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LTC3108-1

31081fa

Peltier-Powered Energy Harvester for Remote Sensor Applications

31081 TA02

VS2

VS1

COOPER BUSSMAN PB-5ROH104-R

OR KR-5R5H104-R

VOUT2

PGOOD

2.2V

499k

COUT*

PGD

VLDO

VSTORE

VOUT

VOUT2_EN

LTC3108-1

VAUX

GND

CSTORE

0.1F

6.3V

5.25V

1μF

1nF

CIN

1:100

T1: COILCRAFT LPR6235-752SML

*COUT VALUE DEPENDENT ON

THE MAGNITUDE AND DURATION

OF THE LOAD PULSE

330pF

ΔT = 1°C TO 20°C

SENSORS

XMTR

μP

2.2μF

OFF

THERMOELECTRIC

GENERATOR

TYPICAL APPLICATIONS

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.

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 +

IBURST •t

Where IQ is the sleep current on VOUT required by the ex-

ternal 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).

In this example, IQ = 5μA, IBURST = 100mA, t = 5ms and

T = one hour. The average charge current required from

the LTC3108-1 would be:

ICHG ≥ 5μA +

100mA • 0.005sec

3600sec

= 5.14μA

Therefore, if the LTC3108-1 has an input voltage that al-

lows 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).

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.

APPLICATIONS INFORMATION

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