PC Card Power Management Techniques – Design Note 76
Tim Skovmand
Most portable computers have sockets built in to accept
small PC cards for use as extended memories, data/fax
modems, network interfaces, wireless communicators,
etc. The Personal Computer Memory Card International
Association (PCMCIA) has released specifications, 1.0
and 2.0, which outline the general voltage and power
requirements for these cards.
Power is provided by the host computer to the PC card
through the card socket via the main VCC supply pin(s)
and the VPP programming supply pins. Both supplies
can be switched to different voltages to accommodate
a wide range of card types and applications.
The VCC supply can be switched from 5V to 3.3V and
must be capable of supplying upwards of 1A for short
periods of time and hundreds of milliamps continuously. Three low resistance MOSFET switches are typically used to select the card VCC power as shown in
Figure 1. The LTC В®1165 inverting triple MOSFET driver
accepts active-low logic commands directly from a
common PCMCIA controller and generates gate drive
voltages above the positive rail to fully enhance low
5V RDS(ON) N-channel MOSFET switches. Two back-to-back
MOSFET switches, Q2 and Q3, isolate the parasitic …