LTC3108

14

3108p

To minimize losses and capacitor charge time, all capaci-

See Table 5 for recommended storage capacitors.

Table 5. Recommended Storage Capacitors

VENDOR

PART NUMBER/SERIES

AVX

www.avx.com

BestCap Series

TAJ and TPS Series Tantalum

Cap-XX

www.cap-xx.com

GZ Series

Cooper/Bussman

www.bussmann.com/3/PowerStor.html

KR Series

P Series

Vishay/Sprague

www.vishay.com/capacitors

Tantamount 592D

595D Tantalum

150CRZ/153CRV Aluminum

013 RLC (Low Leakage)

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.

Due to the very low input voltage the circuit may operate

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.

Design Example 1

This design example will explain how to calculate the

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

supports the load during the transmit burst, and the long

sleep time between bursts allows the LTC3108 to recharge

APPLICATIONS INFORMATION

Figure 3. Example Component Placement for Two-Layer PC Board (DFN Package)

3108 FO3

VIAS TO GROUND PLANE

VLDO

PGOOD

GND

12

11

8

9

10

4

5

3

2

1

VS1

VS2

SW

C2

C1

VLDO

PGD

VAUX

VSTORE

6

7