LTC4126 7.5mA Wireless Li-Ion Charger with 1.2V Step-Down DC/DC Converter FEATURES DESCRIPTION Wireless Li-Ion Battery Charger Plus High Efficiency Multi-Mode Charge Pump DC/DC n Wideband Rx Frequency: DC to >10MHz n Integrated Rectifier with Overvoltage Limit n Pin Selectable Charge Voltage: 4.2V or 4.35V n Charge Current: 7.5mA (Fixed) n Low Battery Disconnect: 3.0V n NTC Pin for Temperature Qualified Charging n DC/DC Regulated Output: 1.2V n DC/DC Output Current: Up to 60mA n 50kHz/75kHz Switching, No Audible Noise n Pushbutton and/or Digital on/off Control for DC/DC n Thermally Enhanced 12-Lead 2mm x 2mm LQFNPackage The LTC(R)4126 is a low-power wireless single-cell Li-Ion battery charger with an integrated step-down DC/DC regulator. The step-down regulator is a low-noise multi-mode charge pump which is powered from the battery and provides a regulated 1.2V at the output. The switching frequency is set to either 50kHz or 75kHz depending on the mode to keep any switching noise out of the audible range. APPLICATIONS The tiny 2mm x 2mm LQFN package and minimal external component count make the LTC4126 well suited for Li-Ion battery powered hearing aid applications and other low power portable devices where a small solution size is required. n The LTC4126 charger is a full-featured constant-current constant-voltage Li-Ion battery charger with automatic recharge, automatic termination by safety timer, and battery temperature monitoring via an NTC pin. Charge current is fixed at 7.5mA with a 6-hour termination timer. Undervoltage protection disconnects the battery from all loads when the battery voltage is below 3.0V. Hearing Aids Low Power Li-Ion Powered Devices n Wireless Headsets n IoT Wearables n n All registered trademarks and trademarks are the property of their respective owners. TYPICAL APPLICATION Top and Bottom View of the IC with Complete Application Circuit EN STAT1 STAT2 ACPR ACIN CRX 68nF AIR GAP TRANSMITTER LTX VIN + - VCC LRX 8H CHRG NTC LTC4126 VSEL GND BAT OUT 4126 TA01 DIGITAL I/O + Li-Ion 4.2V 1.2V 2.2F TO BAT Rev. A Document Feedback For more information www.analog.com 1 LTC4126 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) Input Supply Voltages VCC........................................................... -0.3V to 6V ACIN...........................................................-10V to 6V ACIN - VCC Differential............................-16V to 0.3V Input/Output Currents IACIN................................................................. 200mA IOUT.................................................................. -60mA BAT............................................................... -0.3V to 6V PBEN, NTC, EN, VSEL............................-0.3V to [Max (VCC, BAT) + 0.3V] CHRG............................................................ -0.3V to 6V Operating Junction Temperature Range.... -20C to 85C Storage Temperature Range................... -40C to 125C Maximum Reflow (Package Body) Temperature........................................................... 260C 2 PBEN 3 VSEL 4 VCC EN 12 11 13 GND 5 6 10 STAT1 9 STAT2 8 BAT 7 ACIN CHRG 1 ACPR NTC OUT TOP VIEW LQFN PACKAGE 12-LEAD (2mm x 2mm x 0.74mm) TJMAX = 85C, JA = 92C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION TAPE AND REEL PART NUMBER PART MARKING* LTC4126EV#TRPBF LHCP FINISH CODE PACKAGE** TYPE MSL RATING LQFN (Laminate Package with QFN Footprint) 3 PAD FINISH e4 Au (RoHS) TEMPERATURE RANGE -20C to 85C Contact the factory for parts specified with wider operating temperature ranges. *Device temperature grade is identified by a label on the shipping container. Parts ending with PBF are RoHS and WEEE compliant. **The LTC4126 package dimension is 2mm x 2mm x 0.74mm compared to a standard QFN package dimension of 2mm x 2mm x 0.75mm. This product only available in tape and reel or in mini-reel. Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating temperature range, otherwise specifications are at TA = 25C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted. SYMBOL PARAMETER VCC Input Voltage Range VBAT Battery Voltage Range IVCC VCC Quiescent Current IBATQ BAT Quiescent Current 2 CONDITIONS MIN TYP MAX UNITS 2.7 5.5 V Charging 2.7 4.4 V Not Charging, DC/DC On 3.1 l 4.4 V Charging Done, DC/DC Off, VNTC > VDIS 50 80 A Charging Done, DC/DC Off, VNTC < VDIS 42 70 A Charging Done, DC/DC Off, VBAT = 4.4V 4 8 A VACIN = VCC = 0, DC/DC On, IOUT = 0 37 75 A VACIN = VCC = 0, DC/DC Off 5 10 A VACIN = VCC = 0, Battery Disconnected (VBAT < VDISCONNECT) 0 0.1 A Rev. A For more information www.analog.com LTC4126 ELECTRICAL CHARACTERISTICS l denotes the specifications which apply over the specified operating The junction temperature range, otherwise specifications are at TA = 25C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 5.5 5.75 V 5 5.25 AC Rectification VCC(HIGH) VCC High Voltage Limit VCC Rising 5.25 VCC(LOW) VCC Low Voltage Limit VCC Falling 4.75 ACIN to VCC Voltage Drop 7.5mA from ACIN to VCC 0.6 V V Battery Charger VCHG Battery Charge Voltage ICHG Battery Charge Current VSEL = 0 VSEL = 1 l l 4.158 4.306 4.200 4.350 4.242 4.394 V V l 7.0 6.5 7.5 7.5 8.0 8.5 mA mA 9 55 27 80 45 105 mV mV VUVLO VCC-to-VBAT Differential Undervoltage Lockout Threshold (Indicated at ACPR Pin) VCC Falling VCC Rising VUVCL VCC-to-VBAT Differential Undervoltage Current Limit Threshold Voltage IBAT = 0.9 * ICHG IBAT = 0.1 * ICHG 150 120 mV mV IDUVCL Charge Current Threshold for DUVCL Fault Indication (VCC - VBAT) Falling (VCC - VBAT) Rising 3.1 4.5 mA mA VRECHRG Recharge Battery Threshold Voltage As a Percentage of VCHG 96.5 97.5 98.5 % tTERMINATE Safety Timer Termination Period Timer Starts at the Beginning of the Charge Cycle, VCC > (VBAT + 100mV) 5.1 6 6.9 hours fSLOW Slow Blink Frequency 1.14 Hz fFAST Fast Blink Frequency 4.58 Hz VCOLD Cold Temperature Fault Threshold Voltage VHOT Hot Temperature Fault Threshold Voltage VDIS NTC Disable Threshold Voltage INTC NTC Leakage Current Rising Threshold Voltage 75.0 76.5 33.4 34.9 Hysteresis 78 1.5 Falling Threshold Voltage Hysteresis %VCC 36.4 1.5 150 VNTC = 2.5V -100 VNTC = 0V %VCC %VCC %VCC 250 mV 100 nA -150 nA Step-Down DC/DC Regulator VOUT DC/DC Regulator Output Voltage VBAT > VLOBAT1 or VDISCONNECT < VBAT < VLOBAT2, IOUT = 0 l 1.16 VLOBAT2 < VBAT < VLOBAT1, IOUT = 0 VLOBAT1 Low Battery Alert 1 Threshold VBAT Falling Low Battery Alert 2 Threshold VBAT Falling 3.52 Low Battery Alert 3 Threshold VBAT Falling 3.6 l 3.22 3.3 3.68 3.12 Hysteresis 3.2 V mV 3.38 100 l V V 100 Hysteresis VLOBAT3 1.24 VBAT/3 l Hysteresis VLOBAT2 1.2 V mV 3.28 100 V mV VDISCONNECT Low Battery Disconnect Threshold Voltage VBAT Falling l 2.93 3.0 3.07 fSW DC/DC Switching Frequency 3:1 Mode (VBAT > VLOBAT2) 2:1 Mode (VBAT < VLOBAT2) l l 40 60 50 75 60 90 kHz kHz ROL Effective Open-Loop Output Resistance (Note 4) VBAT = 3.5V, IOUT = 3mA 4.6 6.5 ILIM OUT Current Limit 80 VOUT = 0V V mA Rev. A For more information www.analog.com 3 LTC4126 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25C (Notes 2, 3). VACIN = VCC = 5V, VBAT = 3.8V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Pushbutton Pin (PBEN) VIL Logic Low Input Voltage 0.4 VIH Logic High Input Voltage RPU Pull-up Resistance to BAT VPBEN < VIL IIH Logic High Input Leakage VPBEN = VBAT 0 0.1 A tDBL Debounce Time Low 348 425 503 ms tDBH Debounce Time High 23 43 63 ms 0.4 V l l 1.1 V V 4 M EN, VSEL Pins VIL Logic Low Input Voltage l VIH Logic High Input Voltage l IIL Logic Low Input Leakage 0 1 A IIH Logic High Input Leakage 0 1 A 0.2 V 1.1 V Logic Output Pins (STAT1, STAT2, ACPR) VOL Logic Low Output Voltage 100A into Pin VOH Logic High Output Voltage 25A out of Pin VOUT - 0.2V V Open Drain Output (CHRG) Pin Leakage Current VCHRG = 5V Pin Pull-Down Current VCHRG = 400mV Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 3: The LTC4126E is tested under conditions such that TJ TA. The LTC4126E is guaranteed to meet performance specifications from 0C to 85C junction temperature. Specifications over the -20C to 85C operating junction temperature range are assured by design, 4 200 0 0.5 A 300 450 A characterization and correlation with statistical process controls. The junction temperature (TJ in C) is calculated from the ambient temperature (TA, in C) and power dissipation (PD, in watts) according to the formula: TJ = TA + (PD * JA), where the package thermal impedance JA = 92C/W). Note that the maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance, and other environmental factors. Note 4: See DC/DC Converter in Operation section. Rev. A For more information www.analog.com LTC4126 TYPICAL PERFORMANCE CHARACTERISTICS 8 4.23 7 4.22 5 4 3 2 3 3.3 4.21 4.20 4.19 4.18 4.17 3.6 3.9 VBAT (V) 4.2 4.15 -20 4.5 7.0 4.2 7 4.1 6 5.0 4.0 4.0 3.9 3.0 3.8 2.0 3.7 0 50 CHARGE CURRENT (mA) 8 VBAT (V) CHARGE CURRENT (mA) 4.3 0 10 25 40 55 TEMPERATURE (C) 85 4.34 4.33 4.32 4.30 -20 7.8 I(VCC) (A) -5 10 25 40 55 TEMPERATURE (C) 0 50 100 150 VCC - VBAT (mV) 200 85 7.4 7.3 7.0 -20 250 10 25 40 55 TEMPERATURE (C) 70 85 4126 G05 ACIN and VCC Waveform when Shunt Active 10 VCC ACIN 6 50 48 44 -20 -5 4126 G04 46 70 7.5 7.1 VOLTAGE (V) 300 270 -20 7.6 7.2 VCC = 5V VBAT = 4.5V 52 NTC ENABLED VCC = 5V CHARGING DONE CHRG PIN PULLED UP TO 5V 7.7 VCC Quiescent Current vs Temperature 305 85 VCC = 5V VBAT = 3.8V 7.9 54 285 70 Charge Current vs Temperature 2 0 290 10 25 40 55 TEMPERATURE (C) 8.0 3 3.5 100 150 200 250 300 350 400 TIME (MIN) 295 -5 4126 G02 4 1 310 CURRENT (A) 70 5 3.6 CHRG Pin Current vs Temperature 275 4.35 VBAT = 3.8V 4126 G03 280 4.36 Charge Current vs VCC-to-VBAT Differential Voltage CHARGE CURRENT BATTERY VOLTAGE VCC = 5V 4126 G09 8.0 1.0 -5 4126 G01 VCC = 5V VSEL = 0V Charge Voltage vs Temperature (VSEL = 5V) 4.31 Li-Ion Battery Charge Profile 6.0 4.37 4.16 VSEL = 0V VSEL = 5V 0 2.7 4.38 VCC = 5V CHARGE CURRENT (mA) 1 Charge Voltage vs Temperature (VSEL = 0V) CHARGE VOLTAGE (V) VCC = 5V 6 CHARGE VOLTAGE (V) CHARGE CURRENT (mA) Charge Current vs Battery Voltage TA = 25C, unless otherwise noted. 2 -2 -6 -5 10 25 40 55 TEMPERATURE (C) 70 4126 G06 85 -10 TIME (100s/DIV) 4126 G07 4126 G08 Rev. A For more information www.analog.com 5 LTC4126 TYPICAL PERFORMANCE CHARACTERISTICS DC/DC Efficiency vs Battery Voltage DC/DC Output Voltage vs Temperature 1.20 100 1.206 1.18 90 1.204 1.16 80 1.14 70 1.10 1.06 REG. 2:1 MODE 1.04 1.02 1.00 OPEN LOOP 3:1 MODE 3 3.3 4.2 50 30 0 4.5 75 65 2:1 MODE IOUT (mA) VOUT (V) 80 1.17 1.15 1.14 1.13 3.6 3.9 VBAT (V) 4.2 4.5 3:1 MODE 20 30 40 IOUT (mA) 50 60 1.190 -20 70 4126 G20 10 25 40 55 TEMPERATURE (C) 70 85 DC/DC Effective Open-Loop Output Resistance vs Temperature VBAT = 3.5V 5 60 55 50 30 3.0 -5 4126 G12 6 TA = -20C TA = 25C TA = 85C 35 10 1.192 VOUT = 1.1V 40 1.11 0 1.196 4126 G11 45 1.12 6 3.3 1.198 Maximum DC/DC Output Current vs Battery Voltage 70 1.10 3 1.200 1.194 IOUT = 1mA IOUT = 2mA IOUT = 3mA 4126 G10 1.18 1.16 REG. 2:1 MODE 10 VBAT = 3.8V 1.19 OPEN LOOP 3:1 MODE 40 DC/DC Output Voltage vs Load Current 1.20 REGULATED 3:1 MODE 20 IOUT = 1mA IOUT = 2mA IOUT = 3mA 3.6 3.9 VBAT (V) 60 RESISTANCE () 1.08 VBAT = 3.8V ROUT = 1.2k 1.202 VOUT (V) REGULATED 3:1 MODE 1.12 EFFICIENCY (%) VOUT (V) DC/DC Output Voltage vs Battery Voltage TA = 25C, unless otherwise noted. 3.2 3.4 3.6 3.8 VBAT (V) 4.0 4.2 4.4 4126 G21 4 3 2 1 0 -20 -5 10 25 40 55 TEMPERATURE (C) 70 85 4126 G15 Rev. A For more information www.analog.com LTC4126 TYPICAL PERFORMANCE CHARACTERISTICS DC/DC Switching Frequency vs Battery Voltage DC/DC Switching Frequency in 3:1 Mode vs Temperature 60 FREQUENCY (kHz) 45 2:1 MODE 3:1 STEP-DOWN MODE 52 76 51 75 50 74 49 73 48 47 46 45 44 15 43 0 3 3.3 3.6 3.9 VBAT (V) 4.2 42 -20 4.5 25 5.5 CURRENT (A) 10 5 3.3 3.6 3.9 VBAT (V) 4.2 85 4.5 4.5 4.0 VBAT = 3.1V VBAT = 3.8V VBAT = 4.4V 4126 G16 3.0 -20 -5 10 25 40 55 TEMPERATURE (C) 70 85 4126 G19 DC/DC Output Transient Response to Load Step 5.0 3.5 IOUT = 0 3 70 VCC = 0V 2:1 MODE 0 10 25 40 55 TEMPERATURE (C) 70 40 50 20 40 0 30 -20 20 -40 10 -60 85 -80 COUT = 2.2F VOUT LOAD CURRENT TIME (800s/DIV) LOAD CURRENT (mA) CURRENT (A) 6.0 3:1 MODE (OPEN LOOP) 69 4126 G14 30 15 70 VBAT = 3.1V 66 -20 -5 10 25 40 55 TEMPERATURE (C) BAT Quiescent Current (DC/DC Off) vs Temperature 3:1 STEP-DOWN MODE (REGULATED) 71 67 4126 G13 BAT No-Load Quiescent Current (DC/DC On) vs Battery Voltage 20 -5 72 68 VBAT = 3.5V VBAT = 3.8V VBAT = 4.4V VOUT (AC-COUPLED) (mV) FREQUENCY (kHz) 75 DC/DC Switching Frequency in 2:1 Mode vs Temperature FREQUENCY (kHz) 90 30 TA = 25C, unless otherwise noted. 0 -10 4126 G18 4126 G17 Rev. A For more information www.analog.com 7 LTC4126 PIN FUNCTIONS NTC (Pin 1): Thermistor Input. Connect a thermistor from NTC to GND, and a bias resistor from VCC to NTC. The voltage level on this pin determines if the battery temperature is safe for charging. The charge current and charge timer are suspended if the thermistor indicates a temperature that is unsafe for charging. Once the temperature returns to the safe region, charging resumes. Ground the NTC pin if temperature qualified charging is not needed. EN (Pin 2): Digital Logic Input Pin to Enable the DC/DC Converter. A minimum voltage of 1.1V enables the regulator provided that the LTC4126 is not in battery disconnect mode (see Battery Disconnect/Ship Mode under Operation section). A low voltage (0.4V max) disables the regulator and allows the pushbutton to control it. If only pushbutton control is desired, tie this pin to ground. Tie this pin to BAT if the DC/DC needs to remain enabled all the time. Do not leave this pin unconnected. PBEN (Pin 3): Pushbutton toggle input pin to enable/ disable the DC/DC converter. Enabling of the regulator can only occur if the LTC4126 is not in battery disconnect mode (see Battery Disconnect/Ship Mode under Operation section). A weak internal pull-up forces PBEN high when not driven. A normally open pushbutton is connected from PBEN to ground to force a low state on this pin when the button is pushed. However, the pushbutton is ignored if the EN input is high. If the pushbutton function is not needed, leave this pin unconnected. VSEL (Pin 4): Digital Logic Input Pin to Select the Battery Charge Voltage. A logic high on this pin selects 4.35V and a logic low on this pin selects 4.2V. Do not leave this pin unconnected. ACPR (Pin 5): Digital CMOS Logic Output Pin to indicate if there is enough input power available to charge the battery. This pin goes high when the VCC-to-BAT differential voltage rises above 80mV (typical) and goes low when the differential voltage drops below 27mV (typical). The low level of this pin is referenced to GND and the high level is referenced to the OUT pin voltage. Consequently, this indicator is not available if the DC/DC is disabled. 8 CHRG (Pin 6): Open-Drain Charge Status Output Pin. This pin can be pulled up through a resistor and/or an LED to indicate the status of the battery charger. This pin has four possible states: slow blink to indicate charging, fast blink to indicate a fault, pulled down to indicate charging done, and high impedance to indicate no input power. To conserve power, the pull-down current is limited to 300A. ACIN (Pin 7): AC Input Voltage Pin. Connect the external LC tank, which includes the receive coil, to this pin. Connect this pin to ground when not used. BAT (Pin 8): Battery Connection Pin. Connect a single-cell Li-Ion battery to this pin. Whenever enough input power (AC or DC) is available, the battery will be charged via this pin. Additionally, the DC/DC Converter is powered from the battery via this pin. To minimize the effect of switching noise from the DC/DC converter on charger performance, this pin should be decoupled with a 1F capacitor to GND if the DC/DC converter is enabled while charging. STAT2 (Pin 9), STAT1 (Pin 10): Digital CMOS Logic Status Output Pins. The low level of these pins is referenced to GND and the high level is referenced to VOUT. Consequently, these indicators are not available if the DC/DC is disabled. These two pins together with ACPR indicate the various charging states and fault conditions. However, when no input power is available and the DC/DC converter is enabled, these pins instead indicate the voltage level of the battery. VCC (Pin 11): DC Input Voltage Pin. An internal diode is connected from the ACIN pin (anode) to this pin (cathode). When an AC voltage is present at the ACIN pin, the voltage on this pin is the rectified AC voltage. When the ACIN pin is not used (or shorted to ground), connect this pin to a DC voltage source to provide power to the LTC4126 and charge the battery. OUT (Pin 12): DC/DC Converter Output Pin. This pin provides 1.2V to power hearing aid ASICs. A low ESR ceramic capacitor of at least 2.2F should be placed close to this pin to stabilize the converter. GND (Exposed Pad Pin 13): Ground Pin. The exposed pad on the backside of the package must be soldered to the PCB ground for a low-resistance electrical connection as well as for optimum thermal performance. Rev. A For more information www.analog.com LTC4126 BLOCK DIAGRAM 11 VCC 7 ACIN +- 80mV/ 27mV RECTIFICATION AND INPUT POWER CONTROL +- 154mV - VCC - + - + DUVLO DUVCL 7.5mA BAT 4.2V/ 4.35V TOO COLD 8 + Li-Ion + RBIAS 1 NTC - RNTC TOO HOT LOGIC + + 10 9 4 ACPR STAT1 STAT2 NTC ENABLE OUT TERMINATED OUT C. C./C. V. CHARGER CONTROL AND STATUS LOGIC OUT VSEL RECHARGE + LOW_BAT_ALERTS + BAT_DISCONNECT 3.0V - EN BAT 4M 3 3.3V - CHRG 300A 2 3.6V 3.2V CLK 6 0.975VCHG - 5 - + 150mV PBEN PUSHBUTTON 150kHz OSCILLATOR PUSHBUTTON TIMER AND DEBOUNCER BAT DC/DC ENABLE LOGIC EN MULTI-MODE CHARGE PUMP DC/DC REGULATOR CLK CLK 1.2V OUT 12 GND 13 4126 BD Figure1. LTC4126 Block Diagram Rev. A For more information www.analog.com 9 LTC4126 OPERATION The LTC4126 is a low power battery charger with an integrated step-down DC/DC converter designed to wirelessly charge single-cell Li-Ion batteries and provide a 1.2V output suitable for powering a hearing-aid ASIC. The part has three principal circuit components: an AC power controller, a full-featured linear battery charger, and a step-down DC/DC converter. AC POWER CONTROLLER A complete wireless power transfer system consists of transmit circuitry with a transmit coil and receive circuitry with a receive coil. The LTC4126 resides on the receiver side, where an external parallel resonant LC tank connected to the ACIN pin allows the part to receive power wirelessly from an alternating magnetic field generated by the transmit coil. The Rectification and Input Power Control circuitry (Figure1) rectifies the AC voltage at the ACIN pin and regulates that rectified voltage at the VCC pin to less than VCC(HIGH) (typically 5.5V). Operation without Wireless Power The LTC4126 can be alternately powered by connecting a DC voltage source to the VCC pin directly instead of receiving power wirelessly through the ACIN pin. Ground the ACIN pin if a voltage supply is connected to VCC. BATTERY CHARGER The LTC4126 includes a full-featured constant-current (CC)/constant-voltage (CV) linear battery charger with automatic recharge, automatic termination by safety timer, bad battery detection, and out-of-temperaturerange charge pausing. Charge current is internally fixed at 7.5mA and the final charge voltage is pin-selectable via the VSEL pin to either 4.2V or 4.35V. As soon as the voltage at the VCC pin rises 80mV (typical) above the BAT pin voltage, the charger attempts to charge the battery and a new charge cycle is initiated. A 6-hour charge termination timer starts at the beginning of this new charge cycle. When the VCC-to-BAT differential voltage rises above 154mV (typical), the charger enters constant-current (CC) mode and charges the battery at the full rated current of 7.5mA. When the BAT pin approaches the final charge voltage, the charger enters constant-voltage 10 (CV) mode and the charge current begins to drop. The charge current continues to drop while the BAT pin voltage is maintained at the proper charge voltage. This state of CC/CV charging is indicated by a slow blinking LED (typically 1.14Hz) at the CHRG pin. After the 6-hour charge termination timer expires, charging stops completely. Once the charge cycle terminates, the LED at the CHRG pin stops blinking and assumes a pull-down state. To start a new charge cycle, remove the power source at ACIN or VCC and reapply it. Automatic Recharge After charging has terminated, the charger draws only 3.7A (typical) from the battery. If it remains in this state long enough, the battery will eventually discharge. To ensure that the battery is always topped off, a new charge cycle automatically begins when the battery voltage falls below VRECHRG (typically 97.5% of the charge voltage). In the event that the battery voltage falls below VRECHRG while the safety timer is still running, the timer will not reset. This prevents the timer from restarting every time the battery voltage dips below VRECHRG during a charging cycle. Bad Battery Fault If the battery fails to reach a voltage above VRECHRG by the end of a full charge cycle of 6 hours, the battery is deemed faulty and the LED at the CHRG pin indicates this bad battery fault condition by blinking fast (typically 4.58Hz). Differential Undervoltage Lockout (DUVLO) A differential undervoltage lockout circuit monitors the differential voltage between VCC and BAT and disables the charger if the VCC voltage falls to within 27mV (typical VUVLO) of the BAT voltage. This condition is indicated by a low on the ACPR pin. Charging does not resume until this difference increases to 80mV at which time the ACPR pin transitions back high. The DC/DC must be enabled for proper ACPR indication. Differential Undervoltage Current Limit (DUVCL) The LTC4126 charger also includes differential undervoltage current limiting (DUVCL) which gradually reduces the charge current from the full 7.5mA towards zero as Rev. A For more information www.analog.com LTC4126 OPERATION the VCC-to-BAT differential voltage drops from approximately 154mV to 116mV. See the curve in the Typical Performance Characteristics section. When the charge current reaches approximately 3.1mA, the LED at the CHRG pin blinks fast (typically 4.58Hz) to indicate the DUVCL fault. In the reverse direction, when the charge current reaches approximately 4.5mA, the LED at the CHRG pin resumes slow blinking to indicate normal operation. Due to the finite hysteresis of the DUVCL comparator, it is possible under a very narrow region of coupling conditions for the LTC4126 to alternate between slow blinking and fast blinking. This behavior should be construed as operation at near (but not 100%) full charge current. The DUVCL feature is particularly useful in situations where the wireless power available is limited. Without DUVCL, if the magnetic coupling between the receive coil and the transmit coil is low, DUVLO could be tripped if the charger tried to provide the full charge current. DUVLO forces the charge current to drop to zero instantly, allowing the supply voltage to rise above the DUVLO threshold and switch on the charger again. In the absence of DUVCL, this oscillatory behavior would result in intermittent charging. The DUVCL circuitry prevents this undesirable behavior by gradually increasing or decreasing the charge current as input power becomes more or less available. Temperature Qualified Charging The LTC4126 monitors the battery temperature during the charging cycle by using a negative temperature coefficient (NTC) thermistor, placed close and thermally coupled to the battery pack. If the battery temperature moves outside a safe charging range, the IC suspends charging and signals a fault condition via CHRG (blinks fast at 4.58Hz) and the STAT pins until the temperature returns to the safe charging range. The safe charging range is determined by two comparators (Too Hot and Too Cold) that monitor the voltage at the NTC pin as shown in the Block Diagram. The rising threshold of the Too Cold comparator is set to 76.5% of VCC (VCOLD) and the falling threshold of the Too Hot comparator is set to 34.9% of VCC (VHOT), each with a hysteresis of 1.5% of VCC around the trip point to prevent oscillation. If the battery charger pauses due to a temperature fault, the 6-hour termination timer also pauses until the thermistor indicates a return to a safe temperature. Grounding the NTC pin disables all NTC functionality. Most Li-Ion battery manufacturers recommend a temperature range of 0C to 40C as a safe charging range. Charge Status Indication via CHRG, ACPR, and STAT pins The status of the battery charger is indicated via the opendrain CHRG pin as well as by the logic pins STAT1, STAT2, and ACPR according to Table1. Indication by the logic pins is available only when the DC/DC is enabled. Table1. Charger Status Indication CHRG ACPR STAT1 STAT2 STATUS Hi-Impedance 0 X X Not Charging, No Power, STAT pins indicate Battery Level (see Table2) Pulled LOW 1 0 0 Done Charging Blink Slow (1.14Hz) 1 0 1 Charging Blink Fast (4.58Hz) 1 1 0 Temperature Fault/Bad Battery Blink Fast (4.58Hz) 1 1 1 Differential Undervoltage Current Limit (DUVCL) The open-drain CHRG pin has an internal 300A (typical) pull-down. An LED can be connected between this pin and VCC to indicate the charging status and any fault condition as indicated in the table above. The ACPR, STAT1, and STAT2 pins are digital CMOS logic outputs that can be interpreted by a microprocessor. The low level of these three pins is referenced to GND and the high level is referenced to the OUT pin voltage (typically 1.2V). Hence the status indication via these three pins is only available if the DC/DC converter is turned on via the EN pin or the push button. Status indication via the CHRG pin is always available during charging. DC/DC CONVERTER To supply the system load from the battery to the OUT pin, the LTC4126 contains a proprietary low-noise multi-mode charge pump DC/DC converter which can be switched on by applying a minimum voltage of 1.1V to the EN pin or by pushing the pushbutton. The converter can be active simultaneously with the charger. The switching frequency of the charge pump is set to either 50kHz or 75kHz depending on the mode of operation. This frequency is chosen to keep any switching noise out of the audio band. Rev. A For more information www.analog.com 11 LTC4126 OPERATION Modes of Operation 1.4 1.2 The charge pump DC/DC converter has 3 modes of operation depending on the battery voltage. For VBAT > 3.6V, the charge pump operates in 3:1 step-down mode (Mode 1) and provides a regulated 1.2V output. In Mode 1, the maximum output current that the DC/DC converter can provide is limited by internal current limit circuitry to approximately 65mA. When the battery voltage is between 3.6V and 3.3V, the charge pump still operates in 3:1 step-down mode, but it can no longer maintain 1.2V regulation and provides onethird of the battery voltage at its output (only at no load). This is referred to as Mode 2. The Thevenin equivalent circuit of the converter in Mode 2 is shown in Figure2, where ROL is the effective open-loop output resistance of IOUT ROL + VBAT 3 + - VOUT HEARING AID ASIC - DC/DC CONVERTER 4126 F02 Figure2. DC/DC Converter Thevenin Equivalent Circuit in Mode 2: 3-to-1 Step-Down the converter. ROL is typically 4.6 at room temperature for VBAT = 3.5V and fSW = 50kHz. It varies with the battery voltage, the switching frequency of the converter, and the temperature of the die. Figure2 can be used to determine the output voltage (VOUT) for a specific load current (IOUT) using the following equation: V VOUT = BAT - IOUT * R OL 3 When the battery voltage falls below 3.3V, the charge pump switches to 2:1 step-down mode (Mode 3) and again provides a regulated 1.2V output. In Mode 3, the maximum output current that the DC/DC converter can provide decreases with battery voltage but does not fall below approximately 35mA. See the curve in the Typical Performance Characteristics. The variation of the output voltage versus the battery voltage for the various modes of operation is shown in Figure3. 12 VOUT (V) 1.0 MODE 1 0.8 0.6 MODE 2 0.4 0.2 MODE 3 0 3.0 3.3 3.6 3.9 BATTERY VOLTAGE (V) 4.2 4.35 4126 F03 Figure3. VOUT vs Battery Voltage at IOUT = 0 Handling Large Load While operating in Mode 1 or Mode 2 (3:1 step-down mode), if a large load at the output causes the output voltage to drop below 1.1V, the converter automatically switches over to Mode 3 (2:1 step-down mode) and attempts to regulate the output at 1.2V. The converter stays in Mode 3 for 110ms (typical) and then returns to the previous mode. If the large load condition persists and VOUT drops below 1.1V again, the converter switches back into Mode 3 for another 110ms and the cycle continues. The duration of 110ms is chosen to prevent mode switching at a frequency which could fall into the audible range. The switch over to Mode 3 provides more current drive capability at the cost of efficiency and this is why the converter tries to stay in Mode 1 or Mode 2 as much as possible. Converter Efficiency The LTC4126 DC/DC converter efficiency varies throughout the battery voltage range and is very much dependent on the mode it is operating in. The theoretical maximum efficiency in Mode 1 can be expressed as follows: Efficiency, Mode1 = VOUT VBAT 3 If regulation is maintained at the OUT pin at 1.2V, the theoretical maximum efficiency is 85.7% when VBAT = 4.2V and 100% when VBAT = 3.6V as calculated from the above equation. When the battery voltage is between 3.6V and 3.3V, the converter can no longer maintain a 1.2V regulation at OUT at all loads and is operating in Mode 2. However, the upper Rev. A For more information www.analog.com LTC4126 OPERATION limit on the efficiency that the converter can achieve in this mode is determined by switching losses, ohmic losses, and quiescent current loss. When the battery voltage falls to 3.3V, the converter enters Mode 3 where the theoretical maximum efficiency can be expressed as follows: Efficiency, Mode3 = VOUT VBAT 2 In Mode 3, the theoretical maximum efficiency is 72.7% when VBAT = 3.3V and 80% when VBAT = 3.0V as calculated from the above equation. Figure4 shows graphically the variation of the theoretical maximum efficiency of the converter over the range of battery voltages in the three different modes of operation. 100 90 EFFICIENCY (%) 80 70 60 50 MODE 1 40 30 MODE 2 20 10 MODE 3 0 3.0 3.3 3.6 3.9 BATTERY VOLTAGE (V) 4.2 4.35 4126 F04 Figure4. Theoretical Maximum Converter Efficiency vs Battery Voltage Battery Level Indicator Battery Disconnect/Ship Mode When no input power is available and the battery voltage falls to 3.0V (typical), the LTC4126 shuts down most of its functions to prevent the battery from discharging too deeply, consuming less than 100nA from the battery. Once in battery disconnect mode, normal functioning can only resume when power is applied to the ACIN or VCC pin and the VCC pin voltage rises 80mV (typical) above the BAT pin voltage. The LTC4126 is also in battery disconnect mode after initial installation of the battery regardless of its voltage level. This implements the ship mode functionality. Pushbutton Control The LTC4126 is equipped with a pushbutton controller to turn the DC/DC converter on and off if the EN pin is not used (held low). A logic high on the EN pin overrides the pushbutton function and keeps the regulator on. On the falling edge of the EN signal, the DC/DC shuts off and 1s later, the pushbutton can control the output as long as EN remains low. A push on the pushbutton is considered valid if the PBEN pin is held low for at least 425ms (typical). Additionally, the PBEN pin needs to return to the high state for at least 43ms (typical) in between successive pushes for a push to be considered valid. An invalid push will not change the state of the converter. A 4M internal resistor pulls up the PBEN pin to the BAT voltage. A few different scenarios of valid and invalid pushes are illustrated in Figure 5. LONG ENOUGH LONG ENOUGH PBEN The LTC4126 is equipped with a battery voltage monitor which reports various battery voltage levels via the STAT pins when not charging and the converter is enabled. See Table2. Since the STAT pins indicate either the charger status or the battery levels based on the state of ACPR, there may be a delay of up to 1s before the STAT pins are valid whenever ACPR changes state. LONG ENOUGH 425ms 43ms 425ms VOUT (a) VALID SUCCESSIVE PUSH, DC/DC TURNS ON AND OFF TOO SHORT LONG ENOUGH PBEN 425ms LONG ENOUGH 43ms VOUT (b) HIGH PULSE TOO SHORT, 2ND PUSH IGNORED, DC/DC STAYS ON Table2. Battery Level Indication LONG ENOUGH ACPR STAT1 STAT2 STATUS TOO SHORT PBEN 0 0 0 VBAT < 3.2V, Low Battery Alert 3 0 0 1 3.2V < VBAT < 3.3V 0 1 0 3.3V < VBAT < 3.6V 0 1 1 VBAT > 3.6V 1 X X Power Available, STAT Pins Indicate Charger Status LONG ENOUGH 43ms 425ms VOUT 4126 F05 (c) 1ST PUSH TOO SHORT, DC/DC STAYS OFF, 2ND PUSH VALID, DC/DC TURNS ON Figure5. Various Pushbutton Scenarios Rev. A For more information www.analog.com 13 LTC4126 APPLICATIONS INFORMATION WIRELESS POWER TRANSFER first half of the cycle, M1 is switched on and the current through LTX rises linearly. During the second half of the cycle, M1 is switched off and the current through LTX circulates through the LC tank formed by CTX (= CTX1 + CTX2) and LTX. The current through LTX is shown in Figure8. In a wireless power transfer system, power is transmitted using an alternating magnetic field. An AC current in the transmit coil generates a magnetic field. When the receive coil is placed in this field, an AC current is induced in the receive coil. The AC current induced in the receive coil is a function of the applied AC current at the transmitter and the magnetic coupling between the transmit and receive coils. The LTC4126 internal diode rectifies the AC voltage at the ACIN pin. IAC-TX AIR GAP LTX If the transmit LC tank frequency is set to 1.29 times the driving frequency, switching losses in M1 are significantly reduced due to zero voltage switching (ZVS). Figure9 and Figure10 illustrate the ZVS condition at different fTX-TANK frequencies. IAC-RX fTX-TANK = 1.29 * fDRIVE fDRIVE is set by resistor RSET connected to the LTC6990. fTX-TANK is set by: LRX 1:n 1 4126 F06 fTX-TANK = Figure6. Wireless Power Transfer System The power transmission range across the air gap as shown in Figure6 can be improved using resonance by connecting an LC tank to the ACIN pin tuned to the same frequency as the transmit coil AC current frequency. 2 * L TX * C TX The peak voltage of the transmit coil, LTX, that appears at the drain of M1 is: VTX-PEAK = 1.038 * * VIN And the peak current through LTX is: RECEIVER AND SINGLE TRANSISTOR TRANSMITTER 0.36 * VIN The single transistor transmitter shown in Figure7 is an example of a DC/AC converter that can be used to drive AC current into a transmit coil, LTX. The NMOS, M1, is driven by a 50% duty cycle square wave generated by the LTC6990 oscillator. During the ITX-RMS = 0.66 * ITX-PEAK U1 V+ LTC6990 DIV RSET 205k The RMS current through LTX is: GND ACIN C2 100F C1 4.7F SET fTX-TANK * L TX AIR GAP (2mm TO 4mm) VIN 5V OE I TX-PEAK = CRX 33nF fLC_TANK = 315kHz CTX1 33nF fDRIVE = 244kHz CTX2 1nF LTX 7.5H LTC4126 LRX 13H M1 Si2312CDS OUT VSEL VCC D1 STAT1 STAT2 ACPR BAT DIGITAL I/O + CHRG NTC EN OUT GND Li-Ion 4.35V COUT 2.2F PBEN 1.2V PUSHBUTTON 4126 F07 TRANSMITTER RECEIVER Figure7. DC/AC Converter, Transmit/Receive Coil, Tuned Resonant LTC4126 Receiver (See Table3 and Table4 for Recommended Components) 14 Rev. A For more information www.analog.com LTC4126 APPLICATIONS INFORMATION Note that since fDRIVE can be easily adjusted, it is best practice to choose fRX-TANK using the minimum component count (i.e. CRX) and then adjust fDRIVE to match. 500mA/DIV The amount of AC current in the transmit coil can be increased by increasing the supply voltage (VIN). Since the amount of power transmitted is proportional to the AC current in the transmit coil, VIN can be varied to adjust the power delivery to the receive coil. 0A 2s/DIV 4126 F08 Figure8. Current Through Transmit Coil DRAIN VOLTAGE 5V/DIV CHOOSING TRANSMIT POWER LEVEL 0V GATE VOLTAGE 2V/DIV 0V 2s/DIV 4126 F09 Figure9. Voltage on the Drain and Gate of NMOS M1 when fTX_TANK = fDRIVE DRAIN VOLTAGE 5V/DIV 0V GATE VOLTAGE 2V/DIV 0V 2s/DIV 4126 F10 Figure10. Voltage on the Drain and Gate of NMOS M1 when fTX_TANK = 1.29 * fDRIVE The LC tank at the receiver, LRX and CRX, is tuned to the same frequency as the driving frequency of the transmit LC tank: fRX-TANK = fDRIVE where fRX-TANK is given by, fRX-TANK = The overall power transfer efficiency is also dependent on the quality factor (Q) of the components used in the transmitter and receiver circuitry. Select components with low resistance for transmit/receive coils and capacitors. 1 2 * L RX * CRX As discussed in the previous section, the supply voltage (VIN) can be used to adjust the transmit power of the transmitter shown in Figure7. Transmit power should be set as low as possible to receive the desired output power under worst-case coupling conditions (e.g. maximum transmit distance with the worst-case misalignment). Although the LTC4126 is able to shunt excess received power to maintain the VCC voltage in the desired range, it has the adverse effect of raising the die temperature and possibly the battery temperature, and if the battery temperature exceeds the Too Hot temperature threshold set by the thermistor, the charger pauses charging the battery. Using the rated current of the transmit inductor to set an upper limit, transmit power should be adjusted downward until charge current is negatively impacted under worst-case coupling conditions. Once the transmit power level is determined, the transmit and receive coils should be arranged under best-case coupling conditions with a fully-charged battery or a battery simulator to make sure that the shunting of excess power does not raise the die temperature too much. In addition to temperature, another parameter that needs to be checked is the maximum negative voltage on the ACIN pin. Following the procedure above, when evaluating the rise in temperature of the LTC4126 under the bestcase coupling conditions, ensure that VCC-VACIN does not exceed 16V. Figure11 shows a typical waveform on ACIN showing VCC-VACIN<16V. Rev. A For more information www.analog.com 15 LTC4126 APPLICATIONS INFORMATION resonant capacitance and RL-AC is the equivalent AC load resistance. 10 VCC ACIN VOLTAGE (V) 6 One simplification is as follows: 2 R RL- AC L-DC 2 -2 which assumes that the drop across the Schottky diode is much smaller than the amplitude |VRX|. Additionally, RL-DC can be approximated as the ratio of the output voltage (VOUT) to the output current (IOUT): -6 -10 TIME (100s/DIV) 4126 F11 Figure11. Typical Acceptable Voltage Waveform on the ACIN Pin with VCC - VACIN < 16V. As an alternative to using the empirical method to determine the maximum negative voltage on the ACIN pin, the following formula can be used in conjunction with Figure12, which shows a parallel resonant configuration on the receiver: VRX = ( k L TXL RX ITX 2 L 1- 2 L RX CRX + RX RL- AC LTX ) LRX CRX CRECT IOUT The amplitude of the current in the transmit coil |ITX| can be either measured directly or its initial (no receiver) value can be calculated based on the transmitter circuit. This initial value is a conservative estimate since the amplitude of the transmitter coil current will drop as soon as the receiver, with a load, is coupled to it. The coupling factor (k) between the two coils could be obtained by running a finite element simulation inputting the coil dimensions and physical configurations. An easier method to obtain this coupling number, is to use the series-aiding and series-cancelling measurement method for two loosely coupled coils as shown in Figure13. VOUT ITX V RL-DC = OUT IOUT RL-DC And: L AIDING = L AB L CANCELLING = L CD VRX ITX LTX LRX CRX RL-AC L - L CANCELLING k = AIDING 4 L TXL RX 4126 F12 Figure12. Modeling Parallel Resonant Configuration and Half Wave Rectifier on the Receiver |VRX| is the amplitude of the voltage on the receiver coil, |ITX| is the amplitude of the current in the transmit coil, k is the coupling factor between the transmit and receive coils, is the operating frequency in radians per second, LTX is the self-inductance of the transmit coil, LRX is the self-inductance of the receive coil, CRX is the receiver 16 LTX B * * A LTX LRX * * LRX D C 4126 F13 Figure13. Series-Aiding and Series-Cancelling Method Configurations Used for Measuring the Coupling Factor k Rev. A For more information www.analog.com LTC4126 APPLICATIONS INFORMATION SINGLE TRANSISTOR TRANSMITTER AND LTC4126 RECEIVER-DESIGN EXAMPLE The example in Figure7 illustrates the design of the resonant coupled single transistor transmitter and LTC4126 charger. The steps needed to complete the design are reviewed as follows. 1.Determine the receiver resonant frequency and set component values for the receiver LC tank: It is best practice to select a resonant frequency that yields a low component count. In this example, 244kHz is selected as the receiver resonant frequency. At 244kHz, the tank capacitance (CRX) required with the selected receive coil (13H) is 33nF. Since 33nF is a standard value for capacitors, the tank capacitance requires only one component. The tank capacitance calculation is shown below. 1 CRX = = 32.7nF 33nF 2 2 4 * * f * L RX-TANK RX Select a 33nF capacitor with a minimum voltage rating of 25V and 5% (or better) tolerance for CRX. A higher voltage rating usually corresponds to a higher quality factor which is preferable. However, the higher the voltage rating, the larger the package size usually is. 2.Set the driving frequency (fDRIVE) for the single transistor transmitter: fDRIVE is set to the same value as the receiver resonant frequency: R SET = 1MHz NDIV * 50k 244kHz C TX = 1 2 2 4 * * f TX-TANK * L TX = 34nF Since 34nF is not a standard capacitor value, use a 33nF capacitor in parallel with a 1nF capacitor to obtain a value within 1% of the calculated CTX. The recommended rating for CTX capacitors is 50V with 5% (or better) tolerance. 4.Verify that the AC current through the transmit coil is well within its rating. In this example, the supply voltage to the single transistor transmitter is 5V. The peak AC current through the transmit (LTX) coil can be calculated as: ITX -PEAK = 0.36 * VIN fTX -TANK * L TX = 0.36 * 5V 315kHz * 7.5H = 0.76A and the RMS current as: ITX-RMS = 0.66 * 0.76A = 0.5A The rated current for the transmit coil is 1.55A (see the Wurth 760308103206 data sheet for more information). So the ITX-RMS calculated is well below the rated current. 5.Also verify that the transmit power level chosen does not result in excessive heating of the LTC4126. COMPONENT SELECTION FOR TRANSMITTER AND RECEIVER = 205k where NDIV = 1 as the DIV pin of the LTC6990 is grounded. Select a 205k (standard value) resistor with 1% tolerance. For more information regarding the oscillator, consult the LTC6990 data sheet. 3.Set the LC tank component values for the single transistor transmitter: If fDRIVE is 244kHz, the transmit LC tank frequency (fTX-TANK) is: fTX-TANK = 1.29 * 244kHz = 315kHz The transmit coil (LTX) used in the example is 7.5H. The value of transmit tank capacitance (CTX) can be calculated: To ensure optimum performance from the LTC4126, use the components listed in Table 3 and Table 4 for the receiver and transmitter, respectively, as shown in Figure 7. Select receive and transmit coils with good quality factors to improve the overall power transmission efficiency. Use a ferrite core to improve the magnetic coupling between the transmit and receive coils and to shield the rest of the transmit and receive circuitry from the AC magnetic field. Capacitors with low ESR and low thermal coefficients such as C0G ceramics should be used in the transmit and receive LC tanks. Rev. A For more information www.analog.com 17 LTC4126 APPLICATIONS INFORMATION Table3. Recommended Components for the Receiver Shown in Figure7 ITEM PART DESCRIPTION MANUFACTURER/PART NUMBER LRX 13H, 10mm, Receive Coil Wurth 760308101208 CRX Capacitor, C0G, 33nF, 5%, 50V, 0805 or TDK C2012C0G1H333J125AA Capacitor, C0G, 33nF, 1%, 50V, 1206 Murata GCM3195C1H333FA16D COUT Ceramic CAP, 2.2F, 10%, 6.3V, 0402 Murata GRM155R60J225KE95D D1 LED, 630nm, Red, 0603, SMD Rohm Semiconductor SML-311UTT86 Table4. Recommended Components for the Transmitter Shown in Figure7 ITEM PART DESCRIPTION MANUFACTURER/PART NUMBER LTX 7.5H, 28mm x 15mm, Transmit Coil Wurth 760308103206 CTX1 Capacitor, C0G, 33nF, 5%, 50V, 0805 TDK C2012C0G1H333J125AA CTX2 Capacitor, C0G, 1nF, 5%, 50V, 0603 TDK C1608C0G1H102J080AA M1 MOSFET, N-CH 20V, 6A, SOT-23-3 Vishay Si2312CDS-T1-GE3 RSET Resistor, 205k, 1%, 1/16W, 0402 Vishay CRCW0402205KFKED U1 IC, Voltage Controlled Silicon Oscillator, 2mm x 3mm DFN Analog Devices LTC6990IDCB C1 Capacitor, X5R, 4.7F, 20%, 6.3V, 0402 TDK C1005X5R0J475M C2 Capacitor, X5R, 100F, 20%, 6.3V, 1206 Murata GRM31CR60J107ME39L COMPONENT SELECTION FOR CHRG STATUS INDICATOR VCC LTC4126 The LED connected at the CHRG pin is powered by a 300A (typical) pull-down current source. Select a high efficiency LED with a low forward voltage drop. Some recommended LEDs are shown in Table5. RBIAS NTC BAT NTC RESISTOR THERMALLY COUPLED WITH BATTERY Table5. Recommended LEDs + RNTC Li-Ion 4126 F14 MANUFACTURER/ PART NUMBER PART DESCRIPTION Rohm Semiconductor, SML-311UTT86 LED, 630nm, RED, 0603, SMD Lite-On Inc. LTST-C193KRKT-5A LED, RED, SMT, 0603 Figure14. NTC Thermistor Connection This can be simplified as: RHOT RBIAS = 0.536 Temperature Qualified Charging To use the battery temperature qualified charging feature, connect an NTC thermistor, RNTC, between the NTC pin and GND, and a bias resistor, RBIAS, from the VCC pin to the NTC pin (Figure14). Since the Too Hot comparator threshold in the LTC4126 is internally set to 34.9% of VCC, the resistance of the thermistor at the hot threshold, RHOT, can be computed using the following equation: If RBIAS is chosen to have a value equal to the value of the chosen NTC thermistor at 25C (R25), then RHOT/R25 = 0.536. Thermistor manufacturers usually publish resistance/temperature conversion tables for their thermistors and list the ratio of the resistance, RT, of the thermistor at any given temperature, T, to its resistance, R25, at 25C. For the Vishay thermistor NTCS0402E3104*HT with 25/85 = 3950k, the ratio RT/R25 = 0.536 corresponds to approximately 40C. RHOT RHOT + RBIAS 18 = 0.349 Rev. A For more information www.analog.com LTC4126 APPLICATIONS INFORMATION Similarly, since the Too Cold comparator threshold in the LTC4126 is internally set to 76.5% of VCC, the resistance of the thermistor at the cold threshold, RCOLD, can be computed using the following equation: R COLD R COLD + RBIAS = 0.765 This can be simplified as: R COLD RBIAS = 3.25 Again, if RBIAS is chosen to have a value equal to the value of the chosen NTC thermistor at 25C (R25), then RCOLD/R25 = 3.25. For the same Vishay thermistor with 25/85 = 3950k, the ratio RT/R25 = 3.25 corresponds to approximately 0C. both the hot and cold thresholds lower. Also note that with only one degree of freedom (i.e. adjusting the value of RBIAS), the user can only set either the cold or hot threshold but not both. It is possible to adjust the hot and cold threshold independently by introducing another resistor as a second degree of freedom (Figure15). The resistor RD in effect reduces the sensitivity of the resistance between the NTC pin and ground. Therefore, intuitively this resistor will move the hot threshold to a hotter temperature and the cold threshold to a colder temperature. The value of RBIAS and RD can now be set according to the following formula: RBIAS = (RCOLD - RHOT ) 2.714 RD = 0.197 * R COLD - 1.197 * RHOT The hot/cold temperature thresholds can be increased or decreased by choosing a BIAS resistor which is not the same as R25. For example, if a hot temperature threshold of 50C is desired, consult the resistance/temperature conversion table of the thermistor to find the ratio R50/ R25. For the same Vishay thermistor used above, this ratio is 0.3631. Since RHOT/RBIAS = 0.536, RBIAS can be calculated as follows: RBIAS = RHOT 0.536 = 0.3631* R 25 0.536 RBIAS NTC RD BAT NTC RESISTOR THERMALLY COUPLED WITH BATTERY + RNTC Li-Ion 4126 F15 = 0.677 * R 25 This means: choose an RBIAS value which is 67.7% of the value of the thermistor at 25C to set the hot temperature threshold to 50C. However, this will automatically shift the cold temperature threshold upward too. The cold temperature threshold can be recalculated by computing the RCOLD/R25 ratio as follows: R R = COLD * BIAS = 3.25 * 0.677 = 2.202 R 25 RBIAS R 25 R COLD VCC LTC4126 From the conversion table, this ratio corresponds to about 8C. Note that changing the value of RBIAS to be smaller than R25 moves both the hot and cold thresholds higher. Similarly, RBIAS with a value greater than R25 will move Figure15. NTC Thermistor Connection with Desensitizing Resistor RD Note that this method can only be used to push the hot and cold temperature thresholds apart from each other. When using the formulas above, if the user finds that a negative value is needed for RD, the two temperature thresholds selected are too close to each other and a higher sensitivity thermistor is needed. For example, this method can be used to set the hot and cold thresholds independently to 60C and -5C. Using the same Vishay thermistor with 25/85 = 3950k whose nominal value at 25C is 100k, the formula results in RBIAS = 147k and RD = 52.3k for the closest 1% resistors values. Rev. A For more information www.analog.com 19 LTC4126 APPLICATIONS INFORMATION PC BOARD LAYOUT CONSIDERATIONS Since the exposed pad of the LTC4126 package is the only ground pin and serves as the return path for both the charger and the DC/DC converter, it must be soldered to the PC board ground for a good electrical connection. Although the LTC4126 is a low power IC, the shunt circuitry in the AC power control block can cause a fair 20 amount of on-chip power dissipation if the available AC power is excessive. If the heat is not dissipated properly on the PC board, the temperature of the die and subsequently, the temperature of the battery may rise above the hot temperature threshold set by the NTC thermistor causing the charger to pause charging. For optimum thermal performance, there should be a group of vias directly under the exposed pad on the backside leading directly down to an internal ground plane. To minimize parasitic inductance, the ground plane should be as close as possible to the top plane of the PC board (Layer 2). Rev. A For more information www.analog.com LTC4126 TYPICAL APPLICATIONS Full-Featured Application Circuit VIN 4.75V TO 5.25V 17.8k 47F RBIAS 100k 22m 0.01F NTC VCC 47F 100k IN IN2 IN1 STAT IS+ SW1 IS- DTH CTX LTC4125 FTH 100nF PTH1 SW2 PTH2 IMON EN 100k 20.5k 1.05k 1.5M FB GND D1 AIR GAP (2mm TO 4mm) Li-Ion + 4.2V CHRG CRX 68nF ACIN NTC RESISTOR RNTC THERMALLY COUPLED WITH BATTERY 1.2V OUT 2.2F LRX 8H LTX 6.5H BAT LTC4126 STAT1 STAT2 ACPR EN VSEL GND PBEN PTHM CTS CTD NTC PUSHBUTTON V + P GPIO GND 4126 TA02 CTX: TDK C3216COG2A104J160AC LTX: WURTH 760-308-101-104 RNTC: VISHAY NTCS0402E3104*HT M1: VISHAY Si2312CDS-T1-GE3 D1: ROHM SEMICONDUCTOR SML-311UTT86 Minimum Component Count Application Circuit AIR GAP TRANSMITTER LTX VIN EN BAT ACIN LRX 8H + - CRX 68nF LTC4126 NTC VSEL GND OUT 4126 TA04 + Li-Ion 4.2V 1.2V 2.2F CRX: AVX0603YC683JAT2A LRX: SUNLORD MQQRC060630S8R0 Rev. A For more information www.analog.com 21 For more information www.analog.com 0.70 0.05 2.50 0.05 0.25 0.05 5 0.70 SUGGESTED PCB LAYOUT TOP VIEW 2.50 0.05 0.70 0.0000 aaa Z 2x D PACKAGE TOP VIEW 0.2500 PIN 1 CORNER 0.2500 X aaa Z // bbb Z 0.7500 0.2500 0.0000 0.2500 0.7500 PACKAGE OUTLINE Y E 2x Z H1 MIN 0.65 0.01 0.30 0.22 DETAIL C SUBSTRATE SYMBOL A A1 L b D E D1 E1 e H1 H2 aaa bbb ccc ddd eee fff DETAIL B H2 MOLD CAP NOM 0.74 0.02 0.40 0.25 2.00 2.00 0.70 0.70 0.50 0.24 REF 0.50 REF DIMENSIONS 12b eee M Z X Y fff M Z DETAIL C A1 12x 0.10 0.10 0.10 0.10 0.15 0.08 MAX 0.83 0.03 0.50 0.28 e/2 e L SUBSTRATE THK MOLD CAP HT NOTES DETAIL A DETAIL B A (Reference LTC DWG # 05-08-1530 Rev B) ddd Z Z 22 e 7 6 D1 e 0.250 5 DETAIL A PACKAGE BOTTOM VIEW 6 11 b 12 4 1 PIN 1 NOTCH 0.14 x 45 4 SEE NOTES DETAILS OF PIN 1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PIN 1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE THE EXPOSED HEAT FEATURE MAY HAVE OPTIONAL CORNER RADII 5 6 LQFN 12 0618 REV B METAL FEATURES UNDER THE SOLDER MASK OPENING NOT SHOWN SO AS NOT TO OBSCURE THESE TERMINALS AND HEAT FEATURES 4 3. PRIMARY DATUM -Z- IS SEATING PLANE 2. ALL DIMENSIONS ARE IN MILLIMETERS NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 E1 b 10 ccc M Z X Y ccc M Z X Y LQFN Package 12-Lead (2mm x 2mm x 0.74mm) LTC4126 PACKAGE DESCRIPTION Rev. A LTC4126 REVISION HISTORY REV DATE DESCRIPTION A 02/20 Modified Battery Charger VCHG spec PAGE NUMBER 3 Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license For is granted implication or otherwise under any patent or patent rights of Analog Devices. more by information www.analog.com 23 LTC4126 TYPICAL APPLICATION Wireless 7.5mA Li-Ion Battery Charger (4.35V) Tuned at 266kHz with Pushbutton Enabling NTC RBIAS 100k VIN 5V C2 100F R2 732k C1 4.7F R3 66.5k V+ fDRIVE = 216kHz MOD LTC6992 SET OUT R1 232k DIV VSEL VCC AIR GAP (2mm TO 4mm) CTX2 100nF LTX 2.7H NTC RESISTOR RNTC THERMALLY COUPLED WITH BATTERY Li-Ion + 4.35V D1 CHRG fLC_TANK = 266kHz CTX1 33nF BAT LTC4126 OUT ACIN LRX 8H CRX 68nF M1 Si2312CDS EN STAT1 STAT2 ACPR GND 1.2V 2.2F DIGITAL I/O PBEN PUSHBUTTON GND 4126 TA03 CTX1: TDK C2012COG1H333J125AA CTX2: TDK C3216COG1H104J160AA LTX: SUNLORD MQQTC202030S2R7 CRX: AVX0603YC683JAT2A LRX: SUNLORD MQQRC060630S8R0 RNTC: VISHAY NTCS0402E3104*HT M1: VISHAY Si2312CDS-T1-GE3 D1: ROHM SEMICONDUCTOR STL-311UTT86 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC4120 400mA Wireless Power Receiver Buck Battery Charger Wireless 1 to 2 Cell Li-Ion Charger, 400mA Charge Current, Dynamic Harmonization Control, Wide Input Range: 12.5V to 40V, 16-Lead 3mm x 3mm QFN Package LTC4123 Low Power Wireless Charger for Hearing Aids Wireless Single NiMH Charger, Integrated Rectifier with Overvoltage Limit, 25mA Charge Current, Zn-Air Detect, Temperature Compensated Charge Voltage, 6-Lead 2mm x 2mm DFN Package LTC4125 5W Auto Resonant Wireless Power Transmitter Monolithic Auto Resonant Full Bridge Driver. Transmit Power Automatically Adjusts to Receiver Load, Foreign Object Detection, Wide Operating Switching Frequency Range: 50kHz to 250kHz, Input Voltage Range 3V to 5.5V, 20-Lead 4mm x 5mm QFN Package LTC4070 Li-Ion/Polymer Shunt Battery Charger System Li-Ion/Polymer Shunt Battery Charger, Low Operating Current (450nA), 50mA Internal Shunt Current, Pin Selectable Float Voltages (4.0V, 4.1V, 4.2V), 8-Lead 2mm x 3mm DFN and MSOP Packages LTC4071 Li-Ion/Polymer Shunt Battery Charger System with Low Battery Disconnect Charger Plus Pack Protection in One IC, Low Operating Current (550nA), 50mA Internal Shunt Current, Pin Selectable Float Voltages (4.0V, 4.1V, 4.2V), 8-Lead 2mm x 3mm DFN and MSOP Packages LTC6990 TimerBlox: Voltage Controlled Silicon Oscillator Fixed-Frequency or Voltage-Controlled Operation, Frequency Range of 488Hz to 2MHz, Low-Profile SOT-23 and 2mm x 3mm DFN Packages LTC6992 TimerBlox: Voltage Controlled Pulse-Width Modulator (PWM) 24 Pulse Width Modulation by 0V to 1V Analog Input, Frequency Range of 3.81Hz to 1MHz, Low-Profile SOT-23 and 2mm x 3mm DFN Packages Rev. A 02/20 www.analog.com For more information www.analog.com ANALOG DEVICES, INC. 2018-2020