LTC1470 Просмотр технического описания (PDF) - Linear Technology

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LTC1470

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

Linear Technology 

LTC1470/LTC1471

APPLICATIONS INFORMATION

Truth Table for CL-PD6710 Controller

A_VCC _3 A_VCC_5

EN0

EN1

OUT

0

0

Hi-Z

0

1

3.3V

1

0

5V

1

1

Hi-Z

Interfacing with “365” Type Controllers

The LTC1470 also interfaces directly with “365” type

controllers as shown in Figure 2. Note that the VCC Enable

inputs are connected differently than to the CL-PD6710

controller because the “365” type controllers use active-

high logic control of the VCC switches (see the following

Switch Truth Table). No “glue” logic is required to inter-

face to this type of PCMCIA compatible controller.

3.3V

5V

“365” TYPE

CONTROLLER

A_VCC_EN0

A_VCC_EN1

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 F02

Figure 2. Direct Interface with “365” Type PCMCIA Controller

Truth Table for “365” Type Controller

A_VCC_EN0 A_VCC_EN1

EN0

EN1

OUT

0

0

Hi-Z

0

1

3.3V

1

0

5V

1

1

Hi-Z

Supply Bypassing

For best results bypass the supply input pins with 1µF

capacitors as close as possible to the LTC1470. Some-

times much larger capacitors are already available at the

outputs of the 3.3V and 5V power supply. In this case it is

still good practice to use 0.1µF capacitors as close as

possible to the device, especially if the power supply

output capacitors are more than 2" away on the printed

circuit board.

Output Capacitors and Pull-Down Resistor

The output pin is designed to ramp on slowly, typically

400µs rise time. Therefore, capacitors as large as 150µF

can be driven without producing voltage spikes on the

3VIN or 5VIN supply pins (see graphs in Typical Perfor-

mance Characteristics section). The output pin should

have a 0.1µF to 1µF capacitor for noise reduction and

smoothing.

A 10k pull-down resistor is recommended at the output to

ensure that the output capacitor is fully discharged when the

output is switched OFF. This resistor also ensures that the

output is discharged between the 3.3V and 5V transition.

Supply Sequencing

Because the 5V supply is the source of power for both of the

switch control circuits, it is best to sequence the power

supplies such that the 5V supply is powered before, or

simultaneous to, the application of 3.3V.

It is interesting to note, however, that the switches are NMOS

transistors which require charge pumps to generate gate

voltages higher than the supply rails for full enhancement.

Because the gate voltages start at 0V when the supplies are

first activated, the switches always start in the off state and

do not produce glitches at the outputs when powered.

If the 5V supply must be turned off, it is important to program

all switches to the Hi-Z or 0V state at least 100µs before the

5V power is removed to ensure that the NMOS switch gates

are fully discharged to 0V. Whenever possible, however, it is

best to leave the 5VIN pin(s) continuously powered. The

LTC1470/LTC1471 quiescent current drops to <1µA with all

the switches turned off and therefore no 5V power is

consumed in the standby mode.

14701fa

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