TPS2205

DUAL-SLOT PC CARD POWER-INTERFACE SWITCH

FOR PARALLEL PCMCIA CONTROLLERS

SLVS128D OCTOBER 1995 – REVISED JUNE 1998

17

POST OFFICE BOX 655303

APPLICATION INFORMATION

overview

PC Cards were initially introduced as a means to add EEPROM (flash memory) to portable computers with

limited on-board memory. The idea of add-in cards quickly took hold; modems, wireless LANs, global positioning

satellite system (GPS), multimedia, and hard-disk versions were soon available. As the number of PC Card

applications grew, the engineering community quickly recognized the need for a standard to ensure

compatibility across platforms. To this end, the PCMCIA was established, comprised of members from leading

computer, software, PC Card, and semiconductor manufacturers. One key goal was to realize the

“plug-and-play” concept. Cards and hosts from different vendors should be compatible — able to communicate

with one another transparently.

PC Card power specification

System compatibility also means power compatibility. The most current set of specifications (PC Card Standard)

set forth by the PCMCIA committee states that power is to be transferred between the host and the card through

designing for voltage regulation

traces and the PCMCIA connector. A typical design would limit the total of these resistive losses to less than

PCMCIA voltage regulation less the power supply regulation and less the PCB and connector resistive drops:

V

DS +

V

O reg

–V

PS reg

–V

PCB

Typically, this would leave 100 mV for the allowable voltage drop across the TPS2205. The voltage drop is the

output current multiplied by the switch resistance of the TPS2205. Therefore, the maximum output current that

can be delivered to the PC Card in regulation is the allowable voltage drop across the TPS2205 divided by the

output switch resistance.

I

O

max

+

V

DS

r

DS on

The xVCC outputs have been designed to deliver 700 mA at 5 V within regulation over the operating temperature

range. Current proposals for the PCMCIA specifications are to limit the power dissipated in the PCMCIA slot

to 3 W. With an input voltage of 5 V, 700 mA continous is the maximum current that can be delivered to the PC

Card. The TPS2205 is capable of delivering up to 1 A continuously, but during worst-case conditions the output

may not be within regulation. This is generally acceptable because the majority of PC Cards require less than

700 mA continuous. Some cards require higher peak currents (disk drives during initial platter spin-up), but it

is generally acceptable for small voltage sags to occur during these peak currents.

The xVCC outputs have been designed to deliver 1 A continuously at 3.3 V within regulation over the operating

temperature range. The PCMCIA specification for output voltage regulation of the 3.3-V output is 300 mV. Using

the voltage drop percentages (2%) for power supply regulation and PCB resistive loss (1%), the allowable

voltage drop for the 3.3 V switch is 200 mV.

The xVPP outputs have been designed to deliver 150 mA continuously at 12 V.