TPS2204A_16 Datasheet, PDF (19/34 Pages) Texas Instruments – PC CARD POWER-INTERFACE SWITCH WITH RESET FOR SERIAL PCMCIA CONTROLLER

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TPS2204A
TPS2206A
TPS2210A
SLVS449A − DECEMBER 2002 − REVISED MAY 2003
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 are supplied through the V_pp
terminals.
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 results 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 device would be the PCMCIA voltage regulation less the power supply regulation and
less the PCB and connector resistive drops:
VDS + VO(reg)–VPS(reg)–VPCB
Typically, this would leave 100 mV for the allowable voltage drop across the TPS2204A, TPS2206A, or TPS2210A. The
voltage drop is the output current multiplied by the switch resistance of the device. 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 device, divided by the
output-switch resistance.
IOmax
+
VDS
rDS(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 have been designed to deliver 100 mA
continuously.
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