7

LTC4301L

4301lf

OPERATIO

This delay is always positive and is a function of supply

voltage, temperature and the pull-up resistors and equiva-

lent bus capacitances on both sides of the bus. The Typical

Performance Characteristics section shows the high to

low propagation delay as a function of temperature and

100pF equivalent capacitance on both sides of the part.

Larger output capacitances translate to longer delays (up

to 150ns). Users must quantify the difference in propaga-

Figure 2. Input-Output Connection

High to Low Propagation Delay

tion times for a rising edge versus a falling edge in their

systems and adjust setup and hold times accordingly.

Ready Digital Output

This pin provides a digital flag which is low when either CS

is high or the start-up sequence described earlier in this

section has not been completed. READY goes high when

CS is low and start-up is complete. The pin is driven by an

open-drain pull-down capable of sinking 3mA while hold-

provide the pull-up.

Connection Sense

When the CS pin is driven above 1.4V with respect to the

LTC4301L’s ground, the backplane side is disconnected

from the card side and the READY pin is internally pulled

low. When the pin voltage is low, the part waits for data

transactions on both the backplane and card sides to be

complete (as described in the Start-Up section) before

reconnecting the two sides. At this time the internal

pulldown on READY releases.

Live Insertion and Capacitance Buffering Application

Figure 3 illustrates applications of the LTC4301L with

ability to recognize and buffer bus data levels that are

take advantage of the LTC4301L’s Hot Swap

capacitance buffering and precharge features. If the I/O

cards were plugged directly into the backplane without the

LTC4301L buffer, all of the backplane and card capaci-

tances would add directly together, making rise- and fall-

time requirements difficult to meet. Placing an LTC4301L

on the edge of each card, however, isolates the card

capacitance from the backplane. For a given I/O card, the

LTC4301L drives the capacitance of everything on the card

and the backplane must drive only the capacitance of the

LTC4301L, which is less than 10pF.

APPLICATIO S I FOR ATIO

In most applications the LTC4301L will be used with a

SDA and SCL are medium length pins to ensure that the

precharge circuitry to be activated on SDA and SCL before

they make contact. CS is a short pin that is pulled up when

not connected. This is to ensure that the connection

between the backplane and the cards data and clock

busses is not enabled until the transients associated with

live insertion have settled.

Figure 4 shows the LTC4301L in an application where all

of the pins have the same length. In this case, an RC filter

circuit on the I/O card with a product of 10ms provides a

filter to prevent the LTC4301L from becoming activated

until the transients associated with live insertion have

the resistor from CS to GND.

Hot Swap is a trademark of Linear Technology Corporation.

4301 F02

INPUT

SIDE

55pF

OUTPUT

SIDE

20pF

0.5V/DIV

20ns/DIV