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APPLICATION INFORMATION

OVERVIEW

PC CARD POWER SPECIFICATION

DESIGNING FOR VOLTAGE REGULATION

V

DS +

V

O(reg)

–V

PS(reg)

–V

PCB

I

O

max +

V

DS

r

DS(on)

OVERCURRENT AND OVERTEMPERATURE PROTECTION

TPS2220A, TPS2223A

TPS2224A, TPS2226A

SLVS428B – MAY 2002 – REVISED SEPTEMBER 2004

PC Cards were initially introduced as a means to add flash memory to portable computers. The idea of add-in

cards quickly took hold, and 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. Therefore, the

PCMCIA (Personal Computer Memory Card International Association) was established, comprising members

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

plug-and-play concept, so that cards and hosts from different vendors would be transparently compatible.

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

use 12 V, which is now more of an optional requirement in the host.

and the PCMCIA connector. A typical design would limit the total of these resistive losses to less than 1% (50

and TPS2226A would be the PCMCIA voltage regulation less the power supply regulation and less the PCB and

connector resistive drops:

Typically, this would leave 100 mV for the allowable voltage drop across the 5-V switch. The specification for

output voltage regulation of the 3.3-V output is 300 mV; therefore, using the same equation by deducting 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 voltage drop is the output current multiplied by the switch resistance of

the allowable voltage drop across the IC, divided by the output-switch resistance.

The xVCC outputs have been designed to deliver the peak and average currents defined by the PC Card

specification within regulation over the operating temperature range. The xVPP outputs of the device have been

designed to deliver 100 mA continuously.

PC Cards are inherently subject to damage that can result from mishandling. Host systems require protection

against short-circuited cards that can lead to power-supply or PCB trace damage. Even extremely robust

systems can undergo rapid battery discharge into a damaged PC Card, resulting in the sudden and unacceptable

loss of system power. In comparison, the reliability of fused systems is poor because blown fuses require

troubleshooting and repair, usually by the manufacturer.

The TPS2220A, TPS2223A, TPS2224A, and TPS2226A take a two-pronged approach to overcurrent protection,

which is designed to activate if an output is shorted or when an overcurrent condition is present when switches

are powered up. First, instead of fuses, sense FETs monitor each of the xVCC and xVPP power outputs. Unlike

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