advertisement 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. and generates gate drive voltages above the positive rail to fully enhance low RDS(ON) N-channel MOSFET switches. Two back-to-back MOSFET switches, Q2 and Q3, isolate the parasitic body diode in Q2. 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 LTC1165 drives the three MOSFET gates at roughly the same rate producing a smooth transition between supply voltages. Further, the LTC1165 provides a natural breakbefore-make action due to the asymmetry between the turn-on times and the turn-off times; i.e., no external delays are required. A noninverting version, the LTC1163, is also available. Both devices are available in 8-lead surface mount packaging. 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 LTC1165 inverting triple MOSFET driver accepts active-low logic commands directly from a common PCMCIA controller The second path for card power is via the two VPP programming pins on each card socket which are typically tied together. These two pins were originally intended for programming flash memories but are sometimes used as an alternate power source for the card. The VPP supply voltage is therefore capable of being switched between four operating states: 12V, VCC, 0V and Hi-Z. Figures 2 and 3 are two 5V + 10F PCMCIA CONTROLLER VCC 5V Q1 1/2 Si9956DY VS IN1 VCC OUT1 + LTC1165CS8 VCC 3V IN2 OUT2 IN3 OUT3 GND Q2 Si9956DY Q3 3.3V Figure 1. Card VCC 5V, 3.3V Switch 11/93/76 PC CARD SOCKET 1F DN76 * F01 different approaches to solving the four state output problem. Figure 2 shows a circuit that produces 12V "locally" by converting the incoming VCC supply through a step-up converter for programming flash memories, etc. This circuit has the unique capability of supplying up to 500mA when the VPP pin is programmed to VCC. Figure 3 is a switched output voltage linear regulator which is powered from a auxiliary 13V to 20V unregulated supply. This circuit supplies 120mA at 12V and protects the card slot from overcurrent damage. The supply currents are listed in the truth table to the right of each schematic. All components shown, including the integrated circuits, are available in surface mount packaging. 1 3 + Si9956DY 100F 16V 1N4148 47H** 7, 8 VCC = 3.3V OR 5V VPP = 0V (100) VCC (500mA) 12V (60mA) HI-Z (430k) 47 3 432k 1% 1 2 4 5, 6 2 5V 8 LTC1107CS8 1N4148 5 1N4148 VS IN1 G1 LTC1157CS8 IN2 G2 2 4 5 7 GND EN0 47F 16V 49.9k 1% 1M 4 + SUPPLY CURRENTS 100 3 EN0 EN1 VPP *I5V (A) *IVCC (A) 0 10 0 0 0V 1 150 400 0 12V 0 380 300 1 5V 1 5 0 1 Hi-Z 1N4148 2N7002 EN1 *UNLOADED **DT3316-473 COILCRAFT (708) 956-0666 OR CD75-470 SUMIDA (708) 693-2361 NOR = 74HC02 DN76 * F02 Figure 2. Step-Up Regulator VPP Power Management 8 VAUX 13V TO 20V + 10F 5V IN OUT 1 100pF LT1121CS8 5 1M EN0 SHDN ADJ GND 2N7002 3 2 121k 1% 0.33F ILIM = 250mA 100 365k 1% EN1 56.2k 1% SUPPLY CURRENTS EN0 EN1 VPP *I5V (A) *IVAUX (A) 0 0 15 0 0V 1 15 105 0 12V 0 15 45 1 5V 1 10 15 1 Hi-Z 5V 1N4148 1N4148 VPP = 0V (100) 5V (30mA) 12V (120mA) OR HI-Z (150k) *UNLOADED 1M 2N7002 1M XNOR = 74HC266 DN76 * F03 Figure 3. Current-Limited Linear Regulator VPP Power Management For literature on our Power Products, call (800) 637-5545. For applications help, call (408) 432-1900, Ext. 361 Linear Technology Corporation LT/GP 1193 190K * PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1993