LINER LTC3108 Ultralow voltage step-up converter Datasheet

LTC3108
Ultralow Voltage Step-Up
Converter and Power Manager
FEATURES
DESCRIPTION
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The LTC®3108 is a highly integrated DC/DC converter ideal
for harvesting and managing surplus energy from extremely
low input voltage sources such as TEGs (thermoelectric
generators), thermopiles and small solar cells. The step-up
topology operates from input voltages as low as 20mV.
The LTC3108 is functionally equivalent to the LTC3108-1
except for its unique fixed VOUT options.
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Operates from Inputs of 20mV
Complete Energy Harvesting Power
Management System
- Selectable VOUT of 2.35V, 3.3V, 4.1V or 5V
- LDO: 2.2V at 3mA
- Logic Controlled Output
- Reserve Energy Output
Power Good Indicator
Uses Compact Step-Up Transformers
Small 12-Lead (3mm × 4mm) DFN or 16-Lead
SSOP Packages
Using a small step-up transformer, the LTC3108 provides a
complete power management solution for wireless sensing
and data acquisition. The 2.2V LDO powers an external
microprocessor, while the main output is programmed to
one of four fixed voltages to power a wireless transmitter
or sensors. The power good indicator signals that the main
output voltage is within regulation. A second output can be
enabled by the host. A storage capacitor provides power
when the input voltage source is unavailable. Extremely
low quiescent current and high efficiency design ensure
the fastest possible charge times of the output reservoir
capacitor.
APPLICATIONS
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Remote Sensors and Radio Power
Surplus Heat Energy Harvesting
HVAC Systems
Industrial Wireless Sensing
Automatic Metering
Building Automation
Predictive Maintenance
The LTC3108 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
VOUT Charge Time
1nF
THERMOELECTRIC
GENERATOR
C1
+
220μF
VSTORE
+
LTC3108
330pF
1000
100
PGOOD
PGD
2.2V
VLDO
SW
μP
2.2μF SENSORS
VOUT
VS2
3.3V
+
470μF
VS1 VOUT2_EN
VAUX
GND
VOUT = 3.3V
COUT = 470μF
0.1F
6.3V
VOUT2
C2
20mV TO 500mV
5V
RF LINK
TIME (sec)
1:100
+
10
1
1:100 Ratio
1:50 Ratio
1:20 Ratio
3108 TA01a
0
1μF
0
50
100 150 200 250 300 350 400
VIN (mV)
3108 TA01b
3108fb
1
LTC3108
ABSOLUTE MAXIMUM RATINGS
(Note 1)
SW Voltage ..................................................–0.3V to 2V
C1 Voltage....................................................–0.3V to 6V
C2 Voltage (Note 5).........................................–8V to 8V
VOUT2, VOUT2_EN ...........................................–0.3V to 6V
VAUX....................................................15mA into VAUX
VS1, VS2, VAUX, VOUT, PGD ........................–0.3V to 6V
VLDO, VSTORE ............................................–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
GND
1
16 GND
VAUX
2
15 SW
VSTORE
3
14 C2
VOUT
4
13 C1
9
VOUT2_EN
VOUT2
5
12 VOUT2_EN
5
8
VS1
VLDO
6
11 VS1
6
7
VS2
PGD
7
10 VS2
GND
8
9
DE PACKAGE
12-LEAD (4mm s 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#PBF
LTC3108EDE#TRPBF
3108
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3108IDE#PBF
LTC3108IDE#TRPBF
3108
12-Lead (4mm × 3mm) Plastic DFN
–40°C to 125°C
LTC3108EGN#PBF
LTC3108EGN#TRPBF
3108
16-Lead Plastic SSOP
–40°C to 125°C
LTC3108IGN#PBF
LTC3108IGN#TRPBF
3108
16-Lead Plastic SSOP
–40°C to 125°C
Consult LTC Marketing for parts 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
MIN
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
l
VSTARTUP
UNITS
mV
mA
500
mV
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LTC3108
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VAUX = 5V, unless otherwise noted.
PARAMETER
CONDITIONS
Output Voltage
VS1 = VS2 = GND
VS1 = VAUX, VS2 = GND
VS1 = GND, VS2 = VAUX
VS1 = VS2 = VAUX
VOUT Quiescent Current
VOUT = 3.3V, VOUT2_EN = 0V
VAUX Quiescent Current
No Load, All Outputs Charged
LDO Output Voltage
0.5mA 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
2.30
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
0.2
l
2.134
μA
6
9
μA
2.2
2.266
V
0.5
1
%
0.05
0.2
%
100
200
LDO Dropout Voltage
ILDO = 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
l
VS1, VS2 Threshold Voltage
0.4
V
0.1
μA
0.01
PGOOD Threshold (Rising)
Measured Relative to the VOUT Voltage
–7.5
Measured Relative to the VOUT Voltage
Sink Current = 100μA
PGOOD VOH
Source Current = 0
PGOOD Pull-Up Resistance
VOUT2_EN Threshold Voltage
%
–9
2.1
%
0.15
0.3
V
2.2
2.3
V
1
VOUT2_EN Rising
l
0.4
μA
μA
1.2
VS1 = VS2 = 5V
PGOOD VOL
V
0.85
VS1, VS2 Input Current
PGOOD Threshold (Falling)
mV
mA
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 = 3.3V
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
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
l
0.15
0.3
0.45
A
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.
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LTC3108
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
IVOUT and Efficiency vs VIN,
1:20 Ratio Transformer
IIN vs VIN, (VOUT = 0V)
4000
1000
1:50 RATIO, C1 = 4.7n
1:100 RATIO, C1 = 1n
1:20 RATIO, C1 = 10n
80
C1 = 10nF
70
3500
IVOUT
(VOUT = 0V)
3000
IVOUT (μA)
IIN (mA)
60
50
2500
2000
IVOUT
(VOUT = 4.5V)
EFFICIENCY
(VOUT = 4.5V)
40
1500
30
1000
20
500
10
10
1
0
10
100
VIN (mV)
0
1000
100
200
300
400
EFFICIENCY (%)
100
0
500
VIN (mV)
3108 G00
3108 G01
IVOUT and Efficiency vs VIN,
1:100 Ratio Transformer
IVOUT
(VOUT = 0V)
1200
40
600
30
IVOUT
(VOUT = 4.5V)
400
0
100
200
300
400
50
IVOUT
(VOUT = 4.5V)
40
1200
30
800
20
400
10
0
500
0
0
500
0
100
200
300
400
VIN (mV)
VIN (mV)
3108 G02
3108 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 = 4.5V)
1600
10
0
70
2000
20
200
IVOUT
(VOUT = 0V)
EFFICIENCY (%)
800
2400
50
EFFICIENCY
(VOUT = 4.5V)
80
C1 = 4.7nF
2800
60
EFFICIENCY (%)
IVOUT (μA)
1000
3200
70
C1 = 1nF
IVOUT (μA)
1400
IVOUT and Efficiency vs VIN,
1:50 Ratio Transformer
1:50 RATIO
4
100
3
1:100 RATIO
2
10
1Ω
2Ω
5Ω
10Ω
1
0
0
100
200
300
400
500
VIN (mV)
0
0
100 200 300 400 500 600 700 800
VIN OPEN-CIRCUIT (mV)
3108 G05
3108 G04
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LTC3108
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
IVOUT vs VIN and Source Resistance,
1:100 Ratio
IVOUT vs VIN and Source Resistance,
1:50 Ratio
1000
10000
C1 = 1nF
C1 = 4.7nF
IVOUT (μA)
IVOUT (μA)
1000
100
10
1Ω
2Ω
5Ω
10Ω
0
100
10
100
200
300
400
VIN OPEN-CIRCUIT (mV)
0
100 200 300 400 500 600 700 800
VIN OPEN-CIRCUIT (mV)
0
1Ω
2Ω
5Ω
10Ω
3108 G06
IVOUT vs dT and TEG Size,
1:100 Ratio
10000
VIN = 20mV
1:100 RATIO TRANSFORMER
40mm
TEG
1000
IVOUT (μA)
3108 G07
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
500
10
1
dT ACROSS TEG (°C)
3108 G09
10μs/DIV
100
3108 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
0.00
–1.00
0
0.5
1
1.5 2 2.5
LDO LOAD (mA)
3
3.5
4
3108 G10
0
0.5
1
1.5 2 2.5
LDO LOAD (mA)
3
3.5
4
3108 G11
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LTC3108
TYPICAL PERFORMANCE CHARACTERISTICS
VOUT and PGD Response
During a Step Load
Start-Up Voltage Sequencing
VIN = 50mV
1:100 RATIO TRANSFORMER
COUT = 220μF
CSTORE = 470μF
CLDO = 2.2μF
50mA LOAD STEP
COUT = 220μF
CH1
VSTORE
1V/DIV
CH2, VOUT
1V/DIV
CH3, VLDO
1V/DIV
10sec/DIV
TA = 25°C, unless otherwise noted.
CH2
VOUT
1V/DIV
CH1
PGD
1V/DIV
3108 G12
5ms/DIV
VOUT Ripple
3108 G13
LDO Step Load Response
30μA LOAD
COUT = 220μF
VLDO
20mV/DIV
20mV/
DIV
ILDO
5mA/DIV
100ms/DIV
3108 G14
200μs/DIV
3108 G15
0mA TO 3mA LOAD STEP
CLDO = 2.2μF
Enable Input and VOUT2
Running on Storage Capacitor
CH3
VSTORE
1V/DIV
CSTORE = 470μF
VOUT LOAD = 100μA
CH2, VOUT
1V/DIV
CH2, VOUT2
1V/DIV
CH4, VLDO
1V/DIV
CH1
VOUT2_EN
1V/DIV
CH1, VIN
50mV/DIV
1ms/DIV
3108 G16
5sec/DIV
3108 G17
10mA LOAD ON VOUT2
COUT = 220μF
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LTC3108
PIN FUNCTIONS
(DFN/SSOP)
VAUX (Pin 1/Pin 2): Output of the Internal Rectifier Circuit and VCC for the IC. Bypass VAUX with at least 1μF of
capacitance. An active shunt regulator clamps VAUX to
5.25V (typical).
VSTORE (Pin 2/Pin 3): Output for the Storage Capacitor
or Battery. A large capacitor may be connected from this
pin to GND for powering the system in the event the input
voltage is lost. It will be charged up to the maximum VAUX
clamp voltage. 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
2.35V
GND
VAUX
3.3V
VAUX
GND
4.1V
VAUX
VAUX
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).
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LTC3108
BLOCK DIAGRAM
LTC3108
VOUT2
1.3Ω
VOUT2
ILIM
VOUT2_EN
SYNC RECTIFY
REFERENCE
1.2V
VREF
5M
C1
1:100
VIN
VOUT
C1
VOUT
CIN
COUT
5.25V
C2
+
–
C2
SW
OFF ON
VOUT
SW
VSTORE
VS1
CHARGE
CONTROL
VS2
0.5Ω
VOUT
PROGRAM
VREF
VLDO
1M
–
+
VAUX
1μF
PGD
PGOOD
VSTORE
VOUT
GND (SSOP)
VBEST
VREF
EXPOSED PAD (DFN)
LDO
CSTORE
VLDO
3108 BD
2.2V
2.2μF
OPERATION
(Refer to the Block Diagram)
The LTC3108 is designed to use a small external step-up
transformer to create an ultralow input voltage step-up
DC/DC converter and power manager. It is ideally suited
for low power wireless sensors and other applications in
which surplus energy harvesting is used to generate system
power because traditional battery power is inconvenient
or impractical.
The LTC3108 is designed to manage the charging and
regulation of multiple outputs in a system in which the
average power draw is very low, but there may be periodic
pulses of higher load current required. This is typical of
wireless sensor applications, where the quiescent power
draw is extremely low most of the time, except for transmit
bursts when circuitry is powered up to make 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.
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LTC3108
OPERATION
Oscillator
Synchronous Rectifiers
The LTC3108 utilizes a MOSFET switch to form a resonant
step-up oscillator using an external step-up transformer
and a small coupling capacitor. This allows it to boost input
voltages as low as 20mV high enough to provide multiple
regulated output voltages for powering other circuits. The
frequency of oscillation is determined by the inductance of
the transformer secondary winding and is typically in the
range of 10kHz to 100kHz. 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. 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 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.
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 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
2.35V
GND
VAUX
3.3V
VAUX
GND
4.1V
VAUX
VAUX
5V
Voltage Reference
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 LTC3108 includes a precision, micropower reference,
for accurate regulated output voltages. This reference
becomes active as soon as VAUX exceeds 2V.
The internal programmable resistor divider sets VOUT,
eliminating the need for very high value external resistors
that are susceptible to board leakage.
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LTC3108
OPERATION
In a typical application, a storage capacitor (typically a few
hundred microfarads) is connected to VOUT. As soon as
VAUX exceeds 2.5V, the VOUT capacitor will be allowed to
charge up to its regulated voltage. The current available
to charge the capacitor will depend on the input voltage
and transformer turns ratio, but is limited to about 4.5mA
typical.
PGOOD
A power good comparator monitors the VOUT voltage.
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.
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 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.
3108fb
10
LTC3108
OPERATION
5.0
VSTORE (V)
2.5
0
3.0
2.0
PGD (V)
1.0
VOLTAGE (V)
0
5.0
2.5
VOUT (V)
0
3.0
2.0
VLDO (V)
1.0
0
5.0
VAUX (V)
2.5
0
0
10
20
30
40
50
60
70
80
TIME (ms)
3108 F01a
Figure 1. Output Voltage Sequencing with VOUT Programmed for 3.3V (Time Not to Scale)
3108fb
11
LTC3108
APPLICATIONS INFORMATION
Introduction
Refer to the IIN vs VIN curves in the Typical Performance
Characteristics section to see what input current is required
from the source for a given input voltage.
The LTC3108 is designed to gather energy from very low
input voltage sources and convert it to usable output voltages to power microprocessors, wireless transmitters and
analog sensors. 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 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 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.
1000
100
TEG VOPEN_CIRCUIT (mV)
VOC
10
100
MAX POUT
(IDEAL)
1
10
1
1
10
dT (°C)
TEG MAXIMUM POUT —IDEAL (mW)
TEG: 30mm
127 COUPLES
R = 2Ω
0.1
100
3108 F02
Figure 2. Typical Performance of a Peltier Cell Acting as a Thermoelectric Generator
3108fb
12
LTC3108
APPLICATIONS INFORMATION
this manner, a Peltier cell is referred to as a thermoelectric
generator (TEG).
current capability by providing a higher input voltage
under load.
The low voltage capability of the LTC3108 design allows
it to operate from a TEG with temperature differentials
as low as 1°C, making it ideal for harvesting energy in
applications in which a temperature difference exists
between two surfaces or between a surface and the ambient temperature. 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.
Peltier Cell (TEG) Suppliers
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
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
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
3108fb
13
LTC3108
APPLICATIONS INFORMATION
Thermopile Generator
Thermopile generators (also called powerpile generators)
are made up of a number of series-connected thermocouples enclosed in a metal tube. They are commonly
used in gas burner applications to generate a DC output
of hundreds of millivolts when exposed to the high temperature of a flame. Typical examples are the Honeywell
CQ200 and Q313. 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. 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 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 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.
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
S11100034 (1:100 Ratio)
S11100033 (1:50 Ratio)
S11100032 (1:20 Ratio)
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
3108fb
14
LTC3108
APPLICATIONS INFORMATION
C1 Capacitor
Using External Charge Pump Rectifiers
The charge pump capacitor that is connected from the
transformer’s secondary winding to the C1 pin has an effect on converter input resistance and maximum output
current capability. Generally, a minimum value of 1nF is
recommended when operating from very low input voltages using a transformer with a ratio of 1:100. 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
(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
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.
Certain types of oscillators, including transformer-coupled
oscillators such as the resonant oscillator of the LTC3108,
can exhibit a phenomenon called squegging. This term
refers to a condition that can occur which blocks or stops
the oscillation for a period of time much longer than the
period of oscillation, resulting in bursts of oscillation. An
example of this is the blocking oscillator, which is designed
to squegg to produce bursts of oscillation. Squegging
is also encountered in RF oscillators and regenerative
receivers.
In 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 start-up voltage. See the Typical Applications
schematics for an example.
In the case of the LTC3108, squegging can occur when a
charge builds up on the C2 gate coupling capacitor, such
that the DC bias point shifts and oscillation is extinguished
for a certain period of time, until the charge on the capacitor
bleeds off, allowing oscillation to resume. It is 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.
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.
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.
VOUT and VSTORE Capacitor
COUT (μF) ≥
ILOAD(mA) • tPULSE (ms)
ΔVOUT (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.
3108fb
15
LTC3108
APPLICATIONS INFORMATION
The VSTORE capacitor may be of very large value (thousands of microfarads or even Farads), to provide holdup
at times when the input power may be lost. Note that this
capacitor can charge all the way to 5.25V (regardless of
the settings for VOUT), so ensure that the holdup capacitor
has a working voltage rating of at least 5.5V at the temperature for which it will be used. 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, IQ is
the load on VOUT in between bursts, ILDO is the load on the
LDO between bursts, IBURST is the total load during the
burst, t is the duration of the burst, f is the frequency of
the bursts, TSTORE is the storage time required and VOUT
is the output voltage required. Note that for a programmed
output voltage of 5V, the VSTORE capacitor cannot provide
any beneficial storage time.
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.
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)
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 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, any sources of leakage current on
the output voltage pins must be minimized. An example
board layout is shown in Figure 3.
VIN
VAUX
VSTORE
VOUT
VOUT
VOUT2
VOUT2
VLDO
VLDO
PGOOD
PGD
1
12
2
11
3
10
4
9
5
8
6
7
SW
C2
C1
VOUT2_EN
VS1
VS2
GND
3108 FO3
VIAS TO GROUND PLANE
Storage capacitors requiring voltage balancing are not
recommended due to the current draw of the balancing
resistors.
PCB Layout Guidelines
Due to the rather low switching frequency of the resonant
converter and the low power levels involved, PCB layout
is not as critical as with many other DC/DC converters.
There are, however, a number of things to consider.
Figure 3. Example Component Placement
for Two-Layer PC Board (DFN Package)
Design Example 1
This design example will explain how to calculate the
necessary storage capacitor value for VOUT in pulsed load
applications, such as a wireless sensor/transmitter. In these
types of applications, the load is very small for a 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 to recharge
the capacitor. A method for calculating the maximum rate
3108fb
16
LTC3108
APPLICATIONS INFORMATION
at which the load pulses can occur for a given output current from the LTC3108 will also be shown.
Therefore, in this application example, the circuit can support a 1ms transmit burst every 1.5 seconds.
In this example, VOUT is set to 3.3V, and the maximum
allowed voltage droop during a transmit burst is 10%, or
0.33V. The duration of a transmit burst is 1ms, with a total
average current requirement of 40mA during the burst.
Given these factors, the minimum required capacitance
on VOUT is:
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.
COUT (μF) ≥
40mA • 1ms
= 121μF
0.33V
Note that this equation neglects the effect of capacitor
ESR on output voltage droop. For most ceramic or low
ESR tantalum capacitors, the ESR will have a negligible
effect at these load currents.
A standard value of 150μF or larger could be used for COUT
in this case. Note that the load current is the total current
draw on VOUT, VOUT2 and VLDO, since the current for all of
these outputs must come from VOUT during a burst. Current
contribution from the holdup capacitor on VSTORE is not
considered, since it may not be able to recharge between
bursts. Also, it is assumed that the charge current from
the LTC3108 is negligible compared to the magnitude of
the load current during the burst.
To calculate the maximum rate at which load bursts can
occur, determine how much charge current is available
from the LTC3108 VOUT pin given the input voltage source
being used. This number is best found empirically, since
there are many factors affecting the 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:
150μF • 0.33V
t=
= 1.5sec or fMAX = 0.666Hz
(50μA − 17μA)
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.
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 3.3V and the VOUT capacitor
was 150μF, the time for VOUT to reach regulation would be:
t VOUT =
3.3V • 150μF
+ tLDO
ICHG − IVOUT − ILDO
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:
ICHG ≥ IQ +
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
3108fb
17
LTC3108
APPLICATIONS INFORMATION
duration of the burst and T is the period of the transmit
burst rate (essentially the time between bursts).
hour. It can be determined that the sleep current of 5μA
is the dominant factor because the transmit duty cycle is
so small (0.00014%). Note that for a VOUT of 3.3V, the
average power required by this application is only 17μW
(not including converter losses).
In this example, IQ = 5μA, IBURST = 100mA, t = 5ms and
T = one hour. The average charge current required from
the LTC3108 would be:
ICHG ≥ 5μA +
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.
100mA • 0.005sec
= 5.14μA
3600 sec
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
TYPICAL APPLICATIONS
Peltier-Powered Energy Harvester for Remote Sensor Applications
1nF
1:100
T1
+
VSTORE
5V
+
C1
+
THERMOELECTRIC
GENERATOR
CIN
VOUT2
330pF
ΔT = 1°C TO 20°C
PGOOD
PGD
C2
LTC3108
VLDO
SW
COOPER BUSSMAN PB-5ROH104-R
OR KR-5R5H104-R
CSTORE
0.1F
3.3V
6.3V
VOUT2
SENSORS
μP
2.2V
2.2μF
VOUT
+
VS2
COUT*
VS1
VOUT2_EN
GND
VAUX
T1: COILCRAFT LPR6235-752SML
*COUT VALUE DEPENDENT ON
THE MAGNITUDE AND DURATION
OF THE LOAD PULSE
XMTR
3.3V
OFF ON
1μF
3108 TA02
3108fb
18
LTC3108
TYPICAL APPLICATIONS
Li-Ion Battery Charger and LDO Powered by a Solar Cell
T1
1:20
+
0.01μF
C1
VSTORE
+
SOLAR CELL*
220μF
–
VOUT2
330pF
LTC3108
C2
SW
PGD
2.2V
VLDO
4.1V
VOUT
VS2
VS1
* 2" DIAMETER MONOCRYSTALLINE CELL
LIGHT LEVEL ≥ 900 LUX
VLDO
VOUT
2.2μF
Li-Ion
VOUT2_EN
VAUX
GND
T1: COILCRAFT LPR6235-253PML
4.7μF
3108 TA03
Supercapacitor Charger and LDO Powered by a Thermopile Generator
HONEYWELL
CQ200
THERMOPILE
T1
1:50
4.7nF
C1
VSTORE
+
220μF
VOUT2
330pF
LTC3108
C2
SW
PGD
VOUT
T1: COILCRAFT LPR6235-123QML
PGOOD
2.2V
VLDO
VS2
VS1
2.35V
+
2.2μF
150mF
2.5V
VOUT2_EN
VAUX
VLDO
VOUT
GND
CAP-XX GZ115F
2.2μF
3108 TA04
AC Input Energy Harvester and Power Manager
DC Input Energy Harvester and Power Manager
RIN
RIN > 100Ω / V
C1
+
–
5V
VSTORE
VIN
VIN > 5V
VOUT2
PGD
C2
SW
CSTORE
2.2V
3.3V
+
VOUT
COUT
VS1
VOUT2_EN
VAUX
GND
2.2μF
VOUT2_ENABLE
VSTORE
AC VIN
VIN > 5VP-P
VOUT2
- PIEZO
- 60Hz
PGOOD
VLDO
VOUT
C1
+
VOUT2
LTC3108
VS2
RIN
CIN
RIN > 100Ω/ V
VLDO
2.2μF
PGD
VOUT
SW
CSTORE
PGOOD
2.2V
VLDO
C2
+
VOUT2
LTC3108
5V
+
VOUT
VLDO
2.2μF
COUT
VS2
VOUT2_EN
VS1
VAUX
3108 TA05
5V
VOUT2_ENABLE
GND
2.2μF
3108 TA06
3108fb
19
LTC3108
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
GN Package
16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641 Rev B)
.189 – .196*
(4.801 – 4.978)
.045 ±.005
.009
(0.229)
REF
16 15 14 13 12 11 10 9
.254 MIN
.150 – .165
.229 – .244
(5.817 – 6.198)
.0165 ±.0015
.150 – .157**
(3.810 – 3.988)
.0250 BSC
RECOMMENDED SOLDER PAD LAYOUT
1
.015 ±.004
= 45$
(0.38 ±0.10)
.007 – .0098
(0.178 – 0.249)
2 3
4
5 6
7
.0532 – .0688
(1.35 – 1.75)
8
.004 – .0098
(0.102 – 0.249)
0° – 8° TYP
.016 – .050
(0.406 – 1.270)
.0250
(0.635)
BSC
.008 – .012
(0.203 – 0.305)
TYP
NOTE:
1. CONTROLLING DIMENSION: INCHES
INCHES
2. DIMENSIONS ARE IN
(MILLIMETERS)
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
3. DRAWING NOT TO SCALE
4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE
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
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
3.00 ±0.10
(2 SIDES)
0.75 ±0.05
3.30 ±0.10
1.70 ±0.10
6
0.25 ±0.05
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
1
(UE12/DE12) DFN 0806 REV D
0.50 BSC
0.50 BSC
2.50 REF
2.50 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.40 ±0.10
12
R = 0.05
TYP
3.30 ±0.05
1.70 ±0.05
R = 0.115
TYP
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
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
3108fb
20
LTC3108
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
04/10
Updated front page text and Typical Appliction
1
Updated Absolute Maximum Ratings and Order Information sections
2
Updated Electrical Characteristics
3
Added graph (3108 G00) to Typical Performance Characteristics
4
Updated Block Diagram
8
Text added to Operation section
9
Changes to Applications Information section
Updated Typical Applications
B
12-18
18, 19, 22
Updated Related Parts
22
Added vendor information to Table 5
14
3108fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
21
LTC3108
TYPICAL APPLICATION
Dual TEG Energy Harvester Operates from Temperature Differentials of Either Polarity
1nF
HOT
1:100
C1
+
THERMOELECTRIC
GENERATOR
VSTORE
VOUT2
330pF
LTC3108
C2
COLD
LPR6235-752SML
PGD
VLDO
SW
VS2
VS1
VOUT
5V
CSTORE
PGOOD
2.2V
3.3V
+
VOUT2_EN
VAUX
+
VOUT2
VOUT
VLDO
2.2μF
COUT
GND
OFF ON
1μF
VAUX
1nF
1:100
COLD
C1
VSTORE
+
THERMOELECTRIC
GENERATOR
VOUT2
330pF
LTC3108
C2
HOT
LPR6235-752SML
SW
VS2
VS1
VAUX
PGD
VLDO
VOUT
VOUT2_EN
GND
3108 TA07
RELATED PARTS
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
LTC4O70
Micropower Shunt Li-Ion Charge
Controls Charging with μA Source
3108fb
22 Linear Technology Corporation
LT 0612 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2010