LTC3108 Ultralow Voltage Step-Up Converter and Power Manager FEATURES DESCRIPTION n The LTC®3108 is a highly integrated DC/DC converter ideal for harvesting and managing surplus energy from extremely low input voltage sources such as TEGs (thermoelectric generators), thermopiles and small solar cells. The step-up topology operates from input voltages as low as 20mV. The LTC3108 is functionally equivalent to the LTC3108-1 except for its unique fixed VOUT options. n n n n Operates from Inputs of 20mV Complete Energy Harvesting Power Management System - Selectable VOUT of 2.35V, 3.3V, 4.1V or 5V - LDO: 2.2V at 3mA - Logic Controlled Output - Reserve Energy Output Power Good Indicator Uses Compact Step-Up Transformers Small 12-Lead (3mm × 4mm) DFN or 16-Lead SSOP Packages Using a small step-up transformer, the LTC3108 provides a complete power management solution for wireless sensing and data acquisition. The 2.2V LDO powers an external microprocessor, while the main output is programmed to one of four fixed voltages to power a wireless transmitter or sensors. The power good indicator signals that the main output voltage is within regulation. A second output can be enabled by the host. A storage capacitor provides power when the input voltage source is unavailable. Extremely low quiescent current and high efficiency design ensure the fastest possible charge times of the output reservoir capacitor. APPLICATIONS n n n n n n n Remote Sensors and Radio Power Surplus Heat Energy Harvesting HVAC Systems Industrial Wireless Sensing Automatic Metering Building Automation Predictive Maintenance The LTC3108 is available in a small, thermally enhanced 12-lead (3mm × 4mm) DFN package and a 16-lead SSOP 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 Wireless Remote Sensor Application Powered From a Peltier Cell VOUT Charge Time 1nF THERMOELECTRIC GENERATOR C1 + 220μF VSTORE + LTC3108 330pF 1000 100 PGOOD PGD 2.2V VLDO SW μP 2.2μF SENSORS VOUT VS2 3.3V + 470μF VS1 VOUT2_EN VAUX GND VOUT = 3.3V COUT = 470μF 0.1F 6.3V VOUT2 C2 20mV TO 500mV 5V RF LINK TIME (sec) 1:100 + 10 1 1:100 Ratio 1:50 Ratio 1:20 Ratio 3108 TA01a 0 1μF 0 50 100 150 200 250 300 350 400 VIN (mV) 3108 TA01b 3108fb 1 LTC3108 ABSOLUTE MAXIMUM RATINGS (Note 1) SW Voltage ..................................................–0.3V to 2V C1 Voltage....................................................–0.3V to 6V C2 Voltage (Note 5).........................................–8V to 8V VOUT2, VOUT2_EN ...........................................–0.3V to 6V VAUX....................................................15mA into VAUX VS1, VS2, VAUX, VOUT, PGD ........................–0.3V to 6V VLDO, VSTORE ............................................–0.3V to 6V Operating Junction Temperature Range (Note 2)................................................. –40°C to 125°C Storage Temperature Range.................. –65°C to 125°C PIN CONFIGURATION TOP VIEW TOP VIEW VAUX 1 12 SW VSTORE 2 11 C2 VOUT 3 VOUT2 4 VLDO PGD 13 GND 10 C1 GND 1 16 GND VAUX 2 15 SW VSTORE 3 14 C2 VOUT 4 13 C1 9 VOUT2_EN VOUT2 5 12 VOUT2_EN 5 8 VS1 VLDO 6 11 VS1 6 7 VS2 PGD 7 10 VS2 GND 8 9 DE PACKAGE 12-LEAD (4mm s 3mm) PLASTIC DFN GND GN PACKAGE 16-LEAD PLASTIC SSOP NARROW TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB (NOTE 4) TJMAX = 125°C, θJA = 110°C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3108EDE#PBF LTC3108EDE#TRPBF 3108 12-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C LTC3108IDE#PBF LTC3108IDE#TRPBF 3108 12-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C LTC3108EGN#PBF LTC3108EGN#TRPBF 3108 16-Lead Plastic SSOP –40°C to 125°C LTC3108IGN#PBF LTC3108IGN#TRPBF 3108 16-Lead Plastic SSOP –40°C to 125°C Consult LTC Marketing for parts specified for other fixed output voltages or 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 full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted. PARAMETER CONDITIONS TYP MAX Minimum Start-Up Voltage Using 1:100 Transformer Turns Ratio, VAUX = 0V MIN 20 50 No-Load Input Current Using 1:100 Transformer Turns Ratio; VIN = 20mV, VOUT2_EN = 0V; All Outputs Charged and in Regulation 3 Input Voltage Range Using 1:100 Transformer Turns Ratio l VSTARTUP UNITS mV mA 500 mV 3108fb 2 LTC3108 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted. PARAMETER CONDITIONS Output Voltage VS1 = VS2 = GND VS1 = VAUX, VS2 = GND VS1 = GND, VS2 = VAUX VS1 = VS2 = VAUX VOUT Quiescent Current VOUT = 3.3V, VOUT2_EN = 0V VAUX Quiescent Current No Load, All Outputs Charged LDO Output Voltage 0.5mA Load LDO Load Regulation For 0mA to 2mA Load LDO Line Regulation For VAUX from 2.5V to 5V l l l l MIN TYP MAX UNITS 2.30 3.234 4.018 4.90 2.350 3.300 4.100 5.000 2.40 3.366 4.182 5.10 V V V V 0.2 l 2.134 μA 6 9 μA 2.2 2.266 V 0.5 1 % 0.05 0.2 % 100 200 LDO Dropout Voltage ILDO = 2mA l LDO Current Limit VLDO = 0V l 4 11 VOUT Current Limit VOUT = 0V l 2.8 4.5 7 mA VSTORE Current Limit VSTORE = 0V l 2.8 4.5 7 mA VAUX Clamp Voltage Current into VAUX = 5mA l 5 5.25 5.55 0.3 VSTORE Leakage Current VSTORE = 5V 0.1 VOUT2 Leakage Current VOUT2 = 0V, VOUT2_EN = 0V 0.1 l VS1, VS2 Threshold Voltage 0.4 V 0.1 μA 0.01 PGOOD Threshold (Rising) Measured Relative to the VOUT Voltage –7.5 Measured Relative to the VOUT Voltage Sink Current = 100μA PGOOD VOH Source Current = 0 PGOOD Pull-Up Resistance VOUT2_EN Threshold Voltage % –9 2.1 % 0.15 0.3 V 2.2 2.3 V 1 VOUT2_EN Rising l 0.4 μA μA 1.2 VS1 = VS2 = 5V PGOOD VOL V 0.85 VS1, VS2 Input Current PGOOD Threshold (Falling) mV mA 1 MΩ 1.3 V VOUT2_EN Pull-Down Resistance 5 MΩ VOUT2 Turn-On Time 5 μs 0.15 μs VOUT2 Turn-Off Time (Note 3) VOUT2 Current Limit VOUT = 3.3V VOUT2 Current Limit Response Time (Note 3) 350 ns VOUT2 P-Channel MOSFET On-Resistance VOUT = 3.3V (Note 3) 1.3 Ω N-Channel MOSFET On-Resistance C2 = 5V (Note 3) 0.5 Ω 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 LTC3108 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3108E 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 LTC3108I is guaranteed over the full –40°C to 125°C operating junction temperature range. Note that the maximum ambient temperature is determined by specific operating conditions in conjunction with board layout, the rated thermal package thermal resistance and other environmental factors. The junction l 0.15 0.3 0.45 A temperature (TJ) is calculated from the ambient temperature (TA) and power dissipation (PD) according to the formula: TJ = TA + (PD • θJA°C/W), where θJA is the package thermal impedance. Note 3: Specification is guaranteed by design and not 100% tested in production. Note 4: Failure to solder the exposed backside of the package to the PC board ground plane will result in a thermal resistance much higher than 43°C/W. Note 5: The absolute maximum rating is a DC rating. Under certain conditions in the applications shown, the peak AC voltage on the C2 pin may exceed ±8V. This behavior is normal and acceptable because the current into the pin is limited by the impedance of the coupling capacitor. 3108fb 3 LTC3108 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. IVOUT and Efficiency vs VIN, 1:20 Ratio Transformer IIN vs VIN, (VOUT = 0V) 4000 1000 1:50 RATIO, C1 = 4.7n 1:100 RATIO, C1 = 1n 1:20 RATIO, C1 = 10n 80 C1 = 10nF 70 3500 IVOUT (VOUT = 0V) 3000 IVOUT (μA) IIN (mA) 60 50 2500 2000 IVOUT (VOUT = 4.5V) EFFICIENCY (VOUT = 4.5V) 40 1500 30 1000 20 500 10 10 1 0 10 100 VIN (mV) 0 1000 100 200 300 400 EFFICIENCY (%) 100 0 500 VIN (mV) 3108 G00 3108 G01 IVOUT and Efficiency vs VIN, 1:100 Ratio Transformer IVOUT (VOUT = 0V) 1200 40 600 30 IVOUT (VOUT = 4.5V) 400 0 100 200 300 400 50 IVOUT (VOUT = 4.5V) 40 1200 30 800 20 400 10 0 500 0 0 500 0 100 200 300 400 VIN (mV) VIN (mV) 3108 G02 3108 G03 Input Resistance vs VIN (VOUT Charging) IVOUT vs VIN and Source Resistance, 1:20 Ratio 10 10000 C1 = 10nF 9 1:20 RATIO 8 1000 7 6 5 IVOUT (μA) INPUT RESISTANCE (Ω) 60 EFFICIENCY (VOUT = 4.5V) 1600 10 0 70 2000 20 200 IVOUT (VOUT = 0V) EFFICIENCY (%) 800 2400 50 EFFICIENCY (VOUT = 4.5V) 80 C1 = 4.7nF 2800 60 EFFICIENCY (%) IVOUT (μA) 1000 3200 70 C1 = 1nF IVOUT (μA) 1400 IVOUT and Efficiency vs VIN, 1:50 Ratio Transformer 1:50 RATIO 4 100 3 1:100 RATIO 2 10 1Ω 2Ω 5Ω 10Ω 1 0 0 100 200 300 400 500 VIN (mV) 0 0 100 200 300 400 500 600 700 800 VIN OPEN-CIRCUIT (mV) 3108 G05 3108 G04 3108fb 4 LTC3108 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted. IVOUT vs VIN and Source Resistance, 1:100 Ratio IVOUT vs VIN and Source Resistance, 1:50 Ratio 1000 10000 C1 = 1nF C1 = 4.7nF IVOUT (μA) IVOUT (μA) 1000 100 10 1Ω 2Ω 5Ω 10Ω 0 100 10 100 200 300 400 VIN OPEN-CIRCUIT (mV) 0 100 200 300 400 500 600 700 800 VIN OPEN-CIRCUIT (mV) 0 1Ω 2Ω 5Ω 10Ω 3108 G06 IVOUT vs dT and TEG Size, 1:100 Ratio 10000 VIN = 20mV 1:100 RATIO TRANSFORMER 40mm TEG 1000 IVOUT (μA) 3108 G07 Resonant Switching Waveforms VOUT = 0V 100 C1 PIN 2V/DIV C2 PIN 2V/DIV 10 SW PIN 50mV/ DIV 15mm TEG 1:50 RATIO 1:100 RATIO 1:50 RATIO 1:100 RATIO 0 0.1 500 10 1 dT ACROSS TEG (°C) 3108 G09 10μs/DIV 100 3108 G08 LDO Load Regulation LDO Dropout Voltage 0.00 0.20 0.18 0.16 DROPOUT VOLTAGE (V) DROP IN VLDO (%) –0.25 –0.50 –0.75 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 –1.00 0 0.5 1 1.5 2 2.5 LDO LOAD (mA) 3 3.5 4 3108 G10 0 0.5 1 1.5 2 2.5 LDO LOAD (mA) 3 3.5 4 3108 G11 3108fb 5 LTC3108 TYPICAL PERFORMANCE CHARACTERISTICS VOUT and PGD Response During a Step Load Start-Up Voltage Sequencing VIN = 50mV 1:100 RATIO TRANSFORMER COUT = 220μF CSTORE = 470μF CLDO = 2.2μF 50mA LOAD STEP COUT = 220μF CH1 VSTORE 1V/DIV CH2, VOUT 1V/DIV CH3, VLDO 1V/DIV 10sec/DIV TA = 25°C, unless otherwise noted. CH2 VOUT 1V/DIV CH1 PGD 1V/DIV 3108 G12 5ms/DIV VOUT Ripple 3108 G13 LDO Step Load Response 30μA LOAD COUT = 220μF VLDO 20mV/DIV 20mV/ DIV ILDO 5mA/DIV 100ms/DIV 3108 G14 200μs/DIV 3108 G15 0mA TO 3mA LOAD STEP CLDO = 2.2μF Enable Input and VOUT2 Running on Storage Capacitor CH3 VSTORE 1V/DIV CSTORE = 470μF VOUT LOAD = 100μA CH2, VOUT 1V/DIV CH2, VOUT2 1V/DIV CH4, VLDO 1V/DIV CH1 VOUT2_EN 1V/DIV CH1, VIN 50mV/DIV 1ms/DIV 3108 G16 5sec/DIV 3108 G17 10mA LOAD ON VOUT2 COUT = 220μF 3108fb 6 LTC3108 PIN FUNCTIONS (DFN/SSOP) VAUX (Pin 1/Pin 2): Output of the Internal Rectifier Circuit and VCC for the IC. Bypass VAUX with at least 1μF of capacitance. An active shunt regulator clamps VAUX to 5.25V (typical). VSTORE (Pin 2/Pin 3): Output for the Storage Capacitor or Battery. A large capacitor may be connected from this pin to GND for powering the system in the event the input voltage is lost. It will be charged up to the maximum VAUX clamp voltage. If not used, this pin should be left open or tied to VAUX. VOUT (Pin 3/Pin 4): Main Output of the Converter. The voltage at this pin is regulated to the voltage selected by VS1 and VS2 (see Table 1). Connect this pin to an energy storage capacitor or to a rechargeable battery. VOUT2 (Pin 4/Pin 5): Switched Output of the Converter. Connect this pin to a switched load. This output is open until VOUT2_EN is driven high, then it is connected to VOUT through a 1.3Ω P-channel switch. If not used, this pin should be left open or tied to VOUT. The peak current in this output is limited to 0.3A typical. VLDO (Pin 5/Pin 6): Output of the 2.2V LDO. Connect a 2.2μF or larger ceramic capacitor from this pin to GND. If not used, this pin should be tied to VAUX. PGD (Pin 6/Pin 7): Power Good Output. When VOUT is within 7.5% of its programmed value, PGD will be pulled up to VLDO through a 1MΩ resistor. If VOUT drops 9% below its programmed value PGD will go low. This pin can sink up to 100μA. VS1 (Pin 8/Pin 11): VOUT Select Pin 1. Connect this pin to ground or VAUX to program the output voltage (see Table 1). VOUT2_EN (Pin 9/Pin 12): Enable Input for VOUT2. VOUT2 will be enabled when this pin is driven high. There is an internal 5M pull-down resistor on this pin. If not used, this pin can be left open or grounded. C1 (Pin 10/Pin 13): Input to the Charge Pump and Rectifier Circuit. Connect a capacitor from this pin to the secondary winding of the step-up transformer. C2 (Pin 11/Pin 14): Input to the N-Channel Gate Drive Circuit. Connect a capacitor from this pin to the secondary winding of the step-up transformer. SW (Pin 12/Pin 15): Drain of the Internal N-Channel Switch. Connect this pin to the primary winding of the transformer. GND (Pins 1, 8, 9, 16) SSOP Only: Ground GND (Exposed Pad Pin 13) DFN Only: Ground. The DFN exposed pad must be soldered to the PCB ground plane. It serves as the ground connection, and as a means of conducting heat away from the die. Table 1. Regulated Voltage Using Pins VS1 and VS2 VS2 VS1 VOUT GND GND 2.35V GND VAUX 3.3V VAUX GND 4.1V VAUX VAUX 5V VS2 (Pin 7/Pin 10): VOUT Select Pin 2. Connect this pin to ground or VAUX to program the output voltage (see Table 1). 3108fb 7 LTC3108 BLOCK DIAGRAM LTC3108 VOUT2 1.3Ω VOUT2 ILIM VOUT2_EN SYNC RECTIFY REFERENCE 1.2V VREF 5M C1 1:100 VIN VOUT C1 VOUT CIN COUT 5.25V C2 + – C2 SW OFF ON VOUT SW VSTORE VS1 CHARGE CONTROL VS2 0.5Ω VOUT PROGRAM VREF VLDO 1M – + VAUX 1μF PGD PGOOD VSTORE VOUT GND (SSOP) VBEST VREF EXPOSED PAD (DFN) LDO CSTORE VLDO 3108 BD 2.2V 2.2μF OPERATION (Refer to the Block Diagram) The LTC3108 is designed to use a small external step-up transformer to create an ultralow input voltage step-up DC/DC converter and power manager. It is ideally suited for low power wireless sensors and other applications in which surplus energy harvesting is used to generate system power because traditional battery power is inconvenient or impractical. The LTC3108 is designed to manage the charging and regulation of multiple outputs in a system in which the average power draw is very low, but there may be periodic pulses of higher load current required. This is typical of wireless sensor applications, where the quiescent power draw is extremely low most of the time, except for transmit bursts when circuitry is powered up to make measurements and transmit data. The LTC3108 can also be used to trickle charge a standard capacitor, supercapacitor or rechargeable battery, using energy harvested from a Peltier or photovoltaic cell. 3108fb 8 LTC3108 OPERATION Oscillator Synchronous Rectifiers The LTC3108 utilizes a MOSFET switch to form a resonant step-up oscillator using an external step-up transformer and a small coupling capacitor. This allows it to boost input voltages as low as 20mV high enough to provide multiple regulated output voltages for powering other circuits. The frequency of oscillation is determined by the inductance of the transformer secondary winding and is typically in the range of 10kHz to 100kHz. For input voltages as low as 20mV, a primary-secondary turns ratio of about 1:100 is recommended. For higher input voltages, this ratio can be lower. See the Applications Information section for more information on selecting the transformer. Once VAUX exceeds 2V, synchronous rectifiers in parallel with each of the internal diodes take over the job of rectifying the input voltage, improving efficiency. Charge Pump and Rectifier The AC voltage produced on the secondary winding of the transformer is boosted and rectified using an external charge pump capacitor (from the secondary winding to pin C1) and the rectifiers internal to the LTC3108. The rectifier circuit feeds current into the VAUX pin, providing charge to the external VAUX capacitor and the other outputs. VAUX The active circuits within the LTC3108 are powered from VAUX, which should be bypassed with a 1μF capacitor. Larger capacitor values are recommended when using turns ratios of 1:50 or 1:20 (refer to the Typical Application examples). Once VAUX exceeds 2.5V, the main VOUT is allowed to start charging. An internal shunt regulator limits the maximum voltage on VAUX to 5.25V typical. It shunts to GND any excess current into VAUX when there is no load on the converter or the input source is generating more power than is required by the load. Low Dropout Linear Regulator (LDO) The LTC3108 includes a low current LDO to provide a regulated 2.2V output for powering low power processors or other low power ICs. The LDO is powered by the higher of VAUX or VOUT. This enables it to become active as soon as VAUX has charged to 2.3V, while the VOUT storage capacitor is still charging. In the event of a step load on the LDO output, current can come from the main VOUT capacitor if VAUX drops below VOUT. The LDO requires a 2.2μF ceramic capacitor for stability. Larger capacitor values can be used without limitation, but will increase the time it takes for all the outputs to charge up. The LDO output is current limited to 4mA minimum. VOUT The main output voltage on VOUT is charged from the VAUX supply, and is user programmed to one of four regulated voltages using the voltage select pins VS1 and VS2, according to Table 2. Although the logic threshold voltage for VS1 and VS2 is 0.85V typical, it is recommended that they be tied to ground or VAUX. Table 2. Regulated Voltage Using Pins VS1 and VS2 VS2 VS1 VOUT GND GND 2.35V GND VAUX 3.3V VAUX GND 4.1V VAUX VAUX 5V Voltage Reference When the output voltage drops slightly below the regulated value, the charging current will be enabled as long as VAUX is greater than 2.5V. Once VOUT has reached the proper value, the charging current is turned off. The LTC3108 includes a precision, micropower reference, for accurate regulated output voltages. This reference becomes active as soon as VAUX exceeds 2V. The internal programmable resistor divider sets VOUT, eliminating the need for very high value external resistors that are susceptible to board leakage. 3108fb 9 LTC3108 OPERATION In a typical application, a storage capacitor (typically a few hundred microfarads) is connected to VOUT. As soon as VAUX exceeds 2.5V, the VOUT capacitor will be allowed to charge up to its regulated voltage. The current available to charge the capacitor will depend on the input voltage and transformer turns ratio, but is limited to about 4.5mA typical. PGOOD A power good comparator monitors the VOUT voltage. The PGD pin is an open-drain output with a weak pull-up (1MΩ) to the LDO voltage. Once VOUT has charged to within 7.5% of its regulated voltage, the PGD output will go high. If VOUT drops more than 9% from its regulated voltage, PGD will go low. The PGD output is designed to drive a microprocessor or other chip I/O and is not intended to drive a higher current load such as an LED. Pulling PGD up externally to a voltage greater than VLDO will cause a small current to be sourced into VLDO. PGD can be pulled low in a wire-OR configuration with other circuitry. VOUT2 VOUT2 is an output that can be turned on and off by the host, using the VOUT2_EN pin. When enabled, VOUT2 is connected to VOUT through a 1.3Ω P-channel MOSFET switch. This output, controlled by a host processor, can be used to power external circuits such as sensors and amplifiers, that do not have a low power sleep or shutdown capability. VOUT2 can be used to power these circuits only when they are needed. Minimizing the amount of decoupling capacitance on VOUT2 will allow it to be switched on and off faster, allowing shorter burst times and, therefore, smaller duty cycles in pulsed applications such as a wireless sensor/transmitter. A small VOUT2 capacitor will also minimize the energy that will be wasted in charging the capacitor every time VOUT2 is enabled. VOUT2 has a soft-start time of about 5μs to limit capacitor charging current and minimize glitching of the main output when VOUT2 is enabled. It also has a current limiting circuit that limits the peak current to 0.3A typical. The VOUT2 enable input has a typical threshold of 1V with 100mV of hysteresis, making it logic-compatible. If VOUT2_EN (which has an internal pull-down resistor) is low, VOUT2 will be off. Driving VOUT2_EN high will turn on the VOUT2 output. Note that while VOUT2_EN is high, the current limiting circuitry for VOUT2 draws an extra 8μA of quiescent current from VOUT. This added current draw has a negligible effect on the application and capacitor sizing, since the load on the VOUT2 output, when enabled, is likely to be orders of magnitude higher than 8μA. VSTORE The VSTORE output can be used to charge a large storage capacitor or rechargeable battery after VOUT has reached regulation. Once VOUT has reached regulation, the VSTORE output will be allowed to charge up to the VAUX voltage. The storage element on VSTORE can be used to power the system in the event that the input source is lost, or is unable to provide the current demanded by the VOUT, VOUT2 and LDO outputs. If VAUX drops below VSTORE, the LTC3108 will automatically draw current from the storage element. Note that it may take a long time to charge a large capacitor, depending on the input energy available and the loading on VOUT and VLDO. Since the maximum current from VSTORE is limited to a few milliamps, it can safely be used to trickle-charge NiCd or NiMH rechargeable batteries for energy storage when the input voltage is lost. Note that the VSTORE capacitor cannot supply large pulse currents to VOUT . Any pulse load on VOUT must be handled by the VOUT capacitor. Short-Circuit Protection All outputs of the LTC3108 are current limited to protect against short-circuits to ground. Output Voltage Sequencing A timing diagram showing the typical charging and voltage sequencing of the outputs is shown in Figure 1. Note: time not to scale. 3108fb 10 LTC3108 OPERATION 5.0 VSTORE (V) 2.5 0 3.0 2.0 PGD (V) 1.0 VOLTAGE (V) 0 5.0 2.5 VOUT (V) 0 3.0 2.0 VLDO (V) 1.0 0 5.0 VAUX (V) 2.5 0 0 10 20 30 40 50 60 70 80 TIME (ms) 3108 F01a Figure 1. Output Voltage Sequencing with VOUT Programmed for 3.3V (Time Not to Scale) 3108fb 11 LTC3108 APPLICATIONS INFORMATION Introduction Refer to the IIN vs VIN curves in the Typical Performance Characteristics section to see what input current is required from the source for a given input voltage. The LTC3108 is designed to gather energy from very low input voltage sources and convert it to usable output voltages to power microprocessors, wireless transmitters and analog sensors. Such applications typically require much more peak power, and at higher voltages, than the input voltage source can produce. The LTC3108 is designed to accumulate and manage energy over a long period of time to enable short power bursts for acquiring and transmitting data. The bursts must occur at a low enough duty cycle such that the total output energy during the burst does not exceed the average source power integrated over the accumulation time between bursts. For many applications, this time between bursts could be seconds, minutes or hours. For a given transformer turns ratio, there is a maximum recommended input voltage to avoid excessively high secondary voltages and power dissipation in the shunt regulator. It is recommended that the maximum input voltage times the turns ratio be less than 50. Note that a low ESR bulk decoupling capacitor will usually be required across the input source to prevent large voltage droop and ripple caused by the source’s ESR and the peak primary switching current (which can reach hundreds of milliamps). The time constant of the filter capacitor and the ESR of the voltage source should be much longer than the period of the resonant switching frequency. The PGD signal can be used to enable a sleeping microprocessor or other circuitry when VOUT reaches regulation, indicating that enough energy is available for a burst. Peltier Cell (Thermoelectric Generator) A Peltier cell (also known as a thermoelectric cooler) is made up of a large number of series-connected P-N junctions, sandwiched between two parallel ceramic plates. Although Peltier cells are often used as coolers by applying a DC voltage to their inputs, they will also generate a DC output voltage, using the Seebeck effect, when the two plates are at different temperatures. The polarity of the output voltage will depend on the polarity of the temperature differential between the plates. The magnitude of the output voltage is proportional to the magnitude of the temperature differential between the plates. When used in Input Voltage Sources The LTC3108 can operate from a number of low input voltage sources, such as Peltier cells, photovoltaic cells or thermopile generators. The minimum input voltage required for a given application will depend on the transformer turns ratio, the load power required, and the internal DC resistance (ESR) of the voltage source. Lower ESR will allow the use of lower input voltages, and provide higher output power capability. 1000 100 TEG VOPEN_CIRCUIT (mV) VOC 10 100 MAX POUT (IDEAL) 1 10 1 1 10 dT (°C) TEG MAXIMUM POUT —IDEAL (mW) TEG: 30mm 127 COUPLES R = 2Ω 0.1 100 3108 F02 Figure 2. Typical Performance of a Peltier Cell Acting as a Thermoelectric Generator 3108fb 12 LTC3108 APPLICATIONS INFORMATION this manner, a Peltier cell is referred to as a thermoelectric generator (TEG). current capability by providing a higher input voltage under load. The low voltage capability of the LTC3108 design allows it to operate from a TEG with temperature differentials as low as 1°C, making it ideal for harvesting energy in applications in which a temperature difference exists between two surfaces or between a surface and the ambient temperature. The internal resistance (ESR) of most cells is in the range of 1Ω to 5Ω, allowing for reasonable power transfer. The curves in Figure 2 show the opencircuit output voltage and maximum power transfer for a typical Peltier cell (with an ESR of 2Ω) over a 20°C range of temperature differential. Peltier Cell (TEG) Suppliers TEG Load Matching The LTC3108 was designed to present a minimum input resistance (load) in the range of 2Ω to 10Ω, depending on input voltage and transformer turns ratio (as shown in the Typical Performance Characteristics curves). For a given turns ratio, as the input voltage drops, the input resistance increases. This feature allows the LTC3108 to optimize power transfer from sources with a few ohms of source resistance, such as a typical TEG. Note that a lower source resistance will always provide more output Peltier cells are available in a wide range of sizes and power capabilities, from less than 10mm square to over 50mm square. They are typically 2mm to 5mm in height. A list of Peltier cell manufacturers is given in Table 3. Table 3. Peltier Cell Manufacturers CUI, Inc. www.cui.com (Distributor) Fujitaka www.fujitaka.com/pub/peltier/english/thermoelectric_power.html Ferrotec www.ferrotec.com/products/thermal/modules Kryotherm www.kryothermusa.com Laird Technologies www.lairdtech.com Marlow Industries www.marlow.com Micropelt www.micropelt.com Nextreme www.nextreme.com TE Technology www.tetech.com/Peltier-Thermoelectric-Cooler-Modules.html Tellurex www.tellurex.com Table 4. Recommended TEG Part Numbers by Size MANUFACTURER 15mm × 15mm 20mm × 20mm 30mm × 30mm 40mm × 40mm CUI Inc. (Distributor) CP60133 CP60233 CP60333 CP85438 Ferrotec 9501/031/030 B 9501/071/040 B 9500/097/090 B 9500/127/100 B Fujitaka FPH13106NC FPH17106NC FPH17108AC FPH112708AC Kryotherm TGM-127-1.0-0.8 LCB-127-1.4-1.15 Laird Technology PT6.7.F2.3030.W6 PT8.12.F2.4040.TA.W6 RC3-8-01 RC6-6-01 RC12-8-01LS Marlow Industries Tellurex C2-15-0405 C2-20-0409 C2-30-1505 C2-40-1509 TE Technology TE-31-1.0-1.3 TE-31-1.4-1.15 TE-71-1.4-1.15 TE-127-1.4-1.05 3108fb 13 LTC3108 APPLICATIONS INFORMATION Thermopile Generator Thermopile generators (also called powerpile generators) are made up of a number of series-connected thermocouples enclosed in a metal tube. They are commonly used in gas burner applications to generate a DC output of hundreds of millivolts when exposed to the high temperature of a flame. Typical examples are the Honeywell CQ200 and Q313. These devices have an internal series resistance of less than 3Ω, and can generate as much as 750mV open-circuit at their highest rated temperature. For applications in which the temperature rise is too high for a solid-state thermoelectric device, a thermopile can be used as an energy source to power the LTC3108. Because of the higher output voltages possible with a thermopile generator, a lower transformer turns ratio can be used (typically 1:20, depending on the application). Photovoltaic Cell The LTC3108 converter can also operate from a single photovoltaic cell (also known as a PV or solar cell) at light levels too low for other low input voltage boost converters to operate. However, many variables will affect the performance in these applications. Light levels can vary over several orders of magnitude and depend on lighting conditions (the type of lighting and indoor versus outdoor). Different types of light (sunlight, incandescent, fluorescent) also have different color spectra, and will produce different output power levels depending on which type of photovoltaic cell is being used (monocrystalline, polycrystalline or thin-film). Therefore, the photovoltaic cell must be chosen for the type and amount of light available. Note that the short-circuit output current from the cell must be at least a few milliamps in order to power the LTC3108 converter Non-Boost Applications The LTC3108 can also be used as an energy harvester and power manager for input sources that do not require boosting. In these applications the step-up transformer can be eliminated. these applications the C2 and SW pins are not used and can be grounded or left open. Examples of such input sources would be piezoelectric transducers, vibration energy harvesters, low current generators, a stack of low current solar cells or a 60Hz AC input. A series resistance of at least 100Ω/V should be used to limit the maximum current into the VAUX shunt regulator. COMPONENT SELECTION Step-Up Transformer The step-up transformer turns ratio will determine how low the input voltage can be for the converter to start. Using a 1:100 ratio can yield start-up voltages as low as 20mV. Other factors that affect performance are the DC resistance of the transformer windings and the inductance of the windings. Higher DC resistance will result in lower efficiency. The secondary winding inductance will determine the resonant frequency of the oscillator, according to the following formula. Frequency = 1 Hz 2 • π • L(sec) • C Where L is the inductance of the transformer secondary winding and C is the load capacitance on the secondary winding. This is comprised of the input capacitance at pin C2, typically 30pF, in parallel with the transformer secondary winding’s shunt capacitance. The recommended resonant frequency is in the range of 10kHz to 100kHz. See Table 5 for some recommended transformers. Table 5. Recommended Transformers VENDOR PART NUMBER Coilcraft www.coilcraft.com LPR6235-752SML (1:100 Ratio) LPR6235-253PML (1:20 Ratio) LPR6235-123QML (1:50 Ratio) Würth www.we-online S11100034 (1:100 Ratio) S11100033 (1:50 Ratio) S11100032 (1:20 Ratio) Any source whose peak voltage exceeds 2.5V AC or 5V DC can be connected to the C1 input through a currentlimiting resistor where it will be rectified/peak detected. In 3108fb 14 LTC3108 APPLICATIONS INFORMATION C1 Capacitor Using External Charge Pump Rectifiers The charge pump capacitor that is connected from the transformer’s secondary winding to the C1 pin has an effect on converter input resistance and maximum output current capability. Generally, a minimum value of 1nF is recommended when operating from very low input voltages using a transformer with a ratio of 1:100. Too large a capacitor value can compromise performance when operating at low input voltage or with high resistance sources. For higher input voltages and lower turns ratios, the value of the C1 capacitor can be increased for higher output current capability. Refer to the Typical Applications schematic examples for the recommended value for a given turns ratio. The synchronous charge pump rectifiers in the LTC3108 (connected to the C1 pin) are optimized for operation from very low input voltage sources, using typical transformer step-up ratios between 1:100 and 1:50, and typical C1 charge pump capacitor values less than 10nF. Squegging Operation from higher input voltage sources (typically 250mV or greater, under load), allows the use of lower transformer step-up ratios (such as 1:20 and 1:10) and larger C1 capacitor values to provide higher output current capability from the LTC3108. However, due to the resulting increase in rectifier currents and resonant oscillator frequency in these applications, the use of external charge pump rectifiers is recommended for optimal performance. Certain types of oscillators, including transformer-coupled oscillators such as the resonant oscillator of the LTC3108, can exhibit a phenomenon called squegging. This term refers to a condition that can occur which blocks or stops the oscillation for a period of time much longer than the period of oscillation, resulting in bursts of oscillation. An example of this is the blocking oscillator, which is designed to squegg to produce bursts of oscillation. Squegging is also encountered in RF oscillators and regenerative receivers. In applications where the step-up ratio is 1:20 or less, and the C1 capacitor is 10nF or greater, the C1 pin should be grounded and two external rectifiers (such as 1N4148 or 1N914 diodes) should be used. These are available as dual diodes in a single package. Avoid the use of Schottky rectifiers, as their lower forward voltage drop increases the minimum start-up voltage. See the Typical Applications schematics for an example. In the case of the LTC3108, squegging can occur when a charge builds up on the C2 gate coupling capacitor, such that the DC bias point shifts and oscillation is extinguished for a certain period of time, until the charge on the capacitor bleeds off, allowing oscillation to resume. It is difficult to predict when and if squegging will occur in a given application. While squegging is not harmful, it reduces the average output current capability of the LTC3108. For pulsed load applications, the VOUT capacitor should be sized to provide the necessary current when the load is pulsed on. The capacitor value required will be dictated by the load current, the duration of the load pulse, and the amount of voltage droop the circuit can tolerate. The capacitor must be rated for whatever voltage has been selected for VOUT by VS1 and VS2. Squegging can easily be avoided by the addition of a bleeder resistor in parallel with the coupling capacitor on the C2 pin. Resistor values in the range of 100k to 1MΩ are sufficient to eliminate squegging without having any negative impact on performance. For the 330pF capacitor used for C2 in most applications, a 499k bleeder resistor is recommended. See the Typical Applications schematics for an example. VOUT and VSTORE Capacitor COUT (μF) ≥ ILOAD(mA) • tPULSE (ms) ΔVOUT (V) Note that there must be enough energy available from the input voltage source for VOUT to recharge the capacitor during the interval between load pulses (to be discussed in the next example). Reducing the duty cycle of the load pulse will allow operation with less input energy. 3108fb 15 LTC3108 APPLICATIONS INFORMATION The VSTORE capacitor may be of very large value (thousands of microfarads or even Farads), to provide holdup at times when the input power may be lost. Note that this capacitor can charge all the way to 5.25V (regardless of the settings for VOUT), so ensure that the holdup capacitor has a working voltage rating of at least 5.5V at the temperature for which it will be used. The VSTORE capacitor can be sized using the following: CSTORE ≥ [6μA + IQ + ILDO+ (IBURST • t • f)] • TSTORE 5.25 − VOUT Where 6μA is the quiescent current of the LTC3108, IQ is the load on VOUT in between bursts, ILDO is the load on the LDO between bursts, IBURST is the total load during the burst, t is the duration of the burst, f is the frequency of the bursts, TSTORE is the storage time required and VOUT is the output voltage required. Note that for a programmed output voltage of 5V, the VSTORE capacitor cannot provide any beneficial storage time. To minimize losses and capacitor charge time, all capacitors used for VOUT and VSTORE should be low leakage. See Table 6 for recommended storage capacitors. Table 6. Recommended Storage Capacitors VENDOR PART NUMBER/SERIES AVX www.avx.com BestCap Series TAJ and TPS Series Tantalum Cap-XX www.cap-xx.com GZ Series Cooper/Bussmann www.bussmann.com/3/PowerStor.html KR Series P Series Vishay/Sprague www.vishay.com/capacitors Tantamount 592D 595D Tantalum 150CRZ/153CRV Aluminum 013 RLC (Low Leakage) Due to the very low input voltage the circuit may operate from, the connections to VIN, the primary of the transformer and the SW and GND pins of the LTC3108 should be designed to minimize voltage drop from stray resistance and able to carry currents as high as 500mA. Any small voltage drop in the primary winding conduction path will lower efficiency and increase capacitor charge time. Also, due to the low charge currents available at the outputs of the LTC3108, any sources of leakage current on the output voltage pins must be minimized. An example board layout is shown in Figure 3. VIN VAUX VSTORE VOUT VOUT VOUT2 VOUT2 VLDO VLDO PGOOD PGD 1 12 2 11 3 10 4 9 5 8 6 7 SW C2 C1 VOUT2_EN VS1 VS2 GND 3108 FO3 VIAS TO GROUND PLANE Storage capacitors requiring voltage balancing are not recommended due to the current draw of the balancing resistors. PCB Layout Guidelines Due to the rather low switching frequency of the resonant converter and the low power levels involved, PCB layout is not as critical as with many other DC/DC converters. There are, however, a number of things to consider. Figure 3. Example Component Placement for Two-Layer PC Board (DFN Package) Design Example 1 This design example will explain how to calculate the necessary storage capacitor value for VOUT in pulsed load applications, such as a wireless sensor/transmitter. In these types of applications, the load is very small for a majority of the time (while the circuitry is in a low power sleep state), with bursts of load current occurring periodically during a transmit burst. The storage capacitor on VOUT supports the load during the transmit burst, and the long sleep time between bursts allows the LTC3108 to recharge the capacitor. A method for calculating the maximum rate 3108fb 16 LTC3108 APPLICATIONS INFORMATION at which the load pulses can occur for a given output current from the LTC3108 will also be shown. Therefore, in this application example, the circuit can support a 1ms transmit burst every 1.5 seconds. In this example, VOUT is set to 3.3V, and the maximum allowed voltage droop during a transmit burst is 10%, or 0.33V. The duration of a transmit burst is 1ms, with a total average current requirement of 40mA during the burst. Given these factors, the minimum required capacitance on VOUT is: It can be determined that for systems that only need to transmit every few seconds (or minutes or hours), the average charge current required is extremely small, as long as the sleep current is low. Even if the available charge current in the example above was only 10μA and the sleep current was only 5μA, it could still transmit a burst every ten seconds. COUT (μF) ≥ 40mA • 1ms = 121μF 0.33V Note that this equation neglects the effect of capacitor ESR on output voltage droop. For most ceramic or low ESR tantalum capacitors, the ESR will have a negligible effect at these load currents. A standard value of 150μF or larger could be used for COUT in this case. Note that the load current is the total current draw on VOUT, VOUT2 and VLDO, since the current for all of these outputs must come from VOUT during a burst. Current contribution from the holdup capacitor on VSTORE is not considered, since it may not be able to recharge between bursts. Also, it is assumed that the charge current from the LTC3108 is negligible compared to the magnitude of the load current during the burst. To calculate the maximum rate at which load bursts can occur, determine how much charge current is available from the LTC3108 VOUT pin given the input voltage source being used. This number is best found empirically, since there are many factors affecting the efficiency of the converter. Also determine what the total load current is on VOUT during the sleep state (between bursts). Note that this must include any losses, such as storage capacitor leakage. Assume, for instance, that the charge current from the LTC3108 is 50μA and the total current drawn on VOUT in the sleep state is 17μA, including capacitor leakage. In addition, use the value of 150μF for the VOUT capacitor. The maximum transmit rate (neglecting the duration of the transmit burst, which is typically very short) is then given by: 150μF • 0.33V t= = 1.5sec or fMAX = 0.666Hz (50μA − 17μA) The following formula enables the user to calculate the time it will take to charge the LDO output capacitor and the VOUT capacitor the first time, from 0V. Here again, the charge current available from the LTC3108 must be known. For this calculation, it is assumed that the LDO output capacitor is 2.2μF. 2.2V • 2.2μF tLDO = ICHG − ILDO If there were 50μA of charge current available and a 5μA load on the LDO (when the processor is sleeping), the time for the LDO to reach regulation would be 107ms. If VOUT were programmed to 3.3V and the VOUT capacitor was 150μF, the time for VOUT to reach regulation would be: t VOUT = 3.3V • 150μF + tLDO ICHG − IVOUT − ILDO If there were 50μA of charge current available and 5μA of load on VOUT, the time for VOUT to reach regulation after the initial application of power would be 12.5 seconds. Design Example 2 In many pulsed load applications, the duration, magnitude and frequency of the load current bursts are known and fixed. In these cases, the average charge current required from the LTC3108 to support the average load must be calculated, which can be easily done by the following: ICHG ≥ IQ + IBURST • t T Where IQ is the sleep current on VOUT required by the external circuitry in between bursts (including cap leakage), IBURST is the total load current during the burst, t is the 3108fb 17 LTC3108 APPLICATIONS INFORMATION duration of the burst and T is the period of the transmit burst rate (essentially the time between bursts). hour. It can be determined that the sleep current of 5μA is the dominant factor because the transmit duty cycle is so small (0.00014%). Note that for a VOUT of 3.3V, the average power required by this application is only 17μW (not including converter losses). In this example, IQ = 5μA, IBURST = 100mA, t = 5ms and T = one hour. The average charge current required from the LTC3108 would be: ICHG ≥ 5μA + Note that the charge current available from the LTC3108 has no effect on the sizing of the VOUT capacitor (if it is assumed that the load current during a burst is much larger than the charge current), and the VOUT capacitor has no effect on the maximum allowed burst rate. 100mA • 0.005sec = 5.14μA 3600 sec Therefore, if the LTC3108 has an input voltage that allows it to supply a charge current greater than 5.14μA, the application can support 100mA bursts lasting 5ms every TYPICAL APPLICATIONS Peltier-Powered Energy Harvester for Remote Sensor Applications 1nF 1:100 T1 + VSTORE 5V + C1 + THERMOELECTRIC GENERATOR CIN VOUT2 330pF ΔT = 1°C TO 20°C PGOOD PGD C2 LTC3108 VLDO SW COOPER BUSSMAN PB-5ROH104-R OR KR-5R5H104-R CSTORE 0.1F 3.3V 6.3V VOUT2 SENSORS μP 2.2V 2.2μF VOUT + VS2 COUT* VS1 VOUT2_EN GND VAUX T1: COILCRAFT LPR6235-752SML *COUT VALUE DEPENDENT ON THE MAGNITUDE AND DURATION OF THE LOAD PULSE XMTR 3.3V OFF ON 1μF 3108 TA02 3108fb 18 LTC3108 TYPICAL APPLICATIONS Li-Ion Battery Charger and LDO Powered by a Solar Cell T1 1:20 + 0.01μF C1 VSTORE + SOLAR CELL* 220μF – VOUT2 330pF LTC3108 C2 SW PGD 2.2V VLDO 4.1V VOUT VS2 VS1 * 2" DIAMETER MONOCRYSTALLINE CELL LIGHT LEVEL ≥ 900 LUX VLDO VOUT 2.2μF Li-Ion VOUT2_EN VAUX GND T1: COILCRAFT LPR6235-253PML 4.7μF 3108 TA03 Supercapacitor Charger and LDO Powered by a Thermopile Generator HONEYWELL CQ200 THERMOPILE T1 1:50 4.7nF C1 VSTORE + 220μF VOUT2 330pF LTC3108 C2 SW PGD VOUT T1: COILCRAFT LPR6235-123QML PGOOD 2.2V VLDO VS2 VS1 2.35V + 2.2μF 150mF 2.5V VOUT2_EN VAUX VLDO VOUT GND CAP-XX GZ115F 2.2μF 3108 TA04 AC Input Energy Harvester and Power Manager DC Input Energy Harvester and Power Manager RIN RIN > 100Ω / V C1 + – 5V VSTORE VIN VIN > 5V VOUT2 PGD C2 SW CSTORE 2.2V 3.3V + VOUT COUT VS1 VOUT2_EN VAUX GND 2.2μF VOUT2_ENABLE VSTORE AC VIN VIN > 5VP-P VOUT2 - PIEZO - 60Hz PGOOD VLDO VOUT C1 + VOUT2 LTC3108 VS2 RIN CIN RIN > 100Ω/ V VLDO 2.2μF PGD VOUT SW CSTORE PGOOD 2.2V VLDO C2 + VOUT2 LTC3108 5V + VOUT VLDO 2.2μF COUT VS2 VOUT2_EN VS1 VAUX 3108 TA05 5V VOUT2_ENABLE GND 2.2μF 3108 TA06 3108fb 19 LTC3108 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641 Rev B) .189 – .196* (4.801 – 4.978) .045 ±.005 .009 (0.229) REF 16 15 14 13 12 11 10 9 .254 MIN .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ±.0015 .150 – .157** (3.810 – 3.988) .0250 BSC RECOMMENDED SOLDER PAD LAYOUT 1 .015 ±.004 = 45$ (0.38 ±0.10) .007 – .0098 (0.178 – 0.249) 2 3 4 5 6 7 .0532 – .0688 (1.35 – 1.75) 8 .004 – .0098 (0.102 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.270) .0250 (0.635) BSC .008 – .012 (0.203 – 0.305) TYP NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) GN16 REV B 0212 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 3. DRAWING NOT TO SCALE 4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE DE/UE Package 12-Lead Plastic DFN (4mm × 3mm) (Reference LTC DWG # 05-08-1695 Rev D) 4.00 ±0.10 (2 SIDES) 7 0.70 ±0.05 3.60 ±0.05 2.20 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 PIN 1 TOP MARK (NOTE 6) 0.200 REF 3.00 ±0.10 (2 SIDES) 0.75 ±0.05 3.30 ±0.10 1.70 ±0.10 6 0.25 ±0.05 PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 1 (UE12/DE12) DFN 0806 REV D 0.50 BSC 0.50 BSC 2.50 REF 2.50 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.40 ±0.10 12 R = 0.05 TYP 3.30 ±0.05 1.70 ±0.05 R = 0.115 TYP 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 3108fb 20 LTC3108 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 04/10 Updated front page text and Typical Appliction 1 Updated Absolute Maximum Ratings and Order Information sections 2 Updated Electrical Characteristics 3 Added graph (3108 G00) to Typical Performance Characteristics 4 Updated Block Diagram 8 Text added to Operation section 9 Changes to Applications Information section Updated Typical Applications B 12-18 18, 19, 22 Updated Related Parts 22 Added vendor information to Table 5 14 3108fb 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. 21 LTC3108 TYPICAL APPLICATION Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity 1nF HOT 1:100 C1 + THERMOELECTRIC GENERATOR VSTORE VOUT2 330pF LTC3108 C2 COLD LPR6235-752SML PGD VLDO SW VS2 VS1 VOUT 5V CSTORE PGOOD 2.2V 3.3V + VOUT2_EN VAUX + VOUT2 VOUT VLDO 2.2μF COUT GND OFF ON 1μF VAUX 1nF 1:100 COLD C1 VSTORE + THERMOELECTRIC GENERATOR VOUT2 330pF LTC3108 C2 HOT LPR6235-752SML SW VS2 VS1 VAUX PGD VLDO VOUT VOUT2_EN GND 3108 TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1041 Bang-Bang Controller VIN: 2.8V to 16V; IQ = 1μA; SO-8 Package LTC1389 Nanopower Precision Shunt Voltage Reference VOUT(MIN) = 1.25V; IQ = 0.8μA; SO-8 Package LT1672/LT1673/ LT1674 Single-/Dual-/Quad-Precision 2μA Rail-to-Rail Op Amps SO-8, SO-14 and MSOP-8 Packages LT3009 3μA IQ, 20mA Linear Regulator VIN: 1.6V to 20V; VOUT(MIN): 0.6V to Adj, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, 5V to Fixed; IQ = 3μA; ISD < 1μA; 2mm × 2mm DFN-8 and SC70 Packages LTC3108-1 Ultralow Voltage Step-Up Converter and Power Manager VIN: 0.02V to 1V; VOUT = 2.5V, 3V, 3.7V, 4.5V Fixed; IQ = 6μA; 3mm × 4mm DFN-12 and SSOP-16 Packages LTC3525L-3/ LTC3525L-3.3/ LTC3525L-5 400mA (ISW), Synchronous Step-Up DC/DC Converter with Output Disconnect VIN: 0.7V to 4V; VOUT(MIN) = 5VMAX; IQ = 7μA; ISD < 1μA; SC70 Package LTC3588-1 Piezoelectric Energy Generator with Integrated High Efficiency Buck Converter VIN: 2.7V to 20V; VOUT(MIN): Fixed to 1.8V, 2.5V, 3.3V, 3.6V; IQ = 0.95μA; 3mm × 3mm DFN-10 and MSOP-10E Packages LTC3642 45V, 50mA Synchronous MicroPower Buck Converter VIN: 4.5V to 45V, 60VMAX; VOUT(MIN): 0.8V to Adj, 3.3V Fixed, 5V Fixed; IQ = 12μA; ISD < 1μA; 3mm × 3mm DFN-8 and MSOP-8E Packages LTC6656 850mA Precision Reference Series Low Dropout Precision LT8410/ LT8410-1 MicroPower 25mA/8mA Low Noise Boost Converter with Integrated Schottky Diode and Output Disconnect VIN: 2.6V to 16V; VOUT(MIN) = 40VMAX; IQ = 8.5μA; ISD < 1μA; 2mm × 2mm DFN-8 Package LTC4O70 Micropower Shunt Li-Ion Charge Controls Charging with μA Source 3108fb 22 Linear Technology Corporation LT 0612 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2010