Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - power management - special purpose 3 mA DFN 12 (4x3)

LTC3108

3108fc

For more information www.linear.com/LTC3108

Typical applicaTion

DescripTion

Ultralow Voltage Step-Up

Converter and Power Manager

The LT C

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 V

OUT

options.

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.

The LTC3108 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 2.35V, 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

Remote Sensors and Radio Power

Surplus Heat Energy Harvesting

HVAC Systems

Industrial Wireless Sensing

Automatic Metering

Building Automation

Predictive Maintenance

3108 TA01a

20mV TO 500mV

VS2

VS1

OUT2

PGOOD

2.2V

470µF

PGD

VLDO

VSTORE

OUT

OUT2_EN

LTC3108

VAUX GND

0.1F

6.3V

3.3V

1µF

1nF

220µF

1:100

330pF

SENSORS

RF LINK

µP

2.2µF

THERMOELECTRIC

GENERATOR

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

3108 TA01b

100 150 250

200 300 350 400

OUT

= 3.3V

OUT

= 470µF

1:100 Ratio

1:50 Ratio

1:20 Ratio

Summary of content (22 pages)

PAGE 1
LTC3108 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 2.35V, 3.3V, 4.1V or 5V - LDO: 2.
PAGE 2
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...............................
PAGE 3
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.
PAGE 4
LTC3108 Typical Performance Characteristics IVOUT and Efficiency vs VIN, 1:20 Ratio Transformer IIN vs VIN, (VOUT = 0V) 1000 TA = 25°C, unless otherwise noted. 4000 1:50 RATIO, C1 = 4.
PAGE 5
LTC3108 Typical Performance Characteristics IVOUT vs VIN and Source Resistance, 1:100 Ratio IVOUT vs VIN and Source Resistance, 1:50 Ratio 10000 TA = 25°C, unless otherwise noted. 1000 C1 = 4.
PAGE 6
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.
PAGE 7
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.
PAGE 8
LTC3108 Block Diagram LTC3108 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 3108 BD 2.2V 2.
PAGE 9
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.
PAGE 10
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.
PAGE 11
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) 3108fc For more information www.linear.
PAGE 12
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.
PAGE 13
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.
PAGE 14
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.
PAGE 15
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.
PAGE 16
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.
PAGE 17
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.
PAGE 18
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.
PAGE 19
LTC3108 Typical Applications Li-Ion Battery Charger and LDO Powered by a Solar Cell T1 1:20 SOLAR CELL* + + – 0.01µF C1 220µF VSTORE VOUT2 330pF LTC3108 C2 SW 2.2V VLDO 4.1V VOUT VS2 VS1 * 2" DIAMETER MONOCRYSTALLINE CELL LIGHT LEVEL ≥ 900 LUX PGD 2.2µF Li-Ion VOUT2_EN VAUX VLDO VOUT 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.
PAGE 20
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.
PAGE 21
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 12-18 18, 19, 22 Updated Related Parts 22 B 06/13 Added vendor information
PAGE 22
LTC3108 Typical Application Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity HOT 1:100 1nF C1 + THERMOELECTRIC GENERATOR VSTORE VOUT2 330pF LTC3108 C2 COLD LPR6235-752SML PGD VLDO SW VS2 VS1 VOUT 5V PGOOD 3.3V VOUT2_EN VAUX + CSTORE VOUT2 2.2V + GND VOUT COUT VLDO 2.