PC Card Power Management - Linear Technology

11/93/76

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 require-

ments for these cards.

Power is provided by the host computer to the PC card

through the card socket via the main V

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 V

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 V

power as shown in Figure 1. The LTC1165

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 R

DS(ON)

N-channel MOSFET switches.

Two back-to-back MOSFET switches, Q2 and Q3, isolate

the parasitic body diode in Q2.

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 break-

before-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 second path for card power is via the two VPP program-

ming pins on each card socket which are typically tied

together. These two pins were originally intended for pro-

gramming 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 operat-

ing states: 12V, V

, 0V and Hi-Z. Figures 2 and 3 are two

Figure 1. Card VCC 5V, 3.3V Switch

IN1

LTC1165CS8

IN2

IN3

GND

OUT1

OUT2

OUT3

PCMCIA

CONTROLLER

10µF

Q1

1/2 Si9956DY

3.3V

Si9956DY

Q2



Q3



1µF

PC

CARD

SOCKET

DN76 • F01

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 inte-

grated circuits, are available in surface mount packaging.

For literature on our Power Products,

call (800) 637-5545. For applications help,

call (408) 432-1900, Ext. 361

 LINEAR TECHNOLOGY CORPORATION 1993

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

(408) 432-1900

●

FAX

: (408) 434-0507

●

TELEX

: 499-3977

IN1

LTC1157CS8

IN2

GND

1N41481N4148

EN0

EN1

100µF

16V

= 3.3V OR 5V 7, 8 13

2 4 5, 6

Si9956DY

LTC1107CS8

47Ω

47µH**

100Ω

2N7002

1N4148

49.9k

432k

47µF

16V

VPP = 0V (100Ω)

(500mA)

12V (60mA)

HI-Z (430k)

NOR = 74HC02

EN0

0

1

0

EN1

0

1

VPP

0V

12V

5V

Hi-Z

(µA)

10

150

380

VCC

(µA)

0

400

300

SUPPLY CURRENTS

*UNLOADED

**DT3316-473 COILCRAFT (708) 956-0666

OR CD75-470 SUMIDA (708) 693-2361

DN76 • F02

Figure 2. Step-Up Regulator VPP Power Management

Figure 3. Current-Limited Linear Regulator VPP Power Management

different approaches to solving the four state output prob-

lem. Figure 2 shows a circuit that produces 12V “locally” by

converting the incoming V

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 V

. Figure 3 is a switched output

LT/GP 1193 190K • PRINTED IN THE USA

SHDN

OUT

ADJ

GND

LT1121CS8

100pF 121k

1% 0.33µF

100Ω

2N7002

1N41481N4148

EN1

EN0

AUX



13V TO 20V

10µF

365k

56.2k

2N7002

XNOR = 74HC266

VPP = 0V (100Ω)

5V (30mA)

12V (120mA)

HI-Z (150k)

EN0

0

1

0

EN1

0

1

VPP

0V

12V

5V

Hi-Z

(µA)

0

15

VAUX

(µA)

15

105

45

SUPPLY CURRENTS

*UNLOADED

DN76 • F03

LIM

= 250mA