DN76 - PC Card Power Management Techniques

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 ®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
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 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.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
+
10μF
Q1
1/2 Si9956DY
PCMCIA
CONTROLLER
VCC 5V
IN1
VCC 3V
IN2
OUT2
IN3
OUT3
GND
VS
VCC
OUT1
+
LTC1165CS8
Q2
Si9956DY
Q3
3.3V
Figure 1. Card VCC 5V, 3.3V Switch
11/93/76_conv
PC
CARD
SOCKET
1μF
%/t'
Figures 2 and 3 are two 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
1
7, 8
VCC = 3.3V OR 5V
+
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.
3
Si9956DY
100μF
16V
1N4148
47μH**
VPP = 0V (100Ω)
VCC (500mA)
12V (60mA)
HI-Z (430k)
47Ω
3
432k
1%
1
2
4
5, 6
2
5V
LTC1107CS8
8
1N4148
5
1N4148
VS
IN1
G1
LTC1157CS8
IN2
G2
2
4
5
7
GND
EN0
47+F
16V
49.9k
1%
1M
4
+
SUPPLY CURRENTS
100Ω
3
EN0 EN1 VPP *I5V (μA) *IVCC (μA)
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
%/t'
Figure 2. Step-Up Regulator VPP Power Management
8
VAUX
13V TO 20V
+
10μF
5V
IN
OUT
1
100pF
LT1121CS8
5
1M
EN0
SHDN
ADJ
GND
2N7002
3
2
121k
1%
0.33μF
ILIM = 250mA
1001
365k
1%
EN1
56.2k
1%
VPP = 0V (100Ω)
5V (30mA)
12V (120mA)
OR HI-Z (150k)
SUPPLY CURRENTS
EN0 EN1 VPP *I5V (μA) *IVAUX (μA)
0
0
15
0
0V
1
15
105
0 12V
0
15
45
1
5V
1
10
15
1 Hi-Z
5V
1N4148
1N4148
*UNLOADED
1M
2N7002
1M
XNOR = 74HC266
%/t'
Figure 3. Current-Limited Linear Regulator VPP Power Management
Data Sheet Download
www.linear.com/LTC1165
Linear Technology Corporation
For applications help,
call (408) 432-1900, Ext. 361
dn76f_conv LT/GP 1193 190K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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© LINEAR TECHNOLOGY CORPORATION 1993
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