LTC4305CDHD datasheet(16/20 Pages) LINER

16 / 20 page

LTC4305

4305f

APPLICATIO S I FOR ATIO

Level Shifting Considerations

In Figure 5, the LTC4305 VCC voltage is less than or equal

to both of the downstream bus pull-up voltages, so both

downstream buses can be active at the same time. Like-

wise, the rise time accelerators can be turned on for the

downstream buses, but must never be activated on SCLIN

and SDAIN, because doing so would result in significant

current flow from VCC to VBACK during rising edges.

Other Application Circuits

Figure 6 illustrates how the LTC4305 can be used to

expand the number of devices in a system by using nested

addressing. Each I/O card contains a temperature sensor

having device address 1001 000. If both I/O cards were

plugged directly into the backplane, the two sensors

would require two unique addresses. However, if masters

use the LTC4305 in multiplexer mode, where only one

downstream channel is connected at a time, then each

I/O card can have a device with address 1001 000 and no

problems will occur.

Figures 7 and 8 show two different methods for hot-

swapping I/O cards onto a live two-wire bus using the

LTC4305. The circuitry of Figure 7 consists of an LTC4305

residing on the edge of an I/O card having two separate

downstream buses. Connect a 200k resistor to ground

from the ENABLE pin and make the ENABLE pin the

shortest pin on the card connector, so that the ENABLE pin

remains at a constant logic low while all other pins are

connecting. This ensures that the LTC4305 remains in its

default high impedance state and ignores connection

transients on its SDAIN and SCLIN pins until they have

established solid contact with the backplane 2-wire bus.

In addition, make sure that the ALERT card connector pin

is shorter than the VCC pin, so that VCC establishes solid

contact with the I/O card pull-up supply pin and powers

the pull-up resistors on ALERT1–ALERT2 before ALERT

makes contact.

Figure 8 illustrates an alternate SDA and SCL hot-

swapping technique, where the LTC4305 is located on the

backplane and an I/O card plugs into downstream channel

2. Before plugging and unplugging the I/O card, make sure

that channel 2’s downstream switch is open, so that it does

not disturb any 2-wire transaction that may be occurring

at the moment of connection/disconnection. Note that

pull-up resistor R10 on ALERT2 should be located on the

backplane and not the I/O card to ensure proper operation

of the LTC4305 when the I/O card is not present. The pull-

up resistors on SCL2 and SDA2—R8 and R9, respec-

tively—may be located on the I/O card, provided that

downstream bus 2 is never activated when the I/O card is

not present. Otherwise, locate R8 and R9 on the backplane.

Figure 6. Nested Addressing Application

VCC

10k

0.01

µF

10k

R10

10k

4305 F06

ADDRESS = 1001 000

I/O CARD #1

ADDRESS = 1001 000

I/O CARD #2

OPEN

TEMPERATURE

SENSOR

TEMPERATURE

SENSOR

MICRO-

CONTROLLER

SCLIN

SDAIN

ENABLE

ALERT

READY

ADR2

ALERT1

ADR1

ADR0

GND

SCL1

SDA1

SCL2

SDA2

ALERT2

VCC

ADDRESS = 1010 000

LTC4305

LTC4305CDHD датащи(PDF) 16 Page - Linear Technology

LTC4305CDHD датащи(HTML) 16 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

датащи скачать

ссылки URL