TPS2212

SINGLE-SLOT, PARALLEL INTERFACE POWER SWITCH

FOR LOW POWER PC CARD SLOTS

SLVS193A – APRIL 1999 – REVISED JANUARY 2001

13

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, GPS systems,

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 (Personal Computer Memory Card International Association) 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, i.e. cards and hosts from different vendors should be compatible.

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

eight of the 68 terminals of the PC Card connectors. This power interface consists of two VCC, two VPP, and

four ground terminals. Multiple VCC and ground terminals minimize connector-terminal and line resistance. The

two VPP terminals were originally specified as separate signals, but are commonly tied together in the host to

form a single node to minimize voltage losses. Card primary power is supplied through the VCC terminals;

flash-memory programming and erase voltage is supplied through the VPP terminals.

designing for voltage regulation

The current PCMCIA specification for output voltage regulation of the 5-V output is 5% (250 mV). In a typical

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

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

V

V

O reg

– V

PS reg

– V

PCB

Typically, this would leave 100 mV for the allowable voltage drop across the TPS2212. The voltage drop is the

output current multiplied by the switch resistance of the TPS2212. Therefore, the maximum output current that

can be delivered to the PC Card in regulation is the allowable voltage drop across the TPS2212 divided by the

output switch resistance.

I

O

max

+

V

DS

r

DS on

The VCC outputs deliver 250 mA continuous at 5 V and 3.3 V within regulation over the operating temperature

range. Using the same equations, the PCMCIA specification for output voltage regulation of the 3.3 V output

is 300 mV. Using the voltage drop percentages for power supply regulation (2%) and PCB resistive loss (1%),

the allowable voltage drop for the 3.3 V switch is 200 mV. The 12-V outputs (VPP) of the TPS2212 can deliver

150 mA continuously.