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PC Card Power Control ICs

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.

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 Vpp, and four ground terminals. Multiple V_CC and ground terminals minimize connector-terminal and line resistance. The two Vpp 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 Vpp terminals.

The current PCMCIA specification for output voltage regulation, V_O(reg), of the 5V 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:

V_DS = V_O(reg) × V_PS(reg) - V_PCB

The voltage drop is the output current multiplied by the switch resistance of the device. Therefore, the maximum output current, I_Omax, that can be delivered to the PC Card in regulation is the allowable voltage drop across the device, divided by the output-switch resistance.

I_Omax = V_DS × R_DS(ON)

PC Cards are inherently subject to damage that can result from mishandling. Host systems require protection against short-circuited cards that could lead to power-supply or PCB trace damage. Even extremely robust systems could undergo rapid battery discharge into a damaged PC Card, resulting in the rather sudden and unacceptable loss of system power. The reliability of fused systems is poor, in comparison, as blown fuses require troubleshooting and repair, usually by the manufacturer.

Descriptions of typical PC Card power management ICs follow.

1. This single-slot PC Card/CardBus power controller is a V_CC and V_PP power switch matrix that supports 3.3V and 5V PC Card (PCMCIA) slot power supply pins. The IC can switch PC Card slot V_CC voltages between 0V (ground), 3.3V and 5.0V and V_PP voltages between 0V (ground), 3.3V, 5V, or high impedance at output currents of up to 1A for V_CC and 200mA for V_PP.

Four control bits determine V_{CC OUT} and V_{PP OUT} voltage and standby/operate mode condition. V_CC outputs of 3.3V and 5V at the maximum allowable PC Card current are supported. When the V_CC clam