KΩ, the maximum IEOC/ICH=73% Automatic Battery Recharge After the charge cycle is completed and both the battery and the input power supply (wall adapter) are still Connected, a new charge cycle will begin if the battery voltage drops below 4V/cell due to self-discharge or external loading. This will keep the battery capacity at more than 80% at all times without manually restarting the charge cycle. Battery Temperature Monitoring A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and will not allow charging unless the battery temperature is within an acceptable range. Connect a 10kΩ thermistor from the TEMP pin to ground. Internally, for hot temperature, the low voltage threshold is set at 175mV which is equal to 50℃(RNTC≈ 3.5kΩ). For cold temperature, the high voltage threshold is set at 1.61V which is equal to 0℃(RNTC≈ 32kΩ) with 50uA of pull-up current. Once the temperature is outside the window, the charge cycle will be suspended, and the charge cycle resumes if the temperature is back to the acceptable range. The TEMP pin’s pull up current is about 50uA, so the NTC thermistor’s resistance should be 10kΩ at 25 ℃, about 3.5kΩ at hot temperature threshold, and about 32kΩ at cold temperature threshold. The NTC thermistor such as TH11-3H103F, MF52(10 kΩ), QWX-103 and NCP18XH103F03RB can work well with ACE4702. The above mentioned part numbers are for reference only, the users can select the right NTC thermistor part number based on their requirements. If battery temperature monitoring function is not needed, just connect a 10KΩ resistor from TEMP pin to GND. Status Indication The ACE4702 has 2 open-drain status outputs: CHRG and DONE. CHRG is pulled low when the charger is in charging status, otherwise CHRG becomes high impedance. DONE is pulled low if the charger is in charge termination status, otherwise DONE becomes high impedance. When the battery is not present, the charger charges the output capacitor to the float-charge voltage. VER 1.1 8 ACE4702 2 Cell Li-ion Battery Charger IC quickly, then the BAT pin’s voltage decays slowly to recharge threshold because of low leakage current at BAT pin, which results in ripple waveform at BAT pin, in the meantime, CHRG pin outputs a pulse to indicate that the battery’s absence. The pulse’s frequency is around 10Hz when a 10uF output capacitor is used. The open drain status output that is not used should be tied to ground. The table 1 lists the two indicator status and its corresponding charging status. It is supposed that red LED is connected to CHRG pin and green LED is connected to DONE pin. CHRG Pin DONE pin State Description High Impedance (the green Charging Low (The red LED on) LED off) High Impedance (the red Low (the green LED on) Charging termination LED off) Pulse signal Pulse signal Battery not connected There are three possible state: * The voltage at the VCC pin below the High Impedance (the red High Impedance (the green UVLO level LED off) LED off) * The voltage at the VCC pin below VBAT or * abnormal battery’s temp Table 1 Indication Status VER 1.1 9 ACE4702 2 Cell Li-ion Battery Charger IC Gate Drive The ACE4702’s gate driver can provide high transient currents to drive the external pass transistor. The rise and fall times are typically 40ns when driving a 2000pF load, which is typical for a P-channel MOSFET with Rds(on) in the range of 50mΩ. A voltage clamp is added to limit the gate drive to 8V max. below VCC. For example, if VCC is 20V, then the DRV pin output will be pulled down to 12V min. This allows low voltage P-channel MOSFETs with superior Rds(on) to be used as the pass transistor thus increasing efficiency. Loop Compensation In order to make sure that the current loop and the voltage loop are stable, the following compensation components are necessary: (1) A 470pF capacitor from the COM1 pin to GND (2) A series 220nF ceramic capacitor and 120Ω resistor from the COM2 pin to GND (3) An 100nF ceramic capacitor from the COM3 pin to GND Battery Detection ACE4702 does not provide battery detection function, when the battery is not present, the charger charges the output capacitor to the regulation voltage quickly, then the BAT pin’s voltage decays slowly to recharge threshold because of low leakage current at BAT pin, which results in a ripple waveform at BAT pin, in the meantime, CHRG pin outputs a pulse to indicate that the battery’s absence. The pulse’s frequency is around 10Hz when a10uF output capacitor is used. It is generally not a good practice to connect a battery while the charger is running. The charger may provide large surge current into the battery for a brief time. Input and Output Capacitors Since the input capacitor is assumed to absorb all input switching ripple current in the converter, it must have an adequate ripple current rating. Worst-case RMS ripple current is approximately one-half of output charge current. The selection of output capacitor is primarily determined by the ESR required to minimize ripple voltage and load step transients. Generally speaking, a 10uF ceramic capacitor can be used. Inductor Selection During P-channel MOSFET’s on time, the inductor current increases, and decreases during P-channel MOSFET’s off time, the inductor’s ripple current increases with lower inductance and higher input voltage. Higher inductor ripple current results in higher charge current ripple and greater core losses. So the inductor’s ripple current should be limited within a reasonable range. The inductor’s ripple current is given by the following formula: Where, f is the switching frequency 300KHz L is the inductor value VBAT is the battery voltage VCC is the input voltage A reasonable starting point for setting inductor ripple current is △IL＝0.4*ICH, ICH is the charge current. Remember that the maximum △IL occurs at the maximum input voltage and the lowest inductor value. So lower charge current generally calls for larger inductor value. VER 1.1 10 ACE4702 2 Cell Li-ion Battery Charger IC Use Table 2 as a guide for selecting the correct inductor value for your application. Charge Current Input Voltage Inductor Value 1A 2A 3A 4A 5A >20V 40uH <20V 30uH >20V 30uH <20V 20uH >20V 20uH <20V 15uH >20V 15uH <20V 10uH >20V 10uH <20V 8uH Table 2 Guide to Select Inductor Value MOSFET Selection The ACE4702 uses a P-channel power MOSFET switch. The MOSFET must be selected to meet the efficiency or power dissipation requirements of the charging circuit as well as the maximum temperature of the MOSFET. The peak-to-peak gate drive voltage is set internally, this voltage is typically 5.8V. Consequently, logic-level threshold MOSFETs must be used. Pay close attention to the BVDSS specification for the MOSFET as well; many of the logic level MOSFETs are limited to 30V or less. Selection criteria for the power MOSFET includes the “on” resistance Rds(on), total gate charge Qg, reverse transfer capacitance CRSS, input voltage and maximum charge current. The MOSFET power dissipation at maximum output current is approximated by the equation: Where: Pd is the power dissipation of the power MOSFET VBAT is the maximum battery voltage VCC is the minimum input voltage Rds(on) is the power MOSFET’s on resistance at room temperature ICH is the charge current dT is the temperature difference between actual ambient temperature and room temperature(25℃) In addition to the I2Rds(on) loss, the power MOSFET still has transition loss, which are highest at the highest input voltage. Generally speaking, for VIN＜20V, the I2Rds(on) loss may be dominant, so the MOSFET with lower Rds(on) should be selected for better efficiency; for VIN＞20V, the transition loss may be dominant, so the MOSFET with lower CRSS can provide better efficiency. CRSS is usually specified in the MOSFET characteristics; if not, then CRSS can be calculated using CRSS = QGD/ΔVDS. The MOSFETs such as ACE9435, ACE4443, ACE7401, ACE4409 can be used. The part numbers listed above are for reference only, the users can select the right MOSFET based on their requirements. VER 1.1 11 ACE4702 2 Cell Li-ion Battery Charger IC Diode Selection The diodes D1 and D2 in Figure 1 are schottky diode, the current rating of the diodes should be at least the charge current limit, the voltage rating of the diode should exceed the maximum expected input voltage. The diode that is much larger than that is sufficient can result in larger transition losses due to their larger junction capacitance. Disable Charging with TEMP Pin The charging can be disable with TEMP pin, as shown in Figure3: ACE4702 Figure3 Disable Charging Whth TEMP Pin When control signal is high, N-channel MOSFET M1 is turned on, the voltage at TEMP pin is pulled down to GND, which will disable the charging; When control signal is low, N-channel MOSFET is turned off, the voltage at TEMP pin is determined by NTC thermistor, which performs normal battery temperature monitoring function. About Battery Current in Sleep Mode In the typical application circuit shown in Figure 1, when input voltage is powered off or lower than battery voltage, ACE4702 will enter sleep mode. In sleep mode, the battery current includes: (1) The current into BAT pin and CSP pin, which is about 14uA(VBAT＝8.4V). (2) The current from battery to VCC pin via diode D1, which is determined by D1’s leakage current. The current will charge capacitance C1 at VCC pin, which will make VCC voltage a bit higher. To avoid erratic operation, a resistor in parallel with capacitance C1 may be needed to discharge the capacitance, the resistor value is determined by diode D1’s leakage, generally speaking, a 20KΩ resistor can achieve the task. The current from battery to GND via diode D2, which is also determined by D2’s leakage current. VER 1.1 12 ACE4702 2 Cell Li-ion Battery Charger IC PCB Layout Considerations When laying out the printed circuit board, the following considerations should be taken to ensure proper operation of the IC. (1) To minimize radiation, the 2 diodes, pass transistor, inductor and the input bypass capacitor traces should be kept as short as possible. The positive side of the input capacitor should be close to the source of the P-channel MOSFET; it provides the AC current to the pass transistor. The connection between the catch diode and the pass transistor should also be kept as short as possible. (2) The compensation capacitor connected at the COM1, COM2 and COM3 pins should return to the analog ground pin of the IC. This will prevent ground noise from disrupting the loop stability. (3) Output capacitor ground connections need to feed into same copper that connects to the input capacitor ground before tying back into system ground. (4) Analog ground and power ground(or switching ground) should return to system ground separately. (5) The ground pins also works as a heat sink, therefore use a generous amount of copper around the ground pins. This is especially important for high VCC and/or high gate capacitance applications. (6) Place the charge current sense resistor RCS right next to the inductor output but oriented such that the IC’s CSP and BAT traces going to RCS are not long. The 2 traces need to be routed together as a single pair on the same layer at any given time with smallest trace spacing possible. (7) The CSP and BAT pins should be connected directly to the current sense resistor (Kelvin sensing) for best charge current accuracy. See Figure 4 as an example. Figure 4 Kelvin Sensing of Charge Current VER 1.1 13 ACE4702 2 Cell Li-ion Battery Charger IC Packing Information TSSOP-16 Symbol Dimensions n Millimeters Dimensions In Inches Min Max Min Max D 4.900 5.100 0.193 0.201 E 4.300 4.500 0.169 0.177 b 0.190 0.300 0.007 0.012 c 0.090 0.200 0.004 0.008 E1 6.250 6.550 0.246 0.258 A 1.100 0.043 A2 0.800 1.000 0.031 0.039 A1 0.020 0.50 0.001 0.006 e L H Θ 0.65 (BSC) 0.500 0.026 (BSC) 0.700 0.25 (TYP) 1゜ 0.020 0.028 0.01 (TYP) 7゜ 1゜ 7゜ VER 1.1 14 ACE4702 2 Cell Li-ion Battery Charger IC Notes ACE does not assume any responsibility for use as critical components in life support devices or systems without the express written approval of the president and general counsel of ACE Electronics Co., LTD. As sued herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and shoes failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. ACE Technology Co., LTD. http://www.ace-ele.com/ VER 1.1 15