LTC3108EDE#PBF - Linear Technology

LTC3108

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TYPICAL APPLICATION

DESCRIPTION

Ultralow Voltage Step-Up

Converter and Power Manager

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 ﬁ xed VOUT 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 ﬁ xed 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 efﬁ ciency 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

n Operates from Inputs of 20mV

n 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

n Power Good Indicator

n Uses Compact Step-Up Transformers

n Small 12-Lead (3mm × 4mm) DFN or 16-Lead

SSOP Packages

n Remote Sensors and Radio Power

n Surplus Heat Energy Harvesting

n HVAC Systems

n Industrial Wireless Sensing

n Automatic Metering

n Building Automation

n Predictive Maintenance

3108 TA01a

20mV TO 500mV

VS2

VS1

VOUT2 PGOOD

2.2V

470µF

PGD

VLDO

VSTORE

VOUT

VOUT2_EN

LTC3108

VAUX GND

0.1F

6.3V

3.3V

1µF

1nF

220µF

1:100

330pF

SENSORS

RF LINK

µP

2.2µF

THERMOELECTRIC

GENERATOR

VOUT 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.

VIN (mV)

TIME (sec)

100

1000

3108 TA01b

0100 150 250

50 200 300 350 400

VOUT = 3.3V

COUT = 470µF

1:100 Ratio

1:50 Ratio

1:20 Ratio

LTC3108

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ABSOLUTE MAXIMUM RATINGS

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

(Note 1)

GND

VOUT2_EN

VS1

VS2

VAUX

VSTORE

VOUT

VOUT2

VLDO

PGD

TOP VIEW

DE PACKAGE

12-LEAD (4mm s 3mm) PLASTIC DFN

TJMAX = 125°C, θJA = 43°C/W

EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB (NOTE 4)

GN PACKAGE

16-LEAD PLASTIC SSOP NARROW

TOP VIEW

GND

VAUX

VSTORE

VOUT

VOUT2

VLDO

PGD

GND

VOUT2_EN

VS1

VS2

GND

TJMAX = 125°C, θJA = 110°C/W

PIN CONFIGURATION

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Start-Up Voltage Using 1:100 Transformer Turns Ratio, VAUX = 0V 20 50 mV

No-Load Input Current Using 1:100 Transformer Turns Ratio; VIN = 20mV,

VOUT2_EN = 0V; All Outputs Charged and in Regulation

3mA

Input Voltage Range Using 1:100 Transformer Turns Ratio lVSTARTUP 500 mV

The l denotes the speciﬁ cations which apply over the full operating

junction temperature range, otherwise speciﬁ cations are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted.

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 speciﬁ ed for other ﬁ xed output voltages or wider operating temperature ranges.

*The temperature grade is identiﬁ ed 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 speciﬁ

cations, go to: http://www.linear.com/tapeandreel/

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

LTC3108

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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 speciﬁ cations from 0°C to 85°C

junction temperature. Speciﬁ cations 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 speciﬁ c

operating conditions in conjunction with board layout, the rated thermal

package thermal resistance and other environmental factors. The junction

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: Speciﬁ cation 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.

ELECTRICAL CHARACTERISTICS

The l denotes the speciﬁ cations which apply over the full operating

junction temperature range, otherwise speciﬁ cations are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output Voltage VS1 = VS2 = GND

VS1 = VAUX, VS2 = GND

VS1 = GND, VS2 = VAUX

VS1 = VS2 = VAUX

2.30

3.234

4.018

4.90

2.350

3.300

4.100

5.000

2.40

3.366

4.182

5.10

VOUT Quiescent Current VOUT = 3.3V, VOUT2_EN = 0V 0.2 µA

VAUX Quiescent Current No Load, All Outputs Charged 6 9 µA

LDO Output Voltage 0.5mA Load l2.134 2.2 2.266 V

LDO Load Regulation For 0mA to 2mA Load 0.5 1 %

LDO Line Regulation For VAUX from 2.5V to 5V 0.05 0.2 %

LDO Dropout Voltage ILDO = 2mA l100 200 mV

LDO Current Limit VLDO = 0V l411 mA

VOUT Current Limit VOUT = 0V l2.8 4.5 7 mA

VSTORE Current Limit VSTORE = 0V l2.8 4.5 7 mA

VAUX Clamp Voltage Current into VAUX = 5mA l5 5.25 5.55 V

VSTORE Leakage Current VSTORE = 5V 0.1 0.3 µA

VOUT2 Leakage Current VOUT2 = 0V, VOUT2_EN = 0V 0.1 µA

VS1, VS2 Threshold Voltage l0.4 0.85 1.2 V

VS1, VS2 Input Current VS1 = VS2 = 5V 0.01 0.1 µA

PGOOD Threshold (Rising) Measured Relative to the VOUT Voltage –7.5 %

PGOOD Threshold (Falling) Measured Relative to the VOUT Voltage –9 %

PGOOD VOL Sink Current = 100µA 0.15 0.3 V

PGOOD VOH Source Current = 0 2.1 2.2 2.3 V

PGOOD Pull-Up Resistance 1M

VOUT2_EN Threshold Voltage VOUT2_EN Rising l0.4 1 1.3 V

VOUT2_EN Pull-Down Resistance 5M

VOUT2 Turn-On Time 5µs

VOUT2 Turn-Off Time (Note 3) 0.15 µs

VOUT2 Current Limit VOUT = 3.3V l0.15 0.3 0.45 A

VOUT2 Current Limit Response Time (Note 3) 350 ns

VOUT2 P-Channel MOSFET On-Resistance VOUT = 3.3V (Note 3) 1.3 

N-Channel MOSFET On-Resistance C2 = 5V (Note 3) 0.5 

LTC3108

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TYPICAL PERFORMANCE CHARACTERISTICS

IVOUT and Efﬁ ciency vs VIN,

1:20 Ratio Transformer

Input Resistance vs VIN

(VOUT Charging)

IVOUT vs VIN and Source Resistance,

1:20 Ratio

TA = 25°C, unless otherwise noted.

IVOUT and Efﬁ ciency vs VIN,

1:50 Ratio Transformer

IVOUT and Efﬁ ciency vs VIN,

1:100 Ratio Transformer

VIN (mV)

IVOUT (µA)

EFFICIENCY (%)

2500

3000

3500

2000

1500

100 200 400

300 500

500

1000

4000

3108 G01

IVOUT

(VOUT = 4.5V)

EFFICIENCY

(VOUT = 4.5V)

IVOUT

(VOUT = 0V)

C1 = 10nF

VIN (mV)

IVOUT (µA)

EFFICIENCY (%)

2000

2400

2800

1600

1200

100 200 400

300 500

400

800

3200

3108 G02

C1 = 4.7nF

IVOUT

(VOUT = 4.5V)

EFFICIENCY

(VOUT = 4.5V)

IVOUT

(VOUT = 0V)

VIN (mV)

IVOUT (µA)

EFFICIENCY (%)

1000

1200

800

600

100 200 400

300 500

200

400

1400

3108 G03

C1 = 1nF

IVOUT

(VOUT = 4.5V)

EFFICIENCY

(VOUT = 4.5V)

IVOUT

(VOUT = 0V)

VIN (mV)

INPUT RESISTANCE ()

100 200 400

300 500

3108 G04

1:20 RATIO

1:50 RATIO

1:100 RATIO

VIN OPEN-CIRCUIT (mV)

IVOUT (µA)

100

1000

10000

3108 G05

0200 300 500

100 400 600 700 800

1

2

5

10

C1 = 10nF

VIN (mV)

IIN (mA)

3108 G00

1000

100

110 100 1000

1:50 RATIO, C1 = 4.7n

1:100 RATIO, C1 = 1n

1:20 RATIO, C1 = 10n

IIN vs VIN, (VOUT = 0V)

LTC3108

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IVOUT vs dT and TEG Size,

1:100 Ratio

IVOUT vs VIN and Source Resistance,

1:50 Ratio

IVOUT vs VIN and Source Resistance,

1:100 Ratio

VIN OPEN-CIRCUIT (mV)

IVOUT (µA)

100

1000

10000

3108 G06

0200 300 500

100 400 600 700 800

1

2

5

10

C1 = 4.7nF

VIN OPEN-CIRCUIT (mV)

IVOUT (µA)

100

1000

3108 G07

0100 200 300 400 500

1

2

5

10

C1 = 1nF

dT ACROSS TEG (°C)

IVOUT (µA)

100

1000

10000

3108 G08

0.1 10

1100

VOUT = 0V

40mm

TEG

15mm

TEG

1:50 RATIO

1:100 RATIO

1:50 RATIO

1:100 RATIO

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, unless otherwise noted.

LDO Load Regulation

Resonant Switching Waveforms

LDO Dropout Voltage

LDO LOAD (mA)

–1.00

DROP IN VLDO (%)

–0.75

–0.50

0.5 11.5 2 32.5 3.5

–0.25

0.00

3108 G10

LDO LOAD (mA)

0.00

DROPOUT VOLTAGE (V)

0.04

0.08

0.12

0.5 11.5 2 32.5 3.5

0.16

0.20

0.02

0.06

0.10

0.14

0.18

3108 G11

10µs/DIV

C1 PIN

2V/DIV

C2 PIN

2V/DIV

SW PIN

50mV/

DIV

3108 G09

VIN = 20mV

1:100 RATIO TRANSFORMER

LTC3108

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TYPICAL PERFORMANCE CHARACTERISTICS

Start-Up Voltage Sequencing

VOUT and PGD Response

During a Step Load

VOUT Ripple LDO Step Load Response

Enable Input and VOUT2 Running on Storage Capacitor

TA = 25°C, unless otherwise noted.

10sec/DIV 3108 G12

CH1

VSTORE

1V/DIV

CH2, VOUT

1V/DIV

CH3, VLDO

1V/DIV

VIN = 50mV

1:100 RATIO TRANSFORMER

COUT = 220µF

CSTORE = 470µF

CLDO = 2.2µF

5ms/DIV 3108 G13

CH2

VOUT

1V/DIV

CH1

PGD

1V/DIV

50mA LOAD STEP

COUT = 220µF

100ms/DIV 3108 G14

20mV/

DIV

30µA LOAD

COUT = 220µF

1ms/DIV 3108 G16

CH2, VOUT2

1V/DIV

CH1

VOUT2_EN

1V/DIV

10mA LOAD ON VOUT2

COUT = 220µF

5sec/DIV 3108 G17

CH2, VOUT

1V/DIV

CH1, VIN

50mV/DIV

CH3

VSTORE

1V/DIV

CH4, VLDO

1V/DIV

CSTORE = 470µF

VOUT LOAD = 100µA

VLDO

20mV/DIV

ILDO

5mA/DIV

200µs/DIV 3108 G15

0mA TO 3mA LOAD STEP

CLDO = 2.2µF

LTC3108

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VAUX (Pin 1/Pin 2): Output of the Internal Rectiﬁ er Cir-

cuit 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 1M resistor. If VOUT drops 9%

below its programmed value PGD will go low. This pin

can sink up to 100µA.

VS2 (Pin 7/Pin 10): VOUT Select Pin 2. Connect this pin

to ground or VAUX to program the output voltage (see

Table 1).

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 Rectiﬁ er

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

PIN FUNCTIONS

(DFN/SSOP)

LTC3108

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BLOCK DIAGRAM

OPERATION

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 measure-

ments 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.

(Refer to the Block Diagram)

3108 BD

5.25V

1.2V

VREF

SW VOUT

VSTORE

VLDO

OFF ON

VOUT2

VOUT

PROGRAM

COUT

PGOOD

VOUT2_EN

VOUT

VS1

VS2

PGD

VSTORE

CIN

VIN

VLDO CSTORE

1µF

1:100

SYNC RECTIFY REFERENCE

VOUT

2.2V

CHARGE

CONTROL

VAUX

–

ILIM

LTC3108

1.3

0.5

EXPOSED PAD (DFN)

2.2µF

GND (SSOP)

VREF LDO

VREF

VBEST

LTC3108

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OPERATION

Oscillator

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.

Charge Pump and Rectiﬁ er

The AC voltage produced on the secondary winding of

the transformer is boosted and rectiﬁ ed using an external

charge pump capacitor (from the secondary winding to pin

C1) and the rectiﬁ ers internal to the LTC3108. The rectiﬁ er

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 Applica-

tion 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.

Voltage Reference

The LTC3108 includes a precision, micropower reference,

for accurate regulated output voltages. This reference

becomes active as soon as VAUX exceeds 2V.

Synchronous Rectiﬁ ers

Once VAUX exceeds 2V, synchronous rectiﬁ ers in parallel

with each of the internal diodes take over the job of rectify-

ing the input voltage, improving efﬁ ciency.

Low Dropout Linear Regulator (LDO)

The LTC3108 includes a low current LDO to provide a

regulated 2.2V output for powering low power proces-

sors 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 stor-

age 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, ac-

cording 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

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 internal programmable resistor divider sets VOUT,

eliminating the need for very high value external resistors

that are susceptible to board leakage.

LTC3108

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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

(1M) 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 conﬁ guration 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

ampliﬁ ers, 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/transmit-

ter. 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 cir-

cuitry 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 stor-

age 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.

OPERATION

LTC3108

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Figure 1. Output Voltage Sequencing with VOUT Programmed for 3.3V (Time Not to Scale)

OPERATION

3108 F01a

TIME (ms)

VOLTAGE (V)

3.0

2.0

1.0

0 70

20 40

10 30 50 60 80

3.0

2.0

1.0

5.0

2.5

5.0

2.5

VSTORE (V)

PGD (V)

VOUT (V)

VLDO (V)

VAUX (V)

LTC3108

3108fb

Introduction

The LTC3108 is designed to gather energy from very low

input voltage sources and convert it to usable output volt-

ages 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 transmit-

ting 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.

The PGD signal can be used to enable a sleeping micro-

processor or other circuitry when VOUT reaches regulation,

indicating that enough energy is available for a burst.

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.

APPLICATIONS INFORMATION

Figure 2. Typical Performance of a Peltier Cell Acting as a Thermoelectric Generator

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.

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 ﬁ lter capacitor and

the ESR of the voltage source should be much longer than

the period of the resonant switching frequency.

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 junc-

tions, sandwiched between two parallel ceramic plates.

Although Peltier cells are often used as coolers by apply-

ing 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 tem-

perature 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

3108 F02

1000

100

11 10 100

dT (°C)

TEG VOPEN_CIRCUIT (mV)

TEG MAXIMUM POUT —IDEAL (mW)

100

0.1

VOC

MAX POUT

(IDEAL)

TEG: 30mm

127 COUPLES

R = 2

LTC3108

3108fb

this manner, a Peltier cell is referred to as a thermoelectric

generator (TEG).

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 am-

bient temperature. The internal resistance (ESR) of most

cells is in the range of 1 to 5, allowing for reasonable

power transfer. The curves in Figure 2 show the open-

circuit output voltage and maximum power transfer for a

typical Peltier cell (with an ESR of 2) over a 20°C range

of temperature differential.

TEG Load Matching

The LTC3108 was designed to present a minimum input

resistance (load) in the range of 2 to 10, 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

current capability by providing a higher input voltage

under load.

Peltier Cell (TEG) Suppliers

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

APPLICATIONS INFORMATION

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

Marlow Industries RC3-8-01 RC6-6-01 RC12-8-01LS

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

LTC3108

3108fb

Thermopile Generator

Thermopile generators (also called powerpile generators)

are made up of a number of series-connected thermo-

couples 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 tem-

perature of a ﬂ ame. Typical examples are the Honeywell

CQ200 and Q313. These devices have an internal series

resistance of less than 3, 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 convert-

ers to operate. However, many variables will affect the

performance in these applications. Light levels can vary

over several orders of magnitude and depend on light-

ing conditions (the type of lighting and indoor versus

outdoor). Different types of light (sunlight, incandescent,

ﬂ uorescent) 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-ﬁ lm). Therefore, the photovoltaic

cell must be chosen for the type and amount of light avail-

able. 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.

Any source whose peak voltage exceeds 2.5V AC or 5V

DC can be connected to the C1 input through a current-

limiting resistor where it will be rectiﬁ ed/peak detected. In

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 100/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

efﬁ ciency. The secondary winding inductance will deter-

mine the resonant frequency of the oscillator, according

to the following formula.

Frequency 1

2 • • L(sec)• C Hz

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)

APPLICATIONS INFORMATION

LTC3108

3108fb

C1 Capacitor

The charge pump capacitor that is connected from the

transformer’s secondary winding to the C1 pin has an ef-

fect on converter input resistance and maximum output

current capability. Generally, a minimum value of 1nF is

recommended when operating from very low input volt-

ages 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.

Squegging

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 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 difﬁ cult to

predict when and if squegging will occur in a given ap-

plication. While squegging is not harmful, it reduces the

average output current capability of the LTC3108.

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 1M

are sufﬁ cient 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.

Using External Charge Pump Rectiﬁ ers

The synchronous charge pump rectiﬁ ers 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.

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 cur-

rent capability from the LTC3108. However, due to the

resulting increase in rectiﬁ er currents and resonant oscil-

lator frequency in these applications, the use of external

charge pump rectiﬁ ers is recommended for optimal

performance.

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 rectiﬁ ers (such as 1N4148 or

1N914 diodes) should be used. These are available as

dual diodes in a single package. Avoid the use of Schottky

rectiﬁ ers, as their lower forward voltage drop increases

the minimum start-up voltage. See the Typical Applications

schematics for an example.

VOUT and VSTORE Capacitor

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.

≥Δ

C(µF)I (mA) • t (ms)

V(V)

OUT LOAD PULSE

OUT

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.

APPLICATIONS INFORMATION

LTC3108

3108fb

The VSTORE capacitor may be of very large value (thou-

sands 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 tem-

perature for which it will be used. The VSTORE capacitor

can be sized using the following:

[]

≥++ +

−

C6µA I I (I • t • f) • TSTORE

5.25 V

STORE Q LDO BURST

OUT

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 beneﬁ cial storage time.

To minimize losses and capacitor charge time, all capaci-

tors 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)

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.

Due to the very low input voltage the circuit may operate

from, the connections to VIN, the primary of the trans-

former 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 efﬁ ciency and increase capacitor charge time.

Also, due to the low charge currents available at the out-

puts 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.

APPLICATIONS INFORMATION

3108 FO3

VOUT2

VOUT

VIN

VIAS TO GROUND PLANE

VLDO PGOOD

GND

VOUT2_EN

VS1

VS2

VOUT

VOUT2

VLDO

PGD

VAUX

VSTORE

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 major-

ity 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

LTC3108

3108fb

APPLICATIONS INFORMATION

at which the load pulses can occur for a given output cur-

rent from the LTC3108 will also be shown.

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:

≥=C(µF)

40mA • 1ms

0.33V 121µF

OUT

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 efﬁ ciency 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 ca-

pacitor 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:

=−==t150µF • 0.33V

(50µA 17µA) 1.5sec or f 0.666Hz

MAX

Therefore, in this application example, the circuit can sup-

port a 1ms transmit burst every 1.5 seconds.

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.

The following formula enables the user to calculate the

time it will take to charge the LDO output capacitor and

the VOUT capacitor the ﬁ rst 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.

=−

t2.2V • 2.2µF

LDO

CHG LDO

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:

=−−

+t3.3V •150µF

II It

VOUT

CHG VOUT LDO

LDO

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

ﬁ xed. 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:

≥+II

I•t

CHG Q BURST

Where IQ is the sleep current on VOUT required by the ex-

ternal circuitry in between bursts (including cap leakage),

IBURST is the total load current during the burst, t is the

LTC3108

3108fb

duration of the burst and T is the period of the transmit

burst rate (essentially the time between bursts).

In this example, IQ = 5µA, IBURST = 100mA, t = 5ms and

T = one hour. The average charge current required from

the LTC3108 would be:

≥+ =I5µA

100mA • 0.005sec

3600sec 5.14µA

CHG

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

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).

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.

APPLICATIONS INFORMATION

Peltier-Powered Energy Harvester for Remote Sensor Applications

TYPICAL APPLICATIONS

3108 TA02

VS2

VS1

COOPER BUSSMAN PB-5ROH104-R

OR KR-5R5H104-R

VOUT2 VOUT2

PGOOD

2.2V

COUT*

PGD

VLDO

VSTORE

VOUT

VOUT2_EN

LTC3108

VAUX GND

CSTORE

0.1F

6.3V

3.3V

1µF

1nF

CIN

1:100

T1: COILCRAFT LPR6235-752SML

*COUT VALUE DEPENDENT ON

THE MAGNITUDE AND DURATION

OF THE LOAD PULSE

330pF

∆T = 1°C TO 20°C

SENSORS

XMTR

µP

2.2µF

OFF

3.3V

THERMOELECTRIC

GENERATOR

LTC3108

3108fb

TYPICAL APPLICATIONS

Li-Ion Battery Charger and LDO Powered by a Solar Cell

Supercapacitor Charger and LDO Powered by a Thermopile Generator

3108 TA04

HONEYWELL

CQ200

THERMOPILE

VS2

VS1

VSTORE

VOUT2

PGOOD

VLDO

CAP-XX GZ115F

PGD

VLDO

VOUT

VOUT2_EN

LTC3108

VAUX GND

2.2µF

150mF

2.5V

2.2µF

4.7nF

T1: COILCRAFT LPR6235-123QML

2.2V

2.35V

1:50

330pF

220µF

+VOUT

3108 TA03

SOLAR CELL*

VS2

VS1

VSTORE

VOUT2

VLDO

PGD

VLDO

VOUT

VOUT2_EN

LTC3108

VAUX GND

2.2µF

Li-Ion

4.7µF

0.01µF

2.2V

4.1V

1:20

330pF

220µF

–

VOUT

* 2" DIAMETER MONOCRYSTALLINE CELL

LIGHT LEVEL ≥ 900 LUX

T1: COILCRAFT LPR6235-253PML

DC Input Energy Harvester and Power Manager

3108 TA05

VS2

VS1

VOUT2 VOUT2

PGOOD

2.2V

COUT

PGD

VLDO VLDO

VSTORE

VOUT VOUT

VOUT2_EN VOUT2_ENABLE

LTC3108

VAUX GND

CSTORE

3.3V

2.2µF

VIN

VIN > 5V

RIN

RIN > 100/ V

2.2µF

–

AC Input Energy Harvester and Power Manager

3108 TA06

VS1

VS2

VOUT2 VOUT2

PGOOD

2.2V

COUT

PGD

VLDO VLDO

VSTORE

VOUT VOUT

VOUT2_EN VOUT2_ENABLE

LTC3108

VAUX GND

CSTORE

2.2µF

CIN

VIN

VIN > 5VP-P

- PIEZO

- 60Hz

RIN

RIN > 100/ V

2.2µF

LTC3108

3108fb

GN16 REV B 0212

345678

.229 – .244

(5.817 – 6.198)

.150 – .157**

(3.810 – 3.988)

16 15 14 13

.189 – .196*

(4.801 – 4.978)

12 11 10 9

.016 – .050

(0.406 – 1.270)

.015 ±.004

(0.38 ±0.10) = 45$

0° – 8° TYP

.007 – .0098

(0.178 – 0.249)

.0532 – .0688

(1.35 – 1.75)

.008 – .012

(0.203 – 0.305)

TYP

.004 – .0098

(0.102 – 0.249)

.0250

(0.635)

BSC

.009

(0.229)

REF

.254 MIN

RECOMMENDED SOLDER PAD LAYOUT

.150 – .165

.0250 BSC.0165 ±.0015

.045 ±.005

* 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

INCHES

(MILLIMETERS)

NOTE:

1. CONTROLLING DIMENSION: INCHES

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE

GN Package

16-Lead Plastic SSOP (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1641 Rev B)

4.00 ±0.10

(2 SIDES)

3.00 ±0.10

(2 SIDES)

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

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

1.70 ±0.10

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

2.50 REF

127

PIN 1 NOTCH

R = 0.20 OR

0.35 × 45°

CHAMFER

PIN 1

TOP MARK

(NOTE 6)

0.200 REF

0.00 – 0.05

(UE12/DE12) DFN 0806 REV D

3.30 ±0.10

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

2.20 ±0.05

0.70 ±0.05

3.60 ±0.05

PACKAGE

OUTLINE

1.70 ±0.05

3.30 ±0.05

0.50 BSC

0.25 ±0.05

DE/UE Package

12-Lead Plastic DFN (4mm × 3mm)

(Reference LTC DWG # 05-08-1695 Rev D)

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

LTC3108

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

A 04/10 Updated front page text and Typical Appliction

Updated Absolute Maximum Ratings and Order Information sections

Updated Electrical Characteristics

Added graph (3108 G00) to Typical Performance Characteristics

Updated Block Diagram

Text added to Operation section

Changes to Applications Information section

Updated Typical Applications

Updated Related Parts

12-18

18, 19, 22

B Added vendor information to Table 5 14

LTC3108

3108fb

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0612 REV B • PRINTED IN USA

RELATED PARTS

TYPICAL APPLICATION

PART NUMBER DESCRIPTION COMMENTS

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LT1672/LT1673/

LT1674

Single-/Dual-/Quad-Precision 2µA Rail-to-Rail Op Amps SO-8, SO-14 and MSOP-8 Packages

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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

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Efﬁ ciency 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

3108 TA07

HOT

COLD C2

VS2

VS1

VSTORE

VOUT2 VOUT2

PGOOD

VOUT

VLDO

COUT

PGD

VLDO

VOUT

VOUT2_EN

LTC3108

VAUX GND

2.2µF

CSTORE

VAUX

1µF

1nF

2.2V

3.3V

1:100

LPR6235-752SML

330pF

OFF

VS2

VS1

VSTORE

VOUT2

PGD

VLDO

VOUT

VOUT2_EN

LTC3108

VAUX GND

1nF

1:100

LPR6235-752SML

330pF

COLD

HOT

THERMOELECTRIC

GENERATOR

THERMOELECTRIC

GENERATOR

Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity