LTC3355 20V 1A Buck DC/DC with Integrated SCAP Charger and Backup Regulator FEATURES DESCRIPTION VIN Voltage Range: 3V to 20V nn V OUT Voltage Range: 2.7V to 5V nn 1A Current Mode Buck Main Regulator nn 5A Boost Backup Regulator Powered from Single Supercapacitor nn Boost Regulator Operates Down to 0.5V for Maximum Utilization of Supercapacitor Energy nn Programmable Supercapacitor Charge Current to 1A with Overvoltage Protection nn Charger Supports Single Cell CC/CV Battery Charging nn Programmable V Current Limit IN nn Programmable Boost Current Limit nn V Power Fail Indicator IN nn V CAP Power Good Indicator nn V OUT Power On Reset Output nn Compact 20-Lead 4mm × 4mm QFN Package The LTC®3355 is a complete input power interrupt ridethrough DC/DC system. The part charges a supercapacitor while delivering load current to VOUT, and uses energy from the supercapacitor to provide continuous VOUT backup power when VIN power is lost. The LTC3355 contains a nonsynchronous constant frequency current mode monolithic 1A buck switching regulator to provide a 2.7V to 5V regulated output voltage from an input supply of up to 20V. nn A 1A programmable CC/CV linear charger charges the supercapacitor from VOUT. When the VIN supply drops below the PFI threshold, the devices’s constant frequency nonsynchronous current mode 5A boost switching regulator delivers power from the supercapacitor to VOUT. A thermal regulation loop maximizes charge current while limiting the die temperature to 110°C. The IC has boost, charger and VIN programmable current limits. The LTC3355 is available in a 20-lead 4mm × 4mm QFN surface mount package. APPLICATIONS nn nn Ride-Through “Dying Gasp” Supplies Power Meters/Industrial Alarms/Solid State Drives L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Supercapacitor Charger and Ride-Through Power Supply 10µF 10µF 1µF 5 VIN SW1 6 VINM5 VINS 4 PFO 2.49M BUCK VOUT 1 PFI 200k 15 402k 100k 10 PFOB VCAP 13 RSTB SW2 BOOST 14 16 3.3µH 17 8 EN_CHG 665k 2.4V SCAP 1F TO 50F CFB 11 3 MODE INTVCC 18 1µF ICHG IBSTPK 12 20 60.4k 10 154k VIN 8 6 VOUT 4 VCAP 2 0 332k VCBST 19 CAPACITOR = 3F IVOUT = 0.125A 12 VOUT 4V 47µF 1A (MAX) FB 2 LTC3355 9 CPGOOD 14 7 4.7pF 1A Backup Operation 6.8µH VOLTAGE (V) VIN 12V 0.091Ω 0 5 10 15 20 TIME (SECONDS) 3355 TA01b 220pF 200k 3355 TA01a 3355fb For more information www.linear.com/LTC3355 1 LTC3355 PIN CONFIGURATION VIN, VINS, VINM5.........................................................22V VIN ±VINS................................................................... 0.1V VSW1........................................................... –0.4V to 22V VSW2............................................................. –0.4V to 6V VOUT, INTVCC, PFOB, RSTB, CPGOOD, VCAP.............................................. –0.3V to 6V PFI, EN_CHG, MODE, FB............................... –0.3V to 6V CFB.............................................–0.3V to INTVCC + 0.3V ICPGOOD, IPFOB, IRSTB.................................................1mA Operating Junction Temperature Range (Notes 2, 3)............................................. –40°C to 125°C Storage Temperature Range................... –65°C to 150°C SW2 SW2 INTVCC VCBST IBSTPK TOP VIEW 20 19 18 17 16 PFI 1 15 VOUT FB 2 14 VCAP 21 GND MODE 3 VINS 4 13 RSTB 12 ICHG 11 CFB 8 9 10 PFOB 7 CPGOOD 6 EN_CHG VIN 5 SW1 (Note 1) VINM5 ABSOLUTE MAXIMUM RATINGS UF PACKAGE 20-LEAD (4mm × 4mm) PLASTIC QFN TJMAX = 125°C, θJA = 47°C/W EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3355EUF#PBF LTC3355EUF#TRPBF 3355 20-Lead (4mm × 4mm) Plastic QFN –40°C to 125°C LTC3355IUF#PBF LTC3355IUF#TRPBF 3355 20-Lead (4mm × 4mm) Plastic QFN –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. 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 3355fb For more information www.linear.com/LTC3355 LTC3355 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. (Note 2) SYMBOL PARAMETER VIN VIN Operating Voltage Range IQ VIN Quiescent Current VOUT Quiescent Current VFB FB Reference Voltage FB Line Regulation IFB FB Input Bias Current VVOUT VOUT Voltage Range CONDITIONS Charger Off, Not Switching, VOUT = 3.3V, No Load, In Regulation, Supercapacitor Charged MIN l 3 l l 60 110 l 0.775 VOUT = 2.7V to 5V TYP 120 265 MAX V 215 420 µA µA 0.825 V 0.1 l UNITS 20 %/V –20 20 nA 2.7 5 V VOUT Overvoltage Limit Buck or Boost Enabled 5.4 5.65 5.95 V VOUT Undervoltage Lockout Threshold Boost Enabled 1.8 2 2.2 V VIN > 7V VINM5 VIN-VINM5 VINTVCC INTVCC Internal Voltage Power Supply 2 5 V VVCAP VCAP Voltage Range 0 5 V IVCAP VCAP Current Accuracy –10 10 % VCAP Programmable Current Range EN_CHG = High 0.1 1 A VICHG ICHG Reference Voltage EN_CHG = High 0.78 0.82 V RICHG ICHG Set Resistor Range 60.4 604 kΩ ICFB CFB Input Bias Current 20 nA VCFB CFB Reference Voltage EN_CHG = High 0.82 V CFB Hysteresis EN_CHG = High CFB Overvoltage Hysteretic Comparator Switch Point CFB Rising CFB Falling IICL VIN Input Current Limit VINS-VIN to Disable Charger VINS-VIN to Disable Buck VINS(CMI) VINS Common Mode Range fSW Switching Frequency FB ≥ 0.5V Foldback Frequency (Buck Only) FB ≤ 0.3V VPFI 4.65 VCAP = 2V, VOUT = 3.3V, IVCAP = 1A EN_CHG = High –20 0.78 30 37 42 0.75 V V 43 50 3.0 PFI Falling Threshold mV VCFB+0.035 VCFB 20 1 1.25 100 l 0.775 PFI Hysteresis IPFI 0.8 V 0.8 –20 V MHz kHz 0.825 17 PFI Leakage Current mV mV V mV 20 nA 2 A A 1A Buck Regulator ISW1 SW1 Peak Current tSS Soft-Start Time DC Max Maximum Duty Cycle RPMOS PMOS On-Resistance ILEAKP PMOS Leakage Current PWM Mode (Note 5) Burst Mode® (Note 5) 1.3 1.65 0.5 1000 FB = 0V 100 % 0.5 Buck Disabled µs –2 1 Ω 2 µA 3355fb For more information www.linear.com/LTC3355 3 LTC3355 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 80 160 280 µA 4.5 5 1.5 5.5 A A 5A Boost Regulator IVOUT VOUT Quiescent Current VOUT = 3.3V, No Load, In Regulation, No Switching, Burst Mode ISW2 SW2 Peak Current RIBSTPK = 200k, PWM Mode RIBSTPK = 200k, Burst Mode RNMOS NMOS On-Resistance ILEAKN NMOS Leakage Current DC Max Boost Maximum Duty Cycle VSBOOST Boost Input Supply Voltage Range l 70 Boost Disabled –5 88 92 0.75 mΩ 5 µA 98 % 5 V Boost Minimum Input Supply VOUT(MAX) = 4V 0.5 V AV Boost Error Amplifier Voltage Gain (Note 5) gm Boost Error Amplifier Transconductance VIBSTPK IBSTPK Reference Voltage 0.775 0.825 V RIBSTPK IBSTPK Set Resistor Range 200 1000 kΩ 850 V/V 27 μS Logic (MODE, EN_CHG, CPGOOD, RSTB, PFOB) VIL Input Low Logic Voltage MODE, EN_CHG VIH Input High Logic Voltage MODE, EN_CHG 1.2 0.4 -1 V V IIL, IIH Input Low/High Current MODE, EN_CHG 1 µA VOL Output Logic Low Voltage PFOB, CPGOOD, RSTB; Sink 100µA 50 mV IOH Logic High Leakage Current PFOB, CPGOOD, RSTB; 5V 1 µA CPGOOD Rising Threshold VCAP as a % of Final Target CPGOOD Hysteresis ∆VCAP as a % of Final Value RSTB Falling Threshold VOUT as a % of Final Target RSTB Hysteresis ∆VOUT as a % of Final Value RSTB Delay 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: The LTC3355 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3355E is guaranteed to meet specifications from 0°C to 85°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 LTC3355I is guaranteed over the –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. 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 • θJA) where θJA = 47°C/W for the UF package. 4 90 92.5 95 2.5 90 92.5 % % 95 % 2.5 % 250 ms Note 3: The LTC3355 has a thermal regulation loop that limits the maximum junction temperature to 110°C by limiting the charger current. Note 4: The current limit features of this part are intended to protect the IC from short-term or intermittent fault conditions. Continuous operation above the maximum specified pin current may result in device degradation or failure. Note 5: Guaranteed by design and/or correlation to static test. Note 6: The LTC3355 has a thermal shutdown that will shut down the part when the die temperature reaches 155°C. 3355fb For more information www.linear.com/LTC3355 LTC3355 TYPICAL PERFORMANCE CHARACTERISTICS Boost Efficiency 100 90 90 80 80 70 70 60 50 40 VOUT = 4V MODE = HIGH VIN = 18V VIN = 12V VIN = 6V 30 20 10 0 1.00 60 50 40 VCAP = 2.4V MODE = HIGH VOUT = 3.3V VOUT = 4V VOUT = 5V 30 20 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 0 Maximum Buck Load Current 1.20 0 0.8 0.6 0.4 0.2 2.75 3.25 1200 600 1150 400 300 200 4.6 1000 900 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 FB (V) 3355 G07 75 50 25 TEMPERATURE (°C) 0 100 125 3355 G06 6.3 VOUT = 3.3V L = 6.8µH INPUT CURRENT SET RESISTOR = 0.05Ω Typical Minimum Buck Input Voltage (VOUT = 5V) VOUT = 5V L = 6.8µH INPUT CURRENT SET RESISTOR = 0.05Ω 6.1 5.9 4.2 5.7 4.0 3.8 3.6 3.0 20 950 800 –50 –25 Typical Minimum Buck Input Voltage (VOUT = 3.3V) 5.5 5.3 5.1 4.9 3.2 100 18 1000 0 100 200 300 400 500 600 700 800 900 1000 SWITCH CURRENT (mA) 3.4 200 16 1050 VIN (V) INPUT VOLTAGE (V) FREQUENCY (kHz) 800 300 12 14 VIN (V) 850 4.4 400 10 3355 G05 Buck Frequency vs Feedback Voltage 500 8 900 3355 G04 600 6 1100 500 0 3.75 700 4 Oscillator Frequency vs Temperature 100 2.25 VOUT = 4V L = 6.8µH INPUT CURRENT SET RESISTOR = 0Ω 3355 G03 700 VCAP (V) 0 0 FREQUENCY (kHz) SW VOLTAGE DROP (mV) LOAD CURRENT (A) 1.0 1.75 0.40 Buck Switch Voltage Drop VOUT = 4V 1.25 0.60 3355 G02 Maximum Boost Load Current 0 0.75 0.80 0.20 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 3355 G01 1.2 LOAD CURRENT (A) 100 EFFICIENCY (%) EFFICIENCY (%) Buck Efficiency TA = 25°C unless otherwise noted 4.7 1 10 100 VOUT LOAD CURRENT (mA) 1000 3355 G08 4.5 1 10 100 VOUT LOAD CURRENT (mA) 1000 3355 G09 3355fb For more information www.linear.com/LTC3355 5 LTC3355 TYPICAL PERFORMANCE CHARACTERISTICS Buck Switch Current Limit vs Temperature 5.2 1.8 5.1 VOUT = 3.3V 4.9 4.8 VOUT = 5V 4.7 VIN = 12V 4.6 3.5 VOUT = 5V 1.7 VOUT = 4V CURRENT (A) CURRENT (A) 5.0 VOUT vs VINS-VIN 4.0 3.0 VOUT = 4V 1.6 VOUT = 3.3V VOUT (V) Boost Switch Current Limit vs Temperature TA = 25°C unless otherwise noted 1.0 1.5 100 1.4 –50 125 –25 50 25 0 75 TEMPERATURE (°C) 100 600 400 200 800 250 RICHG = 60.4k 600 400 200 0 30 32 34 36 38 40 42 44 46 48 50 VINS-VIN (mV) 300 VIN = 7V VOUT = 3.3V 1000 CHARGE CURRENT (mA) CHARGE CURRENT (mA) 800 0 0 –50 –25 100 200 300 400 500 600 700 800 VOUT-VCAP (mV) 4.045 4.040 4.040 4.035 4.035 4.030 4.030 VOUT (V) 4.025 4.020 PWM MODE VIN = 18V VIN = 12V VIN = 6V 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 3355 G16 50 25 75 0 TEMPERATURE (°C) 125 Boost Load Regulation 4.050 PWM MODE 4.045 IOUT = 50mA 4.040 4.035 IOUT = 500mA 4.025 4.020 4.030 4.025 4.020 4.015 4.015 4.010 4.010 4.005 4.005 4.000 100 3355 G15 VOUT (V) 4.045 VOUT (V) 4.050 0 100 Buck Line Regulation Buck Load Regulation 4.005 150 3355 G14 4.050 4.010 200 50 RICHG = 604k 3355 G13 4.015 3355 G12 Charge Current vs Junction Temperature Charge Current vs VOUT-VCAP 1200 VIN = 7V VOUT = 3.3V 1000 40 41 42 43 44 45 46 47 48 49 50 VINS-VIN (mV) 3355 G11 Charge Current vs VINS-VIN 1200 0 125 CHARGE CURRENT (mA) 75 50 25 TEMPERATURE (°C) 0 3355 G10 6 VIN = 7V VOUT = 3.3V IVOUT = 200mA 0.5 4.4 –50 –25 4.000 2.0 1.5 4.5 0 2.5 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 VIN (V) 3355 G17 4.000 0.001 PWM MODE VCAP = 3.6V VCAP = 2.4V VCAP = 1.5V 0.01 0.1 LOAD CURRENT (A) 1 3355 G18 3355fb For more information www.linear.com/LTC3355 LTC3355 TYPICAL PERFORMANCE CHARACTERISTICS Logic Input Threshold vs Temperature (EN_CHG, MODE) Boost Line Regulation 4.045 PWM MODE 950 4.040 805 900 4.035 50mA 4.030 THRESHOLD (mV) VOUT (V) PFI Threshold vs Temperature 810 1000 500mA 4.025 4.020 4.015 THRESHOLD (mV) 4.050 TA = 25°C unless otherwise noted 850 800 750 795 700 4.010 800 650 4.005 4.000 0.75 1.25 1.75 2.25 2.75 VCAP (V) 3.75 3.25 600 –50 –25 75 50 25 TEMPERATURE (°C) 0 100 3355 G19 790 –50 125 75 0 25 50 TEMPERATURE (°C) Buck Load Step Burst Mode Operation VOUT 100mV/DIV AC-COUPLED VOUT 100mV/DIV AC-COUPLED LOAD CURRENT 500mA/DIV LOAD CURRENT 500mA/DIV LOAD CURRENT 500mA/DIV 3355 G23 50µs/DIV LOAD STEP = 100mA to 600mA VIN = 12V VOUT = 4V Boost Load Step Burst Mode Operation 125 Boost Load Step PWM VOUT 100mV/DIV AC-COUPLED 3355 G22 100 3355 G21 3355 G20 Buck Load Step PWM 50µs/DIV LOAD STEP = 100mA to 600mA VIN = 12V VOUT = 4V –25 3355 G24 50µs/DIV LOAD STEP = 100mA to 600mA VCAP = 2.4V VOUT = 4V Boost Error Amplifier Voltage Gain vs Temperature Boost Error Amplifier Transconductance vs Temperature 30 750 TRANSCONDUCTANCE (µS) 29 VOUT 100mV/DIV AC-COUPLED GAIN (V/V) 700 LOAD STEP 500mA/DIV 50µs/DIV LOAD STEP = 100mA to 600mA VCAP = 2.4V VOUT = 4V 650 3355 G25 600 28 27 26 25 24 23 22 21 550 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 3355 G30 20 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 3355 G27 3355fb For more information www.linear.com/LTC3355 7 LTC3355 PIN FUNCTIONS PFI (Pin 1): Input to the Power-Fail Comparator. The input voltage below which the PFOB pin indicates a power-fail condition can be programmed by connecting this pin to an external resistor divider between VIN and ground. FB (Pin 2): Sets the VOUT voltage for both the buck and boost voltage control loops via an external resistor divider. The reference voltage is 0.8V. MODE (Pin 3): This pin sets the buck and boost switching modes. A low is PWM mode, a high is Burst Mode operation. VINS (Pin 4): Input Current Limit Sense Voltage Pin. Connect a sense resistor from VINS to VIN. Must be locally bypassed with a low ESR ceramic capacitor. Connect to VIN if input current limit is not needed. VIN (Pin 5): Input Power Pin Supplies Current to the Internal Regulator and Buck Power Switch. Must be locally bypassed with a low ESR ceramic capacitor. VINM5 (Pin 6): This pin is used to filter an internal supply regulator which generates a voltage of VIN – 4.65V. Connect a 1µF ceramic capacitor from VINM5 to VIN. SW1 (Pin 7): Buck Output of the Internal Power Switch. Connect this pin to the catch diode and inductor. Minimize trace area at this pin to reduce EMI. EN_CHG (Pin 8): A high on this pin enables the supercapacitor charger. CPGOOD (Pin 9): Open-drain output is high impedance when the VCAP voltage is higher than 92.5% of the programmed voltage. PFOB (Pin 10): Open Drain of the Power-Fail Comparator. Pulled low and enables the boost converter when the PFI input has determined that the input supply has dropped out. 8 CFB (Pin 11): This pin is used to program the VCAP voltage via an external resistor divider. The reference voltage is 0.8V. ICHG (Pin 12): This pin programs the VCAP charge current by connecting a resistor to ground. RSTB (Pin 13): Open-drain reset output is high impedance when the VOUT voltage is higher than 92.5% of the programmed regulation voltage. VCAP (Pin 14): This pin is the constant current, constant voltage linear charger output and connects to the supercapacitor. VOUT (Pin 15): The Output Voltage Supply. The buck powers this supply from VIN when the input voltage is present and the boost powers this supply from VCAP when the input voltage has dropped out. SW2 (Pin 16, 17): Boost Output of the Internal Power Switch. Connect these pins to the rectifier diode and inductor. Minimize trace area at these pins to reduce EMI. INTVCC (Pin 18): This pin is used to filter an internal supply. Connect a 1µF ceramic capacitor from this pin to ground. INTVCC is 2.5V during start-up until VOUT exceeds 2.5V then INTVCC follows VOUT. VCBST (Pin 19): This pin is the output of the boost internal error amplifier. The voltage on this pin controls the peak switch current for the boost regulator. Connect an RC series network from this pin to ground to compensate the boost control loop. IBSTPK (Pin 20): This pin programs the boost peak current limit by connecting a resistor to ground. GND (Exposed Pad Pin 21): Ground. The exposed pad must be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the part to achieve optimum thermal conduction. 3355fb For more information www.linear.com/LTC3355 LTC3355 SIMPLIFIED BLOCK DIAGRAM VOUT COUT R1 CVINM5 15 6 VOUT VIN + – OVP UVLO START-UP VIN INTVCC 2 VINM5 CAP REG 0.8V 3 FB R2 5 VIN MODE ENB CLK OVP EN 1A LOGIC SW1 VC + – 0.8V R7 1 FB PFI R8 7 D1 SS D2 PFOB ILIM + – 13 ENB 0.8V RSTB OVP ENB MODE FB EN CPGOOD + – 0.74V + – 9 CLK FB 0.8V D INTVCC 0.8V 0.74V CFB 18 LOGIC EN_CHG 11 8 IOUT IREF VCAP 14 R4 0.8V BOOST VINS SW2 MAIN INPUT CIN SUPPLY 4 16 17 V TO I L2 VCBST ICHG 12 R3 C1 5A BILIM VREF EN VIN SW2 – + CC/CV CHARGER CLK 250ms DELAY UVLO + – 10 CVIN RSENSE BUCK + – VLOGIC L1 19 R5 IBSTPK 20 RC SCAP R6 CC 3355 F01 Figure 1. LTC3355 Block Diagram 3355fb For more information www.linear.com/LTC3355 9 LTC3355 OPERATION The LTC3355 is a 1A buck regulator with a built-in backup boost converter to allow temporary backup, or ride-through, of VOUT during a sudden loss of VIN power. The device contains all functions necessary to provide seamless charging of a supercapacitor (or other storage element), monitoring of VIN, VOUT and VCAP, and automatic switch-over to backup power. When the buck is disabled an internal circuit blocks reverse current between VOUT and VIN. Start-Up When the part first starts up the only voltage available is VIN since VOUT and VCAP are at zero volts. An internal 2.5V regulator powers INTVCC from VIN during start-up. INTVCC powers all of the low voltage circuits. The buck regulator is enabled and will drive VOUT positive through an inductor until the feedback voltage at FB equals 0.8V. When VOUT exceeds 2.5V INTVCC will exactly track VOUT and the current for the internal low voltage circuits will now be supplied from VOUT instead of VIN. A 1µF external ceramic capacitor is required for INTVCC to filter internal switching noise. Buck Switching Regulator The LTC3355 uses a 1MHz constant frequency peak current mode nonsynchronous monolithic buck regulator with internal slope compensation to control the voltage at VOUT when VIN is available. An error amplifier compares the divided output voltage at FB with a reference voltage of 0.8V and adjusts the peak inductor current accordingly. Burst Mode operation can also be selected to optimize efficiency at low load currents via the MODE pin. The buck is in PWM mode when the MODE pin is low and in Burst Mode operation when the MODE pin is high. The buck is internally compensated and can operate over an input voltage range of 3V to 20V. An internal soft-start ramp limits inrush current during start-up. Frequency foldback protection helps to prevent inductor current runaway during start-up or short-circuit conditions. Input Current Limit The (optional) input current limit is programmed via an external sense resistor connected between VINS and VIN. As the input current limit is reached the charge current 10 will be reduced. If the charge current has been reduced to zero and the input current continues to increase the buck regulator current drive capability will be reduced. The maximum sense voltage is 50mV. The input current limit includes the LTC3355 quiescent current for high accuracy over a wide current range. Boost Switching Regulator When VIN is not available, a monolithic 1MHz constant frequency peak current mode boost regulator with internal slope compensation is enabled and the buck regulator is disabled via the PFI pin. The boost regulator uses the voltage stored at VCAP as an input supply and regulates the VOUT voltage. An error amplifier compares the divided output voltage at FB with a reference voltage of 0.8V and adjusts the peak inductor current accordingly. The IBSTPK pin sets the peak boost current over a range of 1A to 5A allowing for lower current backup applications. The boost switching regulator is compensated by adding a series RC network from the VCBST pin to ground. The boost regulator can operate over an input voltage range (VCAP) of 0.5V to 5V. The boost regulator uses the same feedback pin and error amplifier as the buck and regulates to the same VOUT voltage. The MODE pin is used to control the boost switching regulator mode. The boost is in PWM mode when the MODE pin is low and in Burst Mode operation when the MODE pin is high. In PWM mode as the load current is decreased, the switch turns on for a shorter period each cycle. If the load current is further decreased, the boost converter will skip cycles to maintain output voltage regulation. Charger The supercapacitor is charged by an internal 1A constant current/constant voltage linear charger that supplies current from VOUT to VCAP. The charger will be enabled when VIN is above a programmable voltage via the PFI pin, when the EN_CHG pin is high and when VOUT is in regulation. The value of the resistor on the ICHG pin determines the charger current. An internal amplifier servos the ICHG voltage to 0.8V to create the reference current for the charge. The VCAP voltage is divided down by an external resistor divider that is connected to the CFB pin. A hysteretic comparator compares the CFB voltage to a For more information www.linear.com/LTC3355 3355fb LTC3355 OPERATION 0.8V reference voltage and turns the charger off when these voltages are the same. The VCAP voltage represents the fully charged supercapacitor voltage available to supply the boost regulator when VIN has dropped out. When CFB decays to 30mV below the CFB reference voltage the charger will be turned on. The LTC3355 includes a softstart circuit to minimize the inrush current at the start of charge. When the charger is enabled, the charge current ramps from zero to full-scale over a period of approximately 1ms. This has the effect of minimizing the transient load current on VOUT. The VCAP output also has an overvoltage protection circuit which monitors the CFB voltage. If the CFB voltage increases above the CFB reference voltage by 35mV a hysteretic comparator switches in an 8k resistor from VCAP to ground. This will bleed any excess charge from the supercapacitor. When the CFB voltage decays to the CFB reference voltage the comparator will remove the 8k bleed resistor. Excess charge can come from leakage currents associated with the boost rectifier diode. VCAP Status Monitor The CPGOOD pin is a 5V open-drain output. An internal comparator determines when VCAP has reached 92.5% of the programmed regulation voltage which then switches the CPGOOD pin high. CPGOOD is normally connected to a low voltage supply (VOUT) via an external pull-up resistor. Thermal Regulation As the die temperature increases due to internal power dissipation, a thermal regulator will limit the die temperature to 110°C by reducing the charger current. The thermal regulation protects the LTC3355 from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without the risk of damaging the LTC3355. Another feature is that the charge current can be set according to typical, rather than worst-case ambient temperatures for a given application with the assurance that the charger will automatically reduce the charge current in worst-case conditions. Thermal Shutdown VIN Status Monitor The PFI input always monitors the VIN voltage and determines when VIN is in dropout. VIN is divided down by an external resistor divider and this voltage is then compared to a reference voltage of 0.8V. If the PFI voltage is below the reference voltage the buck regulator and the charger will be disabled and the boost regulator will be enabled. The PFOB pin is a 5V open-drain output. This pin is driven internally by the PFI comparator. When the PFI comparator determines that VIN has dropped out the PFOB output switches low. PFOB is normally connected to a low voltage supply, via an external pull-up resistor. The pull-up resistor for this output can be connected to VOUT if another supply is not available. The LTC3355 includes a thermal shutdown circuit in addition to the thermal regulator. If for any reason, the die temperature exceeds 155°C, the entire part shuts down. The part will resume normal operation once the temperature drops about 15°C, to approximately 140°C. VOUT Overvoltage, Undervoltage Lockout The LTC3355 includes an overvoltage protection circuit to ensure that VOUT does not exceed 5.65V (nominal). An internal resistor divider from VOUT is connected to an amplifier that will regulate VOUT as the overvoltage limit is reached. The LTC3355 includes undervoltage lockout which disables the boost when VOUT is < 2V typical. VOUT Status Monitor The RSTB pin is a 5V open-drain output. An internal comparator determines when VOUT has reached 92.5% of the programmed regulation voltage which then switches the RSTB pin high. RSTB is normally connected to a low voltage supply (VOUT) via an external pull-up resistor. 3355fb For more information www.linear.com/LTC3355 11 LTC3355 APPLICATIONS INFORMATION FB Resistor Network IBSTPK Set Resistor The VOUT voltage is programmed with a resistor divider between the VOUT pin and the FB pin. Choose the resistor values according to: The boost peak current limit is set by connecting a resistor from IBSTPK to ground. Choose the resistor value according to: ⎛V ⎞ R1= R2 ⎜ OUT – 1⎟ ⎝ 0.8V ⎠ Boost Peak Current Limit (Amps) = 1E6 R6 Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain output voltage accuracy. Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain boost peak current accuracy. CFB Resistor Network PFI Resistor Network The VCAP voltage is programmed with a resistor divider between the VCAP pin and the CFB pin. Choose the resistor values according to: The VIN dropout voltage is programmed with a resistor divider between the VIN pin and PFI pin. Choose the resistor values according to: ⎛V ⎞ R3 = R4 ⎜ CAP – 1⎟ ⎝ 0.8V ⎠ ⎛ V ⎞ R7 = R8 ⎜ IN – 1⎟ ⎝ 0.8V ⎠ Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain the capacitor float voltage accuracy. Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain the PFI threshold voltage accuracy. ICHG Set Resistor The VIN voltage must be greater than the buck dropout voltage (100% duty cycle) when the PFI level is reached to ensure that VOUT stays in regulation. The charge current at VCAP is set by connecting a resistor from ICHG to ground. Choose the resistor value according to: 60400 Charger Current (Amps) = R5 Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain charge current accuracy. 12 Input Voltage Range The minimum input voltage is determined by the dropout of the buck regulator. The dropout is dependent on the maximum load current and the buck internal switch resistance. The minimum input voltage due to buck dropout is: VIN(MIN) = VOUT + (ISW(PEAK) • 1Ω) 3355fb For more information www.linear.com/LTC3355 LTC3355 APPLICATIONS INFORMATION Buck Inductor L1 Selection and Maximum Output Current A good starting point for the inductor value is: L = ( VOUT + VD ) • 1.8 fSW where fSW is the switching frequency in MHz, VOUT is the buck output voltage, VD is the catch diode drop (~0.5V) and L is the inductor value in µH. The inductor’s RMS current rating must be greater than the maximum load current and its saturation current should be 30% higher. To keep the efficiency high, the series resistance (DCR) should be less than 0.1Ω, and the core material should be intended for high frequency applications. Table 1 lists several inductor vendors. For robust operation and fault conditions (start-up or short-circuit) and high input voltage (>15V), the saturation current should be chosen high enough to ensure that the inductor peak current does not exceed 2.2A. The current in the inductor is a triangle wave with an average value equal to the load current. The peak inductor and switch current is: ISW(PEAK) =IL(PEAK) =IOUT(MAX) + When the switch is off, the potential across the inductor is the output voltage plus the catch diode drop. This gives the peak-to-peak ripple current in the inductor: ΔIL 2 where IL(PEAK) is the peak inductor current, IOUT(MAX) is the maximum output load current and ∆IL is the inductor ripple current. The LTC3355 limits the switch current in order to protect the part. Therefore, the maximum output current that the buck will deliver depends on the switch current limit, the inductor value, the input and output voltages. ΔIL = (1–DC) • VOUT + VD L • fSW where fSW is the switching frequency of the buck, DC is the duty cycle and L is the value of the inductor. To maintain output regulation, the inductor peak current must be less than the buck switch current limit. The maximum output current is: IOUT(MAX) =ILIM – ΔIL 2 Choosing an inductor value so that the ripple current is small will allow a maximum output current near the switch current limit. Table 1. Inductor Vendors VENDOR URL PART SERIES TYPE Murata www.murata.com LQH5BPB Shielded TDK www.tdk.com LTF5022T Shielded Toko www.toko.com FDS50xx Shielded Coilcraft www.coilcraft.com XAL40xx, LPS40xx Shielded Sumida www.sumida.com DCRH5D, CDRH6D Shielded Viashay www.vishay.com IHLP2020 Shielded One approach to choosing the inductor is to start with the simple rule above, look at the available inductors, and choose one to meet cost or space goals. Then use the equations to check that the buck will be able to deliver the required output current. These equations assume that the inductor current is continuous. Discontinuous operation occurs when IOUT is less than ∆IL/2. 3355fb For more information www.linear.com/LTC3355 13 LTC3355 APPLICATIONS INFORMATION Buck Input Capacitor Bypass VIN and VINS with a ceramic capacitor of X7R or X5R type. A 10µF to 22µF ceramic capacitor is adequate for bypassing. Note that a larger VINS bypass capacitor may be required if the input power supply source impedance is high or there is significant inductance due to long wires or cables. This can be provided with a lower performance electrolytic capacitor in parallel with the ceramic capacitor. Buck regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitors are required to reduce the resulting voltage ripple at VINS and VIN and to force this very high frequency switching into a tight local loop, minimizing EMI. The capacitors must be placed close to the LTC3355 pins. Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the buck regulator to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the buck regulator control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: ⎛ 100 ⎞ COUT = fSW ⎜ ⎝ VOUT ⎟⎠ where fSW is in MHz and COUT is the recommended output capacitance in µF. Use X5R or X7R types. This choice will provide low output ripple and good transient response. When choosing a capacitor look carefully through the data sheet to find out what the actual capacitance is under 14 operating conditions (applied voltage and temperature). A physically larger capacitor, or one with a higher voltage rating, may be required. High performance tantalum or electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one that is intended for use in switching regulators. The ESR should be specified by the supplier, and should be 0.05Ω or less. Table 2 lists several capacitor vendors. Table 2. Capacitor Vendors VENDOR URL PART SERIES COMMANDS Panasonic www.panasonic.com Ceramic, Polymer, Tantalum EEF Series, POSCAP Kemet www.kemet.com Ceramic, Tantalum T494, T495 Murata www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden www.taiyo-yuden.com Ceramic Buck Catch Diode Selection The catch diode (D1 in the Block Diagram) conducts current only during the switch-off time. The average forward current in normal operation can be calculated from: ID(AVG) = IOUT(1 – DC) where DC is the duty cycle. The only reason to consider a diode with a larger current rating than necessary for nominal operation is for the case of shorted or overloaded output conditions. For the worst case of shorted output the diode average current will then increase to a value that depends on the switch current limit. If operating at high temperatures select a Schottky diode with low reverse leakage current. 3355fb For more information www.linear.com/LTC3355 LTC3355 APPLICATIONS INFORMATION Audible Noise Table 3. Schottky Diode Vendors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can sometimes cause problems when used with switching regulators. Both the buck and boost can run in Burst Mode operation and the switching frequency will depend on the load current which at very light loads can excite the ceramic capacitors at audio frequencies, generating audible noise. Since the buck and boost operate at lower current limits in Burst Mode operation, the noise is typically very quiet. Use a high performance tantalum or electrolytic at the output if the noise level is unacceptable. Buck Soft-Start When the buck is enabled soft-start is engaged. Soft-start reduces the inrush current by taking more time to reach the final output voltage. This is achieved by limiting the buck output current over a 1ms period. Boost Rectifier Diode A Schottky rectifier diode (D2 in the Block Diagram) is recommended for the boost rectifier diode. The diode should have low forward drop at the peak operating current, low reverse current and fast reverse recovery times. The current rating should take into account power dissipation as well as output current requirements. The diode current rating should be equal to or greater than the average forward current which is normally equal to the output current. The reverse breakdown voltage should be greater than the VOUT voltage plus the peak ringing voltage that is generated at the SW2 pin. Generally higher reverse breakdown diodes will have lower reverse currents. Refer to Table 3 for Schottky diode vendors. PART NUMBER VR (V) IAVE (A) VF AT 1A VF AT 2A (mV) (mV) IR AT 5V 85°C (µA) Diodes Inc. B130 30 1 B230 30 2 30 1 60 2.1 460 20 430 100 Rohm RSX201VA-30 360 600 Vishay VS-20MQ060 Boost Inductor L2 Selection and Maximum Output Current The boost inductor L2 should be 3.3µH to ensure fast transfer of power from the buck to the boost after a VIN power outage. Refer to Table 1 for inductor vendors. Boost Frequency Compensation The LTC3355 boost switching regulator uses current mode control to regulate VOUT. This simplifies loop compensation and ceramic output capacitors can be used. The boost regulator does not require the ESR of the output capacitor for stability. Frequency compensation is provided by the components connected to the VCBST pin. Generally a capacitor (CC) and resistor (RC) in series to ground are used as shown in the Block Diagram. Loop compensation determines the stability and transient performance. Optimizing the design of the compensation network depends on the application and type of output capacitor. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance. Stability should then be checked across all 3355fb For more information www.linear.com/LTC3355 15 LTC3355 APPLICATIONS INFORMATION Low Ripple Burst Mode Operation operating conditions, including load current, input voltage and temperature. Figure 2 shows an equivalent circuit for the boost regulator control loop. The error amplifier is a transconductance amplifier with a finite output impedance. The power section consisting of a modulator, power switch and inductor, is modeled as a transconductance amplifier generating an output current proportional to the voltage at the VCBST pin. Note that the output capacitor integrates this current, and that the capacitor on the VCBST pin (CC) integrates the error amplifier output current, resulting in two poles in the loop. In most cases a zero is required and comes from either the ESR of the output capacitor or from a resistor RC in series with CC. This simple model works well as long as the inductor value is not too high and the loop crossover frequency is much lower than the switching frequency. A phase lead capacitor across the feedback divider may improve the transient response. A small capacitor from VCBST to ground may have to be added if phase lead is used. To enhance efficiency at light loads the buck and boost regulator can run in low ripple Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. Setting the MODE pin high sets both the buck and boost into Burst Mode operation. During Burst Mode operation, the enabled regulator delivers single cycle bursts of current to the output capacitor followed by sleep periods where the power is delivered to the load by the output capacitor. Since the power to the output is delivered with single, low current pulses, the output ripple is kept below 15mV for typical applications. As the load current falls towards a no-load condition, the percentage of time in sleep mode increases and the average input current is greatly reduced resulting in high efficiency even at very light loads. At higher load currents the regulators will seamlessly transition into PWM mode. BOOST LOOP SW2 CURRENT MODE POWER STAGE OUTPUT gm = 4mhos R1 FB – gm = 27μS + 32M VCBST CF CPL 0.8V ESR COUT R2 COUT CERAMIC POLYMER, TANTALUM OR ELECTROLYTIC GND RC CC 3355 F02 Figure 2. Model for Boost Loop Response 16 3355fb For more information www.linear.com/LTC3355 LTC3355 APPLICATIONS INFORMATION PCB Layout High Temperature Considerations For proper operation and minimum EMI, care must be taken during printed circuit board layout. Large switched currents flow in the VIN, SW1, SW2 and paddle ground pins, the buck catch diode, boost rectifier diode and the input capacitor. The loop formed by these components should be as small as possible. These components, along with the inductors and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. All connections to GND should be made at a common star ground point or directly to a local, unbroken ground plane below these components. SW1 and SW2 nodes should be laid out carefully to avoid interference. Keep the FB, PFI, ICHG, IBSTPK, VCBST and CFB nodes small so that the ground traces will shield them from the switching nodes. To keep thermal resistance low, extend the ground plane as much as possible and add thermal vias under and near the paddle. Keep in mind that the thermal design must keep the junctions of the LTC3355 below the specified absolute maximum temperature. The PCB must provide heat sinking to keep the LTC3355 cool. The exposed pad on the bottom of the package may be soldered to a copper area which should be tied to large copper layers below with thermal vias; these layers will spread the heat dissipated by the LTC3355. Place additional vias to reduce thermal resistance further. With these steps, the thermal resistance from the die (or junction) to ambient can be reduced to θJA = 47°C/W or less. With 100 LFPM airflow, this resistance can fall by another 25%. The LTC3355 has two thermal circuits. The first thermal circuit is operational when the buck and charger are enabled. If the die temperature exceeds 110°C the charge current will be reduced. When the LTC3355 is in boost mode the high current thermal shutdown will turn the boost off when the die temperature reaches 155°C. The high temperature shutdown is active in all modes of operation. TYPICAL APPLICATIONS Tantalum Capacitor Charger and Ride-Through Backup Supply VIN 12V RS 1Ω CIN 10µF CVIN 10µF R7 2.49M R8 200k CCAP 1µF 5 VIN SW1 L1 6.8µH 7 D1 6 VINM5 VINS 4 PFO BUCK VOUT 15 R1 523k FB 2 1 PFI D2 LTC3355 10 PFOB VCAP 13 RSTB SW2 9 CPGOOD BOOST 14 16 R3 1.05M CFB 11 3 MODE INTVCC 18 C1 1µF VCBST 19 ICHG IBSTPK 12 20 R5 604k R6 1M R2 100k L2 3.3µH 17 8 EN_CHG VOUT 5V 47µF 10mA RC 154k CC 220pF + 5V 1000µF 6.3V TANT R4 200k 3355 TA02 3355fb For more information www.linear.com/LTC3355 17 LTC3355 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UF Package 20-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1710 Rev A) 0.70 ±0.05 4.50 ±0.05 3.10 ±0.05 2.00 REF 2.45 ±0.05 2.45 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 0.75 ±0.05 R = 0.05 TYP R = 0.115 TYP 19 20 0.40 ±0.10 PIN 1 TOP MARK (NOTE 6) 4.00 ±0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER BOTTOM VIEW—EXPOSED PAD 1 2.00 REF 2.45 ±0.10 2 2.45 ±0.10 (UF20) QFN 01-07 REV A 0.200 REF 0.00 – 0.05 0.25 ±0.05 0.50 BSC NOTE: 1. DRAWING IS PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-1)—TO BE APPROVED 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 18 3355fb For more information www.linear.com/LTC3355 LTC3355 REVISION HISTORY REV DATE DESCRIPTION A 08/14 Modified VOUT Overvoltage, Undervoltage Lockout section 11 Modified Input Voltage Range equation 12 Modified ICHG Set Resistor section 12 Modified IBSTPK Set Resistor section 12 B 4/15 PAGE NUMBER Updated conditions for ISW1, ISW2 and IVOUT 3 and 4 Updated units for Boost Error Amplifier Transconductance 4 Updated units for Boost Error Amplifier Transconductance vs Temperature Graph 7 Update TSTB (Pin 13), CPGOOD (Pin 9), PFOB (Pin 10) 8 Updated Block Diagram 9 Updated CFB Resistor Network and PFI Resistor Network 12 Updated Table 2: Capacitor Vendors 14 Updated Boost Error Amplifier Transconductance unit in Figure 2 16 3355fb 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/LTC3355 19 LTC3355 TYPICAL APPLICATION NiMH Trickle Charger and Ride-Through Backup Supply VIN 5V RS* 0.27Ω CIN 10µF CCAP 1µF CVIN* 10µF R7 931k 5 VIN SW1 7 D1 6 VINM5 VINS 4 PFO BUCK VOUT 15 D2 LTC3355 VCAP 14 10 PFOB MICROPROCESSOR SW2 13 RSTB 24 HOURS 9 CPGOOD BOOST R3 499k CFB 11 3 MODE INTVCC 18 ICHG 12 C1 1µF VCBST 19 IBSTPK 20 R5 604k R6 909k R2 100k 200Ω L2 3.3µH 17 8 EN_CHG *OPTIONAL 16 VOUT 3.3V 47µF 50mA (MAX) R1 316k FB 2 1 PFI R8 200k L1 4.7µH RC 154k CC 220pF + 1.4V NiMH 2000mAhr R4 499k 3355 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3225/ LTC3225-1 150mA Supercapacitor Charger Low Noise, Constant Frequency Charging of Two Series Supercapacitors. Automatic Cell Balancing Prevents Capacitor Overvoltage During Charging. Programmable Charge Current (Up to 150mA). 2mm × 3mm DFN Package LTC3226 2-Cell Supercapacitor Charger with Backup PowerPath™ Controller 1×/2× Multimode Charge Pump Supercapacitor Charger Ideal Diode Main PowerPath™ Controller, Internal 2A LDO Back-Up Supply, 16-Lead (3mm × 3mm) QFN Package LT3485 Photoflash Capacitor Chargers with Output Voltage Monitor and Integrated IGBT Drive Integrated IGBT Driver; Voltage Output Monitor; Uses Small Transformers: 5.8mm × 5.8mm × 3mm. Operates from Two AA Batteries, Single Cell Li-Ion or Any Supply from 1.8V Up to 10V. No Output Voltage Divider Needed; No External Schottky Diode Required. Charges Any Size Photoflash Capacitor; 10-Lead (3mm × 3mm) DFN Package LTC3625/ LTC3625-1 1A High Efficiency 2-Cell Supercapacitor Charger with Automatic Cell Balancing High Efficiency Step-Up/Step-Down Charging of Two Series Supercapacitors. Automatic Cell Balancing Prevents Capacitor Overvoltage During Charging. Programmable Charging Current Up to 500mA (Single Inductor), 1A (Dual Inductor). VIN = 2.7V to 5.5V, Low No-Load Quiescent Current: 23µA. 12-lead 3mm × 4mm DFN Package LT®3750 Capacitor Charger Controller Charges Any Size Capacitor; Easily Adjustable Output Voltage. Drives High Current NMOS FETs; Primary-Side Sense—No Output Voltage Divider Necessary. Wide Input Range: 3V to 24V; Drives Gate to VCC – 2V. 10-Lead MS Package LT3751 High Voltage Capacitor Charger Controller with Regulation Charges Any Size Capacitor; Low Noise Output in Voltage Regulation Mode. Stable Operation Under a No-Load Condition; Integrated 2A MOSFET Gate Driver with Rail-to-Rail Operation for VCC ≤ 8V. Wide Input VCC Voltage Range (5V to 24V). 20-Pin QFN 4mm × 5mm and 20-Lead TSSOP Packages LTC4425 Supercapacitor Charger with Current Limited Ideal Diode Constant-Current/Constant-Voltage Linear Charger for 2-cell Series Supercapacitor Stack. VIN: Li-Ion/Polymer Battery, a USB Port, or a 2.7V to 5.5V Current-Limited Supply. 2A Charge Current, Auto Cell Balancing, 20µA Quiescent Current, Shutdown Current <2µA. Low Profile 12-Pin 3mm × 3mm DFN or a 12-Lead MSOP Package 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC3355 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3355 3355fb LT 0415 REV B • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2014