6

LT1313

The LT1313 is two programmable output voltage, low-

dropout linear regulators designed specifically for PCMCIA

VPP drive applications. Input power is typically obtained

from a loosely regulated input supply between 13V and

20V. The LT1313 consists of the following blocks:

Two Low Dropout Voltage Linear Regulators: The heart

of the LT1313 is two PNP-based low-dropout voltage

regulators which drop the unregulated supply voltage

from 13V to 20V down to 12V, 5V, 3.3V, 0V or Hi-Z

depending upon the state of the four Enable inputs and the

limiting and thermal shutdown to protect the device, the

loads, and the sockets against inadvertent short circuiting

to ground.

possible output modes: 0V, 3.3V, 5V, 12V and Hi-Z. These

five modes are selected by the four Enable inputs and the

the LT1313 automatically adjusts each regulated VPP output

voltage to 3.3V or 5V depending upon the voltage present

old voltage for these comparators is set at 4V and there is

approximately 50mV of hysteresis provided to ensure

clean switching between 3.3V and 5V.

VPP VALID Comparator: Two voltage comparators moni-

tor each output voltage when the 12V mode is selected and

are driven low when the output is in regulation above 11V.

These two outputs function separately.

AEN0

AEN1

ASENSE

AVALID

00

X

0V

1

1

0

X

12V

0

0

1

3.0V to 3.6V

3.3V

1

0

1

4.5V to 5.5V

5V

1

1

1

X

Hi-Z

1

X = Don’t Care

LT1313 Truth Table

BEN0

BEN1

BSENSE

BVALID

00

X

0V

1

1

0

X

12V

0

0

1

3.0V to 3.6V

3.3V

1

0

1

4.5V to 5.5V

5V

1

1

1

X

Hi-Z

1

Note: Each channel is independently controlled.

The LT1313 is two voltage programmable linear regula-

tors designed specifically for PCMCIA VPP driver applica-

tions. The device operates with very low quiescent current

(60

µA) in the 0V and Hi-Z modes of operation. In the Hi-Z

mode, the output leakage current falls to 1

µA. In addition

to the low quiescent currents, the LT1313 incorporates

several protection features which make it ideal for PCMCIA

applications. The LT1313 has built-in current limiting

(330mA) and thermal shutdown to protect the device and the

socket VPP pins against inadvertent short-circuit conditions.

Output Capacitance

The LT1313 is designed to be stable with a wide range of

output capacitors. The minimum recommended value is a

1

µF with an ESR of 3Ω or less. The capacitor is connected

directly between the output pin and ground. For applications

where space is very limited, capacitors as low as 0.33

µF can

be used. Extremely low ESR ceramic capacitors with values

less than 1

µF must have a 2Ω resistor added in series with

the output capacitor.

Transient and Switching Performance

The LT1313 is designed to produce minimal overshoot

with capacitors in the range of 1

µF to 10µF. Larger

capacitor values can be used with a slowing of rise and

fall times.

The positive output slew rate is determined by the 330mA

current limit and the output capacitor. The rise time for a

0V to 12V transition is approximately 40

µs and the rise

time for a 10

µF capacitor is roughly 400µs (see the

Transient Response curves in the Typical Performance

Characteristics section).