LTC3108IGN#PBF Linear Technology, LTC3108IGN#PBF Datasheet - Page 16

• Manufacturer Part Number: LTC3108IGN#PBF
• Description: IC CONV BOOST PROG 4.5MA 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC3108IGN#PBF

• Applications: Energy Harvesting
• Current - Supply: 3mA
• Voltage - Supply: 20mV ~ 500mV
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Primary Input Voltage: 500mV
• No. Of Outputs: 3
• Output Voltage: 5V
• Output Current: 300mA
• No. Of Pins: 16
• Operating Temperature Range: -40°C To +85°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Min: 20mV
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

applicaTions inForMaTion
LTC3108
The VSTORE capacitor may be of very large value (thou-
sands 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 V
has a working voltage rating of at least 5.5V at the tem-
perature for which it will be used. The VSTORE capacitor
can be sized using the following:
Where 6µA is the quiescent current of the LTC3108, I
the load on V
LDO between bursts, I
burst, t is the duration of the burst, f is the frequency of
the bursts, TSTORE is the storage time required and V
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 capaci-
tors used for V
See Table 6 for recommended storage capacitors.
Table 6. Recommended Storage Capacitors
VENDOR
AVX
www.avx.com
Cap-XX
www.cap-xx.com
Cooper/Bussmann
www.bussmann.com/3/PowerStor.html
Vishay/Sprague
www.vishay.com/capacitors
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.

C
STORE
≥
OUT
 
6
µA I
OUT
OUT
in between bursts, I
+
and VSTORE should be low leakage.
), so ensure that the holdup capacitor
Q
+
BURST
I
LDO
5
+
. . 25 − V
is the total load during the
(
I
BURST
PART NUMBER/SERIES
BestCap Series
TAJ and TPS Series Tantalum
GZ Series
KR Series
P Series
Tantamount 592D
595D Tantalum
150CRZ/153CRV Aluminum
013 RLC (Low Leakage)
OUT
LDO
• • ) •
t f
is the load on the
 
TSTORE
Q
OUT
is
Design Example 1
This design example will explain how to calculate the
necessary storage capacitor value for V
applications, such as a wireless sensor/transmitter. In these
types of applications, the load is very small for a major-
ity 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 V
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
V
Due to the very low input voltage the circuit may operate
from, the connections to V
former 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 out-
puts 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.
V
OUT2
OUT
VIAS TO GROUND PLANE
Figure 3. Example Component Placement
for Two-Layer PC Board (DFN Package)
VLDO
PGOOD
GND
VSTORE
V
VAUX
VLDO
V
OUT2
PGD
OUT
1
2
3
4
5
6
IN
, the primary of the trans-
3108 FO3
OUT
12
11
10
9
8
7
in pulsed load
SW
C2
C1
V
VS1
VS2
OUT2_EN
V
IN
OUT
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