The Important Information/Disclaimer is incorporated in the catalog where these specifications came from or

available online at www.avx.com/disclaimer/ by reference and should be reviewed in full before placing any order.

25

4.4 BESTCAP® FOR GSM/GPRS PCM- CIA MO-

DEMS

There is an increasing usage of PCMCIA modem cards for wireless LAN

and WAN (Wide Area Network) applications.

The PCMCIA card is used as an accessory to Laptops and PDAs and enables

wide area mobile Internet access, including all associated applications like

Email and file transfer.

With the widespread use of GSM networks, a PCMCIA GSM modem is a

commonly used solution. To achieve higher speed data rates, GSM networks

are now being upgraded to support the GPRS standard.

The design challenge:

GSM/GPRS transmission requires a current of approximately 2A for the

pulse duration. The PCMCIA bus cannot supply this amount of pulsed

current. Therefore, there is a need for a relatively large capacitance to

bridge the gap.

The capacitor supplies the pulse current to the transmitter and is charged

by a low current during the interval between pulses.

Capacitor

2 Ampere

Current

Voltage

V+ from

PCMCIA bus

Transmitter

V

t

V1 = I*ESR

V2 = I* t/C

}

}

THE SOLUTION:

SOLUTION A

SOLUTION B

Chip Tantalum

BestCap®

BZ154B473ZSB

Rated Capacitance

(milli Farad)

2.2

47

Capacitance

@ 0.5msec Pulse

(milli Farad)

2.2

30

Operating Voltage (V)

3.7

3.7

ESR (milli ohm)

50

160

Size (mm)

.4 x 7 x 2

20 x 15 x 2.1

Voltage Drop* (V)

GPRS Pulse

(25% duty cycle)

0.804V

0.268V

Voltage After Pulse (V)

2.896

3.432

Cutoff Voltage (V)

3.1

3.1

Pass/FAIL

FAIL

PASS

* V=V1 +V2 =1.5A*ESR + (1.5A*1.154msec)/C

It is assumed that during the pulse, 0.5A is delivered by the battery and 1.5A

by the capacitor.

Conclusion: High capacitance is needed to minimize voltage drop. A high

value capacitance, even with a higher ESR, results in a lower voltage drop.

Low voltage drop minimizes the conductive and emitted electro magnetic

interference and increases transmitter output power and efficiency.

BestCap® Ultra-low ESR

High Power Pulse Supercapacitors

BestCap® for GSM/GPRS PCMCIA Modems

102419