LTC3108
Ultralow Voltage Step-Up
Converter and Power Manager
FEATURES
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DESCRIPTION
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 V
OUT
options.
Using a small step-up transformer, the LTC3108 provides a
complete power management solution for wireless sensing
and data acquisition. The 2.2V LDO powers an external
microprocessor, while the main output is programmed to
one of four fixed voltages to power a wireless transmitter
or sensors. The power good indicator signals that the main
output voltage is within regulation. A second output can be
enabled by the host. A storage capacitor provides power
when the input voltage source is unavailable. Extremely
low quiescent current and high efficiency design ensure
the fastest possible charge times of the output reservoir
capacitor.
The LTC3108 is available in a small, thermally enhanced
12-lead (3mm
×
4mm) DFN package and a 16-lead SSOP
package.
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Operates from Inputs of 20mV
Complete Energy Harvesting Power
Management System
- Selectable V
OUT
of 2.35V, 3.3V, 4.1V or 5V
- LDO: 2.2V at 3mA
- Logic Controlled Output
- Reserve Energy Output
Power Good Indicator
Uses Compact Step-Up Transformers
Small 12-Lead (3mm
×
4mm) DFN or 16-Lead
SSOP Packages
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
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
1nF
1:100
+
THERMOELECTRIC
GENERATOR
20mV TO 500mV
V
OUT
Charge Time
C1
VSTORE
LTC3108
C2
SW
V
OUT2
PGOOD
PGD
2.2V
VLDO
5V
+
220μF
330pF
+
1000
0.1F
6.3V
100
μP
TIME (sec)
2.2μF SENSORS
10
V
OUT
= 3.3V
C
OUT
= 470μF
VS2
V
OUT
3.3V
+
470μF
RF LINK
1
1:100 Ratio
1:50 Ratio
1:20 Ratio
0
50
100 150 200 250 300 350 400
V
IN
(mV)
3108 TA01b
VS1 V
OUT2_EN
VAUX
GND
1μF
3108 TA01a
0
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
V
OUT2
, V
OUT2_EN
...........................................–0.3V to 6V
VAUX....................................................15mA into VAUX
VS1, VS2, VAUX, V
OUT
, 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
GND
VAUX
VSTORE
V
OUT
V
OUT2
VLDO
PGD
1
2
3
4
5
6
13
GND
12
SW
11
C2
10
C1
9
8
7
V
OUT2_EN
VS1
VS2
VAUX
VSTORE
V
OUT
V
OUT2
VLDO
PGD
GND
1
2
3
4
5
6
7
8
TOP VIEW
16 GND
15 SW
14 C2
13 C1
12 V
OUT2_EN
11 VS1
10 VS2
9
GND
DE PACKAGE
12-LEAD (4mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB (NOTE 4)
GN PACKAGE
16-LEAD PLASTIC SSOP NARROW
T
JMAX
= 125°C,
θ
JA
= 110°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3108EDE#PBF
LTC3108IDE#PBF
LTC3108EGN#PBF
LTC3108IGN#PBF
TAPE AND REEL
LTC3108EDE#TRPBF
LTC3108IDE#TRPBF
LTC3108EGN#TRPBF
LTC3108IGN#TRPBF
PART MARKING*
3108
3108
3108
3108
PACKAGE DESCRIPTION
12-Lead (4mm
×
3mm) Plastic DFN
12-Lead (4mm
×
3mm) Plastic DFN
16-Lead Plastic SSOP
16-Lead Plastic SSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–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
PARAMETER
Minimum Start-Up Voltage
No-Load Input Current
Input Voltage Range
CONDITIONS
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for T
A
= 25°C (Note 2). VAUX = 5V, unless otherwise noted.
MIN
TYP
20
3
l
MAX
50
UNITS
mV
mA
Using 1:100 Transformer Turns Ratio, VAUX = 0V
Using 1:100 Transformer Turns Ratio; V
IN
= 20mV,
V
OUT2_EN
= 0V; All Outputs Charged and in Regulation
Using 1:100 Transformer Turns Ratio
V
STARTUP
500
mV
3108fb
2
LTC3108
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage
CONDITIONS
VS1 = VS2 = GND
VS1 = VAUX, VS2 = GND
VS1 = GND, VS2 = VAUX
VS1 = VS2 = VAUX
V
OUT
= 3.3V, V
OUT2_EN
= 0V
No Load, All Outputs Charged
0.5mA Load
For 0mA to 2mA Load
For VAUX from 2.5V to 5V
I
LDO
= 2mA
V
LDO
= 0V
V
OUT
= 0V
VSTORE = 0V
Current into VAUX = 5mA
VSTORE = 5V
V
OUT2
= 0V, V
OUT2_EN
= 0V
l
l
l
l
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for T
A
= 25°C (Note 2). VAUX = 5V, unless otherwise noted.
MIN
2.30
3.234
4.018
4.90
TYP
2.350
3.300
4.100
5.000
0.2
6
2.134
2.2
0.5
0.05
100
4
2.8
2.8
5
11
4.5
4.5
5.25
0.1
0.1
0.4
0.85
0.01
–7.5
–9
0.15
2.1
l
MAX
2.40
3.366
4.182
5.10
9
2.266
1
0.2
200
7
7
5.55
0.3
1.2
0.1
UNITS
V
V
V
V
μA
μA
V
%
%
mV
mA
mA
mA
V
μA
μA
V
μA
%
%
V
OUT
Quiescent Current
VAUX Quiescent Current
LDO Output Voltage
LDO Load Regulation
LDO Line Regulation
LDO Dropout Voltage
LDO Current Limit
V
OUT
Current Limit
VSTORE Current Limit
VAUX Clamp Voltage
VSTORE Leakage Current
V
OUT2
Leakage Current
VS1, VS2 Threshold Voltage
VS1, VS2 Input Current
PGOOD Threshold (Rising)
PGOOD Threshold (Falling)
PGOOD V
OL
PGOOD V
OH
PGOOD Pull-Up Resistance
V
OUT2_EN
Threshold Voltage
V
OUT2_EN
Pull-Down Resistance
V
OUT2
Turn-On Time
V
OUT2
Turn-Off Time
V
OUT2
Current Limit
V
OUT2
Current Limit Response Time
V
OUT2
P-Channel MOSFET On-Resistance
N-Channel MOSFET On-Resistance
VS1 = VS2 = 5V
Measured Relative to the V
OUT
Voltage
Measured Relative to the V
OUT
Voltage
Sink Current = 100μA
Source Current = 0
V
OUT2_EN
Rising
0.3
2.3
1.3
V
V
MΩ
V
MΩ
μs
μs
2.2
1
1
5
5
0.4
(Note 3)
V
OUT
= 3.3V
(Note 3)
V
OUT
= 3.3V (Note 3)
C2 = 5V (Note 3)
l
0.15
0.15
0.3
350
1.3
0.5
0.45
A
ns
Ω
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 T
J
≈
T
A
. The LTC3108E is guaranteed to meet specifications from 0°C to 85°C
junction temperature. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3108I is guaranteed
over the full –40°C to 125°C operating junction temperature range.
Note that the maximum ambient temperature is determined by specific
operating conditions in conjunction with board layout, the rated thermal
package thermal resistance and other environmental factors. The junction
temperature (T
J
) is calculated from the ambient temperature (T
A
) and
power dissipation (P
D
) according to the formula: T
J
= T
A
+ (P
D
•
θ
JA
°C/W),
where
θ
JA
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.
3108fb
3
LTC3108
TYPICAL PERFORMANCE CHARACTERISTICS
I
IN
vs V
IN
, (V
OUT
= 0V)
1000
4000
1:50 RATIO, C1 = 4.7n
1:100 RATIO, C1 = 1n
1:20 RATIO, C1 = 10n
3500
3000
100
I
VOUT
(μA)
I
IN
(mA)
2500
2000
1500
1000
500
1
0
10
100
V
IN
(mV)
1000
3108 G00
T
A
= 25°C, unless otherwise noted.
I
VOUT
and Efficiency vs V
IN
,
1:20 Ratio Transformer
C1 = 10nF
I
VOUT
(V
OUT
= 0V)
80
70
60
EFFICIENCY (%)
50
EFFICIENCY
(V
OUT
= 4.5V)
I
VOUT
(V
OUT
= 4.5V)
40
30
20
10
0
100
200
300
400
0
500
3108 G01
10
V
IN
(mV)
I
VOUT
and Efficiency vs V
IN
,
1:100 Ratio Transformer
1400
1200
1000
I
VOUT
(μA)
800
600
400
200
0
0
100
200
300
400
V
IN
(mV)
3108 G03
I
VOUT
and Efficiency vs V
IN
,
1:50 Ratio Transformer
70
3200
2800
2400
EFFICIENCY (%)
I
VOUT
(μA)
2000
1600
1200
800
400
0
0
100
200
300
400
V
IN
(mV)
3108 G02
C1 = 1nF
I
VOUT
(V
OUT
= 0V)
EFFICIENCY
(V
OUT
= 4.5V)
C1 = 4.7nF
80
I
VOUT
(V
OUT
= 0V)
70
60
EFFICIENCY (%)
50
I
VOUT
(V
OUT
= 4.5V)
40
30
20
10
0
500
60
50
40
EFFICIENCY
(V
OUT
= 4.5V)
I
VOUT
(V
OUT
= 4.5V)
30
20
10
0
500
Input Resistance vs V
IN
(V
OUT
Charging)
10
9
8
INPUT RESISTANCE (Ω)
7
6
5
4
3
2
1
0
0
100
200
300
400
500
3108 G04
I
VOUT
vs V
IN
and Source Resistance,
1:20 Ratio
10000
C1 = 10nF
1:20 RATIO
1000
I
VOUT
(μA)
1:50 RATIO
100
1:100 RATIO
10
0
0
1Ω
2Ω
5Ω
10Ω
100 200 300 400 500 600 700 800
V
IN
OPEN-CIRCUIT (mV)
3108 G05
V
IN
(mV)
3108fb
4
LTC3108
TYPICAL PERFORMANCE CHARACTERISTICS
I
VOUT
vs V
IN
and Source Resistance,
1:50 Ratio
10000
1000
C1 = 4.7nF
T
A
= 25°C, unless otherwise noted.
I
VOUT
vs V
IN
and Source Resistance,
1:100 Ratio
C1 = 1nF
1000
I
VOUT
(μA)
I
VOUT
(μA)
100
100
10
0
0
1Ω
2Ω
5Ω
10Ω
100 200 300 400 500 600 700 800
V
IN
OPEN-CIRCUIT (mV)
3108 G06
10
0
100
200
300
400
V
IN
OPEN-CIRCUIT (mV)
1Ω
2Ω
5Ω
10Ω
500
3108 G07
I
VOUT
vs dT and TEG Size,
1:100 Ratio
10000
V
OUT
= 0V
40mm
TEG
15mm
TEG
100
C1 PIN
2V/DIV
C2 PIN
2V/DIV
SW PIN
50mV/
DIV
Resonant Switching Waveforms
V
IN
= 20mV
1:100 RATIO TRANSFORMER
1000
I
VOUT
(μA)
10
0
0.1
1:50 RATIO
1:100 RATIO
1:50 RATIO
1:100 RATIO
10
1
dT ACROSS TEG (°C)
100
3108 G08
10μs/DIV
3108 G09
LDO Load Regulation
0.00
0.20
0.18
DROPOUT VOLTAGE (V)
–0.25
DROP IN VLDO (%)
0.16
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
3108 G10
LDO Dropout Voltage
–0.50
–0.75
0.00
0
0.5
1
1.5 2 2.5
LDO LOAD (mA)
3
3.5
4
3108 G11
3108fb
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