Linear LTC3108EDE User manual

LTC3108EDE
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DESCRIPTION
Demonstration Circuit 1582B featuring the LTC3108 is
a highly integrated DC/DC converter optimized for
harvesting and managing energy from extremely low
input voltage sources such as thermoelectric genera-
tors (TEG). The step-up topology operates from input
voltages as low as 20mV.
The DC 1582B Demonstration Circuit has been optimized
for low start-up voltage with a 100:1 turns ratio trans-
former. For application where it is desirable to trade-off
a higher start-up voltage for higher current, a lower turns
ratio transformer can be used. Refer to the LTC3108
datasheet for more information.
The LTC3108 is designed to accumulate and manage
energy over a long period of time to enable short bursts
of power to be used to acquire and transmit data. The
burst 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 accumula-
tion time between bursts.
The Demonstration Circuit has been set up with a storage
capacitor that makes it easy to evaluate the general func-
tionality of the circuit. The lower value capacitor allows
for a fast charge time but limits the pulsed energy that
can be drawn from it. Space is provided, and alternate
part footprints have been built into the PCB to allow ex-
perimentation with larger capacitors for more energy
storage. In a typical application, the larger output capaci-
tors may be used. Refer to the datasheet for more in-
formation including equations to properly size the output
capacitors for a given application.
The LTC3108 is available in two versions, the only differ-
ence being the VOUT and VOUT2 output voltages. Refer
to the datasheets for more information.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, LT, Burst Mode, are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
DEMO CIRCUIT 1582B
QUICK START GUIDE
LTC3108EDE/ LTC3108EDE-1
Ultralow Voltage Step-Up
Converter and Power Manager
TABLE 1. Typical Specifications (25°C)
Input Voltage Range 50mV-400mV (Typical no load start-up = 20mV)
VLDO 2.2V
VOUT Jumper Selectable from 2.35 to 5.0V
VOU
T
2 Switched Output, VOUT2=VOUT
VSTORE 5.25V

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QUICK START PROCEDURE
Using short twisted pair leads for any power connections and with all loads and power supplies off, refer to Fig-
ure 1 for the proper measurement and equipment setup. The Power Supply (PS1) should not be connected to
the circuit until told to do so in the procedure below.
Two versions of the demo board are available. Assembly build –A uses the LTC3108EDE while Assembly build –
B uses the LTC3108EDE-1. The only difference is the VOUT and VOUT2 voltages.
When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the probe tip directly across the VCC or VOUT and GND
terminals. See Figure 2 for proper scope probe technique.
1. Jumper, Power Supply and LOAD Settings to start:
PS1= OFF
LOADS = OFF
JP1 (VOUT2) = ON
JP2= VAUX
JP3 = VAUX
2. Turn on PS1 and slowly increase voltage until the voltage at VIN is 50mV. Monitor input current. If
input current exceeds 50 mA turn off PS1 and look for shorts.
3. Confirm VLDO = 2.2V
4. Increase Vin = 100mV
5. Set LOAD on VLDO to 50μA. Set LOAD on VOUT = 25 μA. Set LOAD on VOUT2 = 25 μA.
6. For the –A version: Verify VLDO = 2.2V, VOUT ≈5.0V, VOUT2≈5.0V, and VSTORE ≈5.2V
7. For the –B version: Verify VLDO = 2.2V, VOUT ≈4.5V, VOUT2≈4.5V, and VSTORE ≈5.2V
The board is now ready for operation. The voltage on VOUT and VOUT2 can be modified by changing jumpers
JP2 and JP3. The jumper combinations are shown on the demo board.
Several variations of this design are possible, including increasing the energy storage by populating C7, or C9.
Please refer to the datasheet for design equations.

LTC3108EDE
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VIN GND
Figure 2. Measuring Input or Output Ripple
Figure 1. Connection Diagram

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Figure 3.
Circuit Schematic

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Figure 4. Bill of Materials