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LTC1471C

Single and Dual PCMCIA Protected 3.3V/5V VCC Switches

Linear Technology 

LTC1470/LTC1471

U

OPERATION

The LTC1470 (or 1/2 of the LTC1471) consists of the

following functional blocks:

on slowly (400µs typical rise time) but turns them off

much more quickly (typically 10µs).

Input TTL/CMOS Converters

The enable inputs are designed to accommodate a wide

range of 3V and 5V logic families. The input threshold

voltage is approximately 1.4V with approximately 100mV

of hysteresis. The inputs enable the bias generator, the

gate charge pumps and the protection circuity which are

powered from the 5V supply. Therefore, when the inputs

are turned off, the entire circuit is powered down and the

5V supply current drops below 1µA.

Bias, Oscillator and Gate Charge Pump

When either the 3.3V or 5V switch is enabled, a bias

current generator and high frequency oscillator are turned

on. The on-chip capacitive charge pump generates ap-

proximately 12V of gate drive for the internal low RDS(ON)

NMOS VCC switches from the 5VIN power supply. There-

fore, an external 12V supply is not required to switch the

VCC output. The 5VIN supply current drops below 1µA

when both switches are turned off.

XOR Input Circuitry

By employing an XOR function, which locks out the 3.3V

switch when the 5V switch is turned on and locks out the

5V switch when the 3.3V switch is turned on, there is no

danger of both switches being on at the same time. This

XOR function also makes it possible to work with either

active -low or active-high PCMCIA VCC switch control logic

(see Applications Information section for further details).

Break-Before-Make Switch Control

Built-in delays are provided to ensure that the 3.3V and 5V

switches are non-overlapping. Further, the gate charge

pump includes circuitry which ramps the NMOS switches

Gate Charge and Discharge Control

All switches are designed to ramp on slowly (400µs typical

rise time). Turn-off time is much quicker (typically 10µs).

To ensure that both VCC NMOS switch gates are fully

discharged, program the switch to the high impedance

mode at least 100µs before turning off the 5V power

supply.

Switch Protection

Both switches are protected against accidental short cir-

cuits with SafeSlot foldback current limit circuits which

limit the output current to typically 1A when the output is

shorted to ground. Both switches also have thermal shut-

down which limits the power dissipation to safe levels.

APPLICATIONS INFORMATION

The LTC1470/LTC1471 are designed to interface directly

with industry standard PCMCIA card controllers.

Interfacing with the CL-PD6710

Figure 1 is a schematic diagram showing the LTC1470

interfaced with a standard PCMCIA slot controller. The

LTC1470 accepts logic control directly from the CL-PD6710.

The XOR input function allows the LTC1470 to interface

directly to the active-low VCC control outputs of the CL-

PD6710 for 3.3V/5V voltage selection (see the following

Switch Truth Table). Therefore, no “glue” logic is required

to interface to this PCMCIA compatible card controller.

6

3.3V

5V

CL-PD6710

VCC_3

VCC_5

0.1µF

3VIN 3VIN

0.1µF

5VIN

LTC1470

EN0

OUT

EN1

OUT

GND

(OFF/3.3V/5V)

+

1µF

TANT

10k

TO CARD

VCC PINS

1470/71 F01

Figure 1. Direct Interface to CL-PD6710 PCMCIA Controller

14701fa

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