LTC3245 Wide VIN Range, Low Noise, 250mA Buck-Boost Charge Pump Description Features 2.7V to 38V VIN Range IQ = 18µA Operating; 4μA in Shutdown 12V to 5V Efficiency = 81% Multimode Operation (2:1, 1:1, 1:2) with Automatic Mode Switching n Low Noise, Constant Frequency Operation n Pin Selectable Burst Mode ® Operation nV OUT: Fixed 3.3V, 5V or Adjustable (2.5V to 5V) nI OUT Up to 250mA n Overtemperature and Short-Circuit Protection n Operating Junction Temperature: 150°C Maximum n Thermally Enhanced 12-Pin MSOP and Low Profile 12-Pin (3mm × 4mm) DFN Packages The LTC®3245 is a switched capacitor buck-boost DC/DC converter that produces a regulated output (3.3V, 5V or adjustable) from a 2.7V to 38V input. The device uses switched capacitor fractional conversion to maintain regulation over a wide range of input voltage. Internal circuitry automatically selects the conversion ratio to optimize efficiency as input voltage and load conditions vary. No inductors are required. Applications Low operating current (20μA with no load, 4μA in shutdown) and low external parts count (three small ceramic capacitors) make the LTC3245 ideally suited for low power, space constrained automotive/industrial applications. The device is short-circuit and overtemperature protected, and is available in thermally enhanced 12-pin MSOP and low profile 3mm × 4mm 12-pin DFN packages. n n n n Automotive ECU/CAN Transceiver Supplies Industrial Housekeeping Supplies n Low Power 12V to 5V Conversion n n L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. The unique constant frequency architecture provides a lower noise output than conventional charge pump regulators. To optimize efficiency at the expense of slightly higher output ripple, the device has pin selectable Burst Mode operation. Typical Application Efficient Regulated 5V Output 5VOUT Efficiency vs Output Current 90 1µF 400 VIN = 12V 80 350 EFFICIENCY C– LTC3245 VIN VIN = 2.7V TO 38V 1µF SEL2 BURST SEL1 VOUT OUTS/ADJ PGOOD GND 500k VOUT = 5V IOUT UP TO 250mA 10µF 300 60 250 50 200 40 150 PLOSS 30 PLOSS (mW) C+ EFFICIENCY (%) 70 100 20 50 3245 TA01a 10 0.1 1 10 IOUT (mA) 100 0 1000 3245 TA01b 3245f For more information www.linear.com/LTC3245 1 LTC3245 Absolute Maximum Ratings (Note 1) VIN, SEL1, SEL2, BURST............................. –0.3V to 38V VOUT, OUTS/ADJ, PGOOD............................. –0.3V to 6V IPGOOD.......................................................................2mA VOUT Short-Circuit Duration.............................. Indefinite Operating Junction Temperature Range (Notes 2, 3) (E-/I-Grade)......................................... –40°C to 125°C (H-Grade)............................................ –40°C to 150°C (MP-Grade)......................................... –55°C to 150°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only) ........................................................... 300°C Pin Configuration TOP VIEW VIN 1 12 GND VIN 2 11 C– VIN 3 BURST 4 SEL1 SEL2 13 GND TOP VIEW VIN VIN VIN BURST SEL1 SEL2 10 VOUT 9 C+ 5 8 PGOOD 6 7 OUTS/ADJ 1 2 3 4 5 6 13 GND 12 11 10 9 8 7 GND C– VOUT C+ PGOOD OUTS/ADJ MSE PACKAGE 12-LEAD PLASTIC MSOP DE PACKAGE 12-LEAD (3mm × 4mm) PLASTIC DFN TJMAX = 150°C, θJA = 40°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB GND TJMAX = 150°C, θJA = 43°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB GND Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3245EDE#PBF LTC3245EDE#TRPBF 3245 12-Lead (3mm × 4mm) Plastic DFN –40°C to 125°C LTC3245IDE#PBF LTC3245IDE#TRPBF 3245 12-Lead (3mm × 4mm) Plastic DFN –40°C to 125°C LTC3245EMSE#PBF LTC3245EMSE#TRPBF 3245 12-Lead Plastic MSOP –40°C to 125°C LTC3245IMSE#PBF LTC3245IMSE#TRPBF 3245 12-Lead Plastic MSOP –40°C to 125°C LTC3245HMSE#PBF LTC3245HMSE#TRPBF 3245 12-Lead Plastic MSOP –40°C to 150°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. 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/ Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C, (Note 2). VIN = 12V, VOUT = 5V, CFLY = 1µF unless otherwise noted. SYMBOL PARAMETER VIN Operating Input Voltage Range VUVLO VIN Undervoltage Lockout Threshold CONDITIONS MIN l VIN Rising VIN Falling l TYP 2.7 2.4 2.2 MAX UNITS 38 V 2.7 V V 3245f 2 For more information www.linear.com/LTC3245 LTC3245 Electrical Characteristics The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C, (Note 2). VIN = 12V, VOUT = 5V, CFLY = 1µF unless otherwise noted. SYMBOL PARAMETER CONDITIONS IVIN VIN Quiescent Current SEL1 = SEL2 = 0V VOUT Enabled, BURST = 0V VOUT Enabled, BURST = VIN MIN TYP MAX Shutdown, VOUT = 0V CP Enabled, Output in Regulation CP Enabled, Output in Regulation VOUT5_BM Fixed 5V Burst Mode Output Regulation (OUTS/ADJ Connected to VOUT, BURST = 0V, SEL2 = VIN, SEL1 = VIN) (Note 5) 5V ≤ VIN < 38V, IOUT ≤ 250mA 4V ≤ VIN < 5V, IOUT ≤ 150mA 3.3V ≤ VIN < 4V, IOUT ≤ 75mA 3V ≤ VIN < 3.3V, IOUT ≤ 45mA l l l l VOUT5_LN Fixed 5V Low Noise Output Regulation (OUTS/ADJ Connected to VOUT, BURST = VIN, SEL2 = VIN, SEL1 = VIN) (Note 5) 5V ≤ VIN < 38V, IOUT ≤ 200mA 4V ≤ VIN < 5V, IOUT ≤ 120mA 3.3V ≤ VIN < 4V, IOUT ≤ 60mA 3V ≤ VIN < 3.3V, IOUT ≤ 35mA VOUT33_BM Fixed 3.3V Burst Mode Output Regulation (OUTS/ADJ Connected to VOUT, BURST = 0V, SEL2 = VIN, SEL1 = VIN) (Note 5) VOUT33_LN 4 18 20 8 35 40 µA µA µA 4.8 4.8 4.8 4.8 5.2 5.2 5.2 5.2 V V V V l l l l 4.8 4.8 4.8 4.8 5.2 5.2 5.2 5.2 V V V V 5V ≤ VIN < 38V, IOUT ≤ 250mA 4V ≤ VIN < 5V, IOUT ≤ 175mA 3.3V ≤ VIN < 4V, IOUT ≤ 110mA 2.7V ≤ VIN < 3.3V, IOUT ≤ 60mA l l l l 3.17 3.17 3.17 3.17 3.43 3.43 3.43 3.43 V V V V Fixed 3.3V Low Noise Output Regulation (OUTS/ADJ Connected to VOUT, BURST = VIN, SEL2 = VIN, SEL1 = VIN) (Note 5) 5V ≤ VIN < 38V, IOUT ≤ 220mA 4V ≤ VIN < 5V, IOUT ≤ 140mA 3.3V ≤ VIN < 4V, IOUT ≤ 90mA 2.7V ≤ VIN < 3.3V, IOUT ≤ 50mA l l l l 3.17 3.17 3.17 3.17 3.43 3.43 3.43 3.43 V V V V VADJ OUTS/ADJ Reference Voltage (Note 4) SEL2 = 0V, SEL1 = VIN, IOUT = 0mA l 1.176 1.224 V 1.200 RCL Load Regulation (Referred to ADJ) SEL2 = 0V, SEL1 = VIN 0.2 VPG_RISE PGOOD Rising Threshold VOUT% of Final Regulation Voltage 95 VPG_FALL PGOOD Falling Threshold VOUT% of Final Regulation Voltage VPG_LOW PGOOD Output Low Voltage IPGOOD = 0.2mA IPG_HIGH PGOOD Output High Leakage VPGOOD = 5V VLOW BURST, SEL1, SEL2 Input Voltage 88 mV/mA 98 91 % % 0.1 0.4 V –1 0 1 µA 0.4 0.9 l l UNITS V VHIGH BURST, SEL1, SEL2 input Voltage ILOW BURST, SEL1, SEL2 Input Current VPIN = 0V –1 IHIGH BURST, SEL1, SEL2 Input Current VPIN = 38V 0.5 ISHORT_CKT IVOUT Short-Circuit Current VOUT = GND 900 mA ROUT Charge Pump Output Impedance 2:1 Step-Down Mode 1:1 Step-Down Mode 1:2 Step-Up Mode (VIN = 3.3V) 3 3.5 14 Ω Ω Ω fOSC Oscillator Frequency l l 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. This IC has overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperatures will exceed 150°C when overtemperature is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 2: The LTC3245E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3245I is guaranteed over the –40°C to 125°C operating junction temperature range. The LTC3245H is guaranteed over the –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes; operating lifetime is derated for junction temperatures greater than 125°C. Note that the maximum ambient 1.2 2 V 0 1 µA 1 3 450 500 µA kHz temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. Note 3: 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 (in °C/W) is the package thermal impedance. Note 4: VOUT programming range is from 2.5V to 5V. See the Programming the Output Voltage section for more detail. Note 5: The maximum operating junction temperature of 150°C must be followed. Certain combinations of input voltage and output current will cause the junction temperature to exceed 150°C and must be avoided. See Thermal Management section for information on calculating maximum operating conditions. 3245f For more information www.linear.com/LTC3245 3 LTC3245 Typical Performance Characteristics Input Operating Current vs Input Voltage Input Shutdown Current vs Input Voltage 500 475 40 16 35 14 30 12 ISD (µA) VOUT = 5V 20 VOUT = 3.3V 15 10 6 4 5 2 0 0 5 10 15 20 25 VIN (V) 125°C 8 10 30 35 0 40 450 150°C 25°C –55°C 0 5 10 15 20 25 VIN (V) 30 5.15 5.15 5.10 5.10 4.80 IOUT = 150mA IOUT = 0mA 5.00 IOUT = 150mA IOUT = 250mA 4.90 IOUT = 250mA 4.80 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) 3.50 3.45 3.45 3.40 3.40 VOUT (V) VOUT (V) 3.35 3.20 IOUT = 150mA 3.10 3.30 3245 G07 LOW NOISE 60 50 40 30 0 0.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) 1 10 IOUT (mA) 100 1000 3245 G06 3.3V Fixed Output Efficiency vs Output Current 100 90 3.10 VIN = 9V 80 IOUT = 0mA IOUT = 150mA IOUT = 250mA 70 Burst Mode OPERATION 60 LOW NOISE 50 40 30 20 3.15 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) Burst Mode OPERATION 10 3.25 3.20 3.15 VIN = 12V 70 3.3V Fixed Output Voltage vs Input Voltage (Low Noise Operation) 3.50 IOUT = 250mA 150 3245 G05 3.3V Fixed Output Voltage vs Input Voltage (Burst Mode Operation) 3.25 120 20 4.85 3.30 0 30 60 90 TEMPERATURE (°C) 5V Fixed Efficiency vs Output Current 80 4.95 IOUT = 0mA –30 3245 G03 90 3245 G04 3.35 300 –60 40 100 5.05 VOUT (V) VOUT (V) IOUT = 0mA 5.00 4.85 35 3245 G02 5.20 4.90 375 5V Fixed Output Voltage vs Input Voltage (Low Noise Operation) 5.20 4.95 400 325 3245 G01 5V Fixed Output Voltage vs Input Voltage (Burst Mode Operation) 5.05 425 350 EFFICIENCY (%) ICC (µA) 20 18 fOSC (kHz) BURST = 0V Oscillator Frequency vs Temperature EFFICIENCY (%) 50 45 25 TA = 25°C, unless otherwise noted. 10 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) 0 0.1 1 10 IOUT (mA) 100 1000 3245 G09 3245 G08 3245f 4 For more information www.linear.com/LTC3245 LTC3245 Typical Performance Characteristics TA = 25°C, unless otherwise noted. 3.3V Fixed Output Voltage vs Falling Input Voltage (Burst Mode Operation) 5V Fixed Output Voltage vs Falling Input Voltage (Burst Mode Operation) ADJ Regulation Voltage vs Temperature 5.100 3.400 1.220 5.075 3.375 1.215 IOUT = 1mA 5.050 3.350 5.025 1.205 4.975 IOUT = 250mA 4.950 3.300 3.275 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) 3.200 800 35 25 10 Burst Mode OPERATION 25 20 15 0 30 60 90 TEMPERATURE (°C) 120 60 90 0 30 TEMPERATURE (°C) –30 120 3245 G13 0 150 Operating Mode Transition Voltage vs Input Voltage 12 IOUT = 150mA 11 BUCK 10 9 9 4 RISING 3 FALLING RISING 7 6 RISING 5 4 BOOST 3 1 0 2.5 3245 G16 3 FALLING 3 2 3.5 4 VOUT (V) 4.5 5 3245 G17 BUCK LDO RISING 4 BOOST FALLING 1 0 2.5 5 7 8 9 10 11 12 13 14 VIN (V) FALLING 5 2 4.5 6 RISING 6 1 0 2.5 3.5 4 VOUT (V) 5 7 2 3 4 8 LDO FALLING VIN (V) VIN (V) 5 8 LDO FALLING 6 3 12 IOUT = 250mA 11 BUCK 10 RISING 2 Operating Mode Transition Voltage vs Input Voltage 9 8 3.3V Burst Mode OPERATION 3245 G15 10 7 3.3V LOW NOISE 300 3245 G14 Operating Mode Transition Voltage vs Input Voltage IOUT = 1mA 400 100 0 –60 150 500 200 Burst Mode OPERATION 5 –30 150 600 LOW NOISE 10 5 0 –60 120 5V LOW NOISE 5V Burst Mode 700 OPERATION VIN = 2.7V IOUT (mA) ROUT (Ω) 15 VIN = 3.3V 30 VIN = 3.3V LOW NOISE 0 30 60 90 TEMPERATURE (°C) Output Current vs Input Voltage (VOUT 5% Below Regulation) 40 VIN = 2.7V 20 –30 3245 G12 3.3V Output Impedance vs Temperature (Boost Mode) 30 ROUT (Ω) 1.180 –60 3245 G11 5V Output Impedance vs Temperature (Boost Mode) VIN (V) 1.185 2 3 4 5 6 7 8 9 10 11 12 13 14 15 VIN (V) 3245 G10 12 11 1.190 –55°C 25°C 125°C 3.225 1.200 1.195 IOUT = 250mA 3.250 –55°C 25°C 125°C 4.925 ADJ (V) VOUT (V) VOUT (V) 3.325 5.000 4.900 1.210 IOUT = 1mA 3 3.5 4 VOUT (V) BOOST 4.5 5 3245 G18 3245f For more information www.linear.com/LTC3245 5 LTC3245 Typical Performance Characteristics 3.3V Output Transient Response 5V Output Transient Response Burst Mode OPERATION AC 50mV/DIV Burst Mode OPERATION AC 50mV/DIV LOW NOISE AC 50mV/DIV LOW NOISE AC 50mV/DIV 200mA IOUT 5mA TA = 25°C, unless otherwise noted. 3245 G19 VIN = 12V VOUT = 5V 150mA IOUT 5mA 3245 G20 VIN = 12V VOUT = 3.3V Pin Functions VIN (Pins 1, 2, 3): Power Input Pins. Input voltage for both charge pump and IC control circuitry. The VIN pin operates from 2.7V to 38V. All VIN pins should be connected together at pins. BURST (Pin 4): Burst Mode Logic Input. A logic high on the BURST pin operates the charge pump in low noise constant frequency. A logic low will operates the charge pump in Burst Mode operation for higher efficiency at low output currents. The BURST pin has a 1μA (typical) pull-down current to ground and can tolerate 38V inputs allowing it to be pin-strapped to VIN. SEL1 (Pin 5): Logic Input Pin. See Table 1 for SEL1/SEL2 operating logic. The SEL1 pin has a 1μA (typical) pull-down current to ground and can tolerate 38V inputs allowing it to be pin-strapped to VIN. SEL2 (Pin 6): Logic Input Pin. See Table 1 for SEL1/SEL2 operating logic. The SEL2 pin has a 1μA (typical) pull-down current to ground and can tolerate 38V inputs allowing it to be pin-strapped to VIN. Table 1: VOUT Operating Modes SEL2 SEL1 MODE LOW LOW Shutdown LOW HIGH Adjustable VOUT HIGH LOW Fixed 5V HIGH HIGH Fixed 3.3V OUTS/ADJ (Pin 7): VOUT Sense / Adjust Input Pin. This pin acts as VOUT sense (OUTS) for 5V or 3.3V fixed outputs and adjust (ADJ) for adjustable output through external feedback. The ADJ pin servos to 1.2V when the device is enabled in adjustable mode. (OUTS / ADJ are selected by SEL1 and SEL2 pins; See Table 1) PGOOD (Pin 8): Power Good Open Drain Logic Output. The PGOOD pin goes high impedance when VOUT is about 6% of its final operating voltage. PGOOD is intended to be pulled up to VOUT or other low voltage supply with an external resistor. C+ (Pin 9): Flying Capacitor Positive Connection. VOUT (Pin 10): Charge Pump Output Voltage. If VIN drops below its UVLO threshold, the connection from VIN becomes high impedance with no reverse leakage from VOUT to VIN. VOUT regulation only takes place above the UVLO threshold. VOUT can be programmed to regulate from 2.5V to 5V. C – (Pin 11): Flying Capacitor Negative Connection. GND (Pin 12, Exposed Pad Pin 13): Ground. The exposed package pad is ground and must be soldered to the PC board ground plane for proper functionality and for rated thermal performance. 3245f 6 For more information www.linear.com/LTC3245 LTC3245 Simplified Block Diagram C+ C– CHARGE PUMP VIN VOUT EN BURST BURST DETECTED OVERTEMPERATURE OUTS/ADJ ADJ 3.3V MUX – + PGOOD 1.2V – 1.14V 5V SD + SEL1 SEL2 GND 3245 BD 3245f For more information www.linear.com/LTC3245 7 LTC3245 Applications Information General Operation The LTC3245 uses switched capacitor based DC/DC conversion to provide the efficiency advantages associated with inductor based circuits as well as the cost and simplicity advantages of a linear regulator. The LTC3245’s unique constant frequency architecture provides a low noise regulated output as well as lower input noise than conventional switch capacitor charge pump regulators. The LTC3245 uses an internal switch network and fractional conversion ratios to achieve high efficiency and regulation over widely varying VIN and output load conditions. Internal control circuitry selects the appropriate conversion ratio based on VIN and load conditions. The device has three possible conversion modes: 2:1 step-down mode, 1:1 step-down mode and 1:2 step-up mode. Only one external flying capacitor is needed to operate in all three modes. 2:1 mode is chosen when VIN is greater than two times the desired VOUT. 1:1 mode is chosen when VIN falls between two times VOUT and VOUT. 1:2 mode is chosen when VIN falls below the desired VOUT. An internal load current sense circuit controls the switch point of the conversion ratio as needed to maintain output regulation over all load conditions. Regulation is achieved by sensing the output voltage and regulating the amount of charge transferred per cycle. This method of regulation provides much lower input and output ripple than that of conventional switched capacitor charge pumps. The constant frequency charge transfer also makes additional output or input filtering much less demanding than conventional switched capacitor charge pumps. The LTC3245 has a Burst Mode operation pin that allows the user to trade output ripple for better efficiency/lower quiescent current. The device has two SEL pins that select the output regulation (fixed 5V, fixed 3.3V or adjustable) as well as shutdown. The device includes soft-start function to limit in-rush current at startup. The device is also short-circuit and overtemperature protected. VOUT Regulation and Mode Selection As shown in the Simplified Block Diagram, the device uses a control loop to adjust the strength of the charge pump to match the current required at the output. The error signal of this loop is stored directly on the output charge storage capacitor. As the load on VOUT increases, VOUT will drop slightly increasing the amount of charge transferred until the output current matches the output load. This method of regulation applies regardless of the conversion ratio. The optimal conversion ratio is chosen based on VIN, VOUT and output load conditions. Two internal comparators are used to select the default conversion ratio. Each comparator has an adjustable offset built in that increases (decreases) in proportion to the increasing (decreasing) output load current. In this manner, the conversion ratio switch point is optimized to provide peak efficiency over all supply and load conditions while maintaining regulation. Each comparator also has built-in hysteresis to reduce the tendency of oscillating between modes when a transition point is reached. Low Noise vs Burst Mode Operation Burst Mode operation is selected by driving the BURST pin low. In Burst Mode operation the LTC3245 delivers a minimum amount of charge each cycle forcing VOUT above regulation at light output loads. When the LTC3245 detects that VOUT is above regulation the device stops charge transfer and goes into a low current sleep state. During this sleep state, the output load is supplied by the output capacitor. The device will remain in the sleep state until the output drops enough to require another burst of charge. Burst Mode operation allows the LTC3245 to achieve high efficiency even at light loads. If the output load exceeds the minimum charge transferred per cycle, then the device will operate continuously to maintain regulation. Unlike traditional charge pumps who’s burst current is dependant on many factors (i.e., supply, switch strength, capacitor selection, etc.), the LTC3245 burst current is regulated which helps to keep burst output ripple voltage relatively constant and is typically 50mV for COUT = 10μF. Driving the BURST pin high puts the LTC3245 in low noise operation. In low noise operation the minimum amount of charge delivered each cycle and sleep hysteresis are reduced compared to Burst Mode operation. This results in lower burst output ripple (typically 20mV for COUT = 10µF) and will transition to constant frequency operation at lighter loads. 3245f 8 For more information www.linear.com/LTC3245 LTC3245 Applications Information Short-Circuit/Thermal Protection The LTC3245 has built-in short-circuit current limiting as well as overtemperature protection. During short-circuit conditions the device will automatically limit the output current. The LTC3245 has thermal protection that will shut down the device if the junction temperature exceeds the overtemperature threshold (typically 175°C). Thermal shutdown is included to protect the IC in cases of excessively high ambient temperatures, or in cases of excessive power dissipation inside the IC. The charge transfer will reactivate once the junction temperature drops back to approximately 165°C. When the thermal protection is active, the junction temperature is beyond the specified operating range. Thermal protection is intended for momentary overload conditions outside normal operation. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Driving both SEL1 and SEL2 low shuts down the device causing VOUT to go high impedance. LTC3245 VOUT VOUT FIXED 3.3V OR FIXED 5V OUTS COUT GND 3245 F01 Figure 1: Fixed Output Operation Adjustable output programming is accomplished by connecting ADJ (OUTS/ADJ pin) to a resistor divider between VOUT and GND as shown in Figure 2. Adjustable operation is enabled by driving SEL1 high and SEL2 low. Driving both SEL1 and SEL2 low shuts down the device causing VOUT to go high impedance. LTC3245 VOUT VOUT RA Soft-Start Operation ADJ To prevent excessive current flow at VIN during start-up, the LTC3245 has built-in soft-start circuitry. Soft-start is achieved by increasing the amount of current available to the output charge storage capacitor linearly over a period of approximately 500μs. Soft-start is enabled whenever the device is brought out of shutdown, and is disabled shortly after regulation is achieved. Programming the Output Voltage (OUTS/ADJ Pin) The LTC3245 output voltage programming is very flexible offering a fixed 3.3V output, fixed 5V output as well as adjustable output that is programmed through an external resistor divider. The desired output regulation method is selected through the SET pins. For a fixed output simply short OUTS (OUTS/ADJ pin) to VOUT as shown in Figure 1. Fixed 3.3V operation is enabled by driving both SEL1 and SEL2 pins high, while fixed 5V operating is selected by driving SEL2 high with SEL1 low. RB ( R 1.2V 1+ A RB ) COUT GND 3245 F02 Figure 2: Adjustable Output Operation Using adjustable operation the output (VOUT) can be programmed to regulate from 2.5V to 5V. The limited programming range provides the required VOUT operating voltage without overstressing the VOUT pin. The desired adjustable output voltage is programmed by solving the following equation for RA and RB: R A VOUT = –1 R 1.2V B Select a value for RB in the range of 1k to 1M and solve for RA. Note that the resistor divider current adds to the total no load operating current. Thus a larger value for RB will result in lower operating current. 3245f For more information www.linear.com/LTC3245 9 LTC3245 Applications Information 2:1 Step-Down Charge Pump Operation 1:2 Step-Up Charge Pump Operation When the input supply is greater than about two times the output voltage, the LTC3245 will operate in 2:1 stepdown mode. Charge transfer happens in two phases. On the first phase the flying capacitor (CFLY ) is connected between VIN and VOUT. On this phase CFLY is charged up and current is delivered to VOUT. On the second phase the flying capacitor (CFLY ) is connected between VOUT and GND. The charge stored on CFLY during the first phase is transferred to VOUT on the second phase. When in 2:1 step-down mode the input current will be approximately half of the total output current. The efficiency (η) and chip power dissipation (PD) in 2:1 are approximately: When the input supply is less than the output voltage the LTC3245 will operate in 1:2 step-up mode. Charge transfer happens in two phases. On the first phase the flying capacitor (CFLY ) is connected between VIN and GND. On this phase CFLY is charged up. On the second phase the flying capacitor (CFLY ) is connected between VIN and VOUT and the charge stored on CFLY during the first phase is transferred to VOUT. When in 1:2 step-up mode the input current will be approximately twice the total output current. Thus efficiency (η) and chip power dissipation (PD) in 1:2 are approximately: η≅ POUT VOUT • I OUT 2VOUT = = PIN V • 1 I VIN IN 2 OUT V PD = IN – VOUT I OUT 2 η≅ 1:1 Step-Down Charge Pump Operation When the input supply is less than about two times the output voltage but more than the programmed output voltage, the LTC3245 will operate in 1:1 step-down mode. This method of regulation is very similar to a linear regulator. Charge is delivered directly from VIN to VOUT through most of the oscillator period. The charge transfer is briefly interrupted at the end of the period. The interruption in charge transfer improves stability and transient response. When in 1:1 step-down mode the input current will be approximately equal to the total output current. Thus efficiency (η) and chip power dissipation (PD) in 1:1 are approximately: η≅ POUT VOUT • I OUT VOUT = = PIN VIN • I OUT VIN PD = ( VIN– VOUT ) I OUT POUT VOUT • I OUT VOUT = = PIN VIN • 2 I OUT 2VIN PD = ( 2VIN– VOUT ) I OUT Due to the limited drive in 1:2 step-up mode the device always operates in Burst Mode operation when operating at this conversion ratio. This is done to delay the onset of dropout at the expense of more output ripple. PGOOD Output Operation The LTC3245 includes an open-drain power good (PGOOD) output pin. If the chip is in shutdown or under UVLO conditions (VIN < 2.2V typical), PGOOD is low impedance to ground. PGOOD becomes high impedance when VOUT rises to 95% (typical) of its regulation voltage. PGOOD stays high impedance until VOUT is shut down or drops below the PGOOD threshold (91% typical) due to an overload condition. A pull-up resistor can be inserted between PGOOD and a low voltage positive logic supply (such as VOUT) to signal a valid power good condition. The use of a large pull-up resistor on PGOOD and a capacitor placed between PGOOD and GND can be used to delay the PGOOD signal if desired. VOUT Ripple and Capacitor Selection The type and value of capacitors used with the LTC3245 determine several important parameters such as regulator control loop stability, output ripple and charge pump 3245f 10 For more information www.linear.com/LTC3245 LTC3245 Applications Information strength. The value of COUT directly controls the amount of output ripple for a given load current when operating in constant frequency mode. Increasing the size of COUT will reduce the output ripple. To reduce output noise and ripple, it is suggested that a low ESR (equivalent series resistance < 0.1Ω) ceramic capacitor (10μF or greater) be used for COUT. Tantalum and aluminum capacitors can be used in parallel with a ceramic capacitor to increase the total capacitance but are not recommended to be used alone because of their high ESR. Both the style and value of COUT can significantly affect the stability of the LTC3245. As shown in the Block Diagram, the device uses a control loop to adjust the strength of the charge pump to match the current required at the output. The error signal of this loop is stored directly on the output charge storage capacitor. The charge storage capacitor also serves to form the dominant pole for the control loop. To prevent ringing or instability it is important for the output capacitor to maintain at least 4μF of capacitance over all conditions (see Ceramic Capacitor Selection Guidelines). Likewise excessive ESR on the output capacitor will tend to degrade the loop stability of the LTC3245. The closed loop output resistance of the device is designed to be 0.3Ω for a 5V output and 0.2Ω for a 3.3V output. For a 250mA load current change, the output voltage will change by about 1.5%V. If the output capacitor has more ESR than the closed loop impedance, the closed loop frequency response will cease to roll off in a simple 1-pole fashion and poor load transient response or instability could result. Ceramic capacitors typically have exceptional ESR performance, and combined with a tight board layout, should yield excellent stability and load transient performance. VIN Capacitor Selection The constant frequency architecture used by the LTC3245 makes input noise filtering much less demanding than with conventional regulated charge pumps. Depending on the mode of operation the input current of the LTC3245 can vary from IOUT to 0mA on a cycle-by-cycle basis. Low ESR will reduce the voltage steps caused by changing input current, while the absolute capacitor value will determine the level of ripple. The total amount and type of capacitance necessary for input bypassing is very dependant on the applied source impedance as well as existing bypassing already on the VIN node. For optimal input noise and ripple reduction, it is recommended that a low ESR ceramic capacitor be used for CIN bypassing. An electrolytic or tantalum capacitor may be used in parallel with the ceramic capacitor on CIN to increase the total capacitance, but due to the higher ESR it is not recommended that an electrolytic or tantalum capacitor be used alone for input bypassing. The LTC3245 will operate with capacitors less than 1μF but depending on the source impedance input noise can feed through to the output causing degraded performance. For best performance 1μF or greater total capacitance is suggested for CIN. Flying Capacitor Selection Warning: A polarized capacitor such as tantalum or aluminum should never be used for the flying capacitors since the voltage can reverse upon start-up of the LTC3245. Ceramic capacitors should always be used for the flying capacitors. The flying capacitors control the strength of the charge pump. In order to achieve the rated output current, it is necessary for the flying capacitor to have at least 0.4μF of capacitance over operating temperature with a bias voltage equal to the programmed VOUT (see Ceramic Capacitor Selection Guidelines). If only 100mA or less of output current is required for the application, the flying capacitor minimum can be reduced to 0.15μF. The voltage rating of the ceramic capacitor should be VOUT + 1V or greater. Ceramic Capacitor Selection Guidelines Capacitors of different materials lose their capacitance with higher temperature and voltage at different rates. For example, a ceramic capacitor made of X5R or X7R material will retain most of its capacitance from –40°C to 85°C, whereas a Z5U or Y5V style capacitor will lose considerable capacitance over that range (60% to 80% loss typical). Z5U and Y5V capacitors may also have a very strong voltage coefficient, causing them to lose an additional 60% or more of their capacitance when the rated voltage is applied. Therefore, when comparing different capacitors, it is often more appropriate to compare the amount of achievable capacitance for a given case size 3245f For more information www.linear.com/LTC3245 11 LTC3245 Applications Information rather than discussing the specified capacitance value. For example, over rated voltage and temperature conditions, a 4.7μF, 10V, Y5V ceramic capacitor in an 0805 case may not provide any more capacitance than a 1μF, 10V, X5R or X7R available in the same 0805 case. In fact, over bias and temperature range, the 1μF, 10V, X5R or X7R will provide more capacitance than the 4.7μF, 10V, Y5V. The capacitor manufacturer’s data sheet should be consulted to determine what value of capacitor is needed to ensure minimum capacitance values are met over operating temperature and bias voltage. Below is a list of ceramic capacitor manufacturers and how to contact them: MANUFACTURER WEBSITE AVX www.avxcorp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com TDK www.tdk.com Because of the wide input operating range it is possible to exceed the specified operating junction temperature and even reach thermal shutdown. Figure 3 shows the available output current vs temperature to ensure the 150°C operating junction temperature is not exceed for input voltages less than 20V. Figure 3 assumes worst-case operating conditions. Under some operating conditions the part can supply more current than shown without exceeding the 150°C operating junction temperature. When operating outside the constraints of Figure 3 it is the responsibility of the user to calculate worst-case operating conditions (temperature and power) to make sure the LTC3245’s specified operating junction temperature is not exceeded for extended periods of time. The 2:1 Step-Down, 1:1 Step-Down, and 1:2 Step-Up Charge Pump Operation sections provide equations for calculating power dissipation (PD) in each mode. 300 Layout Considerations When using the LTC3245 with an external resistor divider it is important to minimize any stray capacitance to the ADJ (OUTS/ADJ pin) node. Stray capacitance from ADJ to C+ or C– can degrade performance significantly and should be minimized and/or shielded if necessary. 250 200 IOUT (mA) Due to the high switching frequency and transient currents produced by the LTC3245, careful board layout is necessary for optimal performance. A true ground plane and short connections to all capacitors will optimize performance, reduce noise and ensure proper regulation over all conditions. VIN < 20V 150 100 50 0 70 80 90 100 110 120 130 TEMPERATURE (°C) 140 150 3245 F03 Figure 3. Available Output Current vs Temperature Thermal Management The on chip power dissipation in the LTC3245 will cause the junction to ambient temperature to rise at rate of 40°C/W or more. To reduce the maximum junction temperature, a good thermal connection to the PC board is recommended. Connecting the die paddle (Pin 13) with multiple vias to a large ground plane under the device can reduce the thermal resistance of the package and PC board considerably. Poor board layout and failure to connect the die paddle (Pin 13) to a large ground plane can result in thermal junction to ambient impedance well in excess of 40°C/W. For example, if it is determined that the maximum power dissipation (PD) is 1.2W under normal operation, then the junction to ambient temperature rise will be: Junction to ambient = 1.2W • 40°C/W = 48°C Thus, the ambient temperature under this condition cannot exceed 102°C if the junction temperature is to remain below 150°C and if the ambient temperature exceeds about 127°C the device will cycle in and out of the thermal shutdown. 3245f 12 For more information www.linear.com/LTC3245 LTC3245 Typical Applications Regulated 5V Low Noise Output 1µF C+ C– LTC3245 VIN + 12V LEAD ACID BATTERY 1µF VOUT BURST OUTS/ADJ SEL2 PGOOD SEL1 GND 100k VOUT = 5V IVOUT UP TO 250mA 10µF 3245 TA02 High Efficiency 3.3V Microcontroller Supply from 9V Alkaline (with Power-On Reset Delay) 1µF C+ C– LTC3245 VIN + 9V ALKALINE BATTERY 1µF VOUT SEL1 OUTS/ADJ SEL2 PGOOD VOUT = 3.3V 510k MICROCONTROLLER VDD 10µF POR 1µF BURST GND GND 3245 TA03 Wide Input Range Low Noise 3.6V Supply 1µF C+ C– LTC3245 VIN VIN = 2.7V TO 38V 1µF VOUT BURST VOUT = 3.6V 499k SEL1 OUTS/ADJ SEL2 PGOOD 10µF 249k GND 3245 TA04 3245f For more information www.linear.com/LTC3245 13 LTC3245 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 12-Lead Plastic MSE MSOPPackage , Exposed Die Pad 12-Lead Plastic Exposed (Reference LTC DWGMSOP, # 05-08-1666 Rev Die F) Pad (Reference LTC DWG # 05-08-1666 Rev F) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ± 0.102 (.112 ± .004) 5.23 (.206) MIN 2.845 ± 0.102 (.112 ± .004) 0.889 ± 0.127 (.035 ± .005) 6 1 1.651 ± 0.102 (.065 ± .004) 1.651 ± 0.102 3.20 – 3.45 (.065 ± .004) (.126 – .136) 12 0.65 0.42 ± 0.038 (.0256) (.0165 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 4.039 ± 0.102 (.159 ± .004) (NOTE 3) 0.12 REF DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 7 NO MEASUREMENT PURPOSE 0.406 ± 0.076 (.016 ± .003) REF 12 11 10 9 8 7 DETAIL “A” 0° – 6° TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) GAUGE PLANE 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 1 2 3 4 5 6 0.22 – 0.38 (.009 – .015) TYP 0.650 NOTE: (.0256) 1. DIMENSIONS IN MILLIMETER/(INCH) BSC 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.86 (.034) REF 0.1016 ± 0.0508 (.004 ± .002) MSOP (MSE12) 0911 REV F 3245f 14 For more information www.linear.com/LTC3245 LTC3245 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev D) 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 3.30 ±0.05 1.70 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) 7 R = 0.115 TYP 0.40 ± 0.10 12 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.30 ±0.10 3.00 ±0.10 (2 SIDES) 1.70 ± 0.10 0.75 ±0.05 6 0.25 ± 0.05 1 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER (UE12/DE12) DFN 0806 REV D 0.50 BSC 2.50 REF 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE A VARIATION OF VERSION (WGED) IN JEDEC PACKAGE OUTLINE M0-229 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 3245f 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/LTC3245 15 LTC3245 Typical Application Wide VIN 5V Supply with Battery Backup 1µF C+ 12V TO 24V C– LTC3245 VIN + + + 1µF 4 × AA SEL2 BURST VOUT OUTS/ADJ PGOOD VOUT = 5V IVOUT UP TO 250mA 10µF SEL1 + GND 3245 TA05 Related Parts PART NUMBER DESCRIPTION COMMENTS LTC1751-3.3/ LTC1751-5 100mA, 800kHz Regulated Doubler VIN: 2V to 5V, VOUT(MAX) = 3.3V/5V, IQ = 20μA, ISD < 2μA, MS8 Package LTC1983-3/ LTC1983-5 100mA, 900kHz Regulated Inverter VIN: 3.3V to 5.5V, VOUT(MAX) = –3V/–5V, IQ = 25μA, ISD < 2μA, ThinSOT™ Package LTC3200-5 100mA, 2MHz Low Noise, Doubler/ White LED Driver VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 3.5mA, ISD < 1μA, ThinSOT Package LTC3202 125mA, 1.5MHz Low Noise, Fractional White LED Driver VIN: 2.7V to 4.5V, VOUT(MAX) = 5.5V, IQ = 2.5mA, ISD < 1μA, DFN, MS Packages LTC3204-3.3/ LTC3204B-3.3/ LTC3204-5/ LTC3204B-5 Low Noise, Regulated Charge Pumps in (2mm × 2mm) DFN Package VIN: 1.8V to 4.5V (LTC3204B-3.3), 2.7V to 5.5V (LTC3204B-5), IQ = 48μA, B Version without Burst Mode Operation, 6-Lead (2mm × 2mm) DFN Package LTC3440 600mA (IOUT) 2MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25μA, ISD ≤ 1μA, 10-Lead MS Package LTC3441 High Current Micropower 1MHz Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25μA, ISD ≤ 1μA, DFN Package LTC3443 High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter 96% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN) = 2.4V, IQ = 28μA, ISD < 1μA, DFN Package LTC3240-3.3/ LTC3240-2.5 3.3V/2.5V Step-Up/Step-Down Charge Pump DC/DC Converter VIN: 1.8V to 5.5V, VOUT(MAX) = 3.3V / 2.5V, IQ = 65μA, ISD < 1μA, (2mm × 2mm) DFN Package LTC3260 Low Noise Dual Supply Inverting Charge Pump VIN Range: 4.5V to 32V, IQ = 100µA, 100mA Charge Pump, 50mA Positive LDO, 50mA Negative LDO LTC3261 High Voltage Low IQ Inverting Charge Pump VIN Range: 4.5V to 32V, IQ = 60µA, 100mA Charge Pump 3245f 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC3245 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3245 LT 0313 • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2013