LTC3108
1
Rev. D
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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 (ther-
moelectric 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.
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 pro-
grammed to one of four fixed voltages to power a wire-
less 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
n Operates from Inputs of 20mV
n Complete Energy Harvesting Power
Management System
n Selectable VOUT of 2.35V, 3.3V, 4.1V or 5V
n LDO: 2.2V at 3mA
n Logic Controlled Output
n 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
C1
20mV TO 500mV
C2
SW
VS2
VS1
VOUT2 PGOOD
2.2V
470µF
PGD
VLDO
VSTORE
+
VOUT
VOUT2_EN
LTC3108
VAUX GND
0.1F
6.3V
5V
3.3V
1µF
1nF
220µF
1:100
330pF
SENSORS
RF LINK
µP
2.2µF
+
+
+
THERMOELECTRIC
GENERATOR
VOUT Charge Time
All registered trademarks and trademarks are the property of their respective owners.
VIN (mV)
TIME (sec)
10
1
100
1000
0
3108 TA01b
0100 150 250
50 200 300 350 400
VOUT = 3.3V
COUT = 470µF
1:100 Ratio
1:50 Ratio
1:20 Ratio
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LTC3108
2
Rev. D
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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)
12
11
10
9
8
7
13
GND
1
2
3
4
5
6
SW
C2
C1
VOUT2_EN
VS1
VS2
VAUX
VSTORE
VOUT
VOUT2
VLDO
PGD
TOP VIEW
DE PACKAGE
12-LEAD (4mm × 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
TJMAX = 125°C, θJA = 110°C/W
1
2
3
4
5
6
7
8
TOP VIEW
16
15
14
13
12
11
10
9
GND
VAUX
VSTORE
VOUT
VOUT2
VLDO
PGD
GND
GND
SW
C2
C1
VOUT2_EN
VS1
VS2
GND
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
3 mA
Input Voltage Range Using 1:100 Transformer Turns Ratio lVSTARTUP 500 mV
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.
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
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
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
3
Rev. D
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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 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
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.
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 MIN TYP MAX UNITS
Output Voltage VS1 = VS2 = GND
VS1 = VAUX, VS2 = GND
VS1 = GND, VS2 = VAUX
VS1 = VS2 = VAUX
l
l
l
l
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
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 100 200 mV
LDO Current Limit VLDO = 0V l4 11 mA
VOUT Current Limit VOUT = 0V l2.8 4.5 7.5 mA
VSTORE Current Limit VSTORE = 0V l2.8 4.5 7.5 mA
VAUX Clamp Voltage Current into VAUX = 5mA l5 5.25 5.60 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 1 MΩ
VOUT2_EN Threshold Voltage VOUT2_EN Rising l0.4 1 1.3 V
VOUT2_EN Pull-Down Resistance 5 MΩ
VOUT2 Turn-On Time 5 µs
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 Ω
N-Channel MOSFET On-Resistance C2 = 5V (Note 3) 0.5 Ω
LTC3108
4
Rev. D
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TYPICAL PERFORMANCE CHARACTERISTICS
IVOUT and Efficiency 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 Efficiency vs VIN,
1:50 Ratio Transformer
IVOUT and Efficiency vs VIN,
1:100 Ratio Transformer
VIN (mV)
0
I
VOUT
(µA)
EFFICIENCY (%)
2500
3000
3500
2000
1500
100 200 400
300 500
500
0
1000
4000
50
60
70
40
30
10
0
20
80
3108 G01
IVOUT
(VOUT = 4.5V)
EFFICIENCY
(VOUT = 4.5V)
IVOUT
(VOUT = 0V)
C1 = 10nF
VIN (mV)
0
IVOUT (µA)
EFFICIENCY (%)
2000
2400
2800
1600
1200
100 200 400
300 500
400
0
800
3200
50
60
70
40
30
10
0
20
80
3108 G02
C1 = 4.7nF
IVOUT
(VOUT = 4.5V)
EFFICIENCY
(VOUT = 4.5V)
IVOUT
(VOUT = 0V)
VIN (mV)
0
IVOUT (µA)
EFFICIENCY (%)
1000
1200
800
600
100 200 400
300 500
200
0
400
1400
50
60
70
40
30
10
0
20
3108 G03
C1 = 1nF
IVOUT
(VOUT = 4.5V)
EFFICIENCY
(VOUT = 4.5V)
IVOUT
(VOUT = 0V)
VIN (mV)
0
INPUT RESISTANCE (Ω)
5
6
7
4
3
100 200 400
300 500
1
0
2
8
9
10
3108 G04
1:20 RATIO
1:50 RATIO
1:100 RATIO
VIN OPEN-CIRCUIT (mV)
IVOUT (µA)
100
10
1000
10000
0
3108 G05
0200 300 500
100 400 600 700 800
1Ω
2Ω
5Ω
10Ω
C1 = 10nF
VIN (mV)
IIN (mA)
3108 G00
1000
100
10
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
5
Rev. D
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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
10
1000
10000
0
3108 G06
0200 300 500
100 400 600 700 800
1Ω
2Ω
5Ω
10Ω
C1 = 4.7nF
VIN OPEN-CIRCUIT (mV)
I
VOUT
(µA)
100
1000
10
3108 G07
0100 200 300 400 500
1Ω
2Ω
5Ω
10Ω
C1 = 1nF
dT ACROSS TEG (°C)
IVOUT (µA)
100
10
1000
10000
0
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)
0
–1.00
DROP IN VLDO (%)
–0.75
–0.50
0.5 11.5 2 32.5 3.5
–0.25
0.00
4
3108 G10
LDO LOAD (mA)
0
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
4
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
6
Rev. D
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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
7
Rev. D
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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.
V
OUT
(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.
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
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
PIN FUNCTIONS
(DFN/SSOP)
LTC3108
8
Rev. D
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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 incon-
venient 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 peri-
odic pulses of higher load current required. This is typi-
cal 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.
(Refer to the Block Diagram)
3108 BD
C1
C2
5M
SW
5.25V
1.2V
VREF
SW VOUT
VSTORE
VLDO
OFF ON
VOUT2
VOUT2
VOUT
VOUT
PROGRAM
COUT
PGOOD
VOUT2_EN
VOUT
VS1
VS2
PGD
VSTORE
C1
CIN
VIN
VLDO CSTORE
1µF
1:100
C2
SYNC RECTIFY REFERENCE
VOUT
2.2V
CHARGE
CONTROL
VAUX
+
–
+
–
ILIM
LTC3108
1.3Ω
0.5Ω
1M
EXPOSED PAD (DFN)
2.2µF
GND (SSOP)
VREF LDO
VREF
VBEST
LTC3108
9
Rev. D
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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 cir-
cuits. 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 volt-
ages 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 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, provid-
ing 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.
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 Rectifiers
Once VAUX exceeds 2V, synchronous rectifiers in parallel
with each of the internal diodes take over the job of rectify-
ing the input voltage, improving efficiency.
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 V
OUT
. 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 recom-
mended 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 regu-
lated 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 resis
-
tors that are susceptible to board leakage.
LTC3108
10
Rev. D
For more information www.analog.com
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 shut-
down capability. VOUT2 can be used to power these cir-
cuits only when they are needed.
Minimizing the amount of decoupling capacitance on
VOUT2 will allow it to be switched on and off faster, allow-
ing 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 out-
put 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
V
OUT2_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 stor-
age capacitor or rechargeable battery after VOUT has
reached regulation. Once V
OUT
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.
OPERATION
LTC3108
11
Rev. D
For more information www.analog.com
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
0 70
20 40
10 30 50 60 80
3.0
2.0
1.0
0
5.0
5.0
2.5
2.5
0
0
5.0
2.5
0
VSTORE (V)
PGD (V)
VOUT (V)
VLDO (V)
VAUX (V)
LTC3108
12
Rev. D
For more information www.analog.com
Introduction
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 dur-
ing 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 regula-
tion, 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 trans-
former turns ratio, the load power required, and the inter-
nal 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 volt-
age times the turns ratio be less than 50.
Note that a low ESR bulk decoupling capacitor will usu-
ally 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.
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
3108 F02
1000
100
10
11 10 100
dT (°C)
TEG VOPEN_CIRCUIT (mV)
OUT
1
100
10
0.1
VOC
MAX POUT
(IDEAL)
TEG: 30mm
127 COUPLES
R = 2Ω
LTC3108
13
Rev. D
For more information www.analog.com
temperature differential between the plates. When used in
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 appli-
cations in which a temperature difference exists between
two surfaces or between a surface and the ambient tem-
perature. 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 open-circuit
output voltage and maximum power transfer for a typi-
cal Peltier cell (with an ESR of 2Ω) 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 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 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
14
Rev. D
For more information www.analog.com
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 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 tempera-
ture. 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 con-
verters 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 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 rectified/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 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 deter-
mine the resonant frequency of the oscillator, according
to the following formula.
=π
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 sec-
ondary winding’s shunt capacitance. The recommended
resonant frequency is in the range of 10kHz to 100kHz.
See Table 5 for some recommended transformers.
APPLICATIONS INFORMATION
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
74488540070 (1:100 Ratio)
74488540120 (1:50 Ratio)
74488540250 (1:20 Ratio)
LTC3108
15
Rev. D
For more information www.analog.com
C1 Capacitor
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 volt-
ages using a transformer with a ratio of 1:100. Too large a
capacitor value can compromise performance when oper-
ating 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 sche-
matic examples for the recommended value for a given
turns ratio.
Squegging
Certain types of oscillators, including transformer-cou-
pled 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 oscilla-
tion. 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 capaci-
tor 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.
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.
Using External Charge Pump Rectifiers
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.
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 result-
ing increase in rectifier currents and resonant oscillator
frequency in these applications, the use of external charge
pump rectifiers 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 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 rec-
tifiers, 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.
≥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 V
OUT
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.
The VSTORE capacitor may be of very large value (thou-
sands of microfarads or even Farads), to provide holdup
APPLICATIONS INFORMATION
LTC3108
16
Rev. D
For more information www.analog.com
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:
[]
≥++ +
−
C
6µAI I(I•t•f) •TSTORE
5.25 V
STORE QLDO 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 pro-
grammed output voltage of 5V, the VSTORE capacitor
cannot provide any beneficial 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.
Storage capacitors requiring voltage balancing are not
recommended due to the current draw of the balancing
resistors.
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 resis-
tance 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 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
V
IN
VIAS TO GROUND PLANE
VLDO PGOOD
GND
12
11
8
9
10
4
5
3
2
1
VOUT2_EN
VS1
VS2
SW
C2
C1
VOUT
VOUT2
VLDO
PGD
VAUX
VSTORE
67
Figure3. Example Component Placement
for Two-Layer PC Board (DFN Package)
Design Example 1
This design example will explain how to calculate the nec-
essary 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 peri-
odically 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
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)
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.
LTC3108
17
Rev. D
For more information www.analog.com
APPLICATIONS INFORMATION
maximum rate at which the load pulses can occur for a
given output current 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 cur-
rent 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:
=−
==
t
150µF •0.33V
(50µA17µA) 1.5sec or f0.666Hz
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 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.
=−
t
2.2V•2.2µF
II
LDO
CHGLDO
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
3.3V•150µF
II It
VOUT
CHGVOUT 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
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:
≥+II
I•t
T
CHGQBURST
Where IQ is the sleep current on VOUT required by the
external circuitry in between bursts (including cap leak-
age), IBURST is the total load current during the burst, t is
LTC3108
18
Rev. D
For more information www.analog.com
the 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
C1
C2
SW
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
5V
3.3V
1µF
1nF
CIN
1:100
T1
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
ON
OFF
3.3V
+
+
+
THERMOELECTRIC
GENERATOR
LTC3108
19
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
Li-Ion Battery Charger and LDO Powered by a Solar Cell
Supercapacitor Charger and LDO Powered by a Thermopile Generator
3108 TA04
C1
HONEYWELL
CQ200
THERMOPILE
C2
SW
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
T1
1:50
330pF
220µF
+
+VOUT
3108 TA03
C1
SOLAR CELL*
C2
SW
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
T1
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
C1
C2
SW
VS2
VS1
VOUT2 VOUT2
PGOOD
2.2V
COUT
PGD
VLDO VLDO
VSTORE
VOUT VOUT
VOUT2_EN VOUT2_ENABLE
LTC3108
VAUX GND
CSTORE
5V
3.3V
2.2µF
VIN
VIN > 5V
RIN
RIN > 100Ω/V
2.2µF
+
–
+
+
AC Input Energy Harvester and Power Manager
3108 TA06
C1
C2
SW
VS1
VS2
VOUT2 VOUT2
PGOOD
2.2V
COUT
PGD
VLDO VLDO
VSTORE
VOUT VOUT
VOUT2_EN VOUT2_ENABLE
LTC3108
VAUX GND
CSTORE
5V
5V
2.2µF
CIN
VIN
VIN > 5VP-P
- PIEZO
- 60Hz
RIN
RIN > 100Ω/V
2.2µF
AC
+
+
LTC3108
20
Rev. D
For more information www.analog.com
GN16 REV B 0212
1 2 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
16
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
LTC3108
21
Rev. D
For more information www.analog.com
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
1
2
3
4
8
9
12-18
18, 19, 22
22
B 06/13 Added vendor information to Table 5 14
C 08/13 Changed Würth transformer part numbers 14
D 03/19 Electrical Characteristics. LDO Dropout Voltage Temperature Range changed from Over Temperature to TA = 25°C,
VOUT, Current Limit Max & VSTORE Current Limit Max changed from 7V to 7.5V; VAUX Clamp Voltage Max changed
from 5.55V to 5.6V
3
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
LTC3108
22
Rev. D
For more information www.analog.com
RELATED PARTS
TYPICAL APPLICATION
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
LTC4070 Micropower Shunt Li-Ion Charge Controls Charging with µA Source
3108 TA07
C1
HOT
COLD C2
SW
VS2
VS1
VSTORE
VOUT2 VOUT2
PGOOD
VOUT
VLDO
COUT
PGD
VLDO
+
VOUT
VOUT2_EN
LTC3108
VAUX GND
2.2µF
CSTORE
5V
VAUX
1µF
1nF
2.2V
3.3V
1:100
LPR6235-752SML
330pF
ON
OFF
C1
C2
SW
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
ANALOG DEVICES, INC. 2010-2019
03/19
www.analog.com