Page 1 of 4
0 M
MOIYNIOlA Technical Developments Volume 24 March 1995
A SPLIT SUPPLY PCMCIA INTERFACE IC
by Barry Moss, Ricardo Lim, David Russo and Denis Beaudoin
Interface IC, the PIPE ASIC, has been designed with features to address the problems of operating in a split supply environment.
INTRODUCTION
Most PCMCIA peripheral cards draw their power from the host computer socket. However, a new class of PCMCIA devices, such as the DataTAC Personal Messenger wireless modem are designed to continue to operate while removed from the socket or while the socket and the host computer are powered OK For example, a wireless modem could remain logged into a network while removed from its host com- puter, and store incoming messages until the modem is reinserted into the host computer's PCMCIA socket. This new class of device requires its own on-board battery and power supply However, existing interface ICs assume that the only source of power is from the PCMCIA port. If this type of IC was used on a PCMCIA peripheral card with internal power supply, the IC would consume excessive power during those times when either the modem card or the host computer was powered off but the other device was still under its internal power, due to power being leaked through the protection diodes of attached ICs which are powered OK A new PCMCIA
The PIPE is designed to work under conditions where the card's power supply is active while the PCMCIA socket is turned off or the card is out of the socket. Also, the PIPE will allow the card's power supply to be turned off while the card remains in a powered PCMCIA socket, without draining exces- sive current from the socket.
Figure 1 shows a high level diagram of the vari- ous power supplies of the PIPE. The PIPE has two separate I/O rings. The first I/O ring is powered by
3.3V and contains those I/O pads which are con- nected to other logic devices on the PCMCIA card, which operate at 3.3V The second I/O ring is pow- ered by a 5V supply from the PCMCIA connector and contains those I/O pads which are connected to the PCMCIA interface.
SPLIT I/O RINGS
i NOT TO SCALE
Figure 1 PIPE Power Supplies
136 0 Moforola 1°C 1995
[This page contains 15 pictures or other non-text objects]
Page 2 of 4
MO-LA Technical Developments Volume 24 March 1995
The PIPE supports the following configurations for the PCMCIA host and card system:
socket are powered off so there is nothing to consider.
CARD POWER ON/SOCKET POWER ON
l
Card Power Off/Socket Power Off
Card Power On/Socket Power On
Card Power Off/Socket Power On
Card Power On/Socket Power Off
CARD POWER OFF/SOCKET POWER OFF
The outputs of the input buffers shown in Fig- ure 2 and Figure 3 are driven to SV level and they can directly drive the CMOS inputs of internal gates, which are powered by 3.3V; without any damage as long as the input of the internal gate is not a trans- mission switch. Care has been taken in the ASIC design to ensure this requirement.
l
l
l
This case is trivial. Both the...
