LTC3108 Linear Technology, LTC3108 Datasheet - Page 16

• Manufacturer Part Number: LTC3108
• Description: Ultralow Voltage Step-Up Converter and Power Manager
• Manufacturer: Linear Technology

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LTC3108
APPLICATIONS INFORMATION
Design Example 2
In many pulsed load applications, the duration, magnitude
and frequency of the load current bursts are known and
fi xed. 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:
Where I
ternal circuitry in between bursts (including cap leakage),
I
duration of the burst and T is the period of the transmit
burst rate (essentially the time between bursts).
In this example, I
T = one hour. The average charge current required from
the LTC3108 would be:
TYPICAL APPLICATIONS
16
BURST
I
I
CHG
CHG
is the total load current during the burst, t is the
Q
≥
≥
is the sleep current on V
I
5
Q
µA
TEG
ΔT = 1°C TO 20°C
+
I
+
BURST
100
Q
= 5μA, I
T
+
mA
T1: COILCRAFT LPR6235-752SML
•
3600
t
+
• .
BURST
0 005
sec
C
Peltier-Powered Energy Harvester for Remote Sensor Applications
IN
OUT
= 100mA, t = 5ms and
1:100
sec
T1
required by the ex-
=
5 14
.
330pF
1nF
µA
C1
C2
SW
VS2
VS1
VAUX
LTC3108
1μF
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
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 V
average power required by this application is only 17μW
(not including converter losses).
Note that the charge current available from the LTC3108
has no effect on the sizing of the V
assumed that the load current during a burst is much larger
than the charge current), and the V
effect on the maximum allowed burst rate.
V
GND
VSTORE
OUT2_EN
V
VLDO
V
OUT2
PGD
OUT
3.3V
OFF
2.2V
5V
+
PGOOD
ON
+
C
OUT
COOPER BUSSMAN PB-5ROH104-R
2.2μF
C
0.1F
6.3V
STORE
V
OUT2
μP
OR KR-5R5H104-R
SENSORS
XMTR
3108 TA02
OUT
OUT
3.3V
capacitor has no
capacitor (if it is
OUT
of 3.3V, the
3108p