LTC3108-1
Ultralow Voltage Step-Up
Converter and Power Manager
Features
Description
Operates from Inputs of 20mV
n Complete Energy Harvesting Power
Management System
- Selectable VOUT of 2.5V, 3V, 3.7V or 4.5V
- 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
The LTC®3108-1 is a highly integrated DC/DC converter ideal
for harvesting and managing surplus energy from extremely
low input voltage sources such as TEGs (thermoelectric
generators), thermopiles and small solar cells. The step-up
topology operates from input voltages as low as 20mV.
n
Using a small step-up transformer, the LTC3108-1 provides
a complete power management solution for wireless sensing and data acquisition. The 2.2V LDO powers an external
microprocessor, while the main output is programmed to
one of four fixed voltages to power a wireless transmitter
or sensors. The power good indicator signals that the main
output voltage is within regulation. A second output can be
enabled by the host. A storage capacitor provides power
when the input voltage source is unavailable. Extremely
low quiescent current and high efficiency design ensure
the fastest possible charge times of the output reservoir
capacitor. The LTC3108-1 is functionally equivalent to the
LTC3108 except for its unique fixed VOUT options.
Applications
n
n
n
n
n
n
n
Remote Sensors and Radio Power
Surplus Heat Energy Harvesting
HVAC Systems
Industrial Wireless Sensing
Automatic Metering
Building Automation
Predictive Maintenance
The LTC3108-1 is available in a small, thermally enhanced
12-lead (3mm × 4mm) DFN package and a 16-lead SSOP
package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Typical Application
Wireless Remote Sensor Application
Powered From a Peltier Cell
THERMOELECTRIC
GENERATOR
+
220µF
C1
VSTORE
+
100
PGOOD
PGD
2.2V
VLDO
SW
µP
2.2µF SENSORS
VOUT
VS2
VS1 VOUT2_EN
VAUX
GND
VOUT = 3V
COUT = 470µF
0.1F
6.3V
VOUT2
C2
20mV TO 500mV
1000
5.25V
LTC3108-1
330pF
VOUT Charge Time
3V
+
470µF
RF LINK
31081 TA01a
1µF
TIME (sec)
1:100
+
1nF
10
1
0
1:100 Ratio
1:50 Ratio
1:20 Ratio
0
50
100 150 200 250 300 350 400
VIN (mV)
31081 TA01b
31081fb
For more information www.linear.com/LTC3108-1
1
LTC3108-1
Absolute Maximum Ratings
(Note 1)
SW Voltage...................................................–0.3V to 2V
C1 Voltage.....................................................–0.3V to 6V
C2 Voltage (Note 5)..........................................–8V to 8V
VOUT2, VOUT2_EN............................................–0.3V to 6V
VAUX.....................................................15mA into VAUX
VS1, VS2, VAUX, VOUT, PGD.........................–0.3V to 6V
VLDO, VSTORE.............................................–0.3V to 6V
Operating Junction Temperature Range
(Note 2).................................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
Pin Configuration
TOP VIEW
TOP VIEW
VAUX
1
12 SW
VSTORE
2
11 C2
VOUT
3
VOUT2
4
VLDO
PGD
13
GND
10 C1
9
VOUT2_EN
5
8
VS1
6
7
VS2
GND
1
16 GND
VAUX
2
15 SW
VSTORE
3
14 C2
VOUT
4
13 C1
VOUT2
5
12 VOUT2_EN
VLDO
6
11 VS1
PGD
7
10 VS2
GND
8
9
DE PACKAGE
12-LEAD (4mm × 3mm) PLASTIC DFN
GND
GN PACKAGE
16-LEAD PLASTIC SSOP NARROW
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB (NOTE 4)
TJMAX = 125°C, θJA = 110°C/W
order information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3108EDE-1#PBF
LTC3108EDE-1#TRPBF
31081
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3108IDE-1#PBF
LTC3108IDE-1#TRPBF
31081
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3108EGN-1#PBF
LTC3108EGN-1#TRPBF
31081
16-Lead Plastic SSOP
–40°C to 125°C
LTC3108IGN-1#PBF
LTC3108IGN-1#TRPBF
31081
16-Lead Plastic SSOP
–40°C to 125°C
Consult LTC Marketing for parts specified for other fixed output voltages or wider operating temperature ranges.
*The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted.
PARAMETER
CONDITIONS
TYP
MAX
Minimum Start-Up Voltage
Using 1:100 Transformer Turns Ratio, VAUX = 0V
20
50
No-Load Input Current
Using 1:100 Transformer Turns Ratio; VIN = 20mV,
VOUT2_EN = 0V; All Outputs Charged and in Regulation
3
Input Voltage Range
Using 1:100 Transformer Turns Ratio
2
MIN
l
VSTARTUP
UNITS
mV
mA
500
mV
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted.
PARAMETER
CONDITIONS
Output Voltage
VS1 = VS2 = GND
VS1 = VAUX, VS2 = GND
VS1 = GND, VS2 = VAUX
VS1 = VS2 = VAUX
VOUT Quiescent Current
VOUT = 3.7V, VOUT2_EN = 0V
VAUX Quiescent Current
No Load, All Outputs Charged
LDO Output Voltage
0.5mA Load
LDO Load Regulation
For 0mA to 2mA Load
LDO Line Regulation
For VAUX from 2.5V to 5V
l
l
l
l
MIN
TYP
MAX
UNITS
2.45
2.94
3.626
4.41
2.50
3.00
3.70
4.50
2.55
3.06
3.774
4.59
V
V
V
V
0.2
l
2.134
µA
6
9
µA
2.2
2.266
V
0.5
1
%
0.05
0.2
%
100
200
mV
LDO Dropout Voltage
IVLDO = 2mA
l
LDO Current Limit
VLDO = 0V
l
4
11
VOUT Current Limit
VOUT = 0V
l
2.8
4.5
7
mA
VSTORE Current Limit
VSTORE = 0V
l
2.8
4.5
7
mA
VAUX Clamp Voltage
Current into VAUX = 5mA
l
5
5.25
5.55
0.3
VSTORE Leakage Current
VSTORE = 5V
0.1
VOUT2 Leakage Current
VOUT2 = 0V, VOUT2_EN = 0V
0.1
VS1, VS2 Threshold Voltage
l
0.4
V
0.1
µA
0.01
PGD Threshold (Rising)
Measured Relative to the VOUT Voltage
–7.5
Measured Relative to the VOUT Voltage
Sink Current = 100µA
PGD VOH
Source Current = 0
%
–9
2.1
PGD Pull-Up Resistance
VOUT2_EN Threshold Voltage
%
0.15
0.3
V
2.2
2.3
V
1
VOUT2_EN Rising
µA
µA
1.2
VS1 = VS2 = 5V
PGD VOL
V
0.85
VS1, VS2 Input Current
PGD Threshold (Falling)
mA
l
0.4
1
MΩ
1.3
V
VOUT2_EN Pull-Down Resistance
5
MΩ
VOUT2 Turn-On Time
5
µs
0.15
µs
VOUT2 Turn-Off Time
(Note 3)
VOUT2 Current Limit
VOUT = 3.7V
VOUT2 Current Limit Response Time
(Note 3)
VOUT2 P-Channel MOSFET On-Resistance
VOUT = 3.7V (Note 3)
1.3
Ω
N-Channel MOSFET On-Resistance
C2 = 5V (Note 3)
0.5
Ω
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3108-1 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3108-1E 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
LTC3108-1I 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
l
0.15
0.3
350
0.45
A
ns
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.
For more information www.linear.com/LTC3108-1
31081fb
3
LTC3108-1
Typical Performance Characteristics
1000
TA = 25°C, unless otherwise noted.
IVOUT and Efficiency vs VIN,
1:20 Ratio Transformer
IIN vs VIN, (VOUT = 0V)
4000
1:50 RATIO, C1 = 4.7n
1:100 RATIO, C1 = 1n
1:20 RATIO, C1 = 10n
80
C1 = 10nF
3500
3000
IVOUT (µA)
IIN (mA)
10
1
10
100
VIN (mV)
60
2500
50
2000
IVOUT
(VOUT = 4V)
EFFICIENCY
(VOUT = 4V)
1500
40
30
1000
20
500
10
0
1000
0
100
200
300
400
EFFICIENCY (%)
100
70
IVOUT
(VOUT = 0V)
0
500
VIN (mV)
31081 G00
31081 G01
IVOUT and Efficiency vs VIN,
1:100 Ratio Transformer
IVOUT and Efficiency vs VIN,
1:50 Ratio Transformer
C1 = 4.7nF
IVOUT
(VOUT = 0V)
2800
70
1200
60
50
IVOUT
(VOUT = 4V)
1600
40
1200
30
800
20
400
10
0
0
100
200
300
400
IVOUT
(VOUT = 0V)
1000
800
50
40
600
30
IVOUT
(VOUT = 4V)
400
20
10
200
0
500
0
0
100
200
300
400
0
500
VIN (mV)
31081 G02
31081 G03
Input Resistance vs VIN
(VOUT Charging)
IVOUT vs VIN and Source Resistance,
1:20 Ratio
10
10000
C1 = 10nF
9
1:20 RATIO
8
1000
7
6
5
IVOUT (µA)
INPUT RESISTANCE (Ω)
60
EFFICIENCY
(VOUT = 4V)
VIN (mV)
1:50 RATIO
4
3
1:100 RATIO
2
100
10
1Ω
2Ω
5Ω
10Ω
1
0
70
C1 = 1nF
EFFICIENCY (%)
EFFICIENCY
(VOUT = 4V)
2000
1400
EFFICIENCY (%)
IVOUT (µA)
2400
80
IVOUT (µA)
3200
0
100
200
300
400
500
VIN (mV)
0
0
100 200 300 400 500 600 700 800
VIN OPEN-CIRCUIT (mV)
31081 G05
31081 G04
4
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Typical Performance Characteristics
IVOUT vs VIN and Source Resistance,
1:50 Ratio
10000
IVOUT vs VIN and Source Resistance,
1:100 Ratio
1000
C1 = 4.7nF
TA = 25°C, unless otherwise noted.
C1 = 1nF
IVOUT (µA)
IVOUT (µA)
1000
100
10
0
1Ω
2Ω
5Ω
10Ω
10
100 200 300 400 500 600 700 800
VIN OPEN-CIRCUIT (mV)
0
100
1Ω
2Ω
5Ω
10Ω
0
31081 G06
IVOUT vs dT and TEG Size,
1:100 Ratio
10000
31081 G07
VIN = 20mV
1:100 RATIO TRANSFORMER
40mm
TEG
1000
IVOUT (µA)
500
Resonant Switching Waveforms
VOUT = 0V
100
C1 PIN
2V/DIV
C2 PIN
2V/DIV
10
SW PIN
50mV/
DIV
15mm
TEG
1:50 RATIO
1:100 RATIO
1:50 RATIO
1:100 RATIO
0
0.1
100
200
300
400
VIN OPEN-CIRCUIT (mV)
10
1
dT ACROSS TEG (°C)
31081 G09
10µs/DIV
100
31081 G08
LDO Load Regulation
LDO Dropout Voltage
0.00
0.20
0.18
0.16
DROPOUT VOLTAGE (V)
DROP IN VLDO (%)
–0.25
–0.50
–0.75
0.14
0.12
0.10
0.08
0.06
0.04
0.02
–1.00
0
0.5
1
1.5 2 2.5
LDO LOAD (mA)
3
3.5
4
0.00
0
0.5
1
31081 G10
1.5 2 2.5
LDO LOAD (mA)
3
3.5
4
31081 G11
31081fb
For more information www.linear.com/LTC3108-1
5
LTC3108-1
Typical Performance Characteristics
VOUT and PGD Response
During a Step Load
Start-Up Voltage Sequencing
VIN = 50mV
1:100 RATIO TRANSFORMER
COUT = 220µF
CSTORE = 470µF
CLDO = 2.2µF
50mA LOAD STEP
COUT = 220µF
CH1
VSTORE
1V/DIV
CH2, VOUT
1V/DIV
CH3, VLDO
1V/DIV
10sec/DIV
TA = 25°C, unless otherwise noted.
CH2
VOUT, 1V/DIV
CH1
PGD, 1V/DIV
31081 G12
5ms/DIV
VOUT Ripple
31081 G13
LDO Step Load Response
30µA LOAD
COUT = 220µF
VLDO
20mV/DIV
20mV/
DIV
ILDO
5mA/DIV
100ms/DIV
31081 G14
200µs/DIV
31081 G15
0mA TO 3mA LOAD STEP
CLDO = 2.2µF
Running on Storage Capacitor
Enable Input and VOUT2
CSTORE = 470µF
VOUT LOAD = 100µA
CH2
CH3
VSTORE
1V/DIV
CH1
VOUT2_EN
1V/DIV
CH2, VOUT
1V/DIV
CH4, VLDO
1V/DIV
CH1, VIN
50mV/DIV
VOUT2
1V/DIV
1ms/DIV
31081 G16
5sec/DIV
31081 G17
10mA LOAD ON VOUT2
COUT = 220µF
6
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Pin Functions
(DFN/SSOP)
VAUX (Pin 1/Pin 2): Output of the Internal Rectifier Circuit and VCC for the IC. Bypass VAUX with at least 1µF of
capacitance. An active shunt regulator clamps VAUX to
5.25V (typical).
VSTORE (Pin 2/Pin 3): Output for the Storage Capacitor
or Battery. A large capacitor may be connected from this
pin to GND for powering the system in the event the input
voltage is lost. It will be charged up to the maximum VAUX
clamp voltage. If not used, this pin should be left open
or tied to VAUX.
VOUT (Pin 3/Pin 4): Main Output of the Converter. The
voltage at this pin is regulated to the voltage selected by
VS1 and VS2 (see Table 1). Connect this pin to an energy
storage capacitor or to a rechargeable battery.
VOUT2 (Pin 4/Pin 5): Switched Output of the Converter.
Connect this pin to a switched load. This output is open
until VOUT2_EN is driven high, then it is connected to
VOUT through a 1.3Ω P-channel switch. If not used, this
pin should be left open or tied to VOUT. The peak current
in this output is limited to 0.3A typical.
VLDO (Pin 5/Pin 6): Output of the 2.2V LDO. Connect a
2.2µF or larger ceramic capacitor from this pin to GND.
If not used, this pin should be tied to VAUX.
PGD (Pin 6/Pin 7): Power Good Output. When VOUT is
within 7.5% of its programmed value, PGD will be pulled
up to VLDO through a 1MΩ resistor. If VOUT drops 9%
below its programmed value PGD will go low. This pin
can sink up to 100µA.
VS1 (Pin 8/Pin 11): VOUT Select Pin 1. Connect this pin
to ground or VAUX to program the output voltage (see
Table 1).
VOUT2_EN (Pin 9/Pin 12): Enable Input for VOUT2. VOUT2
will be enabled when this pin is driven high. There is an
internal 5M pull-down resistor on this pin. If not used,
this pin can be left open or grounded.
C1 (Pin 10/Pin 13): Input to the Charge Pump and Rectifier
Circuit. Connect a capacitor from this pin to the secondary
winding of the step-up transformer.
C2 (Pin 11/Pin 14): Input to the N-Channel Gate Drive
Circuit. Connect a capacitor from this pin to the secondary
winding of the step-up transformer.
SW (Pin 12/Pin 15): Drain of the Internal N-Channel
Switch. Connect this pin to the primary winding of the
transformer.
GND (Pins 1, 8, 9, 16) SSOP Only: Ground
GND (Exposed Pad Pin 13) DFN Only: Ground. The DFN
exposed pad must be soldered to the PCB ground plane.
It serves as the ground connection, and as a means of
conducting heat away from the die.
Table 1. Regulated Voltage Using Pins VS1 and VS2
VS2
VS1
VOUT
GND
GND
2.5V
GND
VAUX
3V
VAUX
GND
3.7V
VAUX
VAUX
4.5V
VS2 (Pin 7/Pin 10): VOUT Select Pin 2. Connect this pin
to ground or VAUX to program the output voltage (see
Table 1).
31081fb
For more information www.linear.com/LTC3108-1
7
LTC3108-1
Block Diagram
LTC3108-1
VOUT2
1.3Ω
ILIM
VOUT2
VOUT2_EN
SYNC RECTIFY
VOUT
C1
VOUT
CIN
COUT
5.25V
C2
SW
OFF ON
5M
C1
1:100
VIN
REFERENCE
1.2V
VREF
+
–
C2
VOUT
SW
VSTORE
CHARGE
CONTROL
VS1
VS2
0.5Ω
VOUT
PROGRAM
VREF
VLDO
1M
–
+
VAUX
1µF
VOUT
GND (SSOP)
VBEST
PGD
PGOOD
VSTORE
VREF
LDO
EXPOSED PAD (DFN)
CSTORE
VLDO
31081 BD
2.2V
2.2µF
operation
(Refer to the Block Diagram)
The LTC3108-1 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 LTC3108-1 is designed to manage the charging and
regulation of multiple outputs in a system in which the
8
average power draw is very low, but there may be periodic
pulses of higher load current required. This is typical of
wireless sensor applications, where the quiescent power
draw is extremely low most of the time, except for transmit
bursts when circuitry is powered up to make measurements and transmit data.
The LTC3108-1 can also be used to trickle charge a standard
capacitor, supercapacitor or rechargeable battery, using
energy harvested from a Peltier or photovoltaic cell.
31081fb
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LTC3108-1
Operation
Oscillator
Synchronous Rectifiers
The LTC3108-1 utilizes a MOSFET switch to form a resonant
step-up oscillator using an external step-up transformer
and a small coupling capacitor. This allows it to boost input
voltages as low as 20mV high enough to provide multiple
regulated output voltages for powering other circuits. The
frequency of oscillation is determined by the inductance of
the transformer secondary winding and is typically in the
range of 10kHz to 100kHz. For input voltages as low as
20mV, a primary-secondary turns ratio of about 1:100 is
recommended. For higher input voltages, this ratio can be
lower. See the Applications Information section for more
information on selecting the transformer.
Once VAUX exceeds 2V, synchronous rectifiers in parallel
with each of the internal diodes take over the job of rectifying the input voltage, improving efficiency.
Charge Pump and Rectifier
The AC voltage produced on the secondary winding of
the transformer is boosted and rectified using an external
charge pump capacitor (from the secondary winding to
pin C1) and the rectifiers internal to the LTC3108-1. The
rectifier circuit feeds current into the VAUX pin, providing charge to the external VAUX capacitor and the other
outputs.
VAUX
The active circuits within the LTC3108-1 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 LTC3108-1 includes a precision, micropower reference, for accurate regulated output voltages. This reference
becomes active as soon as VAUX exceeds 2V.
Low Dropout Linear Regulator (LDO)
The LTC3108-1 includes a low current LDO to provide a
regulated 2.2V output for powering low power processors
or other low power ICs. The LDO is powered by the higher
of VAUX or VOUT. This enables it to become active as soon
as VAUX has charged to 2.3V, while the VOUT storage
capacitor is still charging. In the event of a step load on
the LDO output, current can come from the main VOUT
capacitor if VAUX drops below VOUT. The LDO requires
a 2.2µF ceramic capacitor for stability. Larger capacitor
values can be used without limitation, but will increase
the time it takes for all the outputs to charge up. The LDO
output is current limited to 4mA minimum.
VOUT
The main output voltage on VOUT is charged from the VAUX
supply, and is user programmed to one of four regulated
voltages using the voltage select pins VS1 and VS2, according to Table 2. Although the logic threshold voltage
for VS1 and VS2 is 0.85V typical, it is recommended that
they be tied to ground or VAUX.
Table 2. Regulated Voltage Using Pins VS1 and VS2
VS2
VS1
VOUT
GND
GND
2.5V
GND
VAUX
3V
VAUX
GND
3.7V
VAUX
VAUX
4.5V
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.
31081fb
For more information www.linear.com/LTC3108-1
9
LTC3108-1
Operation
In a typical application, a storage capacitor (typically a few
hundred microfarads) is connected to VOUT. As soon as
VAUX exceeds 2.5V, the VOUT capacitor will be allowed to
charge up to its regulated voltage. The current available
to charge the capacitor will depend on the input voltage
and transformer turns ratio, but is limited to about 4.5mA
typical.
PGOOD
A power good comparator monitors the VOUT voltage.
The PGD pin is an open-drain output with a weak pull-up
(1MΩ) to the LDO voltage. Once VOUT has charged to within
7.5% of its regulated voltage, the PGD output will go high.
If VOUT drops more than 9% from its regulated voltage,
PGD will go low. The PGD output is designed to drive a
microprocessor or other chip I/O and is not intended to
drive a higher current load such as an LED. Pulling PGD
up externally to a voltage greater than VLDO will cause a
small current to be sourced into VLDO. PGD can be pulled
low in a wire-OR configuration with other circuitry.
VOUT2
VOUT2 is an output that can be turned on and off by the
host, using the VOUT2_EN pin. When enabled, VOUT2 is
connected to VOUT through a 1.3Ω P-channel MOSFET
switch. This output, controlled by a host processor, can
be used to power external circuits such as sensors and
amplifiers, that do not have a low power sleep or shutdown
capability. VOUT2 can be used to power these circuits only
when they are needed.
Minimizing the amount of decoupling capacitance on
VOUT2 will allow it to be switched on and off faster, allowing
shorter burst times and, therefore, smaller duty cycles in
pulsed applications such as a wireless sensor/transmitter. A small VOUT2 capacitor will also minimize the energy
that will be wasted in charging the capacitor every time
VOUT2 is enabled.
VOUT2 has a soft-start time of about 5µs to limit capacitor
charging current and minimize glitching of the main output
when VOUT2 is enabled. It also has a current limiting circuit
that limits the peak current to 0.3A typical.
10
The VOUT2 enable input has a typical threshold of 1V
with 100mV of hysteresis, making it logic-compatible. If
VOUT2_EN (which has an internal pull-down resistor) is
low, VOUT2 will be off. Driving VOUT2_EN high will turn on
the VOUT2 output.
Note that while VOUT2_EN is high, the current limiting circuitry for VOUT2 draws an extra 8µA of quiescent current
from VOUT. This added current draw has a negligible effect
on the application and capacitor sizing, since the load on
the VOUT2 output, when enabled, is likely to be orders of
magnitude higher than 8µA.
VSTORE
The VSTORE output can be used to charge a large storage
capacitor or rechargeable battery after VOUT has reached
regulation. Once VOUT has reached regulation, the VSTORE
output will be allowed to charge up to the VAUX voltage.
The storage element on VSTORE can be used to power
the system in the event that the input source is lost, or
is unable to provide the current demanded by the VOUT,
VOUT2 and LDO outputs. If VAUX drops below VSTORE,
the LTC3108-1 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 LTC3108-1 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.
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Operation
5.0
VSTORE (V)
2.5
0
3.0
2.0
PGD (V)
1.0
VOLTAGE (V)
0
5.0
2.5
VOUT (V)
0
3.0
2.0
VLDO (V)
1.0
0
5.0
VAUX (V)
2.5
0
0
10
20
30
40
50
60
70
80
TIME (ms)
31081 F01a
Figure 1. Output Voltage Sequencing with VOUT Programmed for 3V (Time Not to Scale)
31081fb
For more information www.linear.com/LTC3108-1
11
LTC3108-1
Applications Information
Introduction
Refer to the IIN vs VIN curves in the Typical Performance
Characteristics section to see what input current is required
for the source for a given input voltage.
The LTC3108-1 is designed to gather energy from very
low input voltage sources and convert it to usable output
voltages to power microprocessors, wireless transmitters
and analog sensors. Such applications typically require
much more peak power, and at higher voltages, than
the input voltage source can produce. The LTC3108-1 is
designed to accumulate and manage energy over a long
period of time to enable short power bursts for acquiring
and transmitting data. The bursts must occur at a low
enough duty cycle such that the total output energy during the burst does not exceed the average source power
integrated over the accumulation time between bursts.
For many applications, this time between bursts could
be seconds, minutes or hours.
For a given transformer turns ratio, there is a maximum
recommended input voltage to avoid excessively high
secondary voltages and power dissipation in the shunt
regulator. It is recommended that the maximum input
voltage times the turns ratio be less than 50.
Note that a low ESR bulk decoupling capacitor will usually
be required across the input source to prevent large voltage
droop and ripple caused by the source’s ESR and the peak
primary switching current (which can reach hundreds of
milliamps). The time constant of the filter capacitor and
the ESR of the voltage source should be much longer than
the period of the resonant switching frequency.
The PGD signal can be used to enable a sleeping microprocessor or other circuitry when VOUT reaches regulation,
indicating that enough energy is available for a burst.
Peltier Cell (Thermoelectric Generator)
A Peltier cell (also known as a thermoelectric cooler) is
made up of a large number of series-connected P-N junctions, sandwiched between two parallel ceramic plates.
Although Peltier cells are often used as coolers by applying a DC voltage to their inputs, they will also generate
a DC output voltage, using the Seebeck effect, when the
two plates are at different temperatures. The polarity of
the output voltage will depend on the polarity of the temperature differential between the plates. The magnitude of
the output voltage is proportional to the magnitude of the
temperature differential between the plates. When used in
Input Voltage Sources
The LTC3108-1 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.
TEG: 30mm
127 COUPLES
R = 2Ω
100
VOC
10
100
MAX POUT
(IDEAL)
10
1
1
10
dT (°C)
1
TEG MAXIMUM POUT —IDEAL (mW)
TEG VOPEN_CIRCUIT (mV)
1000
0.1
100
31081 F02
Figure 2. Typical Performance of a Peltier Cell Acting as a Thermoelectric Generator
12
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Applications Information
this manner, a Peltier cell is referred to as a thermoelectric
generator (TEG).
The low voltage capability of the LTC3108-1 design allows
it to operate from a TEG with temperature differentials
as low as 1°C, making it ideal for harvesting energy in
applications in which a temperature difference exists
between two surfaces or between a surface and the ambient temperature. The internal resistance (ESR) of most
cells is in the range of 1Ω to 5Ω, allowing for reasonable
power transfer. The curves in Figure 2 show the opencircuit output voltage and maximum power transfer for a
typical Peltier cell (with an ESR of 2Ω) over a 20°C range
of temperature differential.
TEG Load Matching
The LTC3108-1 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 LTC3108-1
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
Fujitaka
www.fujitaka.com/pub/peltier/english/thermoelectric_power.html
FerroTec
www.ferrotec.com/products/thermal/modules
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
Kryotherm
www.kryothermusa.com
Table 4. Recommended TEG Part Numbers by Size
MANUFACTURER
15mm × 15mm
20mm × 20mm
30mm × 30mm
40mm × 40mm
CUI Inc. (Distributor)
CP60133
CP60233
CP60333
CP85438
Ferrotec
9501/031/030 B
9501/071/040 B
9500/097/090 B
9500/127/100 B
Fujitaka
FPH13106NC
FPH17106NC
FPH17108AC
FPH112708AC
Kryotherm
TGM-127-1.0-0.8
LCB-127-1.4-1.15
Laird Technology
PT6.7.F2.3030.W6
PT8.12.F2.4040.TA.W6
RC3-8-01
RC6-6-01
RC12-8-01LS
Marlow Industries
Tellurex
C2-15-0405
C2-20-0409
C2-30-1505
C2-40-1509
TE Technology
TE-31-1.0-1.3
TE-31-1.4-1.15
TE-71-1.4-1.15
TE-127-1.4-1.05
31081fb
For more information www.linear.com/LTC3108-1
13
LTC3108-1
Applications Information
Thermopile Generator
Thermopile generators (also called powerpile generators)
are made up of a number of series-connected thermocouples enclosed in a metal tube. They are commonly
used in gas burner applications to generate a DC output
of hundreds of millivolts when exposed to the high temperature of a flame. Typical examples are the Honeywell
CQ200 and Q313. These devices have an internal series
resistance of less than 3Ω, and can generate as much as
750mV open-circuit at their highest rated temperature. For
applications in which the temperature rise is too high for
a solid-state thermoelectric device, a thermopile can be
used as an energy source to power the LTC3108-1. 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 LTC3108-1 converter can also operate from a single
photovoltaic cell (also known as a PV or solar cell) at light
levels too low for other low input voltage boost converters to operate. However, many variables will affect the
performance in these applications. Light levels can vary
over several orders of magnitude and depend on lighting conditions (the type of lighting and indoor versus
outdoor). Different types of light (sunlight, incandescent,
fluorescent) also have different color spectra, and will
produce different output power levels depending on which
type of photovoltaic cell is being used (monocrystalline,
polycrystalline or thin-film). Therefore, the photovoltaic
cell must be chosen for the type and amount of light available. Note that the short-circuit output current from the
cell must be at least a few milliamps in order to power the
LTC3108-1 converter
Non-Boost Applications
The LTC3108-1 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 currentlimiting resistor where it will be rectified/peak detected. In
14
these applications the C2 and SW pins are not used and
can be grounded or left open.
Examples of such input sources would be piezoelectric
transducers, vibration energy harvesters, low current
generators, a stack of low current solar cells or a 60Hz
AC input.
A series resistance of at least 100Ω/V should be used
to limit the maximum current into the VAUX shunt
regulator.
COMPONENT SELECTION
Step-Up Transformer
The step-up transformer turns ratio will determine how
low the input voltage can be for the converter to start.
Using a 1:100 ratio can yield start-up voltages as low as
20mV. Other factors that affect performance are the DC
resistance of the transformer windings and the inductance
of the windings. Higher DC resistance will result in lower
efficiency. The secondary winding inductance will determine the resonant frequency of the oscillator, according
to the following formula.
Frequency =
1
Hz
2 • π • L(sec)• C
Where L is the inductance of the transformer secondary
winding and C is the load capacitance on the secondary
winding. This is comprised of the input capacitance at pin
C2, typically 30pF, in parallel with the transformer secondary
winding’s shunt capacitance. The recommended resonant
frequency is in the range of 10kHz to 100kHz. See Table 5
for some recommended transformers.
Table 5. Recommended Transformers
VENDOR
PART NUMBER
Coilcraft
www.coilcraft.com
LPR6235-752SML (1:100 Ratio)
LPR6235-253PML (1:20 Ratio)
LPR6235-123QML (1:50 Ratio)
Würth
www.we-online
74488540070 (1:100 Ratio)
74488540120 (1:50 Ratio)
74488540250 (1:20 Ratio)
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Applications Information
C1 Capacitor
Using External Charge Pump Rectifiers
The charge pump capacitor that is connected from the
transformer’s secondary winding to the C1 pin has an effect on converter input resistance and maximum output
current capability. Generally, a minimum value of 1nF is
recommended when operating from very low input voltages using a transformer with a ratio of 1:100. Too large
a capacitor value can compromise performance when
operating at low input voltage or with high resistance
sources. For higher input voltages and lower turns ratios,
the value of the C1 capacitor can be increased for higher
output current capability. Refer to the Typical Applications
schematic examples for the recommended value for a
given turns ratio.
The synchronous charge pump rectifiers in the LTC3108-1
(connected to the C1 pin) are optimized for operation from
very low input voltage sources, using typical transformer
step-up ratios between 1:100 and 1:50, and typical C1
charge pump capacitor values less than 10nF.
Squegging
Certain types of oscillators, including transformer-coupled
oscillators such as the resonant oscillator of the LTC3108-1,
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 LTC3108-1, squegging can occur when
a charge builds up on the C2 gate coupling capacitor, such
that the DC bias point shifts and oscillation is extinguished
for a certain period of time, until the charge on the capacitor
bleeds off, allowing oscillation to resume. It is difficult to
predict when and if squegging will occur in a given application. While squegging is not harmful, it reduces the
average output current capability of the LTC3108-1.
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.
Operation from higher input voltage sources (typically
250mV or greater, under load), allows the use of lower
transformer step-up ratios (such as 1:20 and 1:10) and
larger C1 capacitor values to provide higher output current capability from the LTC3108. However, due to the
resulting increase in rectifier currents and resonant oscillator frequency in these applications, the use of external
charge pump rectifiers is recommended for optimal
performance.
In applications where the step-up ratio is 1:20 or less, and
the C1 capacitor is 10nF or greater, the C1 pin should be
grounded and two external rectifiers (such as 1N4148 or
1N914 diodes) should be used. These are available as
dual diodes in a single package. Avoid the use of Schottky
rectifiers, as their lower forward-voltage drop increases
the minimum startup 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.
COUT (µF) ≥
ILOAD (mA) • tPULSE (ms)
∆VOUT (V)
Note that there must be enough energy available from
the input voltage source for VOUT to recharge the capacitor
during the interval between load pulses (to be discussed
in the next example). Reducing the duty cycle of the load
pulse will allow operation with less input energy.
The VSTORE capacitor may be of very large value (thousands of microfarads or even Farads), to provide holdup
31081fb
For more information www.linear.com/LTC3108-1
15
LTC3108-1
Applications Information
at times when the input power may be lost. Note that this
capacitor can charge all the way to 5.25V (regardless of
the settings for VOUT), so ensure that the holdup capacitor
has a working voltage rating of at least 5.5V at the temperature for which it will be used. The VSTORE capacitor
can be sized using the following:
CSTORE
[6µA +IQ +ILDO +(IBURST • t • f)] • TSTORE
≥
5.25 − VOUT
Where 6µA is the quiescent current of the LTC3108-1, 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.
To minimize losses and capacitor charge time, all capacitors used for VOUT and VSTORE should be low leakage.
See Table 6 for recommended storage capacitors.
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 transformer
and the SW and GND pins of the LTC3108-1 should be
designed to minimize voltage drop from stray resistance
and able to carry currents as high as 500mA. Any small
voltage drop in the primary winding conduction path will
lower efficiency and increase capacitor charge time.
Also, due to the low charge currents available at the outputs
of the LTC3108-1, any sources of leakage current on the
output voltage pins must be minimized. An example board
layout is shown in Figure 3.
VIN
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)
VAUX
Storage capacitors requiring voltage balancing are not
recommended due to the current draw of the balancing
resistors.
VOUT
VSTORE
VOUT
VOUT2
VLDO
VOUT2
VLDO
PGOOD
GND
PGD
1
12
2
11
3
10
4
9
5
8
6
7
SW
C2
C1
VOUT2_EN
VS1
VS2
VIAS TO GROUND PLANE
31081 FO3
Figure 3. Example Component Placement for
Two-Layer PC Board (DFN Package)
16
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Applications Information
Design Example 1
This design example will explain how to calculate the
necessary storage capacitor value for VOUT in pulsed
load applications, such as a wireless sensor/transmitter. In these types of applications, the load is very small
for a majority of the time (while the circuitry is in a low
power sleep state), with bursts of load current occurring periodically during a transmit burst. The storage
capacitor on VOUT supports the load during the transmit
burst, and the long sleep time between bursts allows
the LTC3108-1 to recharge the capacitor. A method for
calculating the maximum rate at which the load pulses
can occur for a given output current from the LTC3108-1
will also be shown.
In this example, VOUT is set to 3V, and the maximum allowed voltage droop during a transmit burst is 10%, or
0.3V. 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:
COUT (µF) ≥
40mA • 1ms
= 133µF
0.3V
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 LTC3108-1 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 LTC3108-1 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
LTC3108-1 is 50µA and the total current drawn on VOUT
in the sleep state is 17µA, including capacitor leakage. In
addition, use the value of 150µF for the VOUT capacitor.
The maximum transmit rate (neglecting the duration of
the transmit burst, which is typically very short) is then
given by:
150µF • 0.3V
t=
= 1.36sec or fMAX = 0.73Hz
(50µA
−
17µA)
Therefore, in this application example, the circuit can support a 1ms transmit burst every 1.3 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 9 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 LTC3108-1 must be
known. For this calculation, it is assumed that the LDO
output capacitor is 2.2µF.
2.2V • 2.2µF
tLDO =
ICHG −ILDO
If there were 50µA of charge current available and a 5µA
load on the LDO (when the processor is sleeping), the time
for the LDO to reach regulation would be 107ms.
If VOUT were programmed to 3V and the VOUT capacitor
was 150µF, the time for VOUT to reach regulation would be:
3V • 150µF
t VOUT =
+ tLDO
ICHG −IVOUT −ILDO
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17
LTC3108-1
Applications Information
If there were 50µA of charge current available and 5µA of
load on VOUT, the time for VOUT to reach regulation after
the initial application of power would be 11.35 seconds.
In this example, IQ = 5µA, IBURST = 100mA, t = 5ms and
T = one hour. The average charge current required from
the LTC3108-1 would be:
Design Example 2
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 LTC3108-1 to support the average load must be
calculated, which can be easily done by the following:
ICHG ≥ IQ +
ICHG ≥ 5µA +
100mA • 0.005sec
= 5.14µA
3600sec
Therefore, if the LTC3108-1 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 3V, the average
power required by this application is only 15.4µW (not
including converter losses).
IBURST • t
T
Where IQ is the sleep current on VOUT required by the external circuitry in between bursts (including cap leakage),
IBURST is the total load current during the burst, t is the
duration of the burst and T is the period of the transmit
burst rate (essentially the time between bursts).
Note that the charge current available from the LTC3108‑1
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.
Typical Applications
Peltier-Powered Energy Harvester for Remote Sensor Applications
+
THERMOELECTRIC
GENERATOR
1nF
1:100
T1
+
CIN
VSTORE
C1
+
VOUT2
330pF
C2
∆T = 1°C TO 20°C
5.25V
LTC3108-1
499k
PGOOD
PGD
VLDO
COOPER BUSSMAN PB-5ROH104-R
OR KR-5R5H104-R
CSTORE
0.1F
3V
6.3V
VOUT2
µP
2.2V
2.2µF
VOUT
SW
VS2
VS1
VOUT2_EN
GND
VAUX
T1: COILCRAFT LPR6235-752SML
*COUT VALUE DEPENDENT ON
THE MAGNITUDE AND DURATION
OF THE LOAD PULSE
18
3V
+
SENSORS
XMTR
COUT*
OFF ON
1µF
31081 TA02
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Typical Applications
Supercapacitor Charger and LDO Powered by a Solar Cell
(Uses External Charge Pump Rectifiers)
0.022µF
IVOUT vs Illuminance
(2" Diameter Monocrystalline Cell)
BAS31
VAUX
10,000
INCANDESCENT LIGHT
+
SOLAR
CELL*
–
+
220µF
C1
330pF
VSTORE
1000
VOUT2
LTC3108-1
PGD
C2
2.2V
VLDO
499k
3.0V
VOUT
* 2" DIAMETER MONOCRYSTALLINE CELL
LIGHT LEVEL ≥ 900 LUX
T1: COILCRAFT LPR6235-253PML
+
SW
VS2
IVOUT (µA)
T1
1:20
VLDO
100
VOUT
2.2µF
4F*
FLOURESCENT LIGHT
VOUT2_EN
VS1
VAUX
OUTDOOR
LIGHT (CLOUDY)
10
100
GND
1000
10,000
ILLUMINANCE (LUX)
*TAIYO YUDEN
PAS1020LA3R0405
VAUX
4.7µF
10,0000
31081 TA03b
31081 TA03
Dual Output Converter and LDO Powered by a Thermopile Generator
HONEYWELL
Q313
THERMOPILE
T1
1:50
+
220µF
4.7nF
C1
VSTORE
VOUT2
330pF
LTC3108-1
C2
PGD
PGOOD
499k
VLDO
T1: COILCRAFT LPR6235-123QML
SW
VS2
VS1
VOUT
VOUT2_EN
VAUX
2.2V
4.5V
+
VOUT
150µF
6.3V
VLDO
2.2µF
GND
2.2µF
31081 TA04
31081fb
For more information www.linear.com/LTC3108-1
19
LTC3108-1
Typical Applications
DC Input Energy Harvester and Power Manager
RIN
RIN > 100Ω/ V
+
–
C1
5.25V
VSTORE
VIN
VIN > 5V
VOUT2
PGD
C2
SW
LTC3108-1
VS1
VOUT2_EN
VAUX
CSTORE
PGOOD
2.2V
VLDO
VOUT
VS2
+
VOUT2
3V
+
VLDO
2.2µF
VOUT
COUT
VOUT2_ENABLE
GND
31081 TA05
2.2µF
AC Input Energy Harvester and Power Manager
RIN
CIN
RIN > 100Ω/ V
C1
VSTORE
AC VIN
VIN > 5VP-P
VOUT2
- PIEZO
- 60Hz
PGD
LTC3108-1
C2
VS2
VOUT2_EN
VS1
VAUX
CSTORE
PGOOD
2.2V
4.5V
+
VOUT
VLDO
2.2µF
COUT
VOUT2_ENABLE
GND
2.2µF
20
+
VOUT2
VLDO
VOUT
SW
5.25V
31081 TA06
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Typical Applications
Low Profile (1.5mm) Step-Up Converter/Harvester Using 1:10 Transformer
VSTORE
T1
1:10
VIN
150mV TO 600mV
CIN
3V AT 20mA
VOUT2
VOUT2
499k
CRES*
390pF
0.1µF
C1
330pF
PGD
LTC3108-1
VLDO
C2
10ms
PGOOD
2.2V
VLDO
2.2µF
VOUT
SW
VS2
0.068µF
VS1
T1: COILCRAFT LPR4012-202LML
BAS31
*CRES LOWERS START-UP VOLTAGE
TO 135mV TYPICAL
VOUT2_EN
GND
VAUX
3V
+
330µF
×3
AVX TPSX337M004R0100
ENABLE
2.2V
OFF ON
10ms
VAUX
10µF
OUTPUT CAN SUPPORT A 20mA,
10ms LOAD PULSE EVERY 0.4s
AT VIN = 150mV
31081 TA07
IVOUT vs VIN (Steady State)
6
5
VOUT ≤ 3V
TYPICAL
IVOUT (mA)
4
3
MINIMUM LIMIT
2
1
0
150 200 250 300 350 400 450 500 550 600
VIN (mV)
31081 TA07b
31081fb
For more information www.linear.com/LTC3108-1
21
LTC3108-1
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DE/UE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695 Rev D)
4.00 ±0.10
(2 SIDES)
7
0.70 ±0.05
3.60 ±0.05
2.20 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.40 ±0.10
12
R = 0.05
TYP
3.30 ±0.05
1.70 ±0.05
R = 0.115
TYP
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
0.50 BSC
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
0.75 ±0.05
6
0.25 ±0.05
1
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
(UE12/DE12) DFN 0806 REV D
0.50 BSC
2.50 REF
2.50 REF
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
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
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641 Rev B)
.189 – .196*
(4.801 – 4.978)
.045 ±.005
16 15 14 13 12 11 10 9
.254 MIN
.009
(0.229)
REF
.150 – .165
.229 – .244
(5.817 – 6.198)
.0165 ±.0015
.150 – .157**
(3.810 – 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
.015 ±.004
× 45°
(0.38 ±0.10)
.007 – .0098
(0.178 – 0.249)
.0532 – .0688
(1.35 – 1.75)
4
5 6
7
8
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
3. DRAWING NOT TO SCALE
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
22
2 3
.008 – .012
(0.203 – 0.305)
TYP
.0250
(0.635)
BSC
GN16 REV B 0212
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
31081fb
For more information www.linear.com/LTC3108-1
LTC3108-1
Revision History
REV
DATE
DESCRIPTION
A
06/12
Added vendor information to Table 5
PAGE NUMBER
14
B
08/13
Changed Würth transformer part numbers
14
31081fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of itsinformation
circuits as described
herein will not infringe on existing patent rights.
For more
www.linear.com/LTC3108-1
23
LTC3108-1
Typical Application
Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity
HOT
1:100
1nF
C1
+
THERMOELECTRIC
GENERATOR
VSTORE
TEC
330pF
VOUT2
C2
COLD
499k
LPR6235-752SML
LTC3108-1
PGD
VLDO
SW
VS2
VS1
VOUT
5.25V
PGOOD
3V
VOUT2_EN
VAUX
GND
+
CSTORE
VOUT2
2.2V
+
VOUT
VLDO
2.2µF
COUT
OFF ON
1µF
COLD
THERMOELECTRIC
GENERATOR
1:100
C1
+
TEC
VAUX
1nF
VSTORE
VOUT2
330pF
LTC3108-1
C2
HOT
499k
LPR6235-752SML
PGD
VLDO
SW
VS2
VS1
VAUX
VOUT
VOUT2_EN
GND
31081 TA08
THERMOELECTRIC
GENERATOR
Related Parts
PART NUMBER
DESCRIPTION
LTC3108
Ultralow Voltage Step-Up Converter and Power Manager VIN: 0.02V to 1V; VOUT = 2.35V, 3.3V, 4.1V, 5V Fixed; IQ = 6µA; ISD
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