8

LT1312

on this line that may damage sensitive PCMCIA flash

memory cards if applied directly to the VPP pins.

Flash Memory Card VPP Power Considerations

PCMCIA compatible flash memory cards require tight

regulation of the 12V VPP programming supply to ensure

that the internal flash memory circuits are never subjected

to damaging conditions. Flash memory circuits are typi-

cally rated with an absolute maximum of 13.5V and VPP

must be maintained at 12V

±5% under all possible load

conditions during erase and program cycles. Undervoltage

can decrease specified flash memory reliability and over-

voltage can damage the device

Generating 14V from 5V or 12V

It is important that the 12V VPP supply for the two VPP

lines to the card be free of voltage spikes. There should be

little or no overshoot during transitions to and from the

12V level.

inductor as shown in Figure 3. MOSFET Q4 and diode D4

have been added and diode D1 is no longer used. In the

previous circuit, power is drawn directly from the batteries

through D1, when the LTC1142 is in Burst Mode operation

and the VPP pin requires 3.3V or 5V. For these lower input

voltages this technique is no longer valid as the input will

fall below the LT1312 regulator’s dropout voltage. To

correct for this situation, the additional switch Q4 forces

the switching regulator into continuous mode operation

whenever 3.3V, 5V or 12V is selected.

LINE POWERED SUPPLIES

In line operated products such as: desktop computers,

dedicated PC card readers/writers, medical equipment,

test and measurement equipment, etc., it is possible to

derive power from a relatively “raw” source such as a 5V

or 12V power supply. The 12V supply line in a desktop

computer however, is usually too “dirty” to apply directly

to the VPP pins of a PCMCIA card socket. Power supply

switching and load transients may create voltage spikes

Intel Corporation, 1992.

D2

MBRS1100

D3

MBRS130T3

Q3

VN7002

5.4V TO 12V

C4

1000pF

C2

1000pF

C3

220µF

C1

68µF

C5

22µF

3.3V

OUTPUT

FROM CARD

Q1

24

23

6

1

28

EN0

EN1

VALID

*LPE-6582-A086 DALE (605) 665-9301

14V AUXILIARY SUPPLY

T1

3.38T

22µH*

Q2

R4

22

Ω

R1

100

Ω

R3

18k

R2

100

Ω

R4

0.033

Ω

D4

18V

LT1312 F3

+

Q4

VN7002

+

+

+

EN0

TO CARD VPP PIN

0V, 3.3V, 5V, 12V OR Hi-Z

LT1312

EN1

VALID

SENSE

GND

1µF

1/2 LTC1142

3.3V REG

PDRIVE

NDRIVE

Figure 3. Deriving Auxiliary 14V Power from an LTC1142 3.3V Regulator