LTC4079 60V, 250mA Linear Charger with Low Quiescent Current Features n n n n n n n n n n n n n Description Wide Input Voltage Range: 2.7V to 60V Adjustable Battery Voltage: 1.2V to 60V Adjustable Charge Current: 10mA to 250mA Low Quiescent Current While Charging: IIN = 4µA Ultralow Battery Drain When Shutdown or Charged: IBAT < 0.01µA Auto Recharge Input Voltage Regulation for High Impedance Sources Thermal Regulation Maximizes Output Current without Overheating Constant Voltage Feedback with ±0.5% Accuracy NTC Thermistor Input for Temperature Qualified Charging Adjustable Safety Timer Charging Status Indication Thermally Enhanced 10-Lead (3mm × 3mm) DFN Package Applications n n n n Embedded Automotive and Industrial Backup Battery Charging from Another Battery Energy Harvesting Charger Thin Film Battery Products The LTC®4079 is a low quiescent current, high voltage linear charger for most battery chemistry types including Li-Ion/Polymer, Lead-Acid or NiMH battery stacks up to 60V. The maximum charge current is adjustable from 10mA to 250mA with an external resistor. The battery charge voltage is set using an external resistor divider. With an integrated power device, current sensing and reverse current protection, a complete charging solution using the LTC4079 requires very few external components. Thermal regulation ensures maximum charge current up to the specified limit without the risk of overheating. Charging can be terminated by either C/10 or adjustable timer. Input voltage regulation reduces charge current when the input voltage falls to an adjustable level or the battery voltage, making it well suited for energy harvesting applications. Other features include temperature qualified charging, bad battery detection, automatic recharge with sampled feedback in standby for negligible battery drain, and an open-drain CHRG status output. The device is offered in a compact, thermally enhanced 10-lead (3mm × 3mm) DFN package. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application Li-Ion Battery Charge Cycle Charging a Backup Battery IN 1µF BAT 8.4V 1.54M LTC4079 EN PROG NTCBIAS 10k TIMER NTC GND T 10k + Li-Ion VBAT 8.4 IBAT 8.2 VBAT (V) FBG 3.01k 120 100 FB 249k CHRG 8.6 500mAh 2-CELL LI-ION IBAT (mA) 9V TO 60V 140 80 8.0 60 7.8 40 C/10 7.6 TERMINATION 20 7.4 0 0 4079 TA01a 1 2 3 4 5 TIME (HOURS) 6 7 8 7.2 4079 TA01b 4079f For more information www.linear.com/LTC4079 1 LTC4079 Absolute Maximum Ratings (Notes 1, 2) IN, BAT, EN, CHRG, FB, FBG Voltage........... –0.3V to 62V PROG TIMER Voltage...................................................3V BAT Current....................................................... –400mA PROG Current...................................................... –1.6mA FBG Current..............................................................2mA CHRG Current...........................................................2mA Operating Junction Temperature Range (Notes 3, 5)................................................. –40 to 125°C Storage Temperature Range.......................–65 to 150°C Pin Configuration TOP VIEW 10 BAT IN 1 EN 2 PROG 3 NTCBIAS 4 7 CHRG NTC 5 6 TIMER 11 GND 9 FB 8 FBG DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC4079EDD#PBF LTC4079EDD#TRPBF LGNQ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LTC4079IDD#PBF LTC4079IDD#TRPBF LGNQ 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on nonstandard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 2 4079f For more information www.linear.com/LTC4079 LTC4079 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C (Notes 2, 3). VIN = 12V, VBAT = 7.4V, VFB = 1.057V, VEN = 12V, RPROG = 3k (100mA charge current) unless otherwise specified. SYMBOL PARAMETER VIN Operating Supply Voltage CONDITIONS MIN l VBAT Battery Voltage Range VUVLO VIN Undervoltage Lockout VIN Rising Hysteresis l VDUVLO Differential Undervoltage Lockout VIN-VBAT Rising Hysteresis l VDVREG Differential Voltage Regulation Minimum VIN-VBAT for Charge Current l IQ(IN) Input Supply Quiescent Current Charging (Note 4) Charging Terminated (VFB = 1.210V) Shutdown (EN = 0) l l IQ(BAT) Battery Drain Current Charging Terminated (VFB =1.210V) Shutdown (EN = 0) VIN = 0 or IN open TYP 2.7 MAX UNITS 60 V 60 V 2.55 140 2.7 V mV –20 15 80 50 mV mV 120 160 200 mV 4 2 0.2 9 4 0.6 µA µA µA 0.01 0.00 0.05 0.2 0.2 0.2 µA µA µA 1.170 1.170 1.175 1.184 V V l Charging Functions VFB(CHG) Feedback Pin Regulation Voltage in ConstantVoltage Charge Mode PROG Pin Regulated Voltage l 1.165 1.156 Constant-Current Mode 1.190 Ratio of BAT Current to PROG Pin Current V 250 mA/mA ICHG Battery Charge Current in Constant-Current Mode (Note 5) RPROG = 1.2k RPROG = 3k RPROG = 30k l l l 236 93 8.5 248 99 10 260 105 11.5 mA mA mA ITERMINATE Charging Termination Threshold RPROG = 1.2k RPROG = 3k RPROG = 30k l l l 22 8.2 0.7 25 10 1 28 11.8 1.3 mA mA mA ICHG Drops Below Termination Threshold 5 9 13 ms 10 % % tTERMINATE Deglitch Filter on C/10 Charge Termination tTIMER Safety Timer Accuracy VRECHRG Recharge Threshold Voltage of FB Pin –10 Relative to VFB(CHG) with VFB Falling VFB(LOWBAT) Low Battery Threshold VFB for Low Battery Detection Low Battery Time Out (Percentage of Safety Timer) l Charging with VFB < VFB(LOWBAT) 96.9 97.6 98.3 0.780 0.800 0.820 V 18 % 5 Ω RON Resistance of the Charge Path IFB Feedback Pin Leakage VFB = 1.170V (in Regulation) VFB = 8.4V (in Shutdown) l l 0.1 0.1 20 100 nA nA IFBG Feedback Ground Pin Leakage VFBG = 8.4V, EN = 0 l 0.1 100 nA RFBG Switch Resistance from FBG Pin to GND 160 Ω Die Temperature (TJ) at Thermal Regulation 118 °C 4079f For more information www.linear.com/LTC4079 3 LTC4079 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C (Notes 2, 3). VIN = 12V, VBAT = 7.4V, VFB = 1.057V, VEN = 12V, RPROG = 3k (100mA charge current) unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS % NTC Temp Monitor VCOLD Low Temp. Fault NTC Threshold Voltage VNTC/VNTCBIAS l 72.3 73.8 75.3 VHOT VNTC(DIS) High Temp. Fault NTC Threshold Voltage VNTC/VNTCBIAS l 35.6 36.6 37.6 % NTC Disable Voltage Threshold VNTC l 60 80 100 mV Pulsed NTCBIAS Voltage 20k from NTCBIAS to Ground NTCBIAS Period NTCBIAS Pulse Width NTC Input Leakage Current VNTC = VNTCBIAS l 4 V 3 Sec 210 µs 0.1 100 nA Enable Input (EN) VEN(SD) Shutdown Threshold VEN Falling Hysteresis l 0.400 0.750 55 1.100 V mV VEN(REG) Enable Pin Regulation Voltage Minimum VEN for Charge Current l 1.170 1.190 1.210 V l 0 20 nA Enable Pin Leakage Current When Pulled High VEN = 60V Status Outputs (CHRG) Output Low Voltage 1mA Into the Open-Drain Output l 0.16 0.4 V Output Leakage Current VCHRG = 60V, VEN = 0V l 0.1 100 nA 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: Unless otherwise specified, current into a pin is positive and current out of a pin is negative. Note 3: The LTC4079 is tested under pulsed load conditions such that TJ ≈ TA. The LTC4079E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC4079I is guaranteed over the full –40°C to 125°C operating junction temperature range. 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 impedance and other environmental factors. 4 Note 4: BAT pin charge current, PROG pin and feedback divider currents are excluded from supply quiescent current. Note 5: Charge current is reduced by thermal regulation as the junction temperature rises above TLIM (118°C). 4079f For more information www.linear.com/LTC4079 LTC4079 Typical Performance Characteristics Regulated Feedback Voltage vs Temperature Load Regulation of Regulated Feedback Voltage Regulated Feedback Voltage vs VIN 1.182 1.182 1.178 1.178 1.178 1.174 1.174 VFB(CHG) (V) INTERNAL REFERENCE 1.170 ONSET OF THERMAL REGULATION 1.166 1.162 VFB(CHG) (V) 1.182 1.174 VFB(CHG) (V) VIN = 12V, TA = 25°C unless otherwise noted. 1.170 1.166 1.162 1.158 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1.158 0 10 20 30 VIN (V) 50 40 5 1.158 0.15 VFB = 1.2V (IBAT = 0) 3 IBAT (µA) IIN (µA) 2 STANDBY (CHARGING TERMINATED) 2 200 250 Battery Quiescent Current vs Temperature 0.20 4 CHARGING STANDBY (CHARGING TERMINATED) 100 150 IBAT (mA) 50 0 4079 G03 CHARGING 4 IIN (µA) 60 Input Supply Quiescent Current vs Supply Voltage VFB = 1.2V (IBAT = 0) 3 1.166 4079 G02 Input Supply Quiescent Current vs Temperature 5 1.170 1.162 4079 G01 6 RPROG = 1.2k ICHG = 248mA VBAT = 8.4V CHARGING TERMINATED OR SHUTDOWN 0.10 0.05 1 1 SHUTDOWN (EN = 0) SHUTDOWN (EN = 0) 0 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 10 20 30 VIN (V) 50 40 4079 G04 60 120 50 SHUTDOWN (EN = 0) 40 30 VBAT (V) 50 60 4079 G07 0 ONSET OF THERMAL REGULATION VIN = 12V VBAT = 8.4V RPROG = 1.2k 200 IBAT (mA) IBAT (nA) IBAT (mA) 20 20 250 RPROG = 3k 60 10 10 300 80 40 0 Battery Charge Current vs Temperature VFB(CHG) = 8.4V 100 STANDBY (CHARGING TERMINATED) 20 0 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G06 Battery Charge Current vs Battery Voltage 30 0 4079 G05 Battery Quiescent Current vs Battery Voltage 40 0 –50 –25 60 150 100 50 RPROG = 30k 0 2 4 6 VBAT (V) RPROG = 3k RPROG = 30k 8 10 4079 G08 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G09 4079f For more information www.linear.com/LTC4079 5 LTC4079 Typical Performance Characteristics Battery Charge Current vs VIN – VBAT Battery Charge Current vs VEN RPROG = 3k 100 RPROG = 3k 100 60 40 OHMIC REGION (DROPOUT) 60 40 20 20 RPROG = 30k 0 1.18 1.19 1.12 VEN (V) 1.21 RPROG = 30k 0 0.0 1.22 0.1 0.2 0.3 0.4 VIN – VBAT (V) 10 0 6 4 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 20 10 30 VIN (V) 40 4079 G13 350 50 0 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G16 6 10 PIN AT 1.2V 5 0 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G15 NTCBIAS Period and Pulse Width vs Temperature 3.2 260 3.1 250 3.0 240 1.1 PERIOD (s) TIMER DURATION (RELATIVE TO 25°C) RFBG (Ω) 100 250 1.0 2.9 230 PERIOD 2.8 0.9 220 PULSE WIDTH 2.7 0.8 –50 –25 PULSE WIDTH (µs) 150 200 PIN AT 60V 0 –50 –25 60 1.2 200 0 –50 –25 50 15 Normalized Timer Duration vs Temperature 250 100 150 IBAT (mA) 4079 G14 Switch Resistance from FBG to GND vs Temperature 300 50 20 2 VIN = 5.0V 0 –50 –25 0 EN and FB Pin Leakages vs Temperature LEAKAGE CURRENT (nA) RON (Ω) RON (Ω) 5 230 4079 G12 PULSED LOAD (TJ ≈TA) VIN – VBAT = 0.6V RPROG = 1.2k 8 VIN = 2.7V 240 210 0.6 THERMAL REGULATION 10 250 Charge Path Dropout Resistance vs VIN PULSED LOAD (TJ ≈TA) VIN – VBAT = 0.6V RPROG = 1.2k 15 260 4079 G11 Charge Path Dropout Resistance vs Temperature 20 270 220 0.5 4079 G10 4 DEVICES TESTED RPROG = 1.2k 280 80 IBAT (mA) 80 IBAT (mA) IBAT/IPROG Ratio vs IBAT 290 120 IBAT/ I PROG (mA/mA) 120 25 VIN = 12V, TA = 25°C unless otherwise noted. 0 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G17 2.6 –50 –25 210 0 200 25 50 75 100 125 150 TEMPERATURE (°C) 4079 G18 4079f For more information www.linear.com/LTC4079 LTC4079 Pin Functions IN (Pin 1): Input Supply Pin. This input provides power to the battery charger. Bypass this pin with a ceramic capacitor of at least 1µF. EN (Pin 2): Enable Input. Charge current starts flowing when this input rises above 1.190V, its regulation threshold. When using a current limited power source, connect this input to an external resistor divider from IN to GND to avoid UVLO oscillations. This configuration can also be used to maintain the source voltage (IN pin) at the maximum power threshold (e.g., for solar panel). Pulling this pin below 0.750V shuts down the device. This pin should not be left floating. PROG (Pin 3): Charge Current Program Pin. The current out of this pin is 1/250th of the current out of the BAT pin. A resistor connected from PROG to ground sets the charge current in constant-current mode. This pin servos to 1.190V during constant-current charging. Do not leave this pin open. Limit parasitic capacitance on this node to less than 50pF. NTCBIAS (Pin 4): NTC Thermistor Bias Output. Connect a low drift bias resistor from NTCBIAS to NTC pin, and a thermistor from NTC pin to GND. The value of the bias resistor is typically equal to the nominal resistance of the thermistor at 25°C. Minimize parasitic capacitance on this pin. NTC (Pin 5): Input to the Battery Temperature Sense Circuit. Connect the NTC pin to a negative temperature coefficient (NTC) thermistor, which is typically co-packaged with the battery, to signal the charger if the battery is too hot or too cold to charge. The room temperature value of the thermistor should be at least 2kΩ. If the battery’s temperature is out of range, charging is paused until the battery temperature re-enters the valid range. Connect a 1%, low drift bias resistor from NTCBIAS to NTC and a thermistor from NTC to ground. Minimize parasitic capacitance on this pin. Tie the NTC pin to GND to disable battery temperature sensing. For maximum charge duration of tTIMER (in Hours), the required capacitance value can be determined as follows: CTIMER = (tTIMER • 18.2nF/Hr) A typical value of CTIMER is 100nF which terminates the charge cycle after 5½ hours. Minimize leakage on this pin to maintain timer accuracy. The timer is disabled when this pin is tied to GND. In this case charging terminates when the charge current falls below 1/10th of the programmed charge current ICHG. CHRG (Pin 7): Open-Drain Charge Status Output. Typically pulled up to a voltage source through a resistor or a low power LED and a resistor. This pin is pulled low by an internal NMOS when LTC4079 is charging the battery. The pin goes to high impedance when the charge current drops below 1/10th of the programmed current, or the charge cycle is timer terminated. FBG (Pin 8): Ground Reference for Battery Voltage Divider. This pin is connected to ground internally through an NMOS switch when the battery is charging and disconnects the battery voltage divider from GND when it is not needed. When sensing the battery voltage the NMOS switch presents a low resistance (RFBG =160Ω) to GND. FB (Pin 9): Sense Pin for Divided Battery Voltage. This pin servos to 1.170V (VFB(CHG)) during the constant-voltage phase of the battery charge algorithm. The battery charge voltage is set by using an appropriate resistor divider from BAT to FB to FBG. Minimize leakage and parasitic capacitance on this pin. BAT (Pin 10): Battery Charger Output. This pin provides charge current to the battery. GND (Exposed Pad Pin 11): Ground. The exposed pad must be soldered to a continuous ground plane of the printed circuit board for electrical connection and the rated thermal performance. TIMER (Pin 6): Timer Capacitor Input. A capacitor on this pin sets the maximum duration for battery charging from charger enable or from the beginning of a recharge cycle. 4079f For more information www.linear.com/LTC4079 7 LTC4079 Block Diagram 1 IN BAT P1 IBAT 250 CC/CV REGULATION, EN REGULATION, VIN-VBAT REGULATION THERMAL REGULATION BG REF 10 RFB1 FB + 9 T – BATTERY PACK + 2 7 EN RECHARGE REFERENCE FBG RFB2 8 UVLO, DIFF UVLO CHRG NTCBIAS CONTROL 4 RBIAS NTC 5 OSC PROG TIMER 6 3 CTIMER 4079 F01 RPROG Figure 1. Block Diagram of LTC4079 8 4079f For more information www.linear.com/LTC4079 LTC4079 Operation The LTC4079 is a full featured constant-current, constantvoltage charger designed to charge multiple chemistry types of batteries from voltage sources up to 60V. The low quiescent current of the device minimizes power drain on the source and the battery, making it suitable for a variety of applications including backup and energy harvesting from an intermittent power source. The battery charge voltage is set using an external resistor divider. Charge duration can be set using a capacitor on the TIMER pin. For safety and improved battery life, the LTC4079 includes a thermistor input for temperature qualified charging. A 6ms filter (tTERMINATE) is used on the C/10 detector to prevent premature termination due to transient loads on the battery during charging. Charge current starts when the EN pin is brought above 1.190V. Figure 2 shows a flow chart of the primary states and state transitions of the LTC4079. A typical charge cycle includes: The battery charge voltage is set by connecting a resistor divider from the battery to the FB and FBG pins as shown in Figure 3. The charge voltage is determined as follows: 1. Constant-Current (CC) Charging: The programmed charge current is used to charge the battery until the battery voltage reaches the charge voltage set using the feedback divider. For a low ESR battery, this mode provides the bulk of the charge. The charge timer should generally be set long enough to charge the battery above the recharge threshold, otherwise another charge cycle would immediately follow. 4. Automatic Recharge: When VBAT drops below the recharge threshold (97.6% of the charge voltage), whether by battery drainage or replacement of the battery, the charger automatically re-engages and starts charging. Setting The Battery Charge Voltage where RFB1 is the resistor from BAT to FB, RFB2 is the resistor from FB to FBG and RFBG is the resistance of the internal switch of the FBG pin (160Ω typical). BAT RFB1 LTC4079 2. Constant-Voltage (CV) Charging: Once the battery reaches the set charge voltage, constant voltage is maintained across the battery by controlling the charge current. The charge current reduces with time in this mode as the battery nears its full charge capacity. 3. Charging Termination: The LTC4079 can be configured to terminate charging automatically based on time or current. The CHRG status pin goes to high impedance when the charge current reduces below 1/10th of the programmed current, indicating that the battery is almost fully charged. The charge current continues to top-off the battery until the timer terminates the charge current. Timer termination can be disabled by connecting the TIMER pin to ground. In this case, charging terminates when the charge current falls below 1/10th of the programmed charge current. RFB1 VCHG = 1.170V • 1+ RFB2 +RFBG FB FBG RFB2 + BATTERY 4079 F03 ENABLE Figure 3. Setting the Battery Charge Voltage Setting and Monitoring the Charge Current The charge current delivered to the battery in constantcurrent mode, ICHG is set using a resistor from the PROG pin to ground. The value of this resistor is calculated using: RPROG = 297.5V ICHG 4079f For more information www.linear.com/LTC4079 9 LTC4079 Operation SHUTDOWN* VEN > 0.805V VIN > 2.57V VIN – VBAT > 15mV? NO YES ASSERT CHRG STATUS START SAFELY TIMER IF TIMER NOT GROUNDED BATTERY TEMP IN RANGE? NO PAUSE CHARGE CURRENT PAUSE TIMER YES EN REG, DIFF REG OR THERMAL REG NO CV REG? YES NO YES BAD BATTERY* CHRG REMAINS ASSERTED YES RUN TIMER PAUSE TIMER CC-CV CHARGING CHARGING IN EN REG, DIFF REG OR THERMAL REG LATCH-OFF* CHRG REMAINS ASSERTED VFB < 0.8V? NO YES SAFETY TIMER EXPIRED? 1/4 SAFETY TIMER EXPIRED? NO YES NO NO VFB < VRECHG? YES RETRY COUNT = 5? NO INCREMENT RETRY COUNTER NO ICHG < C/10? IN CV REG, NO EN REG, DIFF REG OR THERM REG STANDBY CHARGING TERMINATED RESET SAFETY TIMER RESET RETRY COUNTER DEASSERT CHRG STATUS SAMPLE FB PIN EVERY 3 SEC YES VFB < VRECHG 4079 F02 DEASSERT CHRG SATUS TIMER GROUNDED? YES NO * VEN < 0.75V OR ULVO TAKES THE DEVICE TO SHUTDOWN FROM ANY STATE Figure 2. Battery Charger Operations Flow Chart 10 4079f For more information www.linear.com/LTC4079 LTC4079 Operation The PROG pin also provides a voltage signal proportional to the battery charge current. Therefore, the instantaneous battery current can be determined as follows by monitoring the PROG pin voltage: IBAT = 250 • VPROG RPROG Minimize the parasitic capacitance while monitoring the PROG pin voltage as any capacitance on this pin forms a pole that may cause instability in the charge control loop. LTC4079 NTC SAMPLE PULSE BAT NTCBIAS INTERNAL SUPPLY NTC TOO COLD + – TOO HOT + – 36.6% VNTCBIAS IGNORE NTC + – 0.1V Undervoltage Detection RBIAS 73.8% VNTCBIAS RNTC T + 4079 F04 An internal undervoltage lockout circuit monitors the VIN voltage and disables the battery charging circuit until VIN rises above the undervoltage lockout threshold, 2.55V (typically). The UVLO threshold has built-in hysteresis of 140mV. Furthermore, the differential UVLO circuit also keeps the charger in a low quiescent current mode by disabling the battery charging circuits when VIN falls below VBAT by more than 65mV. The differential UVLO has hysteresis of 80mV, with turn-on at VIN-VBAT = 15mV (typical). Battery Temperature Qualified Charging During battery charging, the battery temperature is sensed by sampling the voltage on the NTC pin every 3 seconds. Connect a low drift bias resistor from the NTCBIAS output to the NTC input and a negative temperature coefficient (NTC) thermistor, close to the battery pack, from the NTC pin to ground, as shown in Figure 4. The bias resistor should be equal to the value of the chosen thermistor at 25°C. The LTC4079 pauses charging and the charge timer when the NTC pin voltage indicates that the thermistor resistance has dropped to 0.576 times its room temperature value. For a Vishay curve 2 thermistor, this corresponds to 40°C. Charging is also paused when the thermistor resistance increases to 2.816 times the room temperature value. For a Vishay curve 2 thermistor, this increase corresponds to 0°C. The hot and cold trip points can be adjusted using a different type of thermistor, or a different RBIAS resistor, or by adding a desensitizing resistor in series with the thermistor, or by a combination of these measures. Figure 4. Battery Temperature Sensing Using NTC Thermistor Charging resumes when the battery temperature returns to the normal range and the timer continues from the point where it was paused. Input Voltage Regulation The LTC4079 can regulate a constant voltage on the IN pin when charging from a current-limited power source such as a weak battery or a solar panel. This feature can be used to prevent the input voltage from collapsing below UVLO, or to maintain the input source voltage at peak power. The charge current is reduced as the input voltage falls to the threshold set by an external resistor divider from the input power source to the EN pin and GND, as shown in Figure 5. The input voltage regulation threshold, VIN(REG) is calculated as follows: R VIN(REG) = 1.190V • 1+ EN1 REN2 This regulation mechanism allows the charge current to be selected based on battery requirement and the maximum power available from the charging source. The LTC4079 automatically reduces the charge current when the input source cannot provide the programmed charge current. When input voltage regulation is not needed, connect the EN pin to the input power source or a digital enable signal. For more information www.linear.com/LTC4079 4079f 11 LTC4079 Operation INPUT POWER SOURCE IN REN1 LTC4079 EN REN2 4079 F05 Figure 5. Setting Input Voltage Regulation Differential Voltage (VIN-VBAT) Regulation The LTC4079 provides an additional method to keep the input voltage from collapsing when the input power comes from a weak power source. If the input voltage falls close to the battery voltage, the differential voltage regulation loop in LTC4079 keeps the input voltage above the battery voltage by 160mV (typical value) by reducing the charge current as the input to battery differential voltage falls. When C/10 termination is used, the LTC4079 provides battery charge current as long as the current remains above the C/10 threshold. As the battery terminal voltage reaches the target charge voltage, the charge current falls until the C/10 threshold is reached, at which time the charger terminates and the LTC4079 enters standby mode. Premature termination is prevented when input voltage, differential or thermal regulation is active. To prevent termination-recharge oscillations, it is important to set the termination charge current low enough for batteries with high internal resistance. For a nominal recharge threshold of 2.4% below the charge voltage, the charge current should be set as follows with sufficient margin: V ICHG < 0.24 • CHG RBAT In both of the above regulation conditions, the input source must provide at least the quiescent current of the device to prevent UVLO. The charge timer is paused whenever the charge current is reduced due to input voltage regulation or differential voltage regulation. where RBAT is the battery's internal series resistance. The CHRG status pin is high impedance when the charger is not actively charging. Thermal Regulation The LTC4079 also supports a timer-based termination scheme, where the battery charge cycle is terminated after a specific amount of time elapses. Connect a capacitor from the TIMER pin to ground to engage timer based charge termination. Calculate the capacitance required for the desired charge cycle duration, tTIMER as follows: An internal thermal feedback loop reduces the charge current below the programmed value if the die temperature approaches 118°C. This feature protects the LTC4079 from excessive temperature and allows the user to set the charge current to typical (not worst case) ambient temperature with the assurance that the charger will automatically reduce the current to prevent overheating in worst-case conditions. The charge timer is paused during thermal limiting to prevent under-charging the battery and to allow the full charge current to flow for the set timer duration. C/10 Termination The LTC4079 supports a current based termination scheme, where a battery charge cycle terminates when the current output from the charger falls below one-tenth of the programmed charge current. The C/10 threshold current corresponds to 119mV on the PROG pin. This termination mode is engaged by shorting the TIMER pin to ground. 12 Timer Termination CTIMER = tTIMER • 18.2nF/Hr A 200nA current source is used to source/sink current to/from CTIMER to generate a sawtooth periodic signal (nominally 0.8V to 1.2V) for use by the timer. Since the TIMER pin current is small, minimize leakage on this pin to maintain timer accuracy. The timer starts on charger enable or the beginning of a recharge cycle, and is reset on disable or when VIN falls below UVLO or DUVLO. The timer is paused whenever the charge current is limited by EN pin or differential voltage or thermal regulation, unless the charger is also in constant-voltage regulation mode. It is also paused with the charge current during an NTC fault. The timer is not paused if the charge current is 4079f For more information www.linear.com/LTC4079 LTC4079 Operation limited by dropout. For example, for a programmed charge current of 100mA, this occurs when VIN-VBAT falls below about 0.5V due to the voltage drop across the charge path (5Ω typically). If VIN-VBAT falls below 160mV to trigger differential voltage regulation, the timer will be paused. The CHRG status pin signals charging at a rate of more than C/10, regardless of which termination scheme is used. When timer termination is used, the CHRG status pin pulls low during a charging cycle until the charger output current falls below the C/10 threshold. The charger continues to top off the battery until timer termination, when the LTC4079 enters standby mode. Standby and Automatic Recharge If the LTC4079 remains enabled after charge cycle termination, it monitors the battery voltage in standby mode by sampling the FB pin connected to the external resistor divider. In order to minimize the battery drain, the feedback divider is only turned on (by connecting FBG pin to ground) for 210µs once every 3 seconds. When this sampling detects that the battery voltage has dropped by more than 2.4%, the feedback divider is kept on for 1.5 seconds (typical). If the FB voltage remains below the recharge threshold for more than 2.5ms (typical), a recharge cycle starts. This 2.5ms filter prevents premature recharge due to load transients. The recharge cycle also terminates in constant-voltage charge mode as described above. The automatic recharge function maintains that the battery at, or near, a fully charged condition. If the battery voltage remains below the recharge threshold on timer expiration, another recharge cycle begins as explained below. Timer Retry and Latch-off A new charge cycle is started if the battery voltage remains below the recharge threshold at the end of a charge cycle. This happens in the following situations: 1) the timer is not set long enough for the battery with the programmed charge current, 2) the battery is defective, 3) a load drains the battery during charging, 4) charge current is limited by dropout. In order to avoid wasting power in recharging a defective battery indefinitely, LTC4079 contains a recharge latchoff feature. Charging is latched off and the CHRG pin remains asserted after 5 recharge attempts if the battery voltage remains below the recharge threshold at the end of all five recharge cycles. The latch-off counter is reset if a charge cycle terminates normally during any recharge attempt, or if the charge current falls below ICHG/10 in constant-voltage regulation mode during a charge cycle. Charger disable using the EN pin or UVLO also resets the latch-off counter.. Bad Battery Scenario If the feedback voltage remains below VFB(LOWBAT) for longer than 1/4th of the safety timer set by CTIMER, the battery is considered bad. Charging stops in this case and the CHRG pin remains asserted. NTC sampling and FB sampling for recharge is also turned-off. The charge cycle is restarted by toggling the EN pin below VEN(SD) (typically 0.75V) and then back high. UVLO also clears the bad battery lockout. There is no bad battery detection when the battery charge timer is disabled (TIMER pin grounded). CHRG Status Output The charge status open-drain output (CHRG) has two states: pull down and high impedance. The pull-down state indicates that LTC4079 is in charging mode. A high impedance state indicates that the charge current has dropped below 10% of the programmed charge current. In most cases, charge current is reduced due to the constantvoltage loop, meaning that the battery voltage is near the target charge voltage. But if charge current is reduced due to VIN regulation (through EN or VIN-VBAT regulation) or thermal regulation, CHRG remains asserted until only the constant-voltage regulation loop reduces charge current below 10% of the programmed charge current. A high impedance state at the CHRG pin occurs on timer termination, or UVLO or differential UVLO, or when the LTC4079 is disabled by pulling EN low. This output can be used as a logic interface or to light a low power LED. 4079f For more information www.linear.com/LTC4079 13 LTC4079 Applications Information Feedback Divider Selection Using too low or too high values of resistors for the feedback divider can cause small charge voltage errors due to: 1) Finite on-resistance of the internal switch on the FBG pin and 2) leakage on the FB pin. The impact of these two factors on the target battery charge voltage is calculated as follows: RFB1 VCHG = 1.170V • 1+ +RFB1 •(IFB +ILEAK ) RFB2 +RFBG where RFB1 and RFB2 are the top and bottom resistors of the feedback divider, RFBG is the resistance of the internal switch from the FBG pin to GND (160Ω typical) and ILEAK is the parasitic leakage on the FB pin as shown in Figure 6. A graph of IFB vs Temperature is given in the Typical Performance section. According to the above equation, high value feedback resistors minimize the impact of RFBG, while low values minimize the impact of IFB and lLEAK. A Thevenin equivalent resistance of 100k to 500k on the FB node is generally a good compromise in most scenarios. BAT LTC4079 IFB ENABLE FB FBG + RFB1 RFB2 ILEAK BATTERY 4079 F06 PARASITIC LOAD VCHG RFB1 RFB2 TYPICAL ERROR 3.6V 1070k 511k +0.53% 4.1V 422k 169k –0.27% 4.2V 1070k 412k +0.18% 7.2V 1370k 267k –0.42% 8.2V 1070k 178k -0.04% 8.4V 1540k 249k +0.02% 12.3V 1780k 187k -0.02% 12.6V 2550k 261k -0.05% Stability Considerations When the charger is in constant-current mode, the PROG pin impedance forms part of the charger current control loop. The constant-current mode stability is therefore affected by the roll-off frequency of the PROG pin impedance. With minimum capacitance on this pin (less than about 10pF), the charger is stable with a program resistor, RPROG, as high as 60k (ICHG = 5mA); however, any additional capacitance at this pin limits the maximum allowed program resistor. The constant-voltage loop is stable without any compensation as long as a typical low impedance battery is connected to the BAT pin. However, a 1µF capacitor with 1Ω series resistor is recommended when charging high ESR batteries, typically more than 1kΩ. Charging High Resistance Batteries Figure 6. Feedback Divider Considerations For example, for RFB1 = 1.54M and RFB2 = 249k (for battery charge voltage of 8.4V), accounting for RFBG =160Ω lowers the charge voltage by 0.06%, while ILEAK = 10nA raises it by 0.18%. Table 1 lists possible choices of standard 1% resistor values for common battery charge voltages. The Typical Error column gives systematic error due to the granularity in the values of 1% resistors. 14 Table 1. Recommended 1% Resistors for Common Battery Charge Voltages When charging a battery with high internal resistance, the battery voltage can rise quickly, entering constantvoltage mode. If the charge current falls below 1/10th of the programmed charge current, charging may terminate based on C/10 even if a timer capacitor is connected on the TIMER pin. This is because C/10 termination is assumed if the timer pin remains below 0.3V. With only 200nA being sourced from the TIMER pin, a large timer capacitance may limit the TIMER voltage below 0.3V for a short duration at the beginning of a charge cycle. After charging terminates, a recharge cycle would begin if the 4079f For more information www.linear.com/LTC4079 LTC4079 Applications Information internal battery voltage has not been charged above the recharge threshold, determined by ∆VRECHRG and the feedback divider. As shown in Figure 7, this charge/recharge cycle continues until the TIMER pin rises above 0.3V, at which point timer termination is engaged and the battery is charged for the duration set by the timer capacitor. 4.2V VBAT 0.2V/DIV PROG 0.1V/DIV TA = 118°C – (12V-6.6V) • 100mA • 43°C/W = 95°C Increasing Thermal Regulation Current CHRG 5V/DIV 20ms/DIV 4079 F01 Figure 7. Repeated Charge Terminations on Startup Due to High Resistance of the Battery, CTIMER = 82nF, VCHG = 4.2V, ICHG = 10mA and Battery Resistance = 300Ω Power Dissipation and Thermal Regulation The LTC4079 automatically reduces charge current during high power conditions that result in high junction temperature. Therefore, it is not necessary to design the charging system for worst-case power dissipation scenarios. The conditions that cause the LTC4079 to reduce charge current through thermal regulation can be approximated by considering the power dissipated in the IC. Most of the power dissipation is in the charge path. Thus the power dissipation is approximately: PD = (VIN-VBAT) • IBAT The approximate ambient temperature at which the thermal regulation begins to lower the charge current is: TA = 118°C – PD • θJA TA = 118°C – (VIN-VBAT) • IBAT • θJA The reduced charge current at an ambient temperature above the onset of thermal regulation can be calculated as follows: Assuming θJA is 43°C/W the ambient temperature at which the charge current begins to fall due to thermal regulation is: The LTC4079 can be used above 95°C ambient but the charge current will be reduce linearly from the programmed value of 100mA to 0mA as the ambient temperature increases from 95°C to 118°C. TIMER 0.5V/DIV IBAT = Example: Consider an LTC4079 operating from a 12V input source programmed to supply 100mA current to a discharged 2-cell Li-Ion battery with a voltage of 6.6V. In applications with large VIN to VBAT drop, the charge current can be significantly reduced during thermal regulation. One way to increase the thermally regulated charge current is to dissipate some of the power in a resistor in series with the IN pin. This works well when the resistor value is designed to be small enough to avoid pushing the LTC4079 into dropout. Input Capacitor Selection When an input supply is connected to a portable product, the inductance of the cable and the high Q ceramic input capacitor form an L-C resonant circuit. While the LTC4079 is capable of withstanding input voltages as high as 62V, if the input cable does not have adequate mutual inductance or if there is not much impedance in the cable, it is possible for the voltage at the input of LTC4079 to reach as high as 2x the cable input voltage before it settles out. To prevent excessive voltage from damaging the LTC4079 during a hot insertion, it is best to have a low voltage coefficient capacitor at the supply input pin of the LTC4079. Using a tantalum capacitor or an aluminum electrolytic capacitor for input bypassing, or paralleling with a ceramic capacitor will also reduce voltage overshoot during a hot insertion. 118°C – TA ( VIN – VBAT ) • θJA 4079f For more information www.linear.com/LTC4079 15 LTC4079 Applications Information Board Layout Considerations When laying out the printed circuit board, the following checklist should be followed to ensure proper operation of the LTC4079: 1. Connect the exposed pad of the package (Pin 11) directly to a large PC board ground to minimize thermal impedance. Correctly soldered to a 1500mm2 double sided 1oz copper board, the LTC4079 DFN package has a thermal resistance (θJA) of approximately 43°C/W. Failure to make good contact between the exposed pad on the backside of the package and an adequately sized ground plane results in much larger thermal resistance. 3. Minimize the parasitic capacitance and leakage on the FB node for stability and charge voltage accuracy. 4. Minimize the parasitic capacitance and leakage on the TIMER pin for timer accuracy. 5. Minimize the parasitic capacitance on the PROG pin for stable operation. 6. Minimize the parasitic capacitance and leakage on the EN pin if it is connected to a resistor divider from the input supply for input voltage regulation. 2. The top of the feedback divider resistor should be connected as close to the positive battery terminal as possible in order to avoid inaccuracies due to voltage drop in the charge current path. The negative terminal of the battery should be connected to the chip ground plane directly to avoid any ground loop induced charge voltage inaccuracy. 16 4079f For more information www.linear.com/LTC4079 LTC4079 Typical Applications Li-Ion Charger with Timer Termination In the Figure 8 configuration, the input source charges the battery for 5½ hours and also supplies current to the load. The maximum current provided by the charger (on BAT pin) is limited to the charge current of 246mA set by the 1.21k resistor on the PROG pin. A small resistor is used in series with the input supply to reduce VIN-VBAT, and thereby increase the available charge current during thermal regulation. Once the battery is charged, it supplies power to the load until VBAT falls below the recharge threshold, at which point a recharge cycle starts. Li-Ion Charging from a Solar Panel with Differential Voltage Regulation, C/10 Termination Figure 10 shows a simple charging solution from a solar panel. Differential voltage regulation reduces charge current to prevent the panel voltage from drooping below the battery voltage when charging under low light conditions. The LTC4079 does not require a Schottky diode in series with the panel. IN 1µF 24V SUPPLY 25Ω, 2W IN BAT LTC4079 EN 1µF 1.54M – 249k CHRG FBG NTCBIAS CHRG FBG PROG NTCBIAS TIMER NTC TIMER 100nF NTC GND T VCHG = 8.4V ICHG = 246mA 10k 1.21k VCHG = 8.4V ICHG = 246mA GND T + BATTERY PACK 10k + BATTERY PACK 10k TO LOAD FB 10k 1.21k 1µF 1.54M 249k SOLAR PANEL FB PROG EN + TO LOAD BAT LTC4079 4079 F10 Figure 10. Li-Ion Charger with Differential Voltage Regulation 4079 F08 Figure 8. Li-Ion Charger with Timer Termination Supercapacitor Charger from 2-Cell Li-ion 2-Cell NiMH Trickle Charger from Automotive Supply with Timer Termination Figure 9 shows a trickle charger for 2-cell, 2500mAh, AA NiMH battery with timer termination after 31 hours. Charge current drops when the battery voltage reaches 1.65V per cell. 12V CAR BATTERY IN BAT LTC4079 EN 1µF 324k 2-CELL Li-Ion IN + CHRG FBG EN VCHG = 3.3V ICHG = 99mA PROG NTCBIAS TIMER NTC 3.01k + 2500mAh 2-CELL NiMH 4079 F09 TO LOAD BAT LTC4079 FB 178k 560nF TO LOAD Charging terminates when the stacked supercapacitor voltage reaches the set charge voltage. A recharge cycle begins automatically when the supercap voltage falls below the recharge threshold. A resistor divider balancer can optionally be switched in for balancing a stacked supercapacitor during charging. 1.02M VCHG = 5.0V ICHG = 10mA FB 309k CHRG FBG PROG NTCBIAS TIMER NTC 30.1k 1k FDG6308P CSC 0.6F HS206 1k GND GND SUPERCAP BALANCER (OPTIONAL) 4079 F11 Figure 9. NiMH Trickle Charger with Timer Termination Figure 11. Supercap Charger with C/10 Termination 4079f For more information www.linear.com/LTC4079 17 LTC4079 Typical Applications 12V Lead-Acid Charger from Rectified 24V AC In the following charging circuit example, a lead acid battery is trickle charged at a C/10 rate for 15 hours. An NTC thermistor is used to alter the target charge voltage of the lead-acid battery based on the battery temperature. IN 100µF BAT LTC4079 ICHG = 99mA + 1M EN 100k CHRG FB 102k 24V AC T 1µF TO LOAD 12V LEAD-ACID BATTERY 100k FBG PROG NTCBIAS 3.01k NTC TIMER 270nF GND 4079 F12 Figure 12. Lead-Acid Battery Trickle Charger from Rectified 24V AC 18 4079f For more information www.linear.com/LTC4079 LTC4079 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 0.75 ±0.05 0.00 – 0.05 5 1 (DD) DFN REV C 0310 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 4079f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.com/LTC4079 19 LTC4079 Typical Application Energy Harvesting Charger with Buck, Buck-Boost and LDO Supplies 4V TO 19V 3V TO 19V + 1µF 6.3V 10µF 25V 4.7µF 6.3V SOLAR PANEL – VIN(REG) = 15V VIN SW LTC3330 CAP SWB VIN2 VOUT EN 4.7µF FB 102k 3 3 412k 3 CHRG FBG PROG NTCBIAS 4 TIMER NTC GND T + OUT[2:0] BAL LDO[2:0] EH_ON IPK[2:0] PGVOUT UV[3:0]* PGLDO 47µF 6.3V GND VIN3 Li-Ion 10k 1.8V TO 5V 50mA 10mF 2.7V 10mF 2.7V OPTIONAL LDO_OUT LDO_EN 10k 3.01k 22µH SCAP BAT 1.07M SWA PIEZO MIDE V25W 22µH LDO_IN BAT LTC4079 100nF AC2 ICHG = 99mA IN 1.2M AC1 1µF 6.3V 22µF 6.3V 1.2V TO 3.6V 50mA 4079 TA02 * SET VIN(REG) OF LTC4079 ABOVE THE UVLO THRESHOLDS OF LTC3330. E.G. VIN(REG) = 15V FOR UVLO RISING = 14V AND UVLO FALLING = 13V. THIS ENSURES THAT THE BATTERY IS CHARGED ONLY WHEN EXCESS POWER IS AVAILABLE FROM THE INPUT SOURCE. Related Parts PART NUMBER DESCRIPTION COMMENTS LTC4078 Dual Input Li-Ion Battery Charger with Overvoltage Protection Overvoltage Protection Up to 22V. Charge Current 100mA to 950mA. LTC4065/LTC4065A 250mA Li-Ion Battery Charger 3.75V to 5.5V Input. Up to 250mA Programmable Charge Current. Internal 4.5Hrs Safety Timer. LTC4054L-4.2 150mA Linear Li-Ion Battery Charger 4.25V to 6.5V Input. 10mA to 150mA Programmable Charge Current. LTC4070 Li-Ion/Polymer Shunt Battery Charger IQ = 0.5µA, Pin Selectable Battery Charge Voltage: 4.0V, 4.1V or 4.2V LTC4071 Li-Ion/Polymer Shunt Battery Charger with Low Battery Pack Protection Version of LTC4070 Disconnect LT®3650 High Voltage 2A Monolithic Li-Ion Battery Charger 4.75V to 32V Input. Buck Architecture. LTC4121/ LTC4121-4.2 High Voltage 400mA Synchronous Step-Down Battery Charger 4.4V to 40V Input. Low Dropout Buck Architecture with MPPT. 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC4079 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC4079 4079f LT 0914 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2014