Datasheet

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LTC3108-1

31081fb

For more information www.linear.com/LTC3108-1

Typical applicaTion

DescripTion

Ultralow Voltage Step-Up

Converter and Power Manager

The LT C

3108-1 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.

Using a small step-up transformer, the LTC3108-1 provides

a complete power management solution for wireless sens

ing 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. The LTC3108-1 is functionally equivalent to the

LTC3108 except for its unique ﬁxed V

OUT

options.

The LTC3108-1 is available in a small, thermally enhanced

12-lead (3mm × 4mm) DFN package and a 16-lead SSOP

package.

Wireless Remote Sensor Application

Powered From a Peltier Cell

FeaTures

applicaTions

Operates from Inputs of 20mV

Complete Energy Harvesting Power

Management System

- Selectable V

OUT

of 2.5V, 3V, 3.7V or 4.5V

- 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

Remote Sensors and Radio Power

Surplus Heat Energy Harvesting

HVAC Systems

Industrial Wireless Sensing

Automatic Metering

Building Automation

Predictive Maintenance

31081 TA01a

THERMOELECTRIC

GENERATOR

20mV TO 500mV

VS2

VS1

OUT2

PGOOD

2.2V

470µF

PGD

VLDO

VSTORE

OUT

OUT2_EN

LTC3108-1

VAUX GND

0.1F

6.3V

5.25V

1µF

1nF

220µF

1:100

330pF

SENSORS

RF LINK

µP

2.2µF

OUT

Charge Time

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.

(mV)

TIME (sec)

100

1000

31081 TA01b

100 150 250

200 300 350 400

OUT

= 3V

OUT

= 470µF

1:100 Ratio

1:50 Ratio

1:20 Ratio

Summary of content (24 pages)

PAGE 1
LTC3108-1 Ultralow Voltage Step-Up Converter and Power Manager Features n n n n n Description Operates from Inputs of 20mV Complete Energy Harvesting Power Management System - Selectable VOUT of 2.5V, 3V, 3.7V or 4.5V - LDO: 2.
PAGE 2
LTC3108-1 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.............................
PAGE 3
LTC3108-1 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 = 3.7V, VOUT2_EN = 0V VAUX Quiescent Current No Load, All Outputs Charged LDO Output Voltage 0.
PAGE 4
LTC3108-1 Typical Performance Characteristics 1000 TA = 25°C, unless otherwise noted. IVOUT and Efficiency vs VIN, 1:20 Ratio Transformer IIN vs VIN, (VOUT = 0V) 4000 1:50 RATIO, C1 = 4.
PAGE 5
LTC3108-1 Typical Performance Characteristics IVOUT vs VIN and Source Resistance, 1:50 Ratio 10000 IVOUT vs VIN and Source Resistance, 1:100 Ratio 1000 C1 = 4.7nF TA = 25°C, unless otherwise noted.
PAGE 6
LTC3108-1 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.
PAGE 7
LTC3108-1 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.
PAGE 8
LTC3108-1 Block Diagram LTC3108-1 VOUT2 1.3Ω ILIM VOUT2 VOUT2_EN SYNC RECTIFY VOUT C1 VOUT CIN COUT 5.25V C2 SW OFF ON 5M C1 1:100 VIN REFERENCE 1.2V VREF + – C2 VOUT SW VSTORE CHARGE CONTROL VS1 VS2 0.5Ω VOUT PROGRAM VREF VLDO 1M – + VAUX 1µF VOUT GND (SSOP) VBEST PGD PGOOD VSTORE VREF LDO EXPOSED PAD (DFN) CSTORE VLDO 31081 BD 2.2V 2.
PAGE 9
LTC3108-1 Operation Oscillator Synchronous Rectifiers The LTC3108-1 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.
PAGE 10
LTC3108-1 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.
PAGE 11
LTC3108-1 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) 31081 F01a Figure 1. Output Voltage Sequencing with VOUT Programmed for 3V (Time Not to Scale) 31081fb For more information www.linear.
PAGE 12
LTC3108-1 Applications Information Introduction Refer to the IIN vs VIN curves in the Typical Performance Characteristics section to see what input current is required for the source for a given input voltage. The LTC3108-1 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.
PAGE 13
LTC3108-1 Applications Information this manner, a Peltier cell is referred to as a thermoelectric generator (TEG). The low voltage capability of the LTC3108-1 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.
PAGE 14
LTC3108-1 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.
PAGE 15
LTC3108-1 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.
PAGE 16
LTC3108-1 Applications Information 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.
PAGE 17
LTC3108-1 Applications Information 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.
PAGE 18
LTC3108-1 Applications Information 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 11.35 seconds. In this example, IQ = 5µA, IBURST = 100mA, t = 5ms and T = one hour. The average charge current required from the LTC3108-1 would be: Design Example 2 ICHG ≥ 5µA + In many pulsed load applications, the duration, magnitude and frequency of the load current bursts are known and fixed.
PAGE 19
LTC3108-1 Typical Applications Supercapacitor Charger and LDO Powered by a Solar Cell (Uses External Charge Pump Rectifiers) 0.022µF IVOUT vs Illuminance (2" Diameter Monocrystalline Cell) BAS31 VAUX 10,000 INCANDESCENT LIGHT + SOLAR CELL* – + 220µF C1 330pF VSTORE 1000 VOUT2 LTC3108-1 PGD C2 2.2V VLDO 499k 3.0V VOUT * 2" DIAMETER MONOCRYSTALLINE CELL LIGHT LEVEL ≥ 900 LUX T1: COILCRAFT LPR6235-253PML + SW VS2 IVOUT (µA) T1 1:20 VLDO 100 VOUT 2.
PAGE 20
LTC3108-1 Typical Applications DC Input Energy Harvester and Power Manager RIN RIN > 100Ω/ V + – C1 5.25V VSTORE VIN VIN > 5V VOUT2 PGD C2 SW LTC3108-1 VS1 VOUT2_EN VAUX CSTORE PGOOD 2.2V VLDO VOUT VS2 + VOUT2 3V + VLDO 2.2µF VOUT COUT VOUT2_ENABLE GND 31081 TA05 2.2µF AC Input Energy Harvester and Power Manager RIN CIN RIN > 100Ω/ V C1 VSTORE AC VIN VIN > 5VP-P VOUT2 - PIEZO - 60Hz PGD LTC3108-1 C2 VS2 VOUT2_EN VS1 VAUX CSTORE PGOOD 2.2V 4.5V + VOUT VLDO 2.
PAGE 21
LTC3108-1 Typical Applications Low Profile (1.5mm) Step-Up Converter/Harvester Using 1:10 Transformer VSTORE T1 1:10 VIN 150mV TO 600mV CIN 3V AT 20mA VOUT2 VOUT2 499k CRES* 390pF 0.1µF C1 330pF PGD LTC3108-1 VLDO C2 10ms PGOOD 2.2V VLDO 2.2µF VOUT SW VS2 0.068µF VS1 T1: COILCRAFT LPR4012-202LML BAS31 *CRES LOWERS START-UP VOLTAGE TO 135mV TYPICAL VOUT2_EN GND VAUX 3V + 330µF ×3 AVX TPSX337M004R0100 ENABLE 2.
PAGE 22
LTC3108-1 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) 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 0.40 ±0.10 12 R = 0.05 TYP 3.30 ±0.05 1.70 ±0.05 R = 0.115 TYP PIN 1 TOP MARK (NOTE 6) 0.200 REF 0.50 BSC 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.
PAGE 23
LTC3108-1 Revision History REV DATE DESCRIPTION A 06/12 Added vendor information to Table 5 PAGE NUMBER 14 B 08/13 Changed Würth transformer part numbers 14 31081fb 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 itsinformation circuits as described herein will not infringe on existing patent rights. For more www.
PAGE 24
LTC3108-1 Typical Application Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity HOT 1:100 1nF C1 + THERMOELECTRIC GENERATOR VSTORE TEC 330pF VOUT2 C2 COLD 499k LPR6235-752SML LTC3108-1 PGD VLDO SW VS2 VS1 VOUT 5.25V PGOOD 3V VOUT2_EN VAUX GND + CSTORE VOUT2 2.2V + VOUT VLDO 2.