Datasheet
SLVS317 − MAY 2001
19
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
overview
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. To this end, 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.
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 connector. This power interface consists of two V
CC
, two V
pp
, and four
ground terminals. Multiple V
CC
and ground terminals minimize connector-terminal and line resistance. The two
V
pp
terminals were originally specified as separate signals, but are normally tied together in the host to form
a single node to minimize voltage losses. Card primary power is supplied through the V
CC
terminals;
flash-memory programming and erase voltage is supplied through the V
pp
terminals. Cardbus cards of today
typically do not use 12 V, which is now more of an optional requirement in the host.
designing for voltage regulation
The current PCMCIA specification for output voltage regulation, V
O(reg)
, of the 5-V output is 5% (250 mV). In
a typical PC power-system design, the power supply has an output-voltage regulation, V
PS(reg)
, of 2% (100 mV).
Also, a voltage drop from the power supply to the PC Card will result from resistive losses, V
PCB
, in the PCB
traces and the PCMCIA connector. A typical design would limit the total of these resistive losses to less than
1% (50 mV) of the output voltage. Therefore, the allowable voltage drop, V
DS
, for the TPS2223, TPS2224 and
TPS2226 would be the 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 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 TPS2223, TPS2224, and TPS2226. Therefore, the maximum output current, I
O
max, that can be delivered
to the PC Card in regulation is the allowable voltage drop across the IC, divided by the output-switch resistance.
I
O
max +
V
DS
r
DS(on)
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 TPS2226 have
been designed to deliver 100 mA continuously.